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

Because quarantine and testing are not 100%, good general infection control practices are also required. The presence of quarantine must not create a false sense of security and be used as excuse to avoid good infection control practices. These include things like restricting direct and indirect (e.g. sharing buckets) contact between horses, good hand hygiene by people working with horses and close monitoring for signs of disease, among other things. The intense preparations that are involved here show the importance of infectious disease in the equine industry and an excellent awareness of the problem.

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It was only a matter of time but eastern equine encephalitis (EEE) has been found in more US states this year. EEE is an important seasonally important disease in some areas and cases in Louisiana aren't surprising. More cases in more states, and perhaps into some regions of Canada, are likely over the course of the summer and fall.

This case was an infection in a horse in Rapides Parish. Not surprisingly, it was a fatal infection as EEE has a very high mortality rate in horses and in people.

If you live in a region where EEE cases have been identified or typically occur, you should have your horse vaccinated. Really, you should have ALREADY had your horse vaccinated because it takes time for the vaccine to work after administration. However, even if your horse hasn't been vaccinated, get it done.

Another aspect that is important is mosquito control. EEE, like Western equine encephalitis and West Nile virus, is transmitted by mosquitoes. Measures should be taken to reduce mosquito populations and mosquito exposure, both for your horse and yourself.

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Not long after the first report of vesicular stomatitis in 2009 (in Texas), the disease has now been identified in De Baca County, New Mexico. It's not too surprising because infectious diseases tend not to pay attention to geographical boundaries and New Mexico tends to one of the first states affected during outbreak years. Reportedly, only a single horse has been infected in New Mexico so far and the farm 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. Some years where this disease is present in the US, it is contained to a single state. During other years, multi-state outbreaks involving large numbers of horses can 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 disease:

• 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. (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.

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The Canadian Food Inspection Agency (which, despite the name, is not only in charge of food inspection) has announced import restrictions on horses from Missouri and Texas. Horses that have been in those states in the past 21 days or who have passed through those states during transportation are being flagged because of concerns regarding exposure to piroplasmosis and vesicular stomatitis, respectively. Canadian horses traveling to those states will have to wait until the restrictions are lifted or will have to be moved to a non-affected state for 21 days before being eligible to come home.

If those two outbreaks spread beyond those individual states, it's pretty certain that these restrictions would be expanded .

Still no word about the location of the 2 horses that were busted of our piroplasmosis quarantine in Missouri. It's surprising how little information as been forthcoming.

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TheHorse.com reports that two horses from Missouri that had tested positive for equine piroplasmosis were removed from their quarantined stable Wednesday night. Quarantine and testing of horses on the farm were implemented following identification of piroplasmosis in a quarter horse at a Missouri equine clinic. Five other postiive horses were identified and were euthanized with their owners' consent. (The other alteratives are long-term quarantine until negative or shipping them to a country where the disease is endemic). The Missouri Department of Agriculture, local officials and FBI are investigating.

Taking horses from a reportable disease quarantine is incredibly stupid.

Firstly, someone's going to notice. The authorities know what horses are quarantined and who owns them. No one has said who is suspected to have cut the padlocks to get at the horses and I'm not saying the owners necessarily did it, but who would go to such effort to break an infected horse out of quarantine. I don't imagine they thought that the FBI would be involved.

Secondly, the horses are not being quarantined because someone's just trying to give the owners a hard time. This is being done because of the presence of a severe disease that is not normally present in the US. While it's not highly transmissible, the fact that multiple horses on this farm were postiive certainly shows that transmission can occur in this area, be it through the appropriate tick vectors or other routes (i.e. contaminated needles).

Let's hope the people who took the horses come to their senses or get caught soon, so that there's not more spread of disease. I assume that if there are other horses stabled where these are eventually found, that those horses will be required to be quarantined as well. I wonder if people who might be housing these horses have thought of that.

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Clostridial myonecrosis (also called clostridial myositis or gas gangrene) is a very serious infection caused by growth of Clostridium bacterium in muscle. Clostridia are anaerobic sporeforming bacteria, meaning they only grow in environments without oxygen and they can stay dormant in the form of very tough spores. Clostridal spores can be found in healthy muscle. Presumably they enter the bloodstream periodically from the intestinal tract but aren't able to grow because of the presence of oxygen in healthy muscle. They lie dormant, waiting for the right conditions to start growing (which in most horses never occurs). Clostridial spores can also be introduced into muscle during vaccination, surgery or trauma.

If clostridial spores are in muscle (either residing there or introduced) and an anaerobic (oxygen-free) environment is created, they can start to grow. An anaerobic environment can be created following significant tissue damage from things such as intramuscular injection of irritating drugs or serious trauma. When these spores grow, they can cause very serious infection. Various clostridia can be involved, but Clostridium perfringens is most common. Regardless, infection is characterized by a very rapidly progression of soft tissue swelling, pain and systemic signs like fever and toxemia. The affected area can expand very quickly. Clostridia often produce gas when they grow and crepitus (a crackling feeling) can be felt over the infected area from the presence of gas in the tissues.

Clostridial myonecrosis is a life-threatening disease. It requires aggressive care, and is often fatal. One of the most important (and dramatic) aspects of treatment is opening up the infected area to provide drainage and allow air to enter. Large incisions need to be made into the muscle. While this can look horrific, it's a critical aspect of treatment. High doses of antibiotics are needed, along with other supportive care measures.

Fortunately, this is an uncommon disease. Avoiding it involves decreasing the chance of creating an appropriate environment for clostridial spore growth.

• Intramuscular injection of irritating substances should be avoided. Flunixin (Banamine) is commonly associated with this disease and should not be injected intramuscularly. Other irritating drugs include phenylbutazone (Bute) and ivermectin.
• Any muscle soreness or swelling that develops after an intramuscular injection should be taken seriously. A vet should be contacted promptly, especially if the size of the affected area is rapidly expanding.
• There is no evidence that any pre-injection techniques (i.e swabbing the coat with alcohol) have an influence of infection rates. Clostridial spores are resistant to alcohol, and most other disinfectants.
• If your horse has clostridial myonecrosis, it should be treated at an equine hospital if that is an option because of the intensity of care that is required. Aggressive and expensive treatment is needed. The prognosis is already guarded, and if optimal treatment isn't started promptly, the prognosis is very poor.

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Vesicular stomatitis 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 affected animals when an outbreak is developing. Quick response can help prevent the virus from spilling over into other species. It's of particular concern in cattle and sheep. Vesicular stomatitis can look like foot and mouth disease, a tremendously important disease that results is very aggressive quarantine measures and which can have a devastating economic.  Even though it is not usually fatal, vesicular stomatitis can also result in severe drops in production in food animals, and therefore have a corresponding economic impact.

The impact on infected horses can be variable. 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 cause significant discomfort. This can limit the use of the horse for a period of time (although they wouldn't be competing anyway due to quarantine). 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 outbreak investigation and response. The last outbreak, in 2009, 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 the potential that people could 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. Good communication and cooperation is essential.

Image from: http://www.newsinfo.colostate.edu/index.asp?page=news_item_display&news_item_id=480428605

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Two horses from different farms in the Savannah, Georgia area have been diagnosed with Eastern equine encephalitis (EEE). EEE is severe neurological disease that can strike quickly and seriously, and is fatal in up to 90% of cases. There is no specific treatment, and affected often deteriorate rapidly and dramatically.This viral disease is transmitted from birds to horses by the bites of infected mosquitoes, and it's a very important disease in some regions. Being mosquito-borne, it is a seasonal disease. The risk of EEE is also heavily influence by geography, largely due to the distrubution of mosquito species that effectively transmit the virus. Some areas have recurrent (and often major) problems with EEE, some (like Ontario) have few to no cases but can experiece small clusters and others never experience the disease.

Identification of EEE is important for a few reasons. Obviously, it's relevant for horse health. It indicates that EEE virus is in the area and mosquitoes capable of transmitting it between birds and horses are also present. Horse owners should be aware of the EEE history in their area as part of deciding whether to vaccinate against this deadly disease. Identification of cases in the area should be a reminder to look at farm measures to reduce mosquiotes and decrease mosquito bites. (More information on that is available in an earlier post about West Nile virus). Waiting until the first cases are diagnosed isn't a good plan because there is always a delay from vaccination until peak immunity, and your horse could be infected before the vaccine is given or takes effect. EEE vaccination is best performed about 1 month prior to the at-risk season, with a booster 6 months later if risk of exposure is still present.

The second aspect is with respect to human health. EEE can also affect people, where it also causes very serious (and often fatal) disease. People cannot acquire EEE from horses. They are infected the same from way; a bite from an infected mosquito. A vaccine is not available for people so mosquito avoidance is critical.

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Equine piroplasmosis, a foreign, reportable disease caused by Theileria equi, has been identified in a horse in Missouri. On June 2, the affected horse (a 7 yr-old quarter horse) was presented to an equine hospital. Signs consistent with a bloodborne disease were identified, 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, with results pending.

No source of infection has yet been suggested. The US was considered free of piroplasmosis after the last horse in an Florida outbreak cleared the infection earlier this year. This affected horse was apparently purchased 6 months ago but no information was provided about its origin. 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. Disease is characterized by fever, anemia (decreased red blood cell count), jaundice, respiratory signs, reddish urine and weight loss. Up to 20% of affected horses can die. The parasite is naturally transmitted by ticks. It can also be transmitted through the re-use of needles or other types of blood cross-contamination, and perhaps through breeding if semen is blood-contaminated. 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 be a longterm source of infection of other horses if the appropriate ticks are available to transmit the infection. Horses that are carrying this parasite 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 and how far it has spread is anxiously awaited.

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