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

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.

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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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