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

A rabid horse has been identified in Bandera County, Texas - this is the first case of rabies in a Texas horse in almost 40 years. The horse started acting strangely, erratically and at times violently. Rabies was eventually diagnosed (diagnosis involves testing the brain after the horse dies or is euthanized) and the owners are undergoing post-exposure treatment.

Rabies is a rare disease in horses, but there is always a risk of exposure in regions where rabies is present in wildlife. The fact that equine rabies is rare is a good thing, but it can also breed complacency and lead to decreased vaccination rates.

Decreasing vaccination is a bad thing. Vaccination is cheap insurance for a very serious disease. Rabies is invariably fatal in horses. It's also a risk to anyone around the horse. Transmission of rabies from horses to people is theoretically possible through bites or other contacts that result in introduction of saliva into wounds, cuts or possibly the mouth, nose or eyes. I'm not aware of any documented cases of equine-to-human transmission of rabies, but given the severity of rabies, we need to be careful. Additionally, rabid horses have killed people because they can be unpredictable and aggressive. Based on all these factors, it's important that we not become complacent about rabies in horses, and a key component of rabies control is vaccination. However, vaccination is not the only aspect of rabies control. Using various management practices to reduce the risk of wildlife exposure and controlling rabies in wildlife in the area are other important measures, but individual horse owners can have the greatest impact on their horses' health by ensuring they are properly vaccinated against rabies.

If you own a horse, make sure it's vaccinated against rabies unless you live in a rabies-free region.  More information about rabies in horses is available on the equIDblog Resources page.

Image source: www.bbc.co.uk

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TheHorse.com has a good article about deworming, which includes six good parasite-fighting tips from Dr. Craig Reinemeyer. Check out the full article for all the details. Here are the key points and some comments:

1. Stop focusing on the wrong things

It's easy for people to get hung up on a few concepts or topics and not see the big picture or the real problems. We need to think in terms of the horse(s), not the parasites. We're trying to optimize horse health. That doesn't necessarily mean killing all parasites, nor does it mean relying soley on drugs to control them. Conceptually, we need to think about parasite control, not just deworming.

2. Plan parasite control around parasite biology, not a calendar

There is no "standard" deworming program. Every program needs to be tailored to the geographic region, farm and horse. What happens here is Ontario is very different from what happens in Florida in terms of parasites.  For example, the risk of transmission in horses turned out on pasture in Florida in February is certainly different from those turned out in snowy fields in Ontario at the same time of year. Even in the same region, what happens on one farm may be very different than what happens on another. When designing a parasite control program, you need to consider what is going on with worms in the horses and in the environment to determine the optimal approach.

3. Don't encourage resistant parasites

Most people know antibiotic-resistant bacteria are a bad thing, but often concerns about anti-parasitic resistance are ignored. We only have a limited number of antiparasitic drugs, and there aren't many more coming in the near future. Heavy use or misuse creates an environment where resistance may emerge. It's being seen with certain bugs and certain drugs, and needs to be taken seriously - now.

4. Don't treat all horses the same

As I mentioned above, you need to tailor parasite control to something that is relevant for the region, farm and horse. Different horses are at different risks of exposure. Some horses are naturally more resistant to parasites, so these animals don't need to be (and indeed shouldn't be) treated the same as more susceptible horses. Deworming should be tailored to the needs of the individual horse. Yes, it takes more effort and some thought, but it's worth it.

5. Practice evidence-based parasite control

That means use all available information to make decisions. It includes knowing what parasites are a concern on the farm (which requires testing), what antiparasitic drugs have been effective on the farm (which requires testing to determine treatment success), an understanding of farm management practices, and information from research about deworming strategies and drugs. Performing fecal egg counts is a critical component of this, and something that is not done nearly enough.

6. Be prepared to change

Something that works today may not work in the future. You can't get stuck in your ways and assume that since something worked in the past, it will always work.

Image source: www.ponytalesblog.com

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It's common for people to wipe injection sites in horses with alcohol before inserting the needle. It's so ingrained into some peoples' minds that they may complain if their veterinarian doesn't use an alcohol wipe before injecting. But what does that little swab really do, and is it needed?

Alcohol is a disinfectant and can kill many (but not all) bacteria and viruses. Therefore, wiping an injection site with alcohol could theoretically reduce bacterial counts and maybe reduce the risk of an injection site infection. However, alcohol does not work well in the presence of organic debris (i.e. dirt), and may not (and likely won't in most cases) penetrate through a horse's haircoat down to the skin. The best aspect of alcohol is some situations is wetting down the hair to help see the area you're injecting (for example, when visualizing the vein for an intravenous injection).

The risk of injection site infection is very low in the average horse, and the true benefit of wiping the site with alcohol is unknown. There is no clear evidence that this practice reduces infections. The most serious injection-associated infection, clostridial myonecrosis, is caused by either inoculation of clostridial spores (which are resistant to alcohol) or by spores that are dormant in the muscle tissue. In either case, wiping the skin with alcohol won't help prevent it.

Bottom line: There's no evidence that alcohol wiping is needed, or useful. There's also no reason not to do it, so it's really a matter of personal preference. Not using alcohol wipes is not an indication of poor practice, but a lot of people will use them on the chance that they are effective, knowing that at worst they will do no harm.

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

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I've had a run of questions about testing for Helicobacter in horses with gastric (i.e. stomach) ulcers. Helicobacter pylori is unquestionably an important problem and clear cause of gastric ulcers in people. However, people aren't horses. The human stomach differs greatly from the equine stomach, and gastric ulcers in people are much different than gastric ulcers in horses. There is no (I repeat, NO) evidence that Helicobacter is a cause of ulcers in horses. Despite this some unscrupulous molecular diagnostic companies offer unvalidated tests for Helicobacter in horses, for reasons that make absolutely no sense.

Don't waste your money on Helicobacter testing if your horse has ulcers. Spend it on treatment and management changes to reduce the risks of ulcers recurring.

(click image for source)

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

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

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

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

More information on CEM is available in our archives.

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

Photo credit: David Campbell (click for source)

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

There are basically two answers that I give:

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

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

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

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

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

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

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

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

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

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

Image source: http://animalphotos.info/

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

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

Image source: www.collectgbstamps.co.uk

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I assume that people wouldn't voluntarily and regularly walk around barefoot on dog feces (or feces of any type), yet it's perplexing that some people regularly clean out horse stalls in bare feet (I've seen it done!). While horse manure may not be as inherently gross as dog poop, it's still feces, and like all feces contains a huge population of various bacteria, some of which can be harmful. The risks of barefoot mucking may also extend to bare feet inside boots, although I don't think sock-averse people need to panic.

An article in the International Journal of Infectious Diseases (Friederichs et al) describes infectious arthritis of the shoulder of a horse owner that was caused by Streptococcus zooepidemicus, a bacterium commonly found in horses but rarely associated with disease in people. The person didn't have a wound in the shoulder area or any other obvious route for the bacterium to get to the shoulder joint. They searched for a source of the infection and all they found was a chronic lesion on the person's foot. This, combined with the patient's history of taking care of his horses in "bare feet in boots", led them to implicate the foot as the source of infection.

The idea, I guess, is that socks would be a barrier to help prevent contamination of the foot wound. That makes sense to a degree - the person could contaminate his foot with S. zooepidemicus from his hands (probably acquired from touching the horse's nose) while removing the boots, or manure could work its way into boots and directly contaminate the wound. Both are possible, but we have to be a little cautious in interpreting these conclusions. However, this is a bacterium that is associated with horses and the foot lesion is certainly a possible route of entry.

Overall, this should be considered an interesting report of a very rare problem, not something that indicates a major concern. However, there are a few good points to take away from this story:

• If you have a wound or chronic lesion of any sort, make sure you take measures to reduce the risk of bacterial contamination when working around horses. This might be as simple as making sure it's covered by clothing, or something more involved like using an impermeable bandage.
• Hands are probably the major source of infection transmission, and good hand hygiene is important after horse or stall contact, particularly if you have an underlying disease.

This equIDblog entry was originally posted on our sister site, Worms & Germs Blog, on 20-Jan-10.

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