Equid Blog : Horse Health & Diseases : University of Guelph : Ontario Veterinary College : Equine Infectious Diseases

The massive outbreak of infectious upper respiratory tract disease that hit Iceland four months ago is finally slowing down, and there is now a little more information available about what they've been seeing and what authorities believe has been going on.

There is a fairly clear description of the clinical signs seen in affected horses (as previously described), although signs vary from horse to horse.  Typically illness begins with a serous (clear) nasal discharge which then becomes mucopurulent (snotty).  There is sometimes mild conjunctivitis (e.g. red puffy eyes) and most commonly a dry cough.  Horses that are examined using endoscopy show signs of laryngitis.  Signs generally last 4-6 weeks, but this can vary.

There's also more information about the epidemiology of the disease (i.e. the pattern of spread).  Morbidity seems to be close to 100%, meaning almost every horse that is exposed gets sick.  Fortunately no mortality has been associated with the disease, meaning all the horses eventually recover.  The incubation period (the time from exposure to illness) is 1-4 weeks.  It seems to be spread mostly by direct contact, but indirect transmission is also possible, as even free-roaming herds with little contact with other horses or people have been affected.  Horses are not completely immune after recovering (meaning they can get sick again if they are re-exposed), but there is evidence that the "herd immunity" of the horse population in Iceland is increasing, and the outbreak seems to be dissipating.  It is still lingering in some horse groups where there are naive (unexposed) horses coming into contact with infected horses.

The way this disease has spread is very typical of a virus burning through a naive population which has never been previously exposed to or vaccinated against the disease.  Even the clinical signs are very typical of an upper respiratory virus.  However, extensive testing has been done using both PCR and antibody titres for a multitude of viruses including (but not limited to): equine herpesviruses 1, 2, 4 and 5, equine arteritis virus, equine influenza virus, equine reoviruses, and equine rhinitis viruses.  None of these viruses appear to be the culprit, despite early suspicions that the cause was in fact equine herpesvirus.  They are still testing for new/unknown viruses using viral culture, but this is a difficult and very time-consuming task.

What authorities have been able to find in affected horses is Streptococcus equi subsp. zooepidemicus, which is what is currently being blamed for the outbreak.  They say it has been cultured from almost all coughing horses and all horses with mucopurulent nasal discharge.  But that's not really surprising, as S. zooepidemicus is a very common commensal bacterium that is even carried by healthy horses in their upper respiratory tracts.  It's also a very common opportunistic pathogen in horses, meaning when the animal gets sick for another reason (for example, if a horse is infected with a respiratory virus), then S. zooepidemicus moves in and causes a secondary bacterial infection, which can make the clinical signs worse or last longer, and may lead to other complications.  In this case they are trying to make S. zooepidemicus out to be the primary pathogen, but it would have to be a very unusual strain of the bacterium - very virulent, highly infectious and totally novel to the horse population in Iceland - to cause an outbreak of this scale.  They are doing additional testing to characterize the strain they have isolated from infected horses and to compare it to other strains previously isolated from horses in Iceland.

The good news is that after the horse industry in Iceland was paralyzed by this outbreak for almost four months, equestrian activities are now resuming under the supervision of the Icelandic Food and Veterinary Authority.  That shouldn't pose a problem to the Icelandic horses, as there are very few naive horses left in the country that would still be highly susceptible to this still somewhat mysterious disease.  However, export of horses from Iceland is slated to recommence on September 15.  There are still quarantine requirements preceding export (horses must not be sick nor be in contact with a sick horse for 30-60 days prior, depending on what country they're going to), which always are and will remain very important for infectious disease control.  However, with the cause of the outbreak still being somewhat unclear, it is unknown if any horses may now be healthy carriers of the outbreak pathogen, be it an unusual strain of S. zooepidemicus or an unidentified virus.  If horses in other countries start getting sick a few weeks after exposure to exported Icelandic horses, strict control measures will have to be rapidly implemented to possibly prevent similar outbreaks from developing.

Photo credit: David Blaikie (source: http://commons.wikimedia.org)

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Strangles (Streptococcus equi infection) is suspected to be the cause of death of at least six horses in an Australian outbreak.  At least 30 suspected cases has been identified and affected stables are under some form of quarantine. Local horse and pony club events have been canceled to help limit the spread.

Little information about the clinical signs is available, but usually it's pretty easy to establish a high index of suspicion based on the typical signs of strangles, particularly during an outbreak. Confirmation of strangles in an outbreak is also usually pretty easy, since isolation of the bacterium is quite straightforward. Results are expected soon.

Strangles outbreaks are not uncommon and this disease is constantly circulating in most horse populations at some level. Some references say that approximately 10% of affected horses die, a number that I think is excessive, but the key point is that strangles can be fatal to a small but not inconsequential percentage of affected horses. The potential severity of disease plus the high infectivity are big reasons why good control measures are needed.

One common problem with strangles control is described by horse trainer Joe Byrne, who said "the most damaging thing with strangles is the attitude of "ignorance and secrecy". Owners with infected stables "straight away clam up, don't tell anyone" and remain operating like nothing has happened and that is very problematic."  Indeed it is.

Photo: A horse with strangles (S. equi infection) showing the characteristic severe swelling of the submandibular lymph nodes (click image for source).

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Following a repeating trend that has been ongoing over the past couple of years, piroplasmosis has been identified in more US horses with no clear source. The latest cases were in North Carolina, which has reported 11 infections in four different locations.

This is quite concerning because it now seems to be a regular event to get a report of piroplasmosis in US horses from different areas and with no clear link to other outbreaks. The disease, caused by the blood parasites Theileri equi and Babesia caballi, can produce a wide range of clinical signs, and kills approximately 20% of infected horses. Some horses can become healthy "silent" carriers, complicating recognition and control. The bloodborne parasites are naturally transmitted by ticks, but can also be spread by other forms of bloodborne transmission, most notably the reuse of needles. Often, poor needle handling practices are blamed by officials for spread of piroplasmosis among groups of horses on a farm, but that doesn't address the most important question - where did it come from in the first place?

PIroplasmosis is considered a foreign disease in the US, but the repeated cases of unknown origin in at least 19 US states suggests that the disease is actually endemic (established) in the US. Any explanation of where the causative parasites keep coming from is pretty much always missing from US piroplasmosis reports. It certainly seems possible, if not likely, that there is an unidentified pool of infected horses and tick species in the affected areas that are able to transmit the infection.

If the US is going to get piroplasmosis under control, a serious effort needs to be undertaken to understand how widespread the infection is and how it's being spread. Tracking known cases and their contacts is important, but a more concerted effort is required. That takes time and money, and often governments are reluctant to spend much of either when it comes to horses (as opposed to food animals), but considering the potential implications of endemic piroplasmosis and the often overlooked economic importance of the horse industry, it's a worthy investment.

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The US economic meltdown and slow recovery are being blamed, in part, for the increase in eastern equine encephalitis (EEE) cases in some parts of the US. The premise is that as the economy weakens, people cut down on discretionary spending. One area of discretionary spending is veterinary care, particularly non-emergent care like vaccination. It may be an even greater issue for a rare disease like EEE, as even people who choose to vaccinate their horses may pare down the vaccines they use, by limiting vaccination to core vaccines such as rabies and tetanus.

“The economy is very much a factor” stated veterinarian Steven Halstead of the Michigan Department of Agriculture. Similarly, veterinarian James Connell said "It’s flat out the economy. People can’t afford to feed them, how can they afford to vaccinate them?” Dr. Connell reports a decrease in vaccination rates in his practice of approximately 15% per year over the past 3 years, something that has also been reported by other Michigan vets.

It's always tough to say, with confidence, why disease trends occur. EEE is a sporadic disease in many regions, like Michigan, and there can be no cases some years and clusters other years. So, there's no guarantee that vaccination is the problem. However, it makes sense that it could be involved since decreasing vaccination rates increase the number of susceptible horses.

The only saving grace with regard to decreasing EEE vaccination rates is that it only hurts the horses that are not vaccinated. With some diseases, namely those that are spread horse-to-horse, maintaining a high overall vaccination rate in the horse population is critical to reduce the chance of disease transmission. This is the concept of "herd immunity."  With those diseases, when people stop vaccinating their horses, they also in part increase the risk to other horses in the area. With a disease like EEE that is spread by mosquitoes which cannot be infected by other horses, herd immunity doesn't apply. The percentage of horses in the region that are vaccinated has no impact on the likelihood that any single horse will be exposed.

(click image for source)

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Yet another case of piroplasmosis has been identified in the US. The horse was identified as infected with the bloodborne parasite Babesia caballi through routine testing for interstate movement of horses. Babesia caballi and Theileria equi are both causes of piroplasmosis, and both have been found multiple times in the US over the past year or so. The infected horse is currently under quarantine.

The good news:

• The infected (and infectious) horse was identified so proper measures can be taken to reduce the risk of spread to other horses.
• The surveillance program that is in place is effective at identifying (at least some) positive horses.

The bad news:

• Still, no one has a good explanation as to why these unrelated cases keep occurring. I can't see any other explanation other than this disease must be present (endemically) in the US and is probably being spread by unrecognized insect vectors. 
• The surveillance that is underway only tests a very small percentage of horses. So, for every infected horse that is detected, there may be many more that go undetected.

Clearly, a concerted and coordinated effort needs to be undertaken to determine the scope of the problem and, more importantly, the source and route of transmission (i.e. the insect vector) of these infections. If at least the vector is not identified, there's no way to properly control this disease.

(click image for source)

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Eastern equine encephalitis (EEE) season is well underway. EEE is a devastating mosquito-borne disease that can infect (and usually kill) horses and people. It is a regionally important disease that infects many horses in some regions and none elsewhere, mainly based on the types of mosquitoes and birds in the area. The southeastern US is a hotbed, and cases are now being reported in areas such as Florida and Georgia. It is very important that horse owners make themselves aware of infectious disease risks in their own areas, including the risk of EEE. It is equally important for owners to be aware of the disease risks in any areas to which they may take (or send) their horses. Knowing the risks is necessary to develop a logical and effective infection control program.

EEE causes severe neurological disease in horses and people. Horses and people are infected after being bitten by a mosquito that was infected by feeding from an infected bird. Infection is often fatal.

The keys to prevention (for horses and people) are:

1. Avoid mosquito bites by:

• Reducing mosquito breeding grounds (i.e. standing water)
• Staying away from mosquito-infested areas, particularly at dusk or dawn.
• Wearing clothes that cover your arms and legs
• Wearing a DEET-based repellent when outside

2. Vaccination

• EEE vaccination is important in areas where the disease is present. Ideally, vaccination should be performed approximately one month prior to the time of year when cases start to occur, but late is better than never.

More information about EEE can be found in our archives.

Photo: Horse in a full-body fly sheet.  Good in theory but not very helpful in hot weather. (click image for source)

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Salmonella is the bane of existence of equine hospitals. It's the most common cause of infectious disease outbreaks, some of which can be devastating.

A report about one high-profile outbreak that occurred a couple of years ago was recently published in the Journal of Veterinary Internal Medicine (Dallap Schaer et al 2010). This was a large outbreak caused by a multidrug resistant strain of Salmonella Newport that hit the University of Pennsylvania's New Bolton Center.

• Ultimately 61 animals were infected, 54 of which were horses.
• 22 (36%) infected animals died. This occurred despite the fact that aggressive treatment was provided and cost issues were minimal because the hospital paid for treatment associated with the outbreak. That's an incredibly high rate and shows how "hot" this strain was.
• Environmental sampling during the outbreak identified persistence of the bacterium in the hospital. Because of this, and ongoing cases, the hospital had to be closed for thorough decontamination. The hospital was closed for approximately three months, and the NICU/ICU was closed for eight months.
• There was extensive renovation of some areas, including sandblasting and resurfacing of 4 cement-block barns, replacing dirt flooring with concrete, installation of a polyurethane-based flooring system in all stalls and animal handling areas, and replacing non-cleanable surfaces throughout the facility. Chlorine gas decontamination was used for the ICU/NICU.
• The financial impact was estimated at over $4 million US. That doesn't include the impact on reputation and morale.
• "A paradigm shift in the relevance of biosecurity in a veterinary teaching hospital and the establishment of a stringent infection control program were integral components of successful hospital re-opening."

A good infection control program is a key component of reducing the risk of outbreaks, but they can still happen in any facility at any time. An infection control program was present in this hospital, but it was later determined to have some weaknesses that were corrected. Analysing an outbreak after the fact and trying to correct any underlying causes is a critical component and is often overlooked. By the time the outbreak is over, people often want to immediately forget that it happened and don't want to look for causes, whether it's directed at the facility, management, protocols or personnel. The goal isn't to blame someone and penalize them, it's to find out how to prevent the problem from happening again.

I commend the authors for publishing this report. I've always taken the approach of publishing and talking about any infection control issues we've run into in our hospital. It's a double edged sword, so some people don't like the fact that I do this. It certainly can lead to negative publicity, but I think it's critical that this information be shared so that problems can be prevented in the future. We've become international leaders in some aspects of infectious diseases and infection control by aggressively pursuing and publishing our "dirty laundry." Personally, I'd much rather take my horse to a hospital that isn't afraid to talk about their issues because it shows they're paying attention, and trying to stay on top of any problems, as compared to a facility that never submits a Salmonella culture from diarrheic horses just so they can say they've never found (which isn't the same as never had) Salmonella in their building.

As I've said before, hope isn't an infection control strategy. You have to work at it to do it right.

Image: New Bolton Center, University of Pennsylvania

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A new twist has been encountered in Bahrain's glanders (Burkholderia mallei) outbreak. Controversy and confusion abound, with questions about testing, application of infection control practices and the actual number of infected animals. The latest issue to emerge is a report of diagnosis of glanders in a camel.  Bahraini officials have been adamant that this disease has not spread to camels, but Dubai's Central Veterinary Research Laboratory, one of only two international reference laboratories for the disease, made the diagnosis. This has led to further rounds of accusations and counter-accusations, none of which helps control this problem.

Bahrain's chief veterinarian has stated that different testing must be done for camels and that an invalid technique may have been used. There is, however, no evidence supporting this claim, and the Dubai lab is sticking by the diagnosis. There are also anecdotal reports of other camels that might have been infected.  Efforts are better spent exploring this potentially important problem rather than bickering.

Glanders has been previously reported in camels, so it's not a stretch to believe that camels could be infected in the current Bahraini outbreak. It's concerning because of the potentially large number camels that would need to be investigated and tested as part of the outbreak, if camels became involved. It sounds like there's a lot of reluctance to expand investigation and control efforts to this other species, but blaming the test or the lab is never a good approach to outbreak control. It's much better to over-react initially and put extra effort into potential problems than sit back, debate, deny and then have to deal with an even larger problem. Let's hope that these issues get sorted out soon. If not, even if all horses in the country are tested and declared negative, there will continue to be a threat of ongoing infections if the bacterium is able to get a foothold in the camel population.

(click image for source)

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The Royal Canadian Mounted Police's famed Musical Ride has been hit with strangles, and has canceled shows in Alberta and Saskatchewan. It's reported that only one horse is affected, but it's quite possible (if not likely) that others are also affected or will be soon, considering the highly transmissible nature of the disease. It can be contained with good infection control practices, particularly if caught early, and hopefully that's the case here.

Horses like these, that travel widely to shows and other events, are at high risk for exposure to microorganisms like Streptococcus equi, the cause of strangles. The more horses a horse encounters (particularly transient populations as are encountered at shows), and the fewer the infection control practices at shows, the greater the risk of disease.

More information about strangles can be found on the equIDblog Resources page.

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Another case of piroplasmosis has been identified in the US. The latest case was detected during routine screening of racehorses in New Mexico, which has been implemented because of the ongoing and poorly contained outbreak. The latest case, a Quarter Horse, tested positive and was euthanized. However, what makes this case different from the large number of other recent piroplasmosis cases in the US is that a different cause of infection was identified: Babesia caballi.

Both Babesia caballi and Theileri equi are parasites that cause piroplasmosis. The US has been considered free of these two parasites, but it's clear that's not the case. Piroplasmosis caused by T. equi seems to be well established in some regions, with large numbers of cases having been reported over the past year or two. There is no indication that the recent B. caballi case was acquired in a foreign country, so it's possible this parasite is also established in the US, at least in the region (in this case in New Mexico) from which the infected horse came. Clearly, much more work needs to be done to determine how these two organisms are infecting American horses. Poor needle handling and other potential routes of bloodborne contamination have been frequently blamed for piroplasmosis transmission in these US outbreaks, but these don't explain where the disease actually came from in the first place. Close investigation of potential insect (tick) vectors is required to determine if recognized vector species of ticks are transmitting these pathogens to horses, and whether in some regions there is an unrecognized reservoir in ticks of other species that are capable of transmitting piroplasmosis.

(click image for source)

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Despite initial declarations that known common causes had been ruled out, the investigation into the mysterious respiratory disease outbreak in Iceland is now focusing on the role of equine herpesvirus. Few details are available, but the country's Chief Veterinarian is reporting that equine herpesvirus, complicated by secondary streptococcal infection, is suspected.

That makes sense. As I wrote earlier, it's much more likely for an outbreak to be caused by an uncommon presentation of a common problem than by a completely new bug. More information about how they have diagnosed equine herpesvirus is important, however, to make sure that it's really the culprit. This virus is widely disseminated in the horse population and lives dormant inside a large percentage of healthy horses, so care must be taken to ensure that it's causing the outbreak, and they're not merely finding a virus that happened to be there all along. Outbreaks of herpesvirus-associated respiratory disease in older horses are quite unusual, so if this is the case, it's equally important to determine why this strange outbreak has occurred.

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The rather large, long-lasting and remarkable outbreak of piroplasmosis continues in the US. A report from the OIE on June 10 describes 23 new cases in 3 states (Colorado, Texas, Oklahoma). None of these are linked to the large outbreak in Texas that has been previously reported, which is not good news.

The origin of infection and route of transmission are unclear. The report states "Preliminary results of these investigations indicate that the transmission of the organism may have resulted from management practices (use of shared needles or substances between horses) rather than by a tick vector." That's what's been said for many of the cases in the US. Piroplasmosis is naturally transmitted by certain tick species. Finding cases in areas where those ticks are not found indicates one of a few possibilities:

• Horses were infected in other regions where infected ticks are present: This is relatively easy to rule out based on travel history, and there's no indication that these are travel-associated infections.
• The cause of piroplasmosis, Theileria equi, is being transmitted by human activity: Specifically, this blood-borne parasite can be transmitted by things like reusing needles and syringes between horses.
• The ticks are actually there, they just haven't been identified.
• Other types of ticks are able to transmit the infection, we just don't know it yet.

Typically, these reports have blamed management practices (e.g. re-using needles) for transmission of T. equi. One problem I have with that is it doesn't tell me where the infection came from. Needle sharing can certainly result in T. equi transmission, but that doesn't account for how the pathogen came to be in the horse population in the first place. Without a clear link to an endemic area or earlier outbreak, there's got to be concern that this organism is more widely disseminated than we realize, and/or that there are other natural sources of transmission that aren't know.

Regardless of how T. equi got to these regions, poor management practices need to be addressed. It's just common sense. Anything that could result in transmission of blood between horses must be avoided. The small amount of money and/or time saved by re-using needles or other instruments isn't worth the risk associated with disease transmission.

At some point, they may have to stop calling this an outbreak, and recognize that piroplasmosis is an endemic disease in the US. There's evidence that this outbreak has been underway for years and the presence of cases unrelated to the large Texas outbreak that was reported earlier suggests that there are multiple foci of infection in the US.

(Picture source: http://icanhascheezburger.com)

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The outbreak of respiratory disease that was reported in Iceland a few weeks ago is apparently still undiagnosed and ongoing. Signs of the disease, characterized by weakness, nasal discharge, cough and occasionally fever, can apparently persist for up to six weeks. Icelandic authorities have stated that most known diseases have been ruled out, including influenza, and suspect that the illness is caused by a virus with possible secondary bacterial infection. (The outbreak pre-dated the recent icelandic volcanic eruption, so we can't blame that).

It will be interesting to see what they find, and whether they have really been able to completely exclude the most common offenders, like equine influenza. A general rule of medicine is "common things occur commonly." While that may seem like an obvious statement, the point is that you should look for common causes first.  Strange outbreaks are more often atypical outbreaks caused by a known infectious disease, rather than a completely new disease. New diseases certainly do occur, but they are rare and it's important to not be too quick to rule out the common causes.

If this is a new disease, intensive study is required to determine what it is. As well, if there is real suspicion of a new and highly contagious disease, there should be immediate and complete restriction of movement of horses to and from Iceland. It makes no sense to say that there might be a new infectious disease that is highly transmissible and take no measures to keep it from spreading. If it really is a new disease, it's quite fortunate that it's on an isolated island, where containment might be possible. If such a highly transmissible disease were to reach the horse population in Europe or elsewhere, containment will be very difficult.

(click image for source)

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A large British equine charitable facility has closed temporarily because of a large influenza outbreak. Approximately 80% of horses at the Bransby Home of Rest for Horses have become infected. In a large facility like this, once you have 80% of the horses infected, there's very little chance of controlling the outbreak within the facility, although it's still very important to take precautions (such as closing the facility) to prevent the disease from spreading to other farms. Unless there is a discrete group of horses that is well removed from everyone else on the property, you have to assume that all the horses have been exposed. At that point, you basically just have to let the outbreak burn itself out, and try to manage any complications that develop in individual animals.

In some ways, if you're going to have a major disease outbreak, influenza's a good one to have. It doesn't often cause serious illness, it rarely causes death, it's not transmissible to people and it doesn't have a "silent" carrier state. The lack of a carrier state is very important since, unlike strangles (Streptococcus equi), once horses recover from influenza, they only shed the virus for a short period of time. With strangles, some recovered horses appear healthy but will continue to shed the bacterium for long periods of time, and may continue to infect other susceptible horses.

Facility manager Sally Howard is quoted as saying "Staff are always extremely careful to ensure all animals that are received by the charity are put into quarantine for at least four weeks and then thoroughly tested before being allowed to mix with the herd."

• This is a great quarantine plan. Unfortunately, something went wrong here. If there was a true 4 week quarantine and if good protocols were used, influenza would not have made it into the herd. An investigation should look into why influenza was able to break through this quarantine. Some possible explanations are neglecting to quarantine a horse, not quarantining a horse for the proper length of time, mixing quarantined horses (i.e. a horse could be quarantined for 4 weeks, but if it gets exposed to a newly quarantined horse near the end of this time period, it could become infected and be introduced to the herd before it shows clinical signs of disease), and people spreading the virus from quarantined horses to resident horses on clothing or other items. 

"The source of this infection is not yet known but we will try to discover and eliminate it."

• I understand the sentiment but it's not practical. The initial source is no longer an issue, at least in terms of managing this outbreak. There are no long-term influenza shedders, so the horse that brought influenza onto the farm is likely influenza-free now. What they need to do now is ride out the outbreak and figure out why it happened.

"Vaccines are available but the ongoing cost of protecting 271 horses would add significantly to the already high costs of maintaining the herd."

• That's a tough situation and one that is a constant challenge for centres such as this. If resources are limited, what stays and what goes? Proper herd health for that many horses is certainly expensive, and good infection control practices are very important when you have a lot of horses. This outbreak has shown what can happen when you don't vaccinate, and the costs and disruption of the outbreak certainly would have paid for a lot of vaccine, but hind sight is always 20/20.  Deciding how to spend limited resources is a difficult decision.

Fortunately, this outbreak should be controlled soon, in part because it has spread so widely on the farm. There are few susceptible horses left, and when the influenza virus cannot find any more horses it can infect, it will disappear.

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The glanders outbreak in Bahrain does not appear to be under control or slowing down. Official data are limited, but anecdotal reports that I've received directly and from various internet and news reports paint a concerning picture. A Facebook page has been started, and contains some interesting first-hand information about the outbreak and local efforts to stimulate a more aggressive outbreak response. The latest data from the OIE, which was submitted May 10, reports six infected horses, all of which were euthanized. It also states that the first two positive horses came from Syria and Kuwait six months ago, and that other horses in the same stable then became infected. It will be interesting to see whether any more information is forthcoming, and to find out:

• How many animals have been diagnosed now?
• If there is a history of glanders on the farms from which the index horses originated? (Did it really come from another country, or might there be an unknown local source?)
• What control measures are actually in place? Some people in Bahrain describe a very lax approach to control in some areas.
• How many horses are being tested? You can only identify the scope of the problem with widespread testing.

Image source: Stop-Glanders-in-Bahrain Facebook page

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Iceland's sure having a tough time lately. From financial crises to volcanos, it's been in the news a lot lately. Now there's more bad news, at least for horse owners in the country. An apparent outbreak of respiratory disease is spreading in horses across the country. This is causing concern because of the potential for disruption of the big national horse shows that take place in the summer.

I haven't been able to find much specific information at this point. One news article states that the disease hasn't been "analyzed" yet, but it appears to be an infection that has not been identified in the country before. Playing the odds, an outbreak of respiratory disease that spreads quickly in horses in a region is probably equine influenza. Iceland is considered equine influenza-free, so if the virus made it into the country, it could spread quickly and widely, as was shown in Australia a couple of years ago. Containing influenza in a country where it has not be present before can be difficult, because few to no horses have any natural immunity.

Prompt determination of the cause and aggressive infection control measures are required to contain the problem, whether it's influenza or something else. Vaccination can be a useful tool in response to influenza outbreaks, particularly intranasal vaccination. However, vaccination is only part of the response and can't be the sole measure. Vaccination takes time to have an effect. It also takes time to get the vaccine into the country and into the horses. This can be particularly problematic if there are restrictions on importation of the vaccine. This was and still is a contentious issue in Australia.

Hopefully, a specific diagnosis will soon be determined and proper infection control measures will be implemented. While the summer show season is presumably important to many people, it's critical that control measures, including quarantine of affected properties and restriction of horse movement, take precedence. Failure to properly implement required precautions based on a desire to avoid disrupting shows usually just leads to a prolonged and larger outbreak.  Short-term pain for long-term gain needs to be the philosophy.

Image: Overview of the 2nd fissure on Fimmvörðuháls, close to Eyjafjallajökull (the volcano in Iceland that erupted on April 14, 2010 causing major disruption to international air travel). (Photo credit: Boaworm)

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The current glanders outbreak in Bahrain has led to questions about how to control this disease. When determining an outbreak response plan, you need to know some basic information about the bug and how it is transmitted. Here are some relevant pieces of information about this disease:

Burkholderia mallei, the cause of glanders, is a bacterium that is highly contagious and highly fatal.

• Highly contagious and highly fatal are a bad combination, so the need for a prompt and thorough investigation is clear.

It is transmitted by direct contact. The bacterium is shed mainly through oral and nasal secretions and skin ulcers.

• Horses can transmit the disease by close contact with other horses. Transmission through items that are likely to be contaminated, such as feed and water buckets, is also possible. Transmission through other contaminated items like tack or anything else that has had direct or indirect contact with secretions from the horse could also occur.
• This means that a careful investigation must be performed to ensure that all horses that have potentially been exposed (directly or indirectly) are identified. People working with infected horses (e.g. veterinarians, farriers) can spread the bacterium between farms on their clothing or instruments. All these potential sources need to be investigated, which takes time and effort.

It primarily infects horses, mules and donkeys, but can occasionally infect other species like dogs, cats, camels, goats and people.

• This means that the focus of the investigation and the control meausres cannot focus on horses alone. All animals in contact with infected horses should be tested.

Infected horses may show a range of clinical signs. There are three main forms of glanders: nasal, pulmonary and skin. Nasal discharge is common, as are nasal ulcers. Fever is usually present and can be very high. Other signs that may be present include enlarged lymph nodes and bumps on the skin. Skin ulcers can develop (see image). Affected horses may cough, sometimes severely. Severe disease can develop and death can occur within a few days. Untreated, about 95% of horses will die.

• Signs of glanders, especially early in the course of infection, aren't necessarily dramatic, and could be mistakenly dismissed as routine viral upper respiratory tract infection. During an outbreak, any animal with respiratory disease must be promptly evaluated as a potential glanders case.

Infected animals that survive can shed the bacterium for years.

• This means that the outbreak won't naturally "burn itself out" like some other diseases. If all infected horses are not identified, a reservoir of infected horses may remain to continue to infect other horses.

Glanders can be diagnosed using various tests.

• The availability of tests, some of which are fairly rapid, facilitates control. The key is getting samples for testing and ensuring that the right animals get tested.

Glanders has been eradicated in many areas of the world.

• This means a couple of things: 1) The disease is potentially controllable. 2) Based on the government's response, it seems glanders is not normally seen in Bahrain, therefore significant efforts should be expended to get this outbreak under control at a national level if the coutry is to return to its previous state with regard to this disease.
• A critical question that needs to be answered is from where did the disease come in the first place? It appears glanders is considered a foreign disease in Bahrain, even though it is endemic in other countries in the region. Unless a clear source of infection identified, you have to wonder whether the bacterium is present in some small percentage of the horse population already.

Animals that recover from infection do not develop protective immunity.

• With many infectious diseases, individuals that have been infected are no longer susceptible for a certain period. This helps control the disease because the number of susceptible individuals decreases over time. The fact that the disease is highly fatal reduces the impact of this factor, but any horse that recovers has to be considered susceptible again.

B. mallei is susceptible to most disinfectants, if used properly. It can survive in the environment for prolonged periods of time, but is better able to survive in humid environments.

• Prolonged environmental survival is a concern. Unlike some organisms (e.g. influenza), you can't assume that this bacterium will die quickly on surfaces contaminated by infected horses. You need to identify potentially contaminated sites and disinfect them. Disinfection must be done properly, which is often a problem. One potentially helpful characteristic of this pathogen may be its preference for humid or wet conditions. I don't know much about the Bahraini climate but, based on its location on the Persian Gulf, hopefully at this time of year hot and dry weather predominates.

These are just some of the points to consider when developing an outbreak investigation and intervention plan. A key to any outbreak response is to take the time to think about what is going on, what might happen, and what needs to be done. Sometimes, people start acting without thinking everything through, which may lead to missing important aspects, and wasting time and money on irrelevant areas. Let's hope this investigation is being done in a thorough and thoughtful manner. Hopefully more details about the response will become available.

Image: Artist's rendition of a horse with glanders, showing characteristic purulent skin ulcers on the medial aspect of the hind leg. (click image for source)

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A recently reported outbreak affecting horses in Bahrain has been diagnosed as glanders, a very serious bacterial infection caused by the highly contagious bacterium Burkholderia mallei. So far, it has been reported that 8 horses were euthanized over the past 3 weeks because of the infection.

Bahrain's cabinet has allocated BD150 000 to fight the outbreak. Authorities have apparently stated that the outbreak can be "easily" managed, "We have sent samples from nearly 400 horses to a specialist laboratory in the UAE and the 10 results we have got so far give us the all-clear. We now know we can manage this quite easily and are taking appropriate action."

That's a pretty dangerous sentiment to be expressing (and believing) early in an outbreak, but hopefully it's true. "Easily" and "outbreak" aren't often uttered in the same sentence, and it's far from unusual to be fooled by an allegedly contained or controlled outbreak. I'd be very surprised if all of the positive horses have already been identified. Control of glanders involves widespread testing of horses, typically with euthanasia of any infected animals. It sounds like testing is underway and results of this will give a good indication of the extent of the problem. Ten negative samples don't mean that much to me. As more results come in (and if they continue to be negative), more confidence can be had in the assessment that this outbreak is truly contained.

Glanders is not solely a concern for horses. It's a zoonotic disease that can cause rare but serious infection in humans, with a high mortality rate (almost 100% if proper treatment is not administered). People can become infected by direct contact with infected horses, with the bacterium gaining entry through skin abrasions, inhalation or contact with tissues of the mouth and nose. Pneumonia, bloodstream infections and other problems can develop. Burkholderia mallei is a Class B bioterrorism agent. Hopefully, people working around infected horses are using appropriate infection control precautions to reduce the risk of infection.

Hopefully, more information will be available soon about this outbreak and results of ongoing testing.

Image: A horse with glanders (Burkholderia mallei infection), exhibiting the characteristic infectious nasal discharge.  Glanders is a reportable disease which has been eradicated from North America, Australia and most of Europe.

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A strangles outbreak has been identified in Northern Queensland, Australia.  The number of affected horses, the number of at-risk horses and the scope of the outbreak aren't clear, but Queensland authorities have made recommendations to the horse-owning public.

Veterinary officer Charlotte Williamson states "The best form of protection is an annual vaccination."

• Unfortunately, it's not. Strangles vaccination is moderately effective at best and should not be the primary component of a strangles prevention program. It can be potentially useful in high risk situations, but it's far from a cure-all. If you use vaccination as your main preventive measure, you may have a lower likelihood of your horse getting sick. If you have a good general infection control program that prevents S. equi from getting on the farm, the immune status of your horses doesn't matter.

Fortunately, other good infection control practices were highlighted by Dr. Williamson, including:

• Keeping horse gear and equipment clean and disinfecting equipment between use.
  
• Washing hands before and after handling different horses.
• Monitoring visitor movements on your property and avoiding visitor contact with your horses unless they have clean hands, clothing and boots.
  
• Keeping records of horse movements on and off your property. (Actually, keeping records doesn't help prevent introduction of an infectious disease, it helps identify how it got there when an outbreak occurs. More important is having proper protocols for moving horses.)
  
• Quarantining new horses to your property for at least two weeks before introducing with others. (This is better than no quarantine, but it doesn't pick up healthy strangles carriers, an important source of infection. If you really want to prevent introduction of S. equi, you need to test new horses. This isn't practical in all situations, unfortunately.)
  
• Isolating sick horses from other horses on your property. (This also requires good protocols for handling infectious cases so that S. equi isn't inadvertently spread from an isolated horse)
• Feeding and tending to sick horses after dealing with other horses

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An as-of-yet undiagnosed disease "outbreak" has affected at least 12 horses, killing two, in the Kingdom of Bahrain. Very little (and some conflicting) information is available about the mysterious disease, including a description of the clinical signs and whether it is actually infectious. One official stated that they don't think it's contagious, but it's probably a little premature to be making any assessments about transmissibility or sources of infection, if indeed it is an infection.

Bahraini authorities have "warned" horse and stable owners in the country against moving animals and to avoid equestrian events to help prevent the spread of infection. It's unclear whether this "warning" is a recommendation or a formal (enforceable) quarantine. Anytime there is concern about a new or serious disease, formal quarantine is indicated, at least in the initial period while things are being sorted out.

There are many potential causes for an outbreak like this. Not all of them, in fact, are infectious diseases, since toxin-mediated disease must also be considered. If multiple horses are being affected, the cause is more likely viral than bacterial, but bacterial, viral, fungal and parasitic diseases must all be considered. Samples from the infected horses are being tested in the UAE. Hopefully more information will be available soon.

Picture: Bahrain Coat-of-Arms (click for source)

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Strangles outbreaks are a pain. They can result in infection of a large number of horses and major hassles. Unfortunately, while many people behave properly during outbreaks, there are also people out there who either don't think, don't listen or don't care (or don't do any of these). 

I've had a few strangles outbreak calls this week and problems with people not listening to the veterinarian's or farm manager's recommendations have been a common theme. I realize that keeping horses on the farm while an outbreak is being addressed can be inconvenient, particularly for some people who have trained hard for specific shows, but taking your horse off the farm while a strangles outbreak is underway and exposing other horses to yours is completely unethical. People that take their horse off the farm in the midst of a strangles outbreak are a major cause of new outbreaks, and a big part of the reason this disease continues to be common.

If you have a horse that has been exposed to strangles, act ethically.

• Keep the horse at home while the status of the farm and the horse are being determined.
• Don't expose it to other horses until you know it's negative, ideally through testing it and getting three negative nasopharyngeal (throat) cultures.
• Don't kid yourself into believing that you can prevent infection of other horses at a show or another event. You can do things to reduce the risk, but if your horse is shedding S. equi (the bacterium that causes strangles) you cannot completely prevent the risk of exposure.
• Get good advice regarding how to address the problem (e.g. from your veterinarian), and listen to the advice.

You should also think about this:

• If you knowingly take an exposed horse somewhere and other horses get sick, could you get sued for any resulting problems? I don't know of this happening (yet), but it's certainly a possibility and you don't want to be the test case.
• Do you really want to be known as the strangles vector, and the person that caused an outbreak?
• Ignoring a strangles outbreak won't make it go away. In fact, trying to ignore it usually just leads to it being a more prolonged outbreak. It's really a matter of "short term pain for long term gain."

More information about strangles can be found in on the equIDblog Resources page.

Image source: www.regardinghorses.com

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An outbreak of botulism has killed 5 horses on a farm in Wisconsin, and is apparently also affecting cattle in the area.

It is suspected that the spring melt played a role in this outbreak, as was reported in a review of Type A botulism cases in horses that I discussed the other day. Botulism occurs when the bacterium Clostridium botulinum grows and produces toxins. To grow, it needs an oxygen-free environment. Clostridium botulinum can live in the environment in its dormant spore form for years, waiting for the right conditions to start multiplying. With a spring melt, you can get accumulations of hay that are soaked in water and starting to decompose. That can create a nice moist, oxygen-free environment with a good bacterial food source - perfect conditions for C. botulinum. If horses eat hay that the bacteria are growing in, they can get botulism. Other possible sources include feed that is already contaminated with toxin, something that is of particularly concern with large bales of hay, haylage and silage. Horses are exquisitely susceptible to botulinum toxin and extremely small amounts can cause disease. Identifying the actual source can be tough, but hopefully efforts to do so are underway in Wisconsin.

Three of the 8 horses on this farm survived. They were all treated with anti-toxin, which is very expensive (thousands of dollars). It's hard to say whether the antitoxin worked or whether the surviving horses actually weren't exposed to the toxin as the others were, but treating all potentially exposed horses is the preferred approach if you have rapid access to antitoxin and can afford it.

Photo soucre: www.edu.gov.mb.ca

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Hard to believe that the whole conundrum about contagious equine metritis (CEM) that is still affecting the Canadian equine industry started a little bit more than a year ago, when a Quarter Horse stud in Kentucky tested positive for the causative agent, Taylorella equigenitalis. Tracing the contacts of that stud lead to the quarantine and testing of 990 horses in 40 states, as well as 19 mares in Canada, including 9 in Ontario. Out of 274 exposed stallions, 22 were ultimately found to be positive, none of which had any detectable clinical signs that they were infected, meaning if they hadn’t been tested, they may have kept on going about their business breeding – and possibly infecting – mares for years to come. The rest of the exposed horses were mares, five of which turned out to be infected. One particularly interesting fact was that four of these mares had been bred by artificial insemination - previous to this it was thought that CEM was only readily transmissible by live cover from an infected stud, not via semen shipped in a straw.

Thankfully all of the Canadian mares were negative, but unfortunately the Canadian equine industry is still suffering the consequences of what has happened to our close southern neighbour. Fourteen countries have increased import requirements for Canadian (and obviously US) horses in terms of CEM testing, and another major blow was the loss of Canada’s low-risk status with the UK's Horserace Betting Levy Board (HBLB).

Canada must maintain strict import requirements for horses to prevent CEM from getting into the country. Most of the horses imported into Canada come from CEM-positive countries, and it’s getting more difficult to argue not including the US on that list as well. The risk is constantly present, and remaining diligent about quarantine and testing – and rules like ensuring horses are not on antibiotics for some other reason when they’re cultured – is key. Semen import restrictions for semen coming from the US to Canada will stand for 2010. While this certainly causes a headache for breeders, requiring an import permit and a health certificate for the stud stating that it has not stood on a CEM-quarantined farm, is it enough to protect Canadian horses? The next step would be to require all studs to be tested for CEM before their semen can be imported to Canada. That is no small request. Testing a stud involves culturing the stud himself, and then having him test-breed two mares which then also need to be culture-negative. Anecdotally the entire process can cost in the neighbourhood of $5-7K per horse, which at the moment all needs to be borne by the horse owner. That gives you some idea of what an enormous undertaking it was to quarantine and test 274 exposed stallions during last year’s outbreak.

In the US, 87% of exposed horses have now been cleared, and there have been no new positives in the last 8 months. However, there are still 17 states where there are quarantined farms. There is talk of voluntary testing of over 2000 studs in the US in 2010, as well as targeted surveillance of stallions imported in the last 10 years and those standing at large AI centers. Only time will tell if these extra efforts will serve to calm the fears of countries that are now hesitant to import horses and semen from the US, or whether they will reveal more cases of CEM and confirm the fears that CEM may have unknowingly become endemic in the US in the past decade.

More information on CEM is available in our archives.

This blog is based on a presentation by Dr. Tracey Chenier, a theriogenologist and faculty member at the Ontario Veterinary Collge, given at the recent 2010 Ontario Veterinary Medical Association Conference.

Photo credit: David Campbell (click for source)

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Often, when someone calls and asks about management of strangles, one of the first questions is "What disinfectant should I use?"

There are basically two answers that I give:

1) Streptococcus equi, the cause of strangles, is susceptible to most disinfectants, provided they are used properly. That means using them at the proper concentration, providing the recommended contact time (5-30 minutes, depending on the disinfectant) and ensuring that there is minimal organic debris (e.g. dirt, manure, pus) present on the surface to be disinfected. The latter is a key point, as disinfectants do not work well in the presence of debris, so it's therefore understandably very difficult to really disinfect a stable. Some stable surfaces (e.g. sealed solid walls and floors, buckets) are able to be disinfected if it is done properly, while other surfaces (e.g. dirt floors, unsealed wood walls, leather) are essentially impossible to disinfect.

2) Disinfection is a very minor component of strangles control. It is something to pay attention to and it should be done properly, but too often people to focus on disinfection as the key infection control measure. Just disinfecting surfaces, but ignoring aspects like cohorting exposed and unexposed horses, restricting horse movement, testing for carriers, regular temperature checks of all horses to detect early cases, using good personal hygiene and using protective outerwear, is bound to fail in terms of controlling an outbreak.

So, don't ignore cleaning and disinfection, but don't' rely on it as the main component of strangles control.

More information about strangles can be found on the equIDblog Resources page.

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The latest edition of the journal Emerging Infectious Diseases contains a paper describing the 2008  Australian Hendra virus outbreak in horses and people.

In this outbreak, there were five horses infected and two humans infected. The horses predominantly had signs of neurological disease, not respiratory disease like some other reports describing this disease. Four horses died. One recovered but was euthanized for public health reasons.

Two people became infected after working with the sick horses, which represents 10% of the total veterinary staff that were exposed to the infected horses.  Both people started off with influenza-like illness, which seemed to improve initially, but then signs of severe neurological disease developed. They were treated with ribavirin, an antiviral drug, as part of an experimental treatment. One of them died after 40 days of illness, the other person survived.

The authors stressed that the effectiveness of ribavirin could not be determined, but they recommend it nonetheless because of the severity of Hendra virus infection and lack of other options. Ribavirin was also used in the 2009 outbreak, but it is clearly not 100% effective since one person died there also.

A number of concerning activities occurred that put people at risk of infection, including a "percutaneous blood exposure while euthanizing an infected horses" (they didn't explain exactly what this was, but it could have been a needlestick), low use of personal protective equipment, and contact with potentially infectious body fluids. This is unfortunately not surprising since the approach to infection control (particularly in terms of zoonotic infections) is often lax in equine medicine. That certainly has to change, particularly in areas where Hendra virus may be present.

Much more information about how to control this potentially devastating virus is needed. Fortunately, infections are uncommon and it is restricted to a fairly small geographic range in Queensland, Australia.

Image source: http://animalphotos.info/

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Equine infectious anemia (EIA) virus, a chronic and potentially devastating bloodborne virus, was identified in two horses in Britain. The two affected horses were from a group of horses imported from Romania via Belgium. They were tested as part of standard import testing regulations designed to do exactly what happened here - diagnose this important infectious disease at the time of importation so that the infected horses cannot spread the disease in the country. The two positive horses will be euthanized, the unfortunate but standard response to this virus, because infected horses can pose a risk of infection to other horses for their entire lives. Other horses on the premises are under quarantine and are likely being tested further. The risk of transmission to other horses during the presumably short period of time they've been on the farm is probably low because, as an insect borne disease, biting fly activity has probably been pretty low during the cold British winter weather. (Transmission by sharing needles or other human-associated ways of cross-contamination of blood is also a concern, and has been a problem in other outbreaks.)

Chief veterinary officer Nigel Gibbens stated that these are the first imported cases of EIA identified since 1976. This is a good example of why we need to continue routine infection control measures such as import testing, even when nothing is found for years. Some people try to argue that since certain problems don't seem to be present, or at least are not identified, that infection control testing or activities should be decreased. This situation illustrates why that's bad thinking. Despite only picking up one incident in the past 34 years, this is a very important finding - failure to detect the positive horses could have lead to widespread infection in the country, which would ultimately make it very difficult and expensive to try to control. You never know when the next outbreak is lurking around the corner, and complacency is a big enemy of infection control.

Image source: www.collectgbstamps.co.uk

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At some point, the US is going to have to admit that piroplasmosis, the bloodborne parasitic infection caused by Theileria equi, is endemic in some regions of the country. It's a declaration that will have major impacts on horse movement to some areas but, it's better for everyone to know what's going on. Piroplasmosis is technically still considered an exotic disease in the US, but there have been many cases identified over the past year and a clear source for the individual outbreaks in lacking, indicating there must be a reservoir in some part(s) of the country.

The latest incident involves the diagnosis of piroplasmosis in three race horses in New Mexico, which were picked up as part of routine screening. There were only three positives out of about 1200 horses tested, so the disease is still rare, but the fact that it was there and none of the positive horses had any link with previous outbreaks is definitely a concern. The OIE report states that transmission is suspected to have been from "artificial" means like sharing needles between horses, not natural tick transmission. This could account for the multiple horses affected but doesn't explain where the disease came from it the first place, and it's unclear how solid that hypothesis really is.

It's quite interesting (surprising, frustrating...) that few comments are put forth in any of these outbreaks indicating where the infections may have originated and why we are seeing recurrent, unrelated infections. Is increased testing in different areas helping to pick up cases that would otherwise have been missed (i.e. were already there), or is piroplasmosis in the US an emerging problem? How confident are they that there are no ticks capable of transmitting T. equi in some of these areas? Is wider screening of horses required to determine the extent of the problem and to determine whether it can be controlled? Is broader screening of ticks in the affected areas needed to see if there are ticks known to be able to transmit T. equi? Are studies needed of other tick species in areas where unexplained cases have occurred to determine if some tick species that are not currently known to be able to spread the parasite can actually do so? Lots of questions... hopefully someone's trying to find some answers.

Click image for source.

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Three barns at Calder Race Course in Florida have been quarantined after a horse was diagnosed with equine herpesvirus (EHV-1) infection. Horses from this barn are quarantined for 3 weeks and are not allowed to race. Other horses will not be allowed to enter the grounds for the next 2 weeks, but racing will continue with horses that are currently on the grounds and not under quarantine (1800 horses are present at the track). Track personnel believe the infection has been restricted to one horse but are taking these measures proactively.

Equine herpesvirus can cause a range of clinical signs, including fever and respiratory disease, severe neurological disease and abortion. The affected filly in this case had neurological disease and was euthanized. Outbreaks of abortions or neurological disease are the greatest concern, and a specific type of EHV-1 has been implicated as the main cause of neurological disease.

It's always hard to say what the most appropriate response is to a scenario like this. Equine herpesvirus is an endemic virus that is present throughout the world and lies dormant within a large percentage of healthy horses. Most infections are sporadic and only involve a single horse or small number of horses, but outbreaks can occur and that's why aggressive measures are sometimes taken. With only a single diagnosed case and no apparent evidence of transmission to other horses in this case, it's uncertain whether such an aggressive approach is required. However, it's worse to be too lax initially than too aggressive, and a logical approach is to implement aggressive measures, and then reassess them as more information becomes available. If no other horses develop signs consistent with EHV-1 infection, then loosening of the restrictions would be reasonable. If there is evidence of transmission and disease in other horses on the property, continuation with aggressive measures makes the most sense.

A great resource regarding EHV-1 is the ACVIM Consensus Statement on this subject, which is available on the equIDblog Resources page.

Image source: www.calderracecourse.com

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A large number of infected horses has now been identified in association with the ongoing outbreak of piroplasmosis in the US. Three hundred seventeen (317) positive horses have been identified in 11 states: Texas, Alabama, California, Florida, Georgia, Louisiana, Minnesota, North Carolina, Tennessee and Wisconsin. Two hundred eighty eight (288) of the positive horses are from the index farm in Texas. All positive horses are under quarantine (and will likely be euthanized), and testing of other in-contact horses is ongoing.

This report is very concerning for several reasons:

• A previous report indicates that positive horses were likely on the index farm for at least a year or two, making it likely that more infected horses are out there. The longer a disease like this goes unnoticed, the farther it can be spread before it's detected and controls are put in place. It's possible that an even larger number of infected horses are in the US now.
• The widespread infection makes it more likely that the disease will establish a true foothold in the US. This bloodborne parasitic disease (caused by Theileria equi) is naturally transmitted by certain types of ticks (not all tick species are able to transmit the parasite). The more areas in which infected horses are found, the greater the chances that infected horses will be bitten by ticks that can transmit the parasite. If it gets established in the tick population, it becomes much harder to control.
• It's not known how so many horses became infected. With this number of infected horses, it seems to me that tickborne transmission is more likely, rather than human-associated transmission through re-use of needles or other means of transmitting bloodborne pathogens. If the disease is being spread through it's natural route, it's harder to control.
• It is still not clear where this outbreak (or the other recent US outbreaks) originated. If you don't know how something started, it's hard to prevent it from happening again.

Piroplasmosis may be on its way to becoming an endemic (established) disease in the US. Broad investigation is required to see if it is present beyond the affected premeses identified so far.

Image source: http://animalphotos.info

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Following on the heels of a few outbreaks of piroplasmosis in the US over the past year is a report of two piroplamosis-positive horses from New Jersey. This bloodborne parasitic disease is officially a foreign disease in the US, but the number of recent outbreaks and their unknown origin certainly suggest that this disease has a solid foothold in the US. The latest situation in New Jersey involves two horses purchased from the Texas farm which is currently under quarantine due to its involvement with the most recent outbreak of piroplasmosis in that state. However, these two horses were purchased in 2008, which strongly suggests that this disease has been in the Texas herd (and presumably elsewhere) since at least that time. Odds are this disease is actually wide-spread in some areas of the US.

Losing national piroplasmosis-free status could have significant repercussions on horse movement to and from the US, and a major impact on the equine industry overall. For this reason, some people might prefer to try to ignore the problem and hope it goes away. But, as I've said before, hope is not an infection control strategy.  It's much better to investigate this carefully and transparently to figure out what is going on. Without knowing the scope of the problem, it's impossible to control it.

Image source: www.australiasigns.com.au

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The following report was provided by the Texas Animal Health Commission:

--------------------------------------------------------------

November 4, 2009

Equine Piroplasmosis Disease Investigation Continues

Canada and a number of U.S. states have imposed movement restrictions or additional entry requirements for horses from Texas after equine piroplasmosis, a tick-transmitted blood disease of equine animals, such as horses, donkeys, mules and zebras, was detected in South Texas in mid-October.  Equine piroplasmosis may be carried and transmitted by as many as 15 species of ticks.  Although ticks have been collected from the South Texas ranch for testing, final results are not complete, and it is not known whether any of the ticks can serve as a host for the disease.

“Before moving horses from Texas, we urge you and your veterinarian to check with animal health officials for any state of destination, to ensure the animals have met all entry requirements,” said Dr. Bob Hillman, Texas’ state veterinarian and head of the Texas Animal Health Commission (TAHC), the state’s livestock and poultry health regulatory agency.  “Regulatory requirements can be fluid as disease situations evolve, so it is essential to call each state each time you haul.”  As states provide entry restrictions and requirements, the documents are posted on the TAHC web site at http://www.tahc.state.tx.us.  Dr. Hillman urged equine owners and veterinarians to call state animal health officials directly before hauling, as many states have not yet distributed entry requirement information. Contact information for state veterinarians may be obtained from the TAHC at  800-550-8242, ext. 710, or by emailing ceverett@tahc.state.tx.us.

“We are continuing the equine piroplasmosis disease investigation initiated in October in South Texas. No horse movement is being allowed from or to the ranch where the infection was detected,” said Dr. Hillman.  “While this tick-borne disease has not been considered endemic in the U.S., cases of the disease, scientifically known as Theileria equi, and previously called Babesia equi, have been detected in the U.S.   Our epidemiologists are tracing the movement of specific equine animals. Blood tests will be conducted, and the animals will be examined for ticks. Individual equine owners will be contacted, if their horse needs to be tested by animal health officials.”

Dr. Hillman refrained from speculating on how many equine animals will be tested or how many may be exposed or infected.  “Until the epidemiological work and testing of potentially exposed horses is completed, there is no way to predict how many horses may be affected with this tick-borne illness,” he said.

Dr. Hillman said horses infected with equine piroplasmosis may appear well, while others may exhibit a host of non-specific clinical signs, such as fever or anemia. These clinical signs also could be attributed to a variety of other diseases or causes. Blood tests are needed to diagnosis the disease. 

“Equine owners should talk with their private veterinary practitioners about complying with interstate movement requirements, testing recommendations and protecting their horses from ticks.  If a horse appears to be ill, it should be evaluated by an accredited private veterinary practitioner,” said Dr. Hillman.

Texas Animal Health Commission
Bob Hillman, DVM * Executive Director
For info, contact Carla Everett, information officer, at
1-800-550-8242, ext. 710, or ceverett@tahc.state.tx.us

We thank Carla Everett, Texas Animal Health Commission for sending this report.

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The ongoing large piroplasmosis outbreak on a Texas farm, following on the heels of a few other US outbreaks, raises concern that this infection is not really a "foreign" disease in the US (at least not anymore). Although the source of the earlier outbreaks was not identified, they did not raise too much concern because ticks capable of transmitting this bloodborne infection were not found (which reduces the risk of uncontrolled spread of the disease). However, the situation may be different in Texas. Following identification of the first case, 31 more positive horses were identified on the affected farm. That's a lot of infected horses, and given the number it's probably less likely that the infection was spread by human activity (e.g. reusing contaminated needles) than by ticks. Concern has been expressed over the past couple years that Boophilus microplus and Rhipicephalus microplus, ticks capable of transmitting this parasite, might be establishing themselves in the state of Texas. If this is the case, this may not be an easily controllable situation, and the US may lose its piroplasmosis-free status. Intensive investigation of the source of this outbreak, how it was spread on this farm, whether there are other affected horses in the region and whether these tick species are present, is urgently needed.

Image: A "hard tick" (male brown dog tick (Rhipicephalus sanguineus)) from the same genus as R. microplus, one of the tick species capable of transmitting piroplasmosis (Theileria equi) to horses. (CDC Public Health Image Library #7646)

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For a country that is "piroplasmosis-free," the US sure has a lot of piroplasmosis. The Texas Animal Health Commission has reported that this bloodborne disease, caused by Theileria equi, has been confirmed on a ranch in south Texas. The farm is quarantined and testing is under way to determine the scope of the problem. They are presumably also looking at ticks in the area to see if the types of ticks that are able to transmit the infection are present, and trying to figure out where the infection came from.

This is one of a couple of recent outbreaks of piroplasmosis in the US. The source of infection in these outbreaks is typically not found, but careful testing and quarantine of animals is usually effective at containing the disease. Unfortunately, positive horses can be infected for life, and are therefore usually euthanized. Long-term isolation or shipping infected horses to a country where the disease is endemic are other options.

Interestingly, I've not seen any comments about whether this outbreak could be linked to the recent outbreak is Missouri, where some infected horses were taken out of quarantine and have disappeared. It's certainly logical to consider that one of the fugative horses may have been  smuggled into Texas and been the source of this latest infection. Hopefully this is a small, contained outbreak that doesn't result in widespread death of horses and economic disruption. Hopefully the source is identified promptly and measures are taken to reduce future problems. Only time will tell.

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After a rather lengthy process, Hoosier Park (Anderson, Indiana) has lifted its strangles quarantine. A quarantine was implemented on September 12th after a horse on the premises began exhibiting signs of strangles. Fifty-four horses were placed under quarantine. When S. equi, the bacterium that causes strangles, was identified in a quarantined horses, officials decided to move all quarantined horses out of the track facility. Presumably, once it was clear that the quarantine was not just a matter of waiting for confirmation that all horses were actually negative, they decided that the risk of having potentially infectious horses living at the track was unacceptable (pretty logical thought process). Now that those horses have been removed and no other cases have been found in the approximately 1000 other horses housed in the other track barns, they are back to business as usual. The quarantined barn is being disinfected and will not be used for the rest of the 2009 racing season.

This incident demonstrated a very aggressive but apparently effective response to strangles. They have presumably ended this latest outbreak and hopefully won't have to deal with it again. However, infectious diseases and outbreaks are inherent risks in the racing industry (as well as other competitive horse industries). The way we manage race horses, moving them around, mixing them, having various (and sometimes minimal) preventive medicine programs, having minimal measures to keep sick horses off the track, and a financial disincentive (i.e. people lose money) to keep horses away, means that infectious disease risks are not going to go away. It's not a question of whether there will be another strangles outbreak on a racetrack. It's a question of when and where.

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At the ongoing ASM-ESCMID conference on methicillin resistant staphylococci in animals, Dr. Engeline van Duijkeren of Utrecht University (The Netherlands) presented a study on an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) in their equine hospital.

From 2006-2008, several horses that underwent surgery at their hospital developed MRSA infections.  MRSA was also isolated from some healthy horses and personnel at the clinic. Early in the process, the hospital was closed for a thorough disinfection and the outbreak stopped, however another outbreak occurred later.  Further study again found people in the clinic that were MRSA carriers. Close to 15% of people in the hospital who handled equine patients were MRSA carriers, which is really astounding when you consider that less than 0.1% of the general population in the Netherlands carries MRSA. When they started testing horses coming into the clinic, they found that 9.3% of horses were carriers when they arrived. Weekly sampling of all hospitalized horses over a five-week period determined that 43% of all horses in the hospital carried MRSA at one point or another during their stay. Additionally, 53% of environmental surface samples were positive for MRSA, which is really not surprising if that many people and horses are carriers.

If horses keep coming into a facility carrying MRSA and people keep getting colonized, MRSA is hard to control. These experiences led the equine hospital at Utrecht to implement more stringent infection control practices to try to contain the problem, but the high MRSA rate in their referral population is going to pose a continual risk.

MRSA outbreaks in horses aren’t new. They’ve been reported by a few hospitals (including ours) and occur in many, many, (many!) more without ever being published. Since MRSA is present in the horse population, equine hospitals are at continual risk of MRSA outbreaks. If a large percentage of horses in the general population are carriers, the risk of outbreaks is higher.

MRSA is clearly a problem in horses in many areas. It’s important to realize that it’s a problem in the general population, not just horses in hospitals. Equine hospitals can amplify the spread of MRSA, but ultimately a lot (if not most) MRSA-positive horses originate from farms, not clinics or hospitals. Equine hospitals need solid infection control programs to reduce  the risk of outbreaks, but the risk will never be completely eliminated. Farms need good infection control programs to reduce the risk of spread of MRSA between horses and between farms, as well as from horses to people (and back). Antibiotics need to be used prudently since antibiotic use is a risk factor for MRSA carriage and infection.

More information about MRSA in horses can be found on the equIDblog Resources page.

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Another strangles scare has resulted in a trio of horse trainers being banned from racing in New Zealand until October 7.  New Zealand Thoroughbred Racing (NZTR) is taking a hard line with this particular outbreak, especially with the upcoming Kelt Capital Stakes premier raceday on October 3.  While they're trying to do the right thing to protect the larger racing population, there are a few things going on that simply don't quite add up.

All horses from the affected farms are banned from racing facilities for 21 days after the last known case had run its course (reportedly September 16): That's great, but... 21 days is the isolation period typically used to detect clinical cases of strangles (i.e. exposed horses that get sick will usually do so within 21 days).  However, some horses, particularly those recovering from being sick, can shed the strangles bacterium for much longer than this.  In order for such a ban to really be effective, horses from the property should also be tested to ensure they are not shedding Streptococcus equi subsp equi before being allowed in more public facilities.

In a press release issued by NZTR on September 23, it is stated that "An isolation period of six weeks is usually necessary to ensure that the disease is not still incubating before ending the isolation.": Why would they make such a statement and then only isolate these properties for three weeks?

The same press release states "...controls have been put in place, as recommended, and this should ensure that the risk of further spread will be effectively controlled."  If the NZTR thinks that banning horses from the affected farm and the neighbouring properties from the track is going to eliminate the risk of strangles, they're deluding themselves.  As we've said before, strangles is an endemic disease in the horse population, and there are certainly other horses in New Zealand that are carrying strangles.  Any time a large group of horses get together there is risk.    The best way to reduce the risk is to ensure that simple, practical infectious disease control measures are in place, and followed, every day.  Statements like this just give people a false sense of security.

Strangles was initially identified in a horse from a sale that was brought onto the farm over a month earlier.  The horse was isolated on September 8 for being sick, and diagnosed sometime in the following week:  There are a few good points here.  First of all, it demonstrates a classic example of a "normal" carrier animal (the "trojan horse" if you'll forgive the pun) from a sale (making it high risk for carrying infectious diseases) that was brought onto a farm and likely not isolated and tested, ultimately resulting in an outbreak on the farm which is now affecting the ability of all the horses there to race.  Classic.  Furthermore, this horse from the sale arrived on a truck with several other horses which were delivered to three other properties in the area.  There is no indication that these other horses have been tested to see if they are carriers, nor that the other properties have been inspected.  Based on the ban that has been slapped on the currently affected property and its neighbours, I could see trainers and owners being reluctant to report any new cases, or even horses with a fever, for fear of the same thing happening to them.  Also, I have to wonder, if there was a known strangles case on the index farm since at least last week, why did it take until September 23 for the NZTR to issue the ban? 

"...once strangles was diagnosed, all the horses on the Cottle property - minus the infected ones - were vaccinated [for strangles].": Vaccination in the face of an outbreak is actually not recommended according to the strangles consensus statement from the American College of Veterinary Internal Medicine.  Particularly with a known carrier having been on the farm for a month, by that time all the other horses were likely already exposed, and vaccinating them at that point merely puts another drain on their systems.

"The barn yard was disinfected but the bedding was not replaced.":  I've never seen nor heard of a barn yard that could actually be effectively disinfected.  It would have to made entirely of sealed wood/concrete or metal, and even then it would be a momentous task and likely still impossible.  I don't doubt they gave the area a thorough cleaning, but it was not disinfected.  The fact that the bedding was not replaced surprises me - this seems like one of the simpler, easier things to do.  While it also can't guarantee a strangles-free stall, any horse that is shedding the bacterium is likely to have highly contaminated bedding, and removing it at least decreases the environmental pathogen burden.  The article also states that "the bacteria can survive in bedding and soil for at least eight months."  Perhaps under ideal sheltered conditions this may be possible, but a study presented last year showed that in the "real world" S. equi probably only survives in the environment for a few days.

Both the article and the press release do make a few sound recommendations in the end, including adopting hygiene guidlelines such as replacing bedding, disinfecting water troughs and feed buckets and other equipment, avoiding mixing and moving horses, being aware that people are a potential source of cross-contamination, and of course our favorite: "As with any contagious
disease, handwashing is a simple and effective tool."

More information on strangles is available on the equIDblog Resources page and in our archives.

Image: Banned trainer/owner Tim Symes, with his horse Molly O'Reilly (source: www.hawkesbaytoday.co.nz)

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The Kentucky state veterinarian has banned horses kept at Hoosier Park racetrack (Anderson, Illinois) from barn areas of any Kentucky racing facility because of concerns about strangles. Two Hoosier Park horses were diagnosed with this highly infectious disease caused by the bacterium Streptococcus equi, and 57 horses have been quarantined. Horses from Hoosier Park that have been isolated and monitored for 21 days may enter Kentucky facilities.

The idea behind the 21 day quarantine is that within 21 days, most horses that have been exposed to strangles will develop signs of disease within that time period. However, the problem is that horses that have been infected with strangles can get over the infection and look great for 21 days (or much, much longer) but still carry S. equi in their throats or guttural pouches. So, while this is a reasonable approach, it by no means guarantees that S. equi will be kept out of Kentucky. However, in reality there are never any guarantees when it comes to infectious diseases like this. While some cases of strangles get a lot of attention, it's an endemic disease that is circulating in the horse population, and certainly is present in some horses in Kentucky already. Responding to outbreaks and limiting the risk of outbreak-associated transmission is very important, but it's equally important to make sure that routine infection control practices are in place on tracks (and elsewhere) to reduce the risk of disease transmission every day.

More information about strangles can be found on the equIDblog Resources page.

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The recent piroplasmosis outbreak in Missouri and Kansas has been declared resolved. The concluding report has a few interesting findings:

Evidence indicates that in this outbreak, ticks, the typical vector of the disease, did not play a role in the transmission of the bacterium that causes piroplasmosis, Theileria equi. No infected ticks were identified and all ticks that were found on the farms were species that have not been shown to transmit the infection.

Disease transmission was attributed to poor management practices such as needle sharing between horses, which can result in transmission of bloodborne disease, including piroplasmosis. (Needle sharing is always a bad idea. There aren't too many bloodborne diseases in horses, but it's still stupid to reuse needles. They're incredibly cheap and there is no valid reason to do this).

The failure to find ticks that can transmit disease suggests that the risk peiod is over in the affected area. No one has explained, however, where this infection came from in the first place. That's an important issue that hasn't received a lot of attention.

There's also the sticky issue of the vanishing quarantined horses. Three infected horses were illegally taken out of quarantine and still have not been recovered. Therefore, "resolved" is a questionable term. The local outbreak is probably over, but these three escapee horses could still be a threat to the horse population wherever they are. The report states that unsubstantiated information indicates the horses may have been taken out of the country. That's obviously a concern for neighbouring countries like Canada.

Hopefully, this episode is really over. Hopefully the infected horses have been taken to an area where there are no ticks capable of transmitting disease. Hopefully people that have them are smart enough not to reuse needles. Hopefully the illegal and reckless action of sneaking out infected horses doesn't cause an outbreak elsewhere and result in the deaths of more horses. However, hope should not be an infection control strategy.

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During a strangles outbreak, people often ask how (and when) they can say their farm is "strangles-free." They usually don't like the answer. Declaring a facility to be free of strangles, a highly contagious disease caused by the bacterium Streptococcus equi, is not cheap, easy or quick. It is, however, important.

A major source of the strangles bacterium is horses that have been infected but either didn't get sick or have recovered, yet are still shedding S. equi in their nasal secretions. In some horses, S. equi can persist for long periods of time (i.e. months) in their nasopharynx (throat area) or guttural pouches. Identification of these carriers is crucial for strangles control and must be done to have confidence that strangles has really been eradicated from a farm.

Identification of carriers involves taking samples from the nasopharynx to test for the bacterium. Nasopharyngeal washes are preferred but nasopharyngeal swabs (note: this is different from a nasal swab) are also acceptable. These should be collected by a veterinarian. They can be tested for S. equi by culture or PCR (a molecular test), or both. Any positive horses need to be investigated further, including endoscopy and culture of the guttural pouches.

Three negative samples from the nasopharynx and/or guttural pouches, collected weekly, are required to declare a horse free of strangles. If a positive horse is identified during the process, the clock starts again on its testing, plus all other horses with which it has had contact. Even though a horse may have had three negative samples, if it has been in contact with a positive horse, you have to assume there's a chance it was infected after testing started, so you need three more samples after its last contact with any positive horse.

While this process is not cheap, easy or quick, it is strongly recommended.

At the same time, it's also a good idea to review why the strangles outbreak occurred and how it can be prevented in the future. This is a step that's often overlooked.

More information about strangles can be found on the equIDblog Resources page and in our archives.

Image: A horse with draining tracts from classic strangles abscesses between the lower jaw bones

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An Australian horse group, the Queensland Horse Council, is calling for the equine industry to change its culture in terms of biosecurity. I agree completely, however, as I've said before, I think the term "infection control" is really what we are talking about here. Biosecurity involves keeping pathogens off a farm, as is done with tight controls on pig farms. Infection control also tries to do this, but realizes it's not completely possible with how we manage horses, and therefore also focuses on controlling the impact and spread of infectious diseases on the farm.

This is obviously in response to the recent Hendra virus outbreak in Australia. It usually takes a remarkable (and sometimes tragic) event to get people talking about infection control. It becomes a hot topic, people call for improved efforts and resources, and everyone gets on board... for a few weeks. After a short period of time without problems, people tend to revert to their usual behaviour, and infection control often gets marginalized again. The key, therefore, is establishing a sustained effort. That's the hardest part of infection control, be it in a hospital or on a farm.

Queensland Horse Council (QHC) president Debbie Dekker is quoted in the Sydney Morning Herald as saying "We are a pretty gung-ho lot and biosecurity is treated like some sort of wussy thing. Everyone needs to tighten up their biosecurity practices."

Well said.

"We still have a lot of people who don't know about Hendra virus so we need to get the information out to horse owners."

Communication and education are key. Just telling people they need to do something is not going to be very effective. Infection control practices usually involve some degree of effort or change in normal practices. If people don't understand why they should change, they are less likely to do so.

Sporadic infectious diseases and outbreaks will continue to happen (in horses, people and others). We can never completely eliminate the risk. We can, however, reduce some of the risks. While nothing can change what has happened with the most recent Hendra virus outbreak, we should at least make sure some good comes out of it, and that it leads to improved infection control awareness in Queensland and beyond.

Thanks to Dr. Doug Powell of Barfblog for the headline.

Image source: www.qldhorsecouncil.com

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Colorado State University veterinarians have issued a warning to horse owners in the state to be on the lookout for pigeon fever. They are reporting a spike in cases along the northern Front Range of Colorado.

Pigeon fever is a highly contagious disease caused by the bacterium Corynebacterium pseudotuberculosis. It is an important disease in areas where it's common, but it is essentially unheard of in other regions (I've never seen a case myself). This bacterial infection typically causes abscesses along the horse's chest, midline and groin. The condition can be very painful, and affected horses may be very lame or reluctant to move.  The infection also causes fever, lethargy and weight loss. In some cases, it can be fatal.

Corynebacterium pseudotuberculosis can live in the soil and enter the horse's body through wounds or other breaks in the skin. Flies, especially cattle horn flies, may also transmit the infection. People are not affected, but can transmit the bacterium on their bodies (e.g. hands), clothing or other items.  Despite the name, horses do not get the infection from contact with pigeons.

People in this region of Colorado (plus other areas where this disease occurs) should be on the lookout for affected horses. Initial signs are often vague and the diagnosis may not be apparent until the disease is already advanced. If you think your horse may be affected, contact your veterinarian as soon as possible. In the interim, your horse should be isolated to reduce the risk of further transmission. Areas on the farm where affected horses have been should be quarantined until they are adequately cleaned and disinfected - bacteria in pus from draining abscesses can survive for several weeks in the environment.

Image source: http://docsusan.blogsome.com/

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TheHorse.com reports that a third horse that tested positive for the reportable, foreign disease equine piroplasmosis (Theileri equi infection) was illegally removed from quarantine in Kansas... in June. Two other horses were broken out of quarantine shortly after they were diagnosed in June, and have yet to be found. These horses could be anywhere spreading this disease, and may result in the US losing its piroplasmosis-free status. The latest OIE report indicates that the third horse was reported missing the day after the other two horses. That's one more potentially infectious horse on the loose, and one more threat.

This appears to be a good example of what can happen when you combine recklessness, carelessness and stupidity (perhaps with a little bit of laziness on the side). Any effective quarantine needs to be properly implemented and monitored. Any breaches of quarantine need to be immediately identified, reported, investigated and communicated. I haven't seen any previous information about the missing Kansas horse; I can't find anything in earlier press releases or other statements. If this information was withheld, it shows pretty blatant disregard for effective communications. People need to know when there are disease threats. Knowing that a horse with piroplasmosis is on the loose is important because this horse has to have gone somewhere - possibly a public stable or other facility with other horses. If people knew a horse was broken out of quarantine one night and someone showed up at the barn with a horse the next day, they could ask some questions or call the authorities to help protect their farm and their animals. Without this information, they're helpless.

(Image source: www.funnyphotos.net.au)

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There is apparently still no evidence regarding the location of two horses with piroplasmosis that were stolen out of quarantine in Missouri. I've been trying to find out more information, to no avail. TheHorse.com quotes a senior USDA veterinarian who states that, as of June 30, the location of the horses was still not known.

This is a pretty concerning situation. While piroplasmosis is not highly transmissible, these two missing horses could be putting many other horses at risk, as well as the piroplasmosis-free status of other regions of the US (if they have been moved to other states or infected other horses that have subsequently traveled to other states).

Piroplasmosis, which is caused by the bloodborne parasite Theileria equi, is transmitted by ticks and through contaminated needles.  If these horses are in an area where there are tick species that are capable transmitting this parasite, piroplasmosis could be silently spreading. Whoever took these horses, and anyone associated with this situation, are incredibly irresponsible and are putting many other horses at risk. This is another good reminder of why you need to be careful and ensure you know as much as possible about all horses (and their owners) that you allow on your property.

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Not long after the first reported case of vesicular stomatitis (VS) of 2009 in Texas, the disease has now also been identified in De Baca County, New Mexico. It's not too surprising, because infectious diseases tend not to pay attention to state boundaries, and New Mexico tends to be one of the first states affected by VS during outbreak years. Reportedly, only a single horse has been infected in New Mexico so far, and the farm involved has been quarantined.

This will presumably result in many regions placing travel or import restrictions on horses from New Mexico, as was done with horses from Texas. Previously in some years when this disease has been detected in the US, it has been contained to a single state. During other years, multi-state outbreaks involving large numbers of horses have occur. Only time will tell what this year will bring.

People that live in or adjacent to areas where vesicular stomatitis is present should closely observe their horses for signs of this disease, including:

• Drooling
• Lesions in the mouth, ranging from raised, white lesions to blisters. After lesions rupture, ulcerated areas are present.
• Swelling, inflammation and lesions around the coronary band (these are less common than mouth lesions).

This disease is primarily spread by insects, so direct contact with an infected horse is not required for disease transmission. Therefore, even closed herds need to be on the lookout. If signs consistent with vesicular stomatitis are found, movement of horses on and off the property should immediately cease and a veterinarian should be contacted as soon as possible.

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Vesicular stomatitis (VS) has been identified in a horse in south Texas. This viral disease is highly infectious and is a concern for various reasons.

Horses are often the first animals affected when an outbreak of VS develops. A quick response can help prevent the virus from spilling over into other species. It's a particular concern in cattle and sheep because VS can look very similar to foot and mouth disease, a tremendously important foreign disease that can have a devastating economic impact (just ask anyone from the UK).  Even though it is not usually fatal, vesicular stomatitis can also result in severely decreased production in food animals, and therefore also have a significant economic impact.

The impact of VS on infected horses varies. It causes painful blisters (most commonly on the upper surface of the tongue, surface of the lips and around nostrils, corners of the mouth and the gums) which can limit the use of the horse for a period of time (although infected horses can't compete anyway because the must be strictly quarantined). Some horses may be too sore to eat or drink normally, and therefore require supportive care. In unusual situations, the lesions are so severe that euthanasia is elected.

Vesicular stomatitis is a reportable disease in the US, and identification of this case has prompted a rapid outbreak investigation and response. The last outbreak, in 2006, was contained to 17 horses and 12 cattle in Wyoming. A much larger outbreak in 2005 infected livestock on at least 445 premises in 9 states. To help keep this virus contained, restrictions on livestock movement are promptly implemented. Infected animals and their herdmates are quarantined, neighbouring farms may be investigated and/or quarantined, and people are put on the alert to look for more cases. A fast response and cooperation of horse owners is critical. A major concern is  that people may have horses that develop vesicular stomatitis but don't tell anyone because that want to avoid being quarantined. This type of situation can prevent containment of the problem and lead to ongoing transmission and even bigger problems in the long run. Good communication and cooperation are essential.

Image from: http://www.newsinfo.colostate.edu

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Equine piroplasmosis, a foreign reportable disease, has been identified in a horse in Missouri.  On June 2, the affected horse (a seven-year-old Quarter Horse) was presented to an equine hospital with signs consistent with a bloodborne disease (although the exact signs have not been reported). The horse was isolated because of the potential for piroplasmosis, and an investigation was started. The sick horse and other horses from the same farm were examined for ticks (the vector of piroplasmosis) and none were found.  On June 10, the diagnosis of equine piroplasmosis was confirmed. The other 63 horses on the farm are currently being tested, the results are pending.

No source of infection has yet been suggested. The US was considered free of piroplasmosis after the last horse in a Florida outbreak cleared the infection earlier this year. This newly affected horse was apparently purchased six months ago, but no information was provided about where it came from. The lack of a clear source of infection is concerning because it could indicate that there are unknown cases somewhere else in the US.

Piroplasmosis is a tickborne disease cause by the protozoal parasite Theileria equi. It can cause signs of illness such as fever, anemia (decreased red blood cell count), jaundice, respiratory signs, reddish urine and weight loss. Up to 20% of affected horses may die. The parasite is naturally transmitted by ticks. It can also be transmitted through the re-use of needles or other blood-contaminated medical equipment, and perhaps through breeding if the semen contains blood. One problem with identification and control of piroplasmosis is that many infected horses show no signs of disease. Further, horses that recover can carry the parasite for prolonged periods of time and become long-term sources of infection for other horses, if the appropriate ticks are around to transmit the pathogen. Horses that are carrying this parasite therefore need to be strictly quarantined. Horses that become persistent carriers of piroplasmosis need to  be quarantined for life, euthanized or sent to a country where the disease is endemic. More information about the source of infection in this case and how far it has spread is anxiously awaited.

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Botulism is suspected in the deaths of 10 horses on a farm in Wyoming, USA. Very few details are available to indicate why botulism is suspected or what the source might be. It was reported that six horses died initially, and four others that were lethargic and unable to stand died within 24 hours. These signs fit with botulism, which is characterized by profound muscle weakness and progressive paralysis. Death is caused by an inability to breathe when the paralysis starts to affect the muscles that control breathing. Making a diagnosis of botulism can be difficult in horses - it is often a "diagnosis of exclusion" whereby the diagnosis is made because everything else that could cause the condition has been ruled out.  Testing of some of the affected horses is underway. It was not reported whether possible sources of the disease (e.g. feed) are also being tested.

Botulism is caused by a toxin produced by the anaerobic bacterium Clostridium botulinum. In adult horses, the disease almost always occurs from consuming the toxin in contaminated feed.  If the bacterium (which can be found in the soil in many regions) gets incorporated into feed, under the right conditions the organism will grow and multiply, and produce the powerful neurotoxins that cause botulism. Fermented feeds like haylage and silage are common sources, because the way they are stored is more likely to create an environment where C. botulinum can grow.  However, various other food sources have also been implicated in some outbreaks.

Botulism is rare, but typically fatal in adult horses. Some basic tips to reduce the risk of botulism are:

• Avoid feeding horses haylage and silage, especially in areas where botulism is more common. There are some benefits to using feeds, so they are commonly used in some regions, but if you use fermented feeds you should discuss the risk of botulism with your local veterinarian, and take measures to reduce the risk of C. botulinum growth.
• Vaccines against botulism are available. Adult horses are usually not vaccinated, other than mares which are vaccinated to reduce the risk of botulism in their foals (known as "shaker foal syndrome"). Adult horses being fed high-risk feeds could be considered for vaccination, but if the feed is so high risk that vaccination is warranted, perhaps the feed program should be reconsidered.  Furthermore, there are several types of C. botulinum, but the vaccines only protect against some of them. If you are thinking about vaccinating, you should make sure that the vaccine you're going to use protects against the botulism strains found in your area.

If you ever have a horse that is showing signs of botulism (e.g. weakness, difficulty rising, dropping food out of its mouth, difficulty swallowing), or if botulism is suspected in a sudden death, immediately stop feeding any potential high risk feeds until the cause of the disease is identified. This might help reduce the number of affected horses.

More information on botulism can be found in our botulism archives. An information sheet about botulism in foals can be found on the equIDblog Resources page.

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CNN has reported that Francks Pharmacy, a compounding pharmacy in Ocala, Florida, has acknowledged that it improperly prepared medication that was given to 21 polo ponies that died in Florida on Sunday (April 19).

While few details have been provided, a representative of the pharmacy stated an internal investigation "...concluded that the strength of an ingredient in the medication was incorrect." A problem with the pre-event treatment was suspected early in the course of the investigation because of the nature of the deaths and the fact that all 21 horses that received the treatment died, while 5 other horses from the team that were not treated had no problems.

Hopefully more details will emerge about what the actual problem was, as it is not clear what ingredient in the medication has been implicated.  Franck's Pharmacy has pledged to cooperate fully with the investigation, and it will be very important to determine how such an error happened. Toxicology test results from the dead ponies will also be necessary to determine if the compounding mistake was indeed responsible for the tragedy.  If the pharmacy is found to be at fault, I assume a large lawsuit or insurance settlement would be inevitable, but that's little consolation to the people that worked with those horses.

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At least 21 ponies belonging to a Venezuelan polo team died shortly before a competition yesterday in Florida. Not much information about what happened has been released. It was reported that the ponies exhibited signs of dizziness and disorientation, then collapsed. Some died on site while others died en route to a nearby veterinary facility. It is unclear if any affected horses survived. Necropsies (autopsies) are being performed to try to determine the cause of death.

One veterinarian has stated that it was "clearly" caused by a toxin of some sort. That's a reasonable suspicion based on what has been reported. An infectious cause seems unlikely. Unlike on TV or in the movies, multiple individuals rarely become fatally ill from an infection at the exact same time. Even if all the horses were exposed to an infectious agent at the same time, it's extremely unlikely that they would die in rapid succession. The lack of reported cases in horses other than those on the team also supports a point-source exposure to a toxin. It is likely that it will take some time to determine the cause of these deaths, if it can be determined at all. Hopefully samples of food, water and any other substances to which the horses were all exposed (e.g. supplements, medications) have been collected for testing.

Diagnosing disease caused by toxins is not always easy and often takes a long time. Considering the number of deaths and the value of these horses, I assume that testing will be done as quickly as possible, and we're anxiously awaiting any more information.

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The other day, I wrote about a few different types of surveillance that can be used in equine hospitals - active, passive and syndromic. Infectious disease surveillance, however, is not just for hospitals. Every horse farm should have some form of infection control program. In most situations, it doesn't need to be complicated, fancy or time consuming, but it means organizing some basic infection control policies and procedures. Syndromic surveillance is great for use on horse farms.

Syndromic surveillance involves looking for specific syndromes (e.g. particular clinical signs (not specific diseases per se) such as fever, cough, diarrhea, or off feed) that might indicate an infectious disease. These basic, easy-to-identify syndromes can be the early warning that something might be amiss, then closer examination can be used to determine if there is actually is a problem.

An important key to disease surveillance is it is only effective if something is done with the information collected. There has to be a plan based on the results of the syndromic surveillance, with regard to what needs to be done for the affected horse and on the entire farm.   For the horse, it usually means a visit from a veterinarian to determine what's wrong, and if it might be due to an infectious pathogen.  For the farm, it means making sure that horse doesn't have a chance to infect other horses (in case it is an infectious disease), and ensuring that the information is recorded so bigger problems (e.g. outbreaks) can be identified as early as possible. The plan for what to do when one of these syndromes is detected needs to be written down so it's very clear for everyone, and easy to find if someone's not sure what to do. One of the most important steps is making sure someone (i.e. someone "in charge") is notified.

Here's a scenario: A horse develops a mild fever overnight and doesn't eat all its grain.

Response 1 (what should happen): The fever and decreased appetite are identified and the person in the barn in charge of the surveillance program is notified. They record that a horse has a fever and talk about what to do with the horse so everyone knows. The horse is restricted to its stall until the cause of the fever is identified. An hour later, the same person in charge of surveillance gets reports from two other people about horses with fever. This obviously raises concern and they try to determine what is happening. They know that a new horse arrived a while ago and that the horses with fever were turned out with it. They immediately call the veterinarian, who suspects strangles may be the cause. All horses with a fever are isolated and tested. Other horses in the barn are closely monitored for signs of illness. Because horses with strangles spike a fever a couple days before they are able to transmit the disease, these horses do not spread the disease any further.

Response 2 (what usually does happen): The first fever and decreased appetite may or may not be identified. Since the horse doesn't really look sick, they decide to wait and see how it looks over the next day or two. A couple days later, someone notices the horse has enlarged lymph nodes. Then they call the vet, who diagnoses strangles. As the vet looks around the barn and talks to people, he/she finds out that a few other horses have big lymph nodes, and realizes that an outbreak of strangles is already well underway. Most horses may have been exposed at this point and a large outbreak is probably inevitable.

Which scenario would you want? Which response would be most likely in your barn?

Surveillance scares off many people just because of the name and the thought that it is expensive, complicated or requires special training. It doesn't. All it needs is people in a barn who communicate and some basic written policies on how to handle horses and potential diseases.

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I seem to be on a run of strangles posts at the moment. There was a recent article in the Brown Daily Herald about the school’s equestrian team, in which was mentioned a recent strangles outbreak in the team’s horses. Two horses were affected according to the article, and the encounter with this highly infectious disease was described as a "hiccup". I’ve written about different approaches to infectious diseases and outbreaks (the good and the bad) and commented on the need for a logical, proactive and open response to diseases like strangles. This report includes some glaring deficiencies.

With 2 horses affected, there has presumably been transmission of the disease on the farm. That means that every horse was potentially exposed, and many horses could be incubating infection or be carriers. The proper response would be to consider everyone infected until proven otherwise, ideally by culturing all the horses for the bacterium that causes strangles, Streptococcus equi.

The description of the response to the outbreak was pretty brief, so I’ll go with the assumption (hope) that the writer didn’t describe the entire response. One of the precautions that was described was “dipping their boots into bleach before mounting any horses.” Boots are a minor to irrelevant source of infection, and this alone is not going to do much to prevent the spread of strangles.

"It was easy to tell that something was wrong in the barn on Friday, March 13. The sides of Bristol's stall were boarded with fresh wood and the entrance was blocked off by a rope. Bristol stood in the stall with a green warmer wrapped around him, facing the outside of the barn, and his slow, warm breaths were visible in the cold barn air. But the team had to continue. They had a competition the next day.”

Here’s where I get more concerned. It's good that they took measures to isolate the affected horse, but there was a strangles outbreak in the barn that was (as of yet from the description) uncontrolled, yet the riders were going to a competition the next day, and no additional precautions were mentioned. That’s a great recipe for turning a minor single-farm cluster into a regional outbreak.

“With the strangles infection in the barn last Friday, Coach Michaela Scanlon wanted to make sure that her riders took extra precautions, such as not wearing any equipment that they had worn at earlier practices, so as not to spread the infection.”

This is a more useful measure, to help reduce transmission of S. equi from contaminated gear. However, changing clothes still doesn’t help much in the absence of a concerted infection control response.

Hopefully Brown’s equestrian team didn’t spread strangles to other horses at the show. I understand the desire to go to a competition anyway, when you have infected horses in the barn but many horses that appear healthy. A lot of effort and money can go into preparation for shows. However, people should take infection control seriously and realize their ethical obligation to do their best to protect their and other peoples’ horses. Infectious diseases are always a risk at shows and we can’t eliminate them altogether. Every infectious disease that a horse acquires at a show is not necessarily an indication that someone did something wrong, but a lot of illness could be prevented if people use common sense and have some consideration for the impact their actions may have on other people and their animals.

More information on strangles can be found in on the equIDblog Resources page.

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I usually hesitate to write posts about strangles cases or outbreaks. I don't want to give the impression that these are unusual events, because strangles is not a rare disease, in terms of either single cases or outbreaks. When I post about an outbreak, it's usually because there's something particularly interesting about the outbreak or the report about it. Such is the case with the recent identification of strangles in a horse in a Newmarket (UK) racing stable. At last report, only a single horse was infected, the horse has been isolated, and infection control measures have been implemented (although it would be nice to have some details about exactly what those infection control measures are).

What is noteworthy is the rapid and open response. Mark Tompkins, chairman of the Newmarket Trainers' Federation, said the following about Mr. William Jarvis, the trainer in charge of the stable where the infected horse was found:

"He has done everything right by letting everyone know about it as early as possible. He has been absolutely brilliant... His string of horses are being tested and swabbed constantly and he will exercise his horses in the afternoon when no-one else is on the heath."

This is what needs to happen when strangles is identified: a rapid, no-nonsense response with open communication between all parties involved. Too often, people try to hide cases or don't tell the whole story. Horse owners and trainers that think hiding the disease is the best way to handle things ought to take note of the statement by Tim Morris, the British Horseracing Authority equine science and welfare director, who said no restrictions were being imposed on Mr Jarvis's horses because he had shown a responsible attitude by reporting the sickness.

Strangles is an endemic disease. It's not going away. Having a horse with strangles shouldn't be considered something that needs to be hidden. There's nothing illegal or unethical about having a sick horse, but trying to hide the fact that you have a horse with a disease than can infect other horses... that's another story altogether.

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A mandatory influenza vaccination policy at the Crawford City Fairgrounds (Pennsylvania), implemented this year following an outbreak of influenza at the facility in 2008 is being met with disdain.

Among the complaints:

"A two-day horse show is different than an eight-day fair exhibition.'" Two days is lots of time to transmit infectious diseases.

"If a horse is sick and can’t perform, people won’t bring them to a show." Unfortunately, that's not the case. Also, not all horses that are shedding infectious diseases look sick.

"All these requirements will not guarantee healthy horses." Absolutely true. But, with infection control, we are trying to reduce the risk and incidence of diseases. We know we'll never eliminate the risk.

"There’s no sense giving a shot that will do more damage than the disease." Influenza vaccination is very safe. While adverse effects can occur with any vaccine, influenza vaccines are quite low risk.

"Potentially, requiring a 30-day vaccination for each show will cost horse exhibitors and 4-H members in horse clubs too much money." The cost of vaccination is dwarfed by other costs of participating in such events. People spend a lot of money on board, feed, tack, supplements (many of which are useless), trailering and many other items. In the grand scheme of things, vaccines don't add much to the total yearly cost.

No one knows whether mandatory vaccination against influenza ought to required for all horse shows as an infection control precaution. However, given the fact that outbreaks can occur, that all events involving mixing of large numbers of horses pose a high disease risk, and that vaccination is relatively cheap and effective, it seems like a logical requirement to me.

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 An outbreak of strangles has resulted in at least one death and the closing of one barn at Northlands Park in Edmonton. The 150 horse barn will be cleaned, disinfected and kept empty for three weeks, until March 23.  The article refers to the disease as equine distemper, which is another common name for strangles.  It should not be confused in any way with canine or feline distemper, both of which are caused by viruses.  Strangles (equine distemper) is caused by the bacterium Streptococcus equi subsp. equi.

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In August 2008, there was an outbreak of equine piroplasmosis in the state of Florida.  The index case was a gelding that was euthanized following a three-week illness.  The diagnosis was made based on testing of samples collected at necropsy.  The US has been considered free of this reportable foreign animal disease since 1988, so the discovery lead to automatic notification of the authorities, who started an investigation and implemented quarantine of numerous facilities.  During this outbreak, 20 horses on 7 farms were identified as infected. A total of 25 farms were quarantined.

Representatives from the state of Florida announced recently that the last farms quarantined during the August 2008 outbreak of equine piroplasmosis have now been released. All horses are now free of the parasite. Florida (and the US as a whole) is once again considered free of equine piroplasmosis.

Equine piroplasmosis is a blood-borne disease that is caused by the parasites Babesia equi and Babesia caballi.  Infected horses may develop mild disease characterized by weakness and loss  of appetite. In more serious cases, horses may develop fever, anemia, jaundice (yellow gums and eyes), a swollen belly and respiratory problems. Other signs that are sometimes present include neurological abnormalities, red urine (secondary to destruction of red blood cells) and death. In contrast, many infected horses may no signs of illness whatsoever. Horses that recover may carry the parasite for a long period of time, and these horses can be a source of infection for other horses if there are ticks in the area capable of transmitting the parasite (not all species of ticks can transmit the disease). This can lead to the need for long quarantines. Horses that become persistent carriers of piroplasmosis need to  be quarantined for life, euthanized or sent to a country where the disease is endemic.

How this outbreak started and spread is unclear. No infected ticks were ever identified. A recent update concluded that "Evidence uncovered during the investigation indicated that transmission of the [equine piroplasmosis] organism occurred due to management practices and not by natural transmission which occurs via ticks." I'd love to know exactly what they found and what specific "management factors" were the problem.  Blood-borne pathogens can be transmitted in some cases on equipment that is contaminated with blood, such as reused needles and dental equipment.

A good fact sheet on equine piroplasmosis is available from the US Animal and Plant Health Inspection Service (APHIS).

Photo: Red blood cells infected with Babesia spp. (source: CDC Public Health Image Library, ID#5943)

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I don't know whether Truro Raceway (in Nova Scotia, Canada) has bad luck, bad infection control or is just really open about any problems. Following an outbreak of strangles in December (see here for details), strangles has again been identified in a horse at the track. One horse has tested positive and two barns have been quarantined until 3 negative cultures are obtained from the horses. Racing, fortunately, has not been affected.

This isn't a surprising situation because strangles (caused by the bacterium Streptococcus equi) is an endemic disease in the horse population, meaning it is always present in a small percentage of horses at any time. It circulates regularly through the population - mixing of horses contributes to its spread. Racetracks are a great place for infectious diseases to spread and early control is the key. Truro seems to be on the right track based on their aggressive but balanced response. They've identified a problem, taken a logical course of action, but have not overreacted. Presumably, they feel that the two quarantined barns are the only ones likely to have been exposed to the pathogen, so there is no need to take broader action. Sometimes, people panic and take excessive actions in an outbreak. This can lead to people being hesitant to report problems (for fear of a draconian response), which can end up making things worse in the end. I wonder whether any increased infection control practices were implemented following the December outbreak, and/or whether any are being considered now.

The risk of strangles can be reduced, but not eliminated, through use of good infection control practices. More information on this disease can be found in our strangles archives and on the equIDblog Resources page.

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Following an influenza outbreak that sickened at approximately 70 horses last year, the Crawford Country Fair in Pennsylvania is requiring influenza vaccination for all equine participants this year. This year, all horses must be vaccinated between 6 months and 15 days prior to the fair. Vaccination against such an infectious disease is a sound recommendation to be sure, although the six-month window might be a little long. I'd prefer to see the horses vaccinated closer to the time of the fair, in order to maximize the protective effect during the highest-risk period.

The fair board is also requiring a certificate of veterinary inspection for each horse at the fair, issued within 30 days prior to opening day. I'm not sure that this kind of inspection will do much in terms of preventing sick horses from participating in the fair, as most infectious diseases (including influenza infection) don't last for 30 days.

• If a horse is clinically healthy 30 days before the fair, it certainly doesn't mean the animal won't be infectious at the time of the fair if it is exposed to a virus (or other pathogen) in the interim.
• If a horse has influenza 30 days before the fair, there's not much chance it will still be shedding the virus by the time of the fair.

While I wholeheartedly agree with the sentiment that regular veterinary examination is important for infectious disease control, but the time frame in this case just won't do much for control of influenza. If the fair board really wanted to reduce the risk of sick horses attending, they'd have to require inspection much closer to the date of the fair.  However, such a requirement could turn into a logistical nightmare, since a large number of horses would need to be evaluated by a small number of veterinarians over a short period of time. Furthermore, if someone competed at many fairs during the year and they all had similar requirements, a horse might have to undergo a weekly exam before each event, which could be cost-prohibitive.

Despite the limitations, this is still a good, proactive step on the part of the fair board, and similar precautions ought to be considered elsewhere. We need to stop simply accepting that some horses will get sick following fairs and that outbreaks will happen, and realize that there are practical measures that we can do the reduce (although not eliminate) the risks. One of the best things that could be done would be to require examination of all horses upon arrival at a show or event. The examination could be done by a veterinarian or veterinary technician.  At a minimum,  requirements could include that horses have no signs of respiratory disease, diarrhea or fever. Horses with these problems could then be immediately send home, greatly reducing the risk of disease transmission to other animals at the event. Yes, it would take some effort and money, but it really wouldn't be that hard to do, and could be a very useful preventive measure.  Compared to the cost and headache of quarantining and treating sick animals when an outbreak does occur, the idea really sells itself.

I'm not trying to be negative about the approach taken by this particular fair board. I think their awareness of the need to do things to reduce the risk of infectious diseases at their event is great. 

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The investigation of the outbreak of contagious equine metritis (CEM) in Kentucky last month continues throughout many states in the USA, and has also spilled over into Canada.  At this time, four farms in Alberta and six farms in Ontario remain under quarantine.  These farms either received frozen semen from one of the three infected Kentucky stallions in the spring of 2008, or have mares that were shipped to Kentucky for artificial insemination with semen from one of these stallions.  So far, no confirmed cases of infection have been reported on any of these farms.

The Canadian Food Inspection Agency (CFIA) is responsible for the investigation of reportable animal diseases in Canada, including the current CEM investigation.  Representatives of the CFIA will present an update on the situation at the Breeds & Industry Delegate Assembly at the Equine Canada Convention in Ottawa on February 7.

Any horse in Canada suspected of being affected by CEM must be reported to the CFIA.  The most apparent, classic sign of CEM in mares is a thick, purulent (pus) vaginal discharge after breeding, without systemic illness (i.e. no fever or depression).  However, some mares and almost all stallions can carry the causative organism, Taylorella equigenitalis, without any obvious clinical signs of infection, which is why the disease can be difficult to control if people aren't careful.  Taylorella equigenitalis does not affect people.

The CFIA has made several recommendations to Canadian horse owners to try to prevent the spread of this disease into Canada, and to prevent its spread should it be found here at any time:

• Until the outbreak investigation in the USA is complete and the disease is contained, use extreme caution or simply refrain from importing breeding animals, semen, embryos etc. from the USA.
• Emphasize strict hygiene measures when handling breeding animals.  Wear disposable gloves when washing or otherwise coming into contact with a horse's tail or genitalia.  Change gloves (and wash your hands!) before handling another horse.
• Use separate equipment (e.g. buckets, sponges, tail wraps) for each horse.  Any equipment that must be shared should be thoroughly cleaned and then disinfected between horses.  Taylorella equigenitalis is susceptible to most common disinfectants, including bleach.

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In December 2008, an outbreak of contagious equine metritis (CEM) was reported in Kentucky. The index case was a healthy stallion that underwent routine testing for exportation of semen and the causative agent, Taylorella equigenitalis, was isolated by cutlure on December 15. By the end of the month, three more stallions on the same farm were also identified as infected. At the moment, it is estimated that there are 28 horses in Kentucky and another 156 horses outside Kentucky that have been exposed. Another 250 horses are being traced across 27 states. The last outbreak of CEM in the USA was in 1979 in Missouri, although a few sporadic cases have been identified in the country in the last three decades. It is a reportable disease in both the USA and Canada, and there are strict import (and export) regulations for horses entering the USA and Canada from CEM-positive countries.

CEM is a venereal disease of horses. It is spread by stallions who can carry the bacteria on their external genitalia without any noticeable clinical signs, as well as by infected mares, during breeding. The bacterium can also be transmitted through artificial insemination, particularly on contaminated equipment. The diseases causes temporary infertility in mares. Typically mares do not conceive when they are first infected, but if a mare does become pregnant she may abort, or the foal may be born a carrier. Some mares develop a heavy purulent vaginal discharge (pus) for up to two weeks after breeding, but others may only have a shortened heat cycle. Some mares will clear the infection on their own, but in some cases a mare may become a chronic carrier of T. equigenitalis and transmit the bacteria to stallions during breeding. The organism does not cause any clinical signs in stallions, so the only way to detect the bacteria in males is to culture it. However, T. equigenitalis is notoriously difficult to grow in a laboratory, so false-negative results can occur. Therefore adjunctive tests are also used, and additional testing methodologies (including molecular techniques such as PCR) are being developed for the detection and study of this organism.

The good news is that infected horses can be treated, and T. equigenitalis is typically susceptible to most common antibiotics. Local treatment and repeated flushing of the external genitalia of infected horses is also part of the treatment regimen. Compared to other diseases, the spread of CEM is also relatively easy to control, because it is only transmitted by breeding (either live cover or artificial insemination). The major problem is that this disease is also one that can easily “fly under the radar” for some time before it is discovered, because carrier animals show no clinical signs of infection, and stallions in particular, as in this case, may expose many mares before the bacterium is discovered. Hopefully this outbreak will be brought rapidly under control so that the equine industry in the USA can avoid devastating economic loses due to the presence of this disease.

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Recently, I discussed issues regarding equine influenza vaccines and how they are not updated as regularly as human vaccines.  The H3N8 type of equine influenza is the main concern in horses. This strain has two main groups, European and North American.  Standard WHO/OIE recommendations are that equine vaccines should include a representative of each of these groups. An outbreak of equine influenza in Croatia in 2004 (reported by Barbic et al. in the journal Veterinary Microbiology) highlighted the need to follow these recommendations, and the need to be diligent about looking for causes of vaccine failure.

The outbreak occurred at a racetrack in Zagreb. Not surprisingly, an H3N8 strain was responsible. Investigation of the cases determined that vaccine status had no influence on disease - both vaccinated and unvaccinated horses became equally sick. The vaccine used in Croatia at that time contained three influenza strains, including two different H3N8 strains, but the strains that were used were from 1963 and 1979. When they compared the strain that caused the outbreak and the vaccine strains, there were multiple genetic differences, which is not surprising given influenza's capacity to evolve over time. There were far fewer differences with the more recent strains used in vaccines in most other countries.

The study concluded "Further surveillance of the equine population and updating of equine influenza vaccine strains in accordance with the recommendations of the Expert Surveillance Panel is necessary in Croatia to reduce the likelihood of further outbreaks as a result of vaccine failure."

While this outbreak was clearly a result of not following standard recommendations, it's a good reminder that ongoing surveillance is needed to detect and control emerging strains against which horses will not be protected by current vaccines.

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An outbreak of salmonellosis has killed at least 22 horses in Kjalarnes, Iceland. A total of 41 horses were infected.  This is a very high mortality rate (>50%) for what I assume is a group of otherwise healthy horses, as compared to the more compromised populations which are usually present in equine hospital outbreaks. It is unclear whether the high mortality rate may be due to a particularly nasty (virulent) strain of Salmonella or the unavailability of aggressive supportive medical care which is needed in severe cases of diarrhea in horses.

The source of infection was thought to have been a sedimentation pond in the horses' pasture. The article contained no information about potential sources of contamination of the pond, or about the the strain of Salmonella involved.

• Outbreaks of salmonellosis are uncommon on farms, but they can occur.
• Mortality rates with salmonellosis can be high, especially without (but sometimes even in spite of) aggressive (and expensive) medical care.
• Prompt investigation is critical to identify the source(s) of infection and try to prevent further exposure and additional cases.
• Good routine infection control measures should be in place to reduce the risk of entry of Salmonella onto a farm, as well as transmission of Salmonella between horses (and between horses and humans) if it makes in onto a farm.

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Recently, Truro Raceway (the original home of Standardbred champion racehorse "Somebeachsomewhere"), was quarantined because of two suspected cases of strangles, a highly infectious equine disease caused by the bacterium Streptococcus equi subspecies equi (more information about strangles can be found on the equIDblog Resources page and in the  strangles archives). The first round of tests from December 7 came back negative on December 18, and the quarantine has now been lifted (apart from the barn with affected horses).

That's all good news. In the bigger picture, though, was anything learned, and were any measures taken to reduce the risk of this happening again?  A lot of this comes back to the debate about accepted versus acceptable disease risks, which we've covered before on equIDblog.

I've never been to Truro, but I assume they are no better and no worse than the vast majority of tracks, meaning they are in a perpetual state of waiting for an outbreak to happen. Let's hope they have performed (or will perform) a good review of what happened, and consider how to reduce the risk of future problems, including the following measures:

• A mandatory reporting system for signs potentially associated with infectious diseases of concern: This would allow for prompt investigation and implementation of any needed control measures. A balanced approach to diseases control is necessary so that horsemen don't feel the pressure to withhold such information for fear of being ostracized or having their livelihood compromised by excessive or unnecessary quarantines. Education is key to convincing people that this is important.
• An improved (or establishment of) a 'culture of infection control': People need to be thinking about infection control on a daily basis, not just when there is an outbreak.
• Performance of an infection control review and development of a formal written infection control program for the facility: This should involve experts in veterinary infection control, but also track managers and horsemen so that all relevant parties have input. This type of review needs to consider the facilities (e.g. barn layout, quarantine areas, sinks for handwashing in barns) as well as protocols (e.g. ship-in protocols, reporting and managing potentially infectious horses, infection control education).

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Another presentation from the recent 2008 AAEP Convention, this one by Dr. Simon More, described the outbreak and successful eradication of equine infectious anemia (EIA) from Ireland in 2006.  A review of the outbreak itself, its investigation and management was also published in the most recent issue of the Equine Veterinary Journal (2008; 40(7):702-711).

Equine infectious anemia (EIA) (aka "swamp fever") is a very important disease in horses, and can also affect donkeys and mules.  This is the disease for which horses are given a Coggins test, which is required every six months for horses attending most shows and competitions, and for horses traveling internationally.  EIA is caused by a retrovirus, more specifically a lentivirus.  Other important viruses in this group include several immunodeficiency viruses such as HIV.  When the EIA virus infects a cell, it actually permanently incorporates its genes into cell's DNA, so affected animals are infected for life.  Horses go through repeated bouts of illness - the earliest episodes are usually the most severe.  Horses that survive the acute phase become persistent, often inapparent carriers, and serve as a reservoir for the virus.  The primary means of transmission is via transfer of blood from infected horses.  This can occur through blood-feeding insects such as horse flies and deer flies, or through use of blood-contaminated equipment such as dirty needles, surgical instruments and dental equipment.

Signs of EIA during acute episodes include fever, depression, lack of appetite, decreased red blood cell count (anemia) and decreased platelet count  (thrombocytopenia).  Lack of platelets can lead to petechial hemorrhages (tiny dots of blood, often first noticed on the gums or inside of the lips).  Episodes typically last 3-5 days, but weeks or even months may go by between episodes.  Illness may also be precipitated by stressful events or treatment with immunosuppressive drugs.  In some horses the episodes become more frequent, and signs of chronic EIA develop.  In addition to anemia and thrombocytopenia, these horses (often called "swampers") become very thin and may develop edema over their lower abdomens.  If the condition becomes very severe, a horse may have very pale or yellow mucous membranes (e.g. gums, around the eyes), and some may have nose bleeds or even neurological signs.

Prior to the outbreak of EIA in June 2006, Ireland was free of EIA, an advantageous status for the horses who lived there, as well as their owners.  Between June and December, 38 horses became infected with EIA.  It is believed that the outbreak started with four foals that were given hyperimmune plasma for prevention of Rhodococcus equi infection that had been illegally imported from Italy.  It is likely that the plasma was contaminated with the EIA virus, but unfortunately by the time the outbreak was identified there was no remaining plasma that could be tested.  Transmission of the virus was thought to have occured through mechanical transfer of blood during veterinary procedures and vector transmission via horse flies. Additionally, it was suspected that several mares may have been infected through close contact with foals.  Ongoing surveillance in Ireland has not identified any additional cases in the last two years, so it is believed that the disease has been eradicated.  Investigation and control of the outbreak took a lot of cooperation between many different organizations and individuals.  The study of the epidemiology was also very important in controling the disease, as not all of the cases followed the book!

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A recent article from British Columbia, Canada, described the complaints of horse owners that they were not warned about cases of strangles (Streptococcus equi subsp equi infection) in the Maple Ridge, BC area. The issue revolves around a small number of cases of this highly infectious - but relatively common - equine disease.

One horse owner stated "If I had known it was out there, I would have done things differently." While I understand where she's coming from, it's important for all horse owners to remember than exposure to infectious diseases is an ever-present risk. Streptococcus equi, and various other infectious agents, are widespread in the horse population, and there is never a "no-risk" situation. For that reason, we should be taking practical measures to reduce the risk of disease transmission at all times, not just when we know there is an infectious disease in the area.

Increasing infection control measures during outbreaks or during particularly high risk periods is an important disease prevention measure, however too often, people only pay attention to infection control during high-profile events. While outbreaks get the most attention, most infectious diseases occur as sporadic events, not outbreaks. Focusing solely on outbreaks has a minimal impact on infectious diseases overall.

Addressing strangles infections is a tough and often controversial area. Frequently, cases of strangles are kept quiet because people are afraid of being stigmatized. That certainly doesn't help because it can facilitate spread of the infection. In contrast, sometime excessive (approaching paranoid) responses occur. Like most things, there needs to be a happy medium, where strangles cases are properly diagnosed, appropriate control measures are implemented and relevant people are notified, but without widespread panic and unnecessary restrictions or ostracism.

More information about strangles can be found on the equIDblog Resources page and in our strangles archives.

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A few years ago, I investigated an equine herpesvirus (EHV) outbreak associated with a yearling sale. We found a lot of sick horses, both from the sale and horses that were infected when purchased horses were brought home. A lot of actively racing horses got sick and missed races, which cost people even more money.  Part of the investigation was asking people what percentage of horses from sales they expected to get sick right after the sale. The average answer was 80%, and many people said 100%. When you think about it, it's absolutely astounding that people will spend what is often a great deal of money to buy a horse that they expect will get sick, and then (more often than not) put it in the same barn as their other horses, thereby putting all the animals at risk of infection.

Why do we put up with a system where we accept this degree of illness? Is this expected and accepted rate of disease really acceptable? More specifically, are there practical (and really just common sense) measures that can be used to reduce the risk of horses getting infected at sales and/or transmitting disease to other horses once they reach the home farm?

Specific thoughts and facts about how to reduce disease transmission on farms, tracks, sales and everywhere else horses gather will come in other posts, but infection control is not rocket science. Basic measures can greatly reduce the risk of disease transmission. However, the first step is to change people's attitudes - it should never be considered "normal" for such a high percentage of animals to be sick.  If 80% of the horses get sick, we're doing something wrong.

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As of this morning, no new cases of equine herpesvirus (EHV) infection have been identified at Laurel Park in Maryland. (See our previous reports regarding this situation.) More than 50 horses on the premises have tested  negative for the virus, and no new horses have developed signs of disease. While they are not yet at the end of the period during which horses infected by the sick filly could develop disease, the fact that no new cases have been found so far is very encouraging. Horses at Laurel Park will remain under close monitoring for new cases for 21 days, but if no cases are found in the first 7-14 days, then it is unlikely that additional cases will develop.

Unfortunately, the affected filly had to be euthanized on Saturday. The track will still be under quarantine until around December 6.  This will be 21 days after the last evidence of clinical disease in any horse (in this case November 15 when the filly was euthanized), which represents the last chance of exposure of other horses to the virus.

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Equine herpesvirus type 1 (EHV-1) infection was confirmed in a filly at Laurel Park in Maryland (see yesterday's post). As a result, the track is now under strict quarantine.  Horses are not allowed to be shipped onto the track (except from an associated training facility) and horses already at those facilities may not leave. This is being done to reduce the risk of transmission of the virus to horses on other properties. As discussed yesterday, EHV is tough to control because it can be found in a dormant state in so many healthy horses, and we really don't understand enough about how the neurological form of disease is transmitted. It's possible that these quarantine restrictions are over-kill, but since we don't have enough information to say with certainty what is or is not necessary, and because large outbreaks of EHV-1 have occurred in the past, using a very cautious approach is understandable. Only time will tell whether there was transmission of this virus before the restrictions were implemented.

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Recently, I wrote about a large disease outbreak involving horses in Israel that resulted in a country-wide quarantine. Equine viral arteritis (EVA) has now been identified as the cause of the outbreak. This viral disease can cause a wide range of clinical signs in horses. It is often associated with abortion, but flu-like disease is common in adult horses, and is consistent with what was reported in Israel. The EVA virus is spread mainly by the respiratory route - contact with infectious nasal discharge is a prime means of transmission between horses.

It is currently unclear where the Israeli outbreak originated, or how it was propagated.  Transportation of horses to shows, races and other events with subsequent mixing of horses is a great way to rapidly spread such a virus over a large area. The World Organization for Animal Health (OIE) reports that this virus has never been identified in Israel before. If this is indeed true, it could explain why the outbreak was so rapid and widespread - when a virus encounters a population of horses who don't have any immunity because they have not been exposed or vaccinated, more animals are likely to become sick and spread the virus further.  The massive influenza outbreak in Australia last year was a great example of that.

It will be interesting to see what happens with this outbreak. The implementation of a nationwide quarantine, while certainly disruptive to many people, may have been an important step in limiting further transmission of the virus.  A vaccine for EVA (which cannot be used in pregnant mares) is available, and could be used as part of outbreak control. However, good infection control practices are more important - vaccination will not be effective if it is the only measure taken.

Click here for more information on equine viral arteritis (EVA).

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An outbreak of an unknown infectious disease has occurred in Israel, sickening hundreds of horses and possibly causing death in a few. The disease is characterized by fever, lethargy and loss of appetite, yet the cause has not been identified. At least 30 different farms have been affected, and the spread of disease has prompted the Ministry of Agriculture to implement a nation-wide quarantine of horses. All horse events in Israel have been canceled.  Similar precautions were taken when the outbreak of  equine influenza hit Australia last year.

The described clinical signs in affected horses are very non-specific, so it's hard to speculate about the causative pathogen. There are a variety of potential culprits, including equine influenza virus (EIV), but so far testing has not detected EIV or any other known pathogens.  This "mystery" disease does not appear to affect other animals or people (but without knowing what is causing it, this is difficult to say for certain).  It is possible that this is a "new" disease, but the vast majority of infectious disease outbreaks are caused by pathogens that we already know about. Specialists from Britain have been called in to help with the investigation. Hopefully more information will be available soon.

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Eastern equine encephalitis (EEE) was recently identified as the cause of an outbreak of disease in emus on a farm near Brockville, Ontario. EEE is a viral disease that is spread by mosquitoes, and can cause severe neurological disease in horses.  Previous equIDblog posts describe EEE in more detail.

Emus are quite susceptible to EEE.  Although EEE cannot be transmitted fro emus to horses, the relevance of this report to horse owners is that the emu outbreak indicates that the virus is present in mosquitoes in that region.

Most of the emu deaths in this outbreak occurred in mid-October.  It is unclear whether there is any further risk to horses, people or other animal species. Being a mosquito-borne disease, EEE transmission should decrease dramatically after the first few hard frosts in the fall. It is unlikely that there is a significant risk of further EEE transmission in the Brockville area this year.

Vaccination of horses in Ontario at this time of year is probably not useful because of the low risk of mosquito transmission and the time required for immunity to develop after vaccination. However, people should consider the risk of exposure in subsequent years, and try to reduce this risk. This can be done through a combination of avoiding and controlling mosquitoes (which are also important for prevention of West Nile virus infection) and vaccination against EEE. Since EEE is so rare in Ontario, it is not typically considered a "core" vaccine in horses. However, vaccination for EEE should be considered in regions where the disease has previously been identified.

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Preliminary evidence has suggested that botulism might be the cause of botulism may be the cause of death of approximately 100 horses at a large breeding facility in Florida housing approximately 400 mares. The horses died over a period of about 7 days, with signs of neurological disease. There are no reports of affected horses at other facilities in the area.  The clinical signs in these horses and lack of evidence of another disease are strongly suggestive of botulism. This farm apparently fed the horses haylage (although some reports seem to alternate between using the words "hay" and "haylage"), which is a high-risk feed source for botulism.

In adult horses, botulism is caused by ingesting a toxin produced by the bacterium Clostridium botulinum. This bacterium will not grow in the presence of oxygen, however in can grow in conditions that are sometimes present in improperly fermented haylage and silage. As the bacterium grows, it produces botulinum toxin, one of the most potent toxins on the planet. Ingestion of botulinum toxin leads to progressive paralysis (i.e. severe weakness and flacid muslces).

Treatment of botulism is difficult and can be expensive, and the mortality rate for this disease is high. Some people choose to feed haylage and silage despite the risk of botulism. If you choose to feed haylage, silage or other high-risk feeds:

• Ensure that haylage/silage is properly prepared and stored.
• Consider vaccinating horses that are fed haylage/silage against botulism. Be aware, however, that vaccines do not protect against all strains of botulism.
• Immediately stop feeding haylage or silage if any horses show signs that could be consistent with botulism (e.g. weakness, problems eating).

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This summer, a small outbreak of the potentially deadly Hendra virus was identified in a group of horses near Brisbane, Australia. This virus has caused periodic cases of illness and death in horses, and can be transmitted to people working closely with infected horses. In the latest outbreak, 3 horses died, making this the worst outbreak since 1994 when 14 horses and 2 people died.  A human case was also identified. This person worked at a veterinary clinic that treated infected horses. This individual was admitted to hospital overnight but was discharged, so  presumably was not very ill.

While Hendra virus (genus Henipavirus) is only found in Australia, it is a good reminder for everyone about the strange nature of some infectious diseases. The natural reservoir of the virus is the fruit bat. It is believed that horses become exposed when infected fruit bats give birth and contaminate horse pastures with uterine fluids. Horses develop respiratory disease ranging from mild to fatal. Human cases have been reported in people working closely with infected horses. A horse trainer and veterinarian's assistant died in the 1994 outbreak. Close contact is required for transmission to people.

Picture: Locations of previous Henipavirus outbreaks (red stars – Hendra virus; blue stars – Nipah virus) and distribution of Henipavirus flying fox reservoirs (red shading – Hendra virus; blue shading – Nipah virus)

It's very difficult to take specific measures to protect horses, people or other animals from sporadic, rare diseases such as Hendravirus infection. However, common sense infection control measures can reduce the risks associated with any animal contact.

• Wash your hands after contact with any animal.
• Avoid contact with sick animals - consider sick animals to be potentially infectious until proven otherwise.
• Remember that  new animal diseases are regularly being identified, and that they might be able to infect people.
• People that work in veterinary clinics must be diligent and use good infection control practices because they are at higher risk of exposure to various diseases.

This equIDblog entry was originally posted on the Worms & Germs blog on 15-Jul-08.

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