Equid Blog

Do horse owners need tetanus shots?

jsweese@uoguelph.ca (Scott Weese) — Fri, 10 Jul 2009 09:31:57 -0500

Here's a question I received the other day:

"Do people who work with animals and who work in barns need a tetanus shot as a result of this type of work? We have Therapeutic Riding Programs in the region and there is a sense that perhaps the volunteers and those who frequently tend the horses need to receive this. Is this the case?"

Tetanus is a disease that we are quite concerned about in horses because horses are very susceptible to it. That's why we vaccinate them yearly. Tetanus can also affect people, but is very rare (because of vaccination and lower susceptibility). While we pay a lot of attention to tetanus and horses, that does not mean that being around horses increases your likelihood of exposure to tetanus. The bacterium that causes tetanus, Clostridium tetani, is widely present in the environment. The more environmental (esp. soil) exposure that you have, the greater your risk of exposure. Being around horses doesn't increase your risk any more than doing other things outside.

Whether you have contact with horses or not should not change your approach towards tetanus. You should be vaccinated against tetanus every 10 years. Many (probably most, actually) adults are not up-to-date on tetanus vaccination. Adults tend not to voluntarily get booster shots and often this only happens when they have had a wound that requires medical care. (If you get stitches, they will almost certainly inquire about your last tetanus shot and give you another one if you haven't been vaccinated in the past 10 years).

More information about tetanus in horses is available in our Resources section.

Bug of the month: equine infectious anemia virus

jsweese@uoguelph.ca (Scott Weese) — Tue, 07 Jul 2009 09:48:42 -0500

Equine infectious anemia (EIA) is a rare disease but one that a lot of time, effort and money are put into avoiding. Most people know about this disease based on the most common test used to diagnose it: Coggin's test (see image).

Equine infectious anemia is caused by a virus (logically, equine infectiious anemia virus, EIAV). This virus is a 'lentivirus' and like other lentiviruses, causes persistent infection. Unlike most other lentiviruses that cause slow, gradual preogression of disease, EIAV infection usually causes a sudden onset of disease (acute phase) followed by recurrent disease. After the initial (acute) phase, horses can appear normal, which means they can be a silent reservoir of disease. That's why routine testing for EIAV is required in many circumstances; to detect silent carriers so they cannot continue to transmit infection.

Acute EIA is variable but usually results in fever, lethargy and decreased appetite. Anemia (decreased red blood cell count) and thrombocytopenia (decreased platelet count) can be detected. Anemia is more common and pronounced with recurrent infections. Periodic disease often develops after the acute episode. Affected horses may experience short (3-5 day) periods of fever, lethargy and decreased appetite. Severity of anemia often correlates with the severity and frequency of these disease cycles. In some horses, these cycles are very common, long and severe, and horses often have severe weight loss and anemia. However, most infected horses stop developing obvious cycles of disease after a year and seem perfectly healthy (good for the horse, bad for other horses).

EIAV is a bloodborne virus that can be transmitted by blood-feeding insects, especially tabanid flies (horseflies, deerflies). Stable flies can also transmit EIAV but do so less effectively. Contaminated medical supplies can also transmit EIAV, such as resue of syringes.

Fortunately, EIA is rare in most regions and positive tests are quite uncommon. Routine testing for EIA is usually required for shows, sales, transportation and other situations where horses are mixed. This allows for detection and removal of carriers. Unfortunately, identification of a horse as a carrier is not good for the horse or owner (or other horses in the vicinty). EIA is not treatable, and horses that have positive tests ('reactors') are quarantined, as are all other horses that are housed within 200 yards. Horses living close to reactors are tested (usually 30 and 60 days after removal of the reactor) and only released from quarantine after getting negative test results at least 60 days after the last reactor was removed. Reactors are usually euthanized. If prompt euthanasia is not chosen, reactors are usually prominently branded or tattooed. They must be kept under quarantine at least 200 yards from other horses. (200 yards is used because these flies don't travel that far.)

The best way to reduce the risk of EIA is ensuring that all horses are regularly tested. New horses coming onto a farm must be tested BEFORE arrival or after arrival but while in quarantine at least 200 yards away from other horses. Needles and other items that might be blood contaminated should never be re-used (for EIA risk among other potential problems).

Overall, it's a very rare disease but the implications of a positive test mean that we need to be vigilent.

image from http://www.aht.org.uk/science_eia.html

Still no sign of missing piroplasmosis horses

jsweese@uoguelph.ca (Scott Weese) — Thu, 02 Jul 2009 16:20:17 -0500

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 2 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 travelled.

This disease, caused by the bloodborne parasite Theileria equi, is transmitted by ticks and through contaminated needles, and if these horses are in an area where there are tick species that are capable transmitting this parasite, piroplasmosis could be silently increasing. 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.

Parking lot quarantine for World Equestrian Games

jsweese@uoguelph.ca (Scott Weese) — Tue, 30 Jun 2009 10:11:23 -0500

International events like the World Equestrian Games are important and high profile competitions. They are also great places for disease transmission, with large numbers of horses from different areas brought together, along with associated stressors that can increase the risk of disease.

For the 2010 games at the Kentucky Horse Park, a long term parking lot at Cincinnati/Northern Kentucky International Airport has been designated as a quarantine facility. Up to 600 horses will be temporarily stabled there after arriving from other countries. They will be required to stay in quarantine for at least 42 hours, to be monitored for signs of infectious diseases and for completion of selected laboratory tests. While it may seem strange at first, this site was chosen because it's readily access, close to the event and can provide the needed security. [Horses from some regions are subject to different quarantines at different facilities. For example, horses from Asia will be quarantined in Los Angeles while South American horses are quarantined in Miami and tested for additional diseases such as Venezuelan equine encephalitis and screwworm.]

Quarantine is a highly effective measure, if done properly, but it is not foolproof. You can never completely eliminate infectious disease risks because some diseases can have longer incubation periods than the quarantine and others can be carried by healthy animals. Testing for specific pathogens can help pick up these hidden carriers but you can't test for everything. You can never declare a horse to be free of all potential causes of disease, because such a horse doesn't exist. All horses carry something that could cause disease in certain situations, but in general these are low risk. The key is focusing efforts on the most common and most serious 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.

EEE in Louisiana

jsweese@uoguelph.ca (Scott Weese) — Mon, 29 Jun 2009 08:12:39 -0500

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.

Vesicular stomatitis in New Mexico

jsweese@uoguelph.ca (Scott Weese) — Thu, 25 Jun 2009 08:22:27 -0500

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.

Canadian import restrictions for Missouri and Texas horses

jsweese@uoguelph.ca (Scott Weese) — Mon, 22 Jun 2009 20:06:33 -0500

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.

FBI chasing piroplasmosis quarantine escapees

jsweese@uoguelph.ca (Scott Weese) — Fri, 19 Jun 2009 15:36:32 -0500

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.

Intramuscular injections and clostridial myonecrosis

jsweese@uoguelph.ca (Scott Weese) — Fri, 19 Jun 2009 08:31:29 -0500

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.

Vesicular stomatitis in Texas

jsweese@uoguelph.ca (Scott Weese) — Tue, 16 Jun 2009 16:35:51 -0500

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

Eastern equine encephalitis in Georgia

jsweese@uoguelph.ca (Scott Weese) — Sun, 14 Jun 2009 21:17:13 -0500

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.

Piroplasmosis in Missouri

jsweese@uoguelph.ca (Scott Weese) — Fri, 12 Jun 2009 15:49:58 -0500

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.

Horses leaving the farm: what to do when they return

jsweese@uoguelph.ca (Scott Weese) — Tue, 09 Jun 2009 17:05:56 -0500

The horse population is perpetually at risk for major disease outbreaks. Sometimes we get lucky and nothing happens, sometimes we get regional outbreaks of disease, and rarely we see large national outbreaks (i.e. influenza in Australia). There are many reasons for this risk, and most involve how we manage horses. Unlike other domestic animals that rarely travel and are not commonly exposed to large numbers of 'new' animals on a routine basis, some sectors of the horse population are highly mobile and there are regular chances for disease exposure. Some of these risks are inevitable (i.e. traveling for competition, emergency visits to an equine hospital...).

Ideally, every horse that leaves the property for any reason, be it a show or a stay at an equine hospital, should be isolated upon return. Keeping a horse isolated for 1-2 weeks provides time for infections to be identified and for elimination of certain infectious diseases that are only shed for a short period of time (i.e. equine influenza). This is most important when there are high risk horses on the property (i.e. pregnant mares) or when horses are traveling to places with a high risk of exposure to an infectious disease.

Obviously, isolation of all horses upon return is not practical in all situations, such as when horses are leaving for events on a regular basis or when appropriate facilities do not exist. In those situations, you have to accept that you are putting yourself at increased risk for infectious diseases. Therefore, other components of a good infection control program are even more critical, such as rapid identification of horses that might have an infection, a good general infection control plan, a good preventive medicine program and good general hygiene measures. Good management practices will reduce (but not eliminate) the risk of disease transmission when an unknown carrier gets on the farm.

If isolation of all returning horses is not possible, you should pay particular care around:

Horses that have been to events where sick horses are present.
Horses that have been in contact with horses from sales.
Horses that have been at an equine hospital (especially one without an infection control program).

Even if you can't (or won't) isolate new arrivals, you can do other things.

Keep new arrivals away from the highest risk horses, like broodmares.
Make sure that new horses are checked carefully on a daily basis (or more often) for signs like fever, loss of appetite, cough, nasal discharge, enlarged lymph nodes and diarrhea. Also, make sure something happens with that information! It's not helpful if someone is checking temperatures but doesn't know what to do if they identify a horse with a fever.
Keep new horses as far away as possible from resident horses. Keeping them at the end of the barn as far away from other horses (maybe with an empty stall in between) can help. It doesn't replace true isolation but is better than nothing,
If you have to turn out new arrivals, turn them out by themselves or keep them turned out with the same group horses, so that if they are infectious, a limited number of horses are exposed.
If in doubt, err on the side of getting a new horse examined by a veterinarian. Some diseases have narrow windows of time where horses may be showing signs of infection but where they are not yet able spread the disease (i.e. horses with strangles will spike a fever before they start to shed the bacterium). Therefore, prompt action is critical. Getting a vet out earlier can help determine the appropriate measures and make the difference between one sick horse and one sick farm.

Malignant catarrhal fever in a horse

jsweese@uoguelph.ca (Scott Weese) — Thu, 04 Jun 2009 22:01:58 -0500

An article in a recent edition of Emerging Infectious Diseases describes a case of malignant catarrhal fever (MCF) in a horse. MCF is a severe (usually fatal) disease caused by ovine herpesvirus type 2 (OvHV-2) or alcephaline herpesvirus type 1. It mainly affects cattle, and horses have traditionally been considered to be resistant. This recent report from Brazil challenges that belief. It describes a 6 month-old foal with severe neurological disease that died 1 day after abnormalities were first noted. When veterinary pathologists examined tissues from the foal, there was severe damage to small blood vessels (lympho-histiocytic fibrinoid necrotizing vasculitis....(pathologists like long names)) that was strikingly similar to MCF.

Sheep and goats are the main reservoir of OvHV and this foal came from a farm that also had goats. Molecular testing was performed on tissues from the foal and OvHV-2 DNA was identified. This virus was also detected in the blood of 3 adult horses and 8 goats on the farm. (The horses were all healthy).

This is an interesting and quite thorough investigation that challenges current dogma about MCF and horses. It's hard to say whether horses have always been slightly susceptible with rare disease going undiagnosed, or whether this is an emerging problem. It's unlikely this is a 'hot' strain of OvHV-2 that can now infect horses because other horses on the farm were fine and there have been no other reports of disease in horses. It's possible that this foal had some underlying problems that made it susceptible to infection by a virus that normally does not cause disease. We certainly shouldn't panic about MCF based on this study and keep all horses away from sheep and goats, but it should be a reminder that infectious diseases like to challenge conventional wisdom and that we need to be on the lookout for new diseases and different patterns of old diseases.

Equine herpesvirus consensus statement

jsweese@uoguelph.ca (Scott Weese) — Mon, 01 Jun 2009 16:14:12 -0500

The American College of Veterinary Internal Medicine (ACVIM) has released a consensus statement on equine herpesvirus type 1 (EHV-1). The ACVIM is the specialty organization for veterinary internal medicine in North America, and every year it produces consensus statements on selected large and small animal topics. These are developed by a group of experts in the field, who review current knowledge (and knowledge gaps) and come up with a comprehensive overview of the subject. This consensus statement is no different, and has detailed information on various aspects of EHV-1, including diagnosis, vaccination and infection control. It can be accessed through the ACVIM website, our Resources section or by clicking here.

Bug of the Month: Clostridium piliforme

jsweese@uoguelph.ca (Scott Weese) — Thu, 28 May 2009 10:00:00 -0500

Tyzzer's disease is a rare but devastating disease caused by the bacterium Clostridium piliforme. This bacterium causes severe liver disease and sudden illness in young, otherwise healthy foals between the ages of 1 and 6 weeks. Usually on any particular farm only one foal is affected at a time, but small outbreaks can occur.

There is still a great deal we don't know about C. piliforme and Tyzzer's disease. It is presumed that foals become infected by ingesting the bacterium from the manure of other horses or from the environment. No one knows how often foals are exposed to the bacterium in this way - it may happen to a lot of foals, but only a few of them get sick, or it may happen very uncommonly, but make most of the exposed foals sick. Tyzzer's disease occurs very suddenly and progresses incredibly fast. Affected foals are often simply found dead, even though they looked completely normal only hours earlier. If they are found alive, foals may be slightly to extremely weak and lethargic, and they may have a fever, diarrhea, and increased heart and respiratory rates. The gums and whites of the eyes may be yellowish (i.e. jaundice), which is sign of liver failure. Even if foals with Tyzzer's disease are found alive, their condition usually worsens very quickly and they often start having seizures before they die.

A diagnosis of Tyzzer's disease is usually made by post mortem (necropsy) examination. Clostridum piliforme cannot be grown on regular culture plates in the lab like most of the disease-causing bacteria with which we deal (this also makes it very difficult to study). Special stains of liver tissue (silver stain) can help identify C. piliforme under the microscope. Real-time PCR, a molecular method that detects the DNA of C. piliforme, is also available.

Unfortunately, most foals with Tyzzer's disease die before, or shortly after, they are found to be ill. In most cases there is hardly enough time to even start treatment because the disease is so severe and progresses so rapidly. There are only three foals ever reported to have survived Tyzzer's disease, or what was strongly suspected to be Tyzzer's disease. Very aggressive therapy (i.e. in a referral hospital) is needed immediately to try to save affected foals, but the prognosis is very grave.

There are no known measures that can be taken to help prevent Tyzzer's disease in foals. Fortunately, the condition is rare, and there is no evidence that it is transmissible to humans.

Papillomavirus Part 2: Plaque Problems

mander01@uoguelph.ca (Maureen Anderson) — Mon, 25 May 2009 10:00:00 -0500

From Guest Author Dr. Angelika Schoster, Department of Clinical Studies, University of Guelph.

No, not dental plaque like you get on your teeth - in this case we’re talking about aural plaques, which are a type of skin lesion that some horses develop on the inside surface of their ears. These plaques are usually depigmented, meaning the skin cells of which they are made do not have the same pigment in them as the cells of the surrounding skin, making the lesions appear pale grey or off-white. Other than being considered unsightly in some cases, aural plaques usually don’t cause problems for the horse – they’re not itchy, sensitive or painful. They can occur in any horse, no matter the age, breed or sex. Occasionally some horses may develop similar plaques on the udder or around the anus or vulva (under the tail). The diagnosis of an aural plaque is typically made based on the horse’s clinical signs alone (i.e. a raised, depigmented skin lesion inside the ear that is not associated with any inflammation or discomfort).

The exact cause of aural plaques is still not clear, but using extremely high-powered electron microscopy, researchers have been able to demonstrate that in some cases there is a papillomavirus infecting the cells within these plaques. No one has yet been able to isolate the virus to determine what type of papillomavirus it might be. Aural plaques are not known to be transmissible from horse to horse, but since there may be a virus involved, it's prudent to consider the possibility that virus transmission may play a role in their development (although there are likely many other factors involved as well). Unlike regular papillomas (i.e. warts, caused by equine papillomaviurs), aural plaques do not disappear on their own. It the past, the only way to remove the plaques was to actually cut them away surgically. In more recent years, successful treatment has been reported using an immune-response modifier cream such as imiquimod (Aldara), which is used in people to treat several different skin conditions, including genital warts.

Photo: Aural plaque on the ear of a horse (source: University of Minnesota - College of Veterinary Medicine)

Papillomavirus Part 1: Wart Worries

mander01@uoguelph.ca (Maureen Anderson) — Thu, 21 May 2009 16:00:00 -0500

From Guest Author Dr. Angelika Schoster, Department of Clinical Studies, University of Guelph.

Papillomaviruses (PVs) are small DNA-based viruses that are recognized causes of disease in many animal species and humans. More than 100 different human papillomavirus types (HPV) have been identified, which can cause a range of problems from annoying (but benign) warts to malignant cervical cancer. The ability of papillomaviruses to cause cancer was first recognized in animals, specifically with cottontail rabbit papillomavirus (CRPV), bovine papillomavirus (BPV) and canine oral papillomavirus (COPV). In general, PV infection causes benign disease in the vast majority of individuals, but the viruses have the potential to cause malignant disease in a small proportion of the mammals they infect as well.

Horses can be infected by both equine papillomavirus (EPV) and some bovine papillomaviruses. Infection with BPV is associated with equine sarcoids – look for more information on BPV in horses in an upcoming post. Infection with EPV (specifically Equuus caballus papillomavirus types I and II) causes cutaneous papillomas – small proliferative skin lesions better known as warts. Warts are benign growths that appear on animals less than two years of age. They typically persist for 6-12 months and then disappear without any specific treatment, and they do not otherwise make the animal sick. Usually warts appear on the muzzle and lips, but rarely genital warts can occur (usually with infection by the type II virus). Occasionally warts can also occur on the lower limbs, ears and eyelids.

Warts can be spread between horses by fomites (e.g. objects, equipment, tack, clothing that has been contaminated with EPV), or by close horse-to-horse contact. Spread is common when young are horses are brought together in large groups for shows, sales or breeding. Infection is usually diagnosed by the characteristic skin lesions, the horse’s history and age - more than 90% of affected horses are less than three years old. Usually the warts regress spontaneously and they do not require treatment. However, if treatment is sought for esthetic reasons, cryosurgery (i.e. freezing, usually with something like liquid nitrogen) can be performed. Caustic chemicals such as trifluoracetic acid can also be used to “burn” the warts off. Even after treatment, though, the warts can recur.

Controlling warts caused by EPV is fairly simple: if you have an affected horse, keep it away from other young horses. Do not allow the horses to have direct contact, and make sure the horse with the warts has its own tack, grooming supplies, water bucket, hay net/trough etc. so the virus is not indirectly transmitted to others. There is no vaccine available for horses for EPV. There are a lot of “voodo” treatments for warts out there, and some people swear by them, but (just like people who treat foal heat diarrhea) that’s usually because they’re treating a condition which goes away on its own anyway. People cannot be infected by EPV.

Photo: Warts on the nose and lips of a horse (source: http://www.yourveterinaryclinic.com)

Severe Diarrhea Caused By Clostridium difficile

jsweese@uoguelph.ca (Scott Weese) — Tue, 19 May 2009 08:00:00 -0500

The latest issue of the Journal of Veterinary Diagnostic Investigation contains a case report by Dr. Glenn Songer's research group about a 14-year-old Quarterhorse that had been treated with ceftiofur (an antibiotic) because of suspected salmonellosis, and subsequently died of severe colitis (sometimes called colitis X, but I don't like that name). This pattern is all too familiar when it comes to horses: antibiotic treatment for an undiagnosed infectious disease results in death due to colitis (diarrhea). It's even more frustrating when you consider there is very little indication to treat adult horses with salmonellosis with antibiotics.

The colitis in this case was caused by Clostridium difficile. The strain of C. difficile was ribotype 027 (also called NAP1, BI and toxinotype III, depending on the method used to type the strain), which is typically considered the most serious strain in people. It is often associated with outbreaks of disease, and has been blamed for the increased frequency and severity of C. difficile infections in people internationally over the past few years. This strain has also been found in dogs, cattle and pigs, as well as retail meat samples (e.g. from the grocery store).

While the information in this paper isn't particularly surprising, it should act as a reminder that C. difficile is an important problem in horses and that important strains of C. difficile can infect many different animal species. When you consider how big of a problem C. difficile is in human medicine, it should be a reminder that we need to take this problem seriously in horses too, and also continue to investigate whether people can be infected by horses. A small percentage of healthy horses shed C. difficile in their manure, and we don't really know if that poses a risk to people. When you consider how much C. difficile can be present in diarrhea, the huge volume of diarrhea that a horse can pass and the potential for human exposure because of the big mess that is made, we certainly should consider diarrheic horses as a possible source of infection for people, just as we do for Salmonella.

Antibiotic use is a well known trigger for C. difficile infection in people. While disease in horses can occur even when antibiotics are not given, it is widely suspected that antibiotic use is a major risk factor for severe colitis due to C. difficile. Anecdotally, ceftiofur seems worse for this than many other drugsin some regions. This is consistent with studies in humans that have shown that antibiotic drug class used can have a significant impact on the risk of C. difficile infection.

What should we take home from this report?

Only use antibiotics when they are really needed. Antibiotic administration can lead to fatal complications, although these are rare.
Consider C. difficile in all cases of diarrhea in horses.
Consider all horses with diarrhea potentially infectious to other horses and people, and handle/house them appropriately.

Photo source: http://www.microvet.arizona.edu/Faculty/songer/diag.htm

Foal Diarrhea Part 2: Foal Heat Diarrhea

jsweese@uoguelph.ca (Scott Weese) — Fri, 15 May 2009 10:00:00 -0500

As previously discussed, diarrhea in young foals can range from a messy inconvenience to a rapidly life-threatening condition. A very common but fortunately relatively harmless cause is a syndrome called foal heat diarrhea, so named because it usually occurs around the time of the mare's first heat after foaling, when the foal is about 7-10 days old. Foals with foal heat diarrhea have diarrhea but no other problems like weakness, decreased appetite, colic or fever. If any of these other signs are present, then the foal has something other than (or in addition to) foal heat diarrhea.

The cause of foal heat diarrhea is not known. It doesn't actually have anything to do with the mare's heat, or the mare at all in fact - it even occurs in foals that are bottle raised and have no contact with a mare. It's likely the result of normal changes in the bacterial microflora in the intestinal tract of the foal that just happens to occur at this age.

Foals are usually diagnosed with foal heat diarrhea when they are the right age and have mild diarrhea but no other problems. Testing for (and ruling out) other causes of diarrhea like salmonellosis helps to support this diagnosis.

Any foal with diarrhea must be monitored closely for developing signs of illness. Don't fall into the trap of simply chalking up a diarrhea episode to foal heat diarrhea and forgetting about it. If you're wrong, a foal with diarrhea due to an infectious cause can go from looking "okay" to too weak to stand and nurse (or worse) within a matter of hours.

Foal heat diarrhea does not require any treatment in almost all cases. Occasionally, foals can get weak or dehydrated if they don't drink enough to make up for the fluid lost in the diarrhea, but this is quite rare. Foals almost always get better on their own. If they don't, there is probably something else going on and diagnostic testing is needed to determine what that is.

The fact that foal heat diarrhea gets better on its own may be one reason there are so many "proven" foal diarrhea treatments by which people swear. Some people are convinced that certain treatments are highly effective because when they treat foals, they get better. However, with foal heat diarrhea, which is probably the most common cause of diarrhea in foals, the animals get better regardless of (or despite) what you do. That's why well-designed research trials that include untreated control groups are needed to determine if treatments actually work.