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

Infectious disease outbreaks in barns get a lot of attention, and none of it's good. Unfortunately, the same degree of attention is rarely given to measures used to reduce the risk of infectious diseases. Infectious diseases are an inherent risk of horse ownership, but there are a lot of things that we can do better to help reduce the risks. Developing a good infection control plan is one thing. Enforcing it is another. The best laid infection control plans are often rendered useless because people don't comply with them. This is a particular problem in some boarding stables that have multiple different horse owners with different ideas, perceptions, veterinarians and willingness to cooperate. One way to help improve infection control in these situations is a good boarding contract. Why? Because a boarding contact can lay out exactly what is expected from everyone up front, and the repercussions that can occur if someone (barn owner or horse owner) doesn't do what is expected. Infection control responsibilities should be built into every boarding contract. This helps improve infection control by laying the foundation for application of good infection control practices. There are several infection control topics that should be addressed in boarding contracts. Some things to consider include:

• When does a veterinarian have to be called? You don't want to mandate unnecessary veterinary visits, but prompt examination of horses that might have infectious diseases is very important. For example, horses that have strangles are not able to infect other horses for the first couple of days after their initial fever spike. Identifying these horses early lets you get them isolated and reduce the risk of infection. Waiting a couple of days can put the whole barn at risk.
• What information has to be shared? Veterinarians are bound by confidentiality rules and can't share information about their patients with other people unless they have permission. That means a veterinarian may tell an owner they have an infectious horse, but if that person doesn't do anything or tell anyone, the veterinarian can't inform the barn owner that a risky situation is present. Mandating reporting of certain things to the barn could help with this.
• What happens when a horse with an infectious disease is identified? It's best to spell this out in advance so that everyone knows that there may be restrictions on horse movement or other activities to reduce the risk of transmission.
• Will testing be required in certain situations? In some cases, testing of horses is very important to determine if there is a problem and what it is. It needs to be determined up front if the barn can mandate such testing in specific situations, and who pays for it. If one person refuses to test as part of a program to determine if a farm is free of strangles after an exposure or outbreak, all of the other efforts might be jeopardized.

Will all these ideas be popular? No. Infection control practices are often somewhat cumbersome, but they are important. Yes, some people will fight them. Yes, some people may threaten to leave.  But:

If you are a barn owner, wouldn't you rather have a barn full of people that are reasonable, have respect for the health of all horses in the barn, and are willing to commit to doing things right?

If you are a horse owner, wouldn't you want your horse is a barn where you know that people are committed to reducing the risk of infections?

For me, the answers are clear.

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Few things get the horse rumour mill going like strangles. This infectious disease carries such a stigma that the simple act of having a sick horse (or even the suggestion that someone has a sick horse) can lead to rumours that spread like wildfire, along with complaints, accusations and other generally antisocial behaviour. Currently, depending on what rumours you listen to, there are either major strangles outbreaks going on in multiple large facilities across Ontario, or everyone is fine and there are no sick horses of any type in the province. (Like most things, the truth probably lies somewhere in between.)

Strangles, caused by the bacterium Streptococcus equi, is an important equine infectious disease. It's present in horses internationally and there are always cases and small outbreaks underway in Canada (as in other countries). It's also potentially controllable using good infection control practices, but the stigma, rumours, denials and other associated problems hamper such efforts.

Because of the stigma associated with strangles, some peoples' approach is to deny the possibility that their horse may have the disease, or to avoid getting proper testing done. I've heard people deny that they have strangles on their premises, but in the same sentence say that they aren't letting any people on the farm for a couple of weeks with no explanation as to why. I've also seen situations where strangles is clearly present but people refuse to have culture samples taken - because if no cultures are taken and found to be positive, they can still say that they haven't had any horses diagnosed with strangles (even with stall after stall of horses with fever, nasal discharge and draining abscesses). Fortunately, most horse owners and farm managers don't take this approach, but the fact that some do gives strength to the rumours that often circulate.

Denying that an infectious disease problem exists is never a good idea, because it usually hampers implementation of the required control measures. It's also unethical if these denials and improper practices lead to more infections. If strangles is on a farm, people need to own up to the fact and act accordingly. Yes, the proper control measures are a hassle and can interfere with showing, racing or other uses. But closing your eyes and hoping it goes away does not work. At the same time, people need to take a balanced approach when they hear about strangles. Having a horse with strangles does not necessarily mean that there is bad management on the farm. Yes, many infections could be prevented with good infection control precautions, but we can't prevent all infections at this point. The more people point fingers about strangles cases, the greater the pressure for people to hide the problem.

• If you have strangles on your farm, admit it. There's no use hiding it because the truth will  come out eventually, and the rumours may be worse than the truth, anyway. Let people know what's going on and what you are doing to control it. It's often the absence of information that causes most of the fear and complaints.
• If your horse is on a particular farm when a case of strangles is diagnosed, be part of the solution, not a hindrance. Help out by supporting the barn owner and other horse owners. Do what is being asked of you. Don't immediately take your horse off the property (and possibly spread the outbreak to another facility). And cut them some slack - it may not be their fault, and it could just as easily have been your horse that was infected.
• If you've had strangles in your horse or on your farm, take the time to figure out what happened and why. This shouldn't be done to assign blame. It should be done to figure out how to prevent it the next time.

Strangles isn't Ebola. It's a problem, but one that can and should be handled with a reasonable and logical approach. More information about strangles can be found on the equIDblog Resources page.

Image: Draining abscesses of the submandibular lymph nodes of a horse with a classic case of strangles (credit: Dr. Nancy Loving, thehorse.com)

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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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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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Rhodococcus equi is a bacterium that is an important cause of respiratory disease in foals. It typically causes numerous abscesses in the lungs, and it is an important cause of illness and death in foals from a few weeks to about six months of age. Infections of other parts of the body can occur, and these can cause serious problems because they can be hard to diagnose and hard to treat.

A recent study in the Journal of the American Veterinary Medical Association (Reuss et al 2009) described extra-pulmonary disorders (EPDs, disorders in parts of the body besides the respiratory tract). They studied 150 foals, and 74% had a least on EPD. These included:

• Immune-mediated synovitis (25%): This is a well-recognized problem where R. equi-infected foals get enlarged joints because of accumulation of excess joint (synovial) fluid. Fluid-distended joints can occur with joint infections, but with immune-mediated synovitis it's caused by the immune system alone. This typically does not result in long-term joint problems, although it's important to determine whether the foal has an infection which needs aggressive care, or just inflammation which is best left alone.
• Abdominal abscesses (17%): This is a very serious problem and abscesses in the abdomen can be very difficult to treat. These foals often die.
• Uveitis (11%): Inflammation of the eye, which can occur as a result of the immune response or infection. 
• Septic synovitis (9%): As opposed to immune-mediated synovitis, this is an infection in the joint. This is very serious and can cause permanent joint damage.
• Pyogranulomatous hepatitis (11%): This is inflammation of the liver with abscesses and pus.
• Pleural effusion (3%): Accumulation of fluid between the lungs and body wall. This can be the result of severe lung disease.
• Meningitis (3%): Infection of the layer covering the brain, which is never a good thing.

Foals that had EPDs were more likely to die than foals with infections only involving the lungs, which isn't particularly surprising. In particular, the presence of uveitis, bloodstream infection, joint infection (not immune-mediated synovitis) and abdominal abscessation were associated with failure to survive.

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Herd immunity is an important infectious disease concept. Basically, it involves trying to ensure that a high enough percentage of a population is resistant to an infectious disease so that the disease cannot be spread easily through the group. Ensuring that a large percentage of the population is vaccinated helps protect individuals that cannot be vaccinated (because of allergy, disease or other reasons) or that did not properly respond to vaccination (not all vaccines protect all vaccinated individuals).

"Herd immunity" usually refers to this concept when applied to herds of animals (such as horses or cows), but the "herd" can be a a small local population, a regional population, or broader, and it can be people or animals. For some human infectious diseases, it's been shown that vaccination of 75-95% of the population is required to prevent outbreaks. If vaccination rates start to slip, the chance of an outbreak increases. This is best seen in some areas where vaccination rates decline in certain groups of kids because parents are reluctant to have their children vaccinated (for one reason or another), and subsequently outbreaks of disease start occurring (or increasing).

Vaccination is an important (but not the only!) infection control tool. For diseases that are transmissible between horses (or dogs, or people, or whatever other "herd" is being considered), vaccination of a single horse helps protect that individual from disease, and also helps protect the rest of the population.

During a public health infectious disease course that I teach, a student showed a link to this interesting and amusing demonstration of herd immunity from the UK. Make sure you have your sound turned on. It's an entertaining description of the concept of herd immunity.

When you're deciding on your vaccination program, for both individual horses or a farm, be conscious of the herd immunity concept.

This equIDblog entry was originally posted on the Worms & Germs blog on 05-Oct-09.

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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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It's a good general practice to isolate and monitor any horse that has been off the farm, especially one that has been to an equine hospital. This is often a touchy area for equine hospitals - telling people to isolate and monitor their horses might suggest to owners that the hospital has an infectious disease problem, and lead to negative perceptions of the facility or having people take their business elsewhere. However, it's been proven time and again that the "head in the sand" approach does not work for infectious diseases. Discussions of infectious disease risks in horses that have been hospitalized should be taken as an indication that the facility has an open and proactive infection control program. Therefore, places that talk about disease rates may very well be the safest facilities, because they are monitoring infectious disease, taking precautions and showing that they care about infection control.

Horses coming home from equine hospitals are always going to be at some increased risk of shedding infectious agents. Here's why:

• Some healthy horses carry various infectious agents at any given time. Stress, shipping, diet change, antibiotic treatment and other factors that occur during hospitalization can result in increased shedding of these organisms that the horse was already carrying. For example, equine herpesvirus lives dormantly in a reasonable percentage of healthy horses. They don't usually shed the virus, but may start shedding when they are stressed. So, a horse that was not shedding herpesvirus could start shedding as a result of hospitalization, and thereby expose other horses on the farm. Similarly, stress, shipping, diet change, antibiotics and anesthesia can cause horses that were already carrying low levels of Salmonella to start shedding high levels of the bacterium, potentially resulting in disease in the affected horses or transmission to others.
• Horses can acquire infectious agents in hospitals. An inherent risk of visiting any hospital (like any fair or other event) is exposure to infectious agents. Horses that go to hospitals are at higher risk of picking up things because of the reasons described above. The more horses present and the poorer the infection control program, the greater the risk. Regardless of the quality of infection control at the equine hospital, some risk always remains, but a good infection control program can greatly reduce the risk.
• Horses that return from hospitals are often at higher risk of becoming infected with (i.e. more susceptible to) various bacteria and viruses for a short time after they return home. Therefore, they might be at greater risk of picking up something that is circulating on the farm already but not causing major problems to the otherwise healthy horses.

Routine isolation and monitoring of horses returning from equine hospitals is a good management practice. The likelihood of a problem developing is low, but it's much better to have problems occur when the horse is isolated so they can be contained. A short isolation period lets horses get rid of infectious agents they have picked up or started shedding as a result of hospitalization, so they don't expose other horses. It also lets you identify problems that develop (e.g. diarrhea, cough, fever) as a result of being off the farm, before the horse is expose to other animals on the farm.

The ability to properly quarantine horses on a farm is variable, depending on the facility, but effort should be taken to provide the greatest degree of isolation/quarantine that is feasible and practical. Every farm should have an infection control program that includes a plan on how to handle horses that have returned from equine hospitals.

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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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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 (e.g. influenza in Australia). There are many reasons for this risk, and most involve how we manage our 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 (e.g. 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 transmissible infections to be identified, and for elimination of certain infectious diseases that are only shed for a short period of time (e.g. equine influenza). This is most important when there are high-risk horses on the property (e.g. 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 these situations, you have to accept that you are putting yourself (and the other horses in the barn) 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 sound infection control plan when such horses are detected, a solid 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 take particular precautions 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, such as:

• 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. For example, keep them at the least-used end of the barn, maybe with an empty stall in between them and any other horses. It doesn't replace true isolation but it's better than nothing.  In particular, keep new horses away from the highest risk horses, like broodmares.
• If you have to turn out new arrivals, turn them out by themselves or at least always turn them out with the same group horses, so that if they are infectious, a limited number of horses are exposed.
• If you have any doubts about the health of a new horse, get it examined by a veterinarian. Some diseases have narrow windows of time when horses may show signs of infection but not yet be able spread the disease (e.g. horses with strangles will spike a fever before they start to shed the bacterium). Therefore, prompt action is critical. Calling a veterinarian out earlier can help determine the appropriate measures to take and make the difference between one sick horse and one sick farm.

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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 has detailed information on various aspects of EHV-1, including diagnosis, vaccination and infection control. It can be accessed through the ACVIM website, on the equIDblog Resources page, or by clicking here.

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Disinfection of stalls is an important infection control tool, especially stalls that have housed horses with potentially infectious diseases and stalls used for foaling. Unfortunately, proper disinfection of stalls is difficult even at the best of times, and is rarely achieved on most farms.

Three things are required to successfully disinfect a surface:

• A surface that is amenable to disinfection
• The right disinfectant
• Proper use of the selected disinfectant

Surface amenable to disinfection can be difficult to come by in a barn. Surfaces must be cleaned prior to disinfection. You cannot disinfect dirt, bedding, manure or similar substances. You also cannot thoroughly disinfect porous surfaces because bacteria can live in the pores and cracks, and thereby avoid contact with the disinfectant.   Another issue is biofilms - accumulations of debris produced by bacteria on surfaces that protect the bacteria from disinfectants. Good physical cleaning helps reduce biofilm accumalation. A common problem with disinfection in barns is failure to remove organic debris (e.g. bedding, manure, dirt) prior to applying a disinfectant.

Using the right disinfectant is critical. I’ve done many infection control investigations on farms where I've found that the "disinfectant" being used is actually just a cleaning agent with no disinfectant properties. Even among disinfectants, not all products are created alike. There are differences in range of activity against microorganisms, activity in the presence of organic debris, how quickly they kill, toxicity to animals and people, and how hard they are on surfaces.

Even an excellent disinfectant will be ineffective if it’s not used properly. Common errors include not diluting the disinfectant properly and not providing adequate contact time with the surface in question. Disinfectants do not typically kill instantly - they need time to take effect. Often, 10-30 minutes of contact time is recommended.

Here are some tips for disinfecting stalls:

• Make the stall as disinfection-friendly as possible. Wood surfaces should be sealed with two coats of marine-quality varnish or paint, and repainted whenever defects in the surface are found. Concrete is very porous - any concrete that needs to be disinfected should also be painted to seal it.
• If you use removable rubber floor mats, remove them and disinfect them separately. Sunlight is a great "disinfectant" - leaving mats in the sun for a day or two is a great supplemental disinfection tool. If you leave mats in the stall during cleaning and disinfection, bacteria will live in the nice moist area under the mats that you don't reach with the disinfectant.
• Thoroughly clean the stall before trying to disinfect it. Disinfection cannot be achieved without proper pre-cleaning. Remove all bedding and other debris. Scrub surfaces so they are clean prior to disinfection. However, avoid power washers as these can damage surfaces, creating nooks and crannies in which bacteria can hide, and can spread bacteria into the air.
• Choose a disinfectant that works relatively well in the presence of some organic debris.
• Read the label of the disinfectant carefully to ensure that you are using the proper concentration and contact time.
• Don't forget to also disinfect buckets, hay nets and other items that are in the stall.

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Canadian horse breeders are calling for efforts to streamline semen importation requirements that have been implemented by the Canadian Food Inspection Agency in response to the "outbreak" of contagious equine metritis (CEM) in the US. The new regulations and increased paperwork are causing tremendous problems for breeders trying to import semen in a timely manner. Any delays in clearing semen shipments at customs can result in decreased viability of the semen as well as problems scheduling personnel to perform insemination of the recipient mares. Sometimes, samples can't get through at all. Breeders shipping semen from the US must get health papers (sometimes from someone a few hours away) to send with shipments. Many of the challenges are simply logistical and bureaucratic problems that should be able to be addressed with some common sense and willingness to help. Regulatory and industry personnel need to figure out ways to address these problems without compromising the health of Canadian horses. 

While important regulations should be reviewed to see if they can be more practical and efficient, it is critical that biosafety not be sacrificed for convenience. The impact of a single case of CEM in Canada would be tremendous. It's increasingly clear the the CEM situation in the US is not completely understood.  It is not a readily definable outbreak with a clear source that can be tracked. Rather, this disease appears to be have been present in the US for a few years (at least), and that efforts to get the situation back under control will be very complicated. A "loose" effort in Canada could have disasterous effects.

Many equine veterinarians are concerned that the regulations currently in place are not adequate to prevent CEM from entering Canada. One major concern is the failure to evaluate horses moving across the border. The current regulations only deal with horses from farms where CEM has been diagnosed - it's far from certain that US authorities know where all the CEM-infected animals are. Since transmission of CEM is more likely during live breeding than artificial insemination, horses from these farms are a big concern. This is also potentially a situation where well-intentioned rules could have the wrong effect. Some people are shipping their horses to the US for breeding, because sending them down and bringing them back up doesn't require any extra precautions for CEM if the farm is not a "known" CEM farm. If there are some breeding farms that are infected but not identified, which is definitely possible, then the unregulated movement of these breeding animals could create a very hazardous scenario.

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Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging problem in horses. Owners often ask if they should have their horses tested to see if they are MRSA carriers. There's no simple answer that applies to all farms, but basic points that need to be considered include:

• MRSA is endemic in the horse population. A small percentage (<5%) of healthy horses carry MRSA at any given time, and it likely circulates regularly between groups of horses.
• MRSA infection only occurs in a small percentage of the horses that are exposed to the bacterium - most horses never develop signs of illness.
• MRSA can be transmitted to between horses and people.

So you can see why people might want to test their horses and there are few situations where screening really makes sense. Remember, though, that screening is only useful if you plan to do something about the results. If your horse is MRSA positive, what will you do? If the answer is nothing, or you'll just make sure you wash your hands well after handling your horse, I'd tell you that you should be doing that anyway and not bother with the test. However, there are a few scenarios when screening horses for MRSA is a good idea:

• Screening is a key component to any plan to eliminate MRSA from the farm. Eradication of MRSA can usually be accomplished quite effectively using screening and good infection control practices (and, if there are no clinically infected horses, not one dose of antibiotics!).
• Some farms routinely screen incoming horses for strangles before they are allowed to have contact with resident horses. This can be done for MRSA as well, to reduce the risk of MRSA getting onto the farm and silently spreading from horse to horse. It's not as straightforward for MRSA as it is for strangles, because we know less about the best  screening methods and, probably more importantly, people (not just horses) can bring MRSA onto the farm.
• When an MRSA outbreak is underway, or when efforts are being made to determine why a particular horse developed an MRSA infection, screening can be useful - but again, only if there's a plan to use the results.
• Our equine hospital screens horses for MRSA on admission, so that we can isolate carriers and reduce the risk of transmission to our highly susceptible hospitalized patients. It also helps us identify farms with MRSA problems that might benefit from implementing an eradication program. We also screen horses at the time of discharge to make sure MRSA has not been transmitted to them while they were in hospital.

Screening your average horse on your average farm is harder to justify. A single negative result might give you a false sense of security, because a horse that is negative today might be positive tomorrow, or it might positive already but the current testing methods couldn't detect it.  The use of good infection control practices is much more important than testing for day-to-day MRSA control.  Screening for MRSA is something that is usually only considered in specific circumstances.

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

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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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Infectious diseases are a major problem in young foals. Diseases, including diarrhea, pneumonia, meningitis, umbilical infections and joint infections can range from mild to rapidly fatal.  Even in foals that survive the initial infection, these conditions can sometimes result in permanent problems. A study published in a recent edition of the Equine Veterinary Journal (Wohlfender et al, 2009) looked at infectious diseases in the first 30 days of life in 1031 foals on 36 breeding farms in the Newmarket, UK area. This very large study provided some interesting information:

• The overall incidence of infectious diseases was 8.3%, meaning around 1 in 12 foals developed some type of infectious disease during the first 30 days of life.
• The most common infectious problem was diarrhea, which occurred in 5.9% of foals. Foals with diarrhea that didn't have other signs of illness were not included.  This is because most young foals with diarrhea and no other abnormalities likely have foal heat diarrhea, which is not an infectious disease.
• Umbilical infections developed in 0.7% of foals.
• Joint infections occurred in 0.4% of foals.
• Bone infections occurred in 0.2% of foals.
• Respiratory infections were uncommon, occurring in only 0.6% of foals.
• There was no difference in the incidence of infections in foals that were treated routinely with antibiotics to "prevent" infections. Whether or not this practice is effective has been a controversial issue for a long time.  The best way to answer the question would be to have a study that randomly assigned foals to receive antibiotics or no antibiotics, and then monitored both groups for infections.  This study didn't do that, so there could be some "bias" to this particular finding, but the results are still useful. I don't find the results surprising - there has never been good evidence that antibiotics are routinely needed in newborn foals. This study may help control routine (and in my opinion unnecessary) antibiotic treatment in healthy newborn foals.

This study provided more information confirming that infectious diseases are a significant problem in foals, and that measures are needed to reduce the incidence of infections. It also provided evidence that routine antibiotic use is NOT an effective means of doing this. While there is a lack of good, objective evidence, routine hygiene, sound management and every-day infection control practices are probably critical factors for infectious disease prevention in these young animals.

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As part of the 2008 Conference of the American Association of Equine Practitioners, equIDblog's own Dr. Maureen Anderson gave a presentation about MRSA in horses and people. While there, she gave in an interview for the The Horse, which can be found here. This short video gives some good general information about MRSA in horses and people that work with horses.

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

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Diarrhea is a potentially life-threatening condition in horses. It's also frustrating from a diagnostic standpoint because, even with the most complete/comprehensive testing, a cause is only identified in a minority of cases. This is true for other species too, including people, and is a reflection of the complex nature of the intestinal tract and the numerous possible causes of intestinal disease. Diagnostic testing obviously costs money, so if it gives us an answer less than half the time anyway, it begs the question - why bother? Well, here are some points to consider:

• In some situations, you may find a cause that requires a different treatment, so diagnosis has a direct impact on patient care and probably the outcome.
• Many causes of diarrhea are infectious and it's important to know if other horses may have been exposed to a transmissible pathogen.
• Some causes of diarrhea, especially Salmonella, can also infect people, and it's important to know to what people have been exposed.
• It's also important to know whether a horse might still be shedding a transmissible pathogen after its diarrhea resolves. For example, horses with salmonellosis can shed Salmonella for a while (often a few weeks, sometimes longer) after they have recovered from their diarrhea. This could be a source of infection for other horses and people.
• Outbreaks of diarrhea can occur. It's much better to know early on what you are dealing with, rather than waiting until mulitple horses have been infected.

I consider diagnostic testing money well spent in cases of diarrhea. Some people don't want to test because they don't want to know, particularly about Salmonella. However, it's been proven again and again that the "head-in-the-sand" approach will backfire when it comes to infectious diseases.

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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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While it's a little early in the foaling season, it never hurts to think about vaccination plans for foals. Vaccination is an important part of the disease prevention program - but it's only one part... general infection control practices are as, or often even more, important. Vaccination of foals is not the same as vaccination of adult horses. Foals may be more or less susceptible to certain infections. They may have greater or lower risks of exposure, and they may respond differently to vaccines.

There is no standard vaccination program for foals. Specific vaccination programs need to be designed for each horse on each farm based on risk of exposure and infection, cost and many other factors. Your veterinarian can help you determine what your animals should be vaccinated against. When it comes to foals, here are some important things to considered:

• Foals typically need to be vaccinated several times to get the desired immune response. There are at least a couple of reasons for this. First, if a foal has high antibody levels from colostrum, it may not respond properly to the vaccine until those antibodies are used up. These antibody levels drop over time, but the rate and timing of the drop is different for each foal. Vaccinating the foal several times (at appropriate intervals) helps reduce the risk of vaccine failure from colostral antibodies. Second, foals are born with a fully functional immune system, but the immune response to an infectious agent or vaccine is slow and low the first time an individual encounters it. The first dose of vaccine may produce some response, but a much higher response is generated with boosters.  This is actually true of adult horses as well.
• Over-vaccination can be a problem. Vaccination too early and/or too frequently could actually result in a decreased immune response or complete vaccine failure, a phenomenon known as immune tolerance. So, giving many doses of vaccine starting at a very young age may actually be counter-productive. This is probably a bigger concern with influenza vaccination compared to other vaccines.

Talk to your veterinarian about vaccination. Over-, under- and improper vaccination can lead to increased disease risks, plus wasted time and money.

Guidelines for vaccination of foals have been developed by the American Association of Equine Practitioners. These are also available from the link on the equIDblog Resources page.

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This post originally appeared (in modified form) on www.wormsandgermsblog.com on January 1, 2009.

An important step in diagnosing infectious diseases and determining the optimum approach to treatment and management is rapid and accurate diagnostic testing. Many different testing methods are used, particularly bacterial culture (at least for bacterial diseases). Molecular testing has revolutionized the field of microbiology, and is making inroads into the field of diagnostic testing. Polymerase chain reaction (PCR) testing is a very powerful tool that can be used to detect DNA or RNA from specific microorganisms.  This technique can be very useful, but it can also be easily misused or misinterpreted.

The potential PROS of molecular diagnostic testing include:

• Rapid turnaround time: Testing can take as little as a few hours versus a few days for other tests like bacterial culture.
• Sensitivity: Organisms that are difficult or impossible to grow in a lab can be detected, and they can often be detected at lower levels than with other diagnostic methods.

The potential CONS of molecular diagnostic testing include:

• Sample contamination: This is a common concern with highly sensitive molecular tests - even a minute amount of contamination in the sample can cause a false positive result.
• Test inhibition: Samples from complex biological sites (e.g. stool) can contain substances that interfere with the many complex molecular reactions upon which the tests rely. Without good (and proven) methods to prepare the sample, this can result in a false negative result.
• Biologically irrelevant results: Some bacteria that cause disease are also commonly found as part of the normal microflora in healthy animals - simply finding it does not tell you that it is necessarily relevant to the problem. For example, Clostridium difficile can be found in the intestine of normal, healthy horses, but the diagnosis of C. difficile diarrhea requires detection of the bacterial toxins in stool samples, not just the bacterium itself.  A molecular test that simply identifies the presence of C. difficile, even if it identifies strains that possess the genes to produce toxins, tells you nothing about whether the bacterium was actually producing toxins in the animal.
• Lack of validation: This is a common problem with many (if not most) molecular tests. Some companies, especially those that just run molecular tests, offer a huge array of completely unvalidated and sometimes illogical tests.  It is also important to remember that tests must be validated for each species in which they are used - a test that works well in people will not necessarily work on a sample from a horse or a dog.

Molecular testing can be useful in some situations. If you are unsure, here are some things to ask the lab:

• Do they have a validated test that provides relevant results?  If they don't have good data (ideally published data) that their test is useful, accurate and reproducible, I'd avoid it.
• Do they have a quality control program, which includes running positive and negative control samples with each test batch?

Finally, as with any test that we use in veterinary (or human) medicine, it's important to evaluate all  results in the context of what is happening with the animal - treat the patient, not the test result.

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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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Lawsonia intracellularis is a bacterium that causes an intestinal disease called proliferative enteropathy in young horses. One of the reasons we still don't know a lot about this disease is that this bacterium can't be grown in a lab. One of the areas in which researchers are working to find more information is from where horses that become sick initially get Lawsonia...  Is it from healthy horses that are carriers? Does it circulate in the horse population, or is there an outside source? Does it come from pigs (pigs can also be affected by disease due to Lawsonia infection)?  Do other animal species such as wildlife carry it?

A recent study by researchers at the University of California (Davis), published in the Journal of Wildlife Diseases (2008 44:992-998), looked at the presence of Lawsonia in wildlife on horse farms. They found DNA from the bacterium in feces from jackrabbits, striped skunks, Virginian opossums, and coyotes, but not from feral cats, Brewer's Blackbirds, raccoons, or ground squirrels.

This study provides some interesting insights about Lawsonia in horses, and raises the possibility that wildlife could be a source of infection. However, it does not tell us how to prevent the disease or whether wildlife really are a relevant issue when it comes to infecting horses. We certainly do NOT recommend trying to eradicate wildlife in the vicinity of horse farms as a Lawsonia prevention tool. However, making horse barns (especially feed storage areas) less inviting to wildlife is a good idea - this is a sound standard infection control measure that everyone should consider, as it may reduce the risk of several infectious diseases (e.g. equine protozoal myeloencephalitis (EPM)).

More information on Lawsonia can be found on the equIDblog Resources page, and in our earlier post entitled "Lawsonia intracellularis - New Horizons".

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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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Respiratory tract disease is a very common problem in horses that has a wide range of causes, including bacterial and viral infections, as well as non-infectious conditions. Nasal discharge (i.e. a "snotty nose") is often one of the first signs of respiratory disease noticed by owners. Unfortunately, the nasal discharge itself cannot tell you what the problem is, nor how to deal with it.  If your horse develops nasal discharge, you should contact your veterinarian to determine the best approach to diagnose the cause and the best way to treat the animal.  Here are just a few of the factors that need to be considered:

• Does the nasal discharge come from one or both nostrils? Discharge that predominantly comes from just one nostril is more likely due to a problem in a sinus, or possibly one of the guttural pouches (but guttural pouch infection can also cause discharge from both nostrils, even if only one side is affected).
• Does the horse have a fever? Bacterial or viral infections usually (but not always) also cause a fever.
• Are there any other signs of illness, such as decreased appetite or decreased energy. If so, an infection is more likely.
• Is there more than one horse affected? This may indicate that a transmissible pathogen (virus or bacterium) is involved.
• Have new horses been introduced to the barn, or has the horse encountered other horses while off the farm? If so, this increases the likelihood of a viral infection.
• What does the discharge look like? Thick, yellow discharge is more often (but not always) caused by bacterial infection.  Clear, watery discharge may be caused by viral infection, or sometimes non-infectious causes such as heaves. Bloody discharge can indicate serious problems.
• Does the horse cough, and if so, when?  Is coughing more common during exercise, when the horse is inside, or while the horse is eating hay?  These signs may be associated with a non-infectious condition such as heaves.

Nasal discharge is a sign that something abnormal is going on. Some causes of nasal discharge are very minor, but others are very serious. Some are not infectious, but others can be easily transmitted to other horses. Good communication with your veterinarian is important.  Do NOT give your horse antibiotics unless your veterinarian prescribes them.  Nonetheless, if there are any signs that suggest an infection (viral or bacterial) might be present, you should isolate your horse right away, at least until it has been examined by a veterinarian, in order to prevent possible infection of other horses.

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Infectious disease risks increase whenever you mix large numbers of horses together, especially horses from many different farms. The risk is further increased if horses are allowed to have direct contact with each other, and indirect contact through people that touch many different horses. Add a little stress from shipping and you have a prime situation for infectious disease transmission.  Unfortunately, this very same situation is something that happens countless times every week, at horse shows and other events. Diseases associated with horses being at shows are very common. Some people think that horses getting sick is an unavoidable aspect of competing. While it is true that you can never completely eliminate the risk of infection, I think that our traditionally "accepted" degree of illness in show horses should not be considered "acceptable," and that we should be working harder to decrease the risks of disease transmission in these animals.

Here are some general recommendations to help do just that:

• Avoid direct contact between your horse and other horse - don’t let horses touch each other. 
• Make an extra effort to avoid going near any horses that appear to be sick, such as those that are coughing, or have nasal discharge or diarrhea.
• Don’t share items like water buckets, feed bins and hay nets between horses.
• Wash your hands or use an alcohol-based hand sanitizer after touching another horse.
• Don’t take a sick horse, or a horse that might have been exposed to a horse with an infection, to an event. You don’t want your horse to get sick at a show, and you also shouldn't put other peoples’ horses at risk of infection.
• Make sure your horse is appropriately vaccinated. Horses that go to shows or other events are at higher risk of exposure to certain infectious diseases. Your veterinarian should design a vaccination program that is appropriate for your horse.
• Make sure events that you attend have strict rules for keeping sick horses off the property. If they don’t, or if those rules aren’t being followed, let them know that you think it is unacceptable.

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Streptococcus equi is the bacterium that causes of strangles, and important and highly infectious disease of horses. This bacterium is widespread in the horse population and outbreaks of strangles are not uncommon. Outbreaks are manageable if adequate time and resources are available, but some aspects of strangles control are complicated by a lack of good information.

One area that people often ask questions about is the ability of S. equi to survive outside of a horse, and how to handle the general environment (e.g. barn, paddocks) during an outbreak of strangles. Two older studies reported that S. equi can survive on environmental surfaces for up to 60 days. This has led some people to recommend prolonged quarantine of pastures that have been used by infected horses. However, these studies were conducted in the controlled and relatively hospitable environment of a laboratory, without exposure to sunlight, temperature changes and competing bacteria that are found in the "real world".

A recent study, presented the 2008 Forum of the American College of Veterinary Internal Medicine (ACVIM), evaluated S. equi survival in a more "real world" situation: outdoors, on objects like fence rails, feed bins and water buckets. These items were experimentally contaminated with S. equi, and the length of time that the bacteria survived was studied. Surprisingly, S. equi only lived for a short period of time under these conditions, typically a day or less.

Does this mean that we should allow horses into potentially contaminated areas after only a couple days? Probably not. The results of this study only apply to the conditions that were studied, that is outside with exposure to sunlight, and during the summer. It is safe to assume that survival is short term on farms under these conditions, but it could be longer during cloudy periods and in shady areas. We don’t know the optimal time for which to quarantine stalls and paddocks, but it is reasonable to assume that long-term quarantine, as has been recommended in the past, is not needed in most situations. If it is sunny and there is exposure to sunlight, 1 to 2 weeks is probably well beyond the survival period of S. equi.

More information about strangles will soon be available on the equIDblog Resources page.

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You may notice a recurring theme on equIDblog anytime we talk about infectious disease control, particularly when it comes to zoonotic diseases (those that can be transmitted between animals and people): an emphasis on handwashing. There is increasing emphasis on hand hygiene (i.e. hand washing and use of alcohol hand sanitizers) education in hospitals because the hands of healthcare workers are a major (if not the most important) means of disease transmission between patients. Despite hand hygiene being easy, cheap and effective, people rarely wash their hands as often as they should, and they often don't do it properly.

Most of the research about hand hygiene that has been published has focused on its use and impact in human hospitals, but this area is now also being studied more with regard to animals and veterinary medicine. A study published earlier this year in Veterinary Microbiology provided more evidence that hand hygiene is a critical infection control measure when dealing with animals. The study looked at MRSA carriage rate in veterinarians who work with horses. In addition to finding a high rate of MRSA carriage among these veterinarians (which was consistent with other reports indicating that equine vets are at higher than average risk for exposure to MRSA), the study looked at factors associated with MRSA carriage. Vets that reported routinely washing their hands between farms and those that reported washing their hands after contact with potentially infectious cases had a significantly less likely to be carrying MRSA. That should come as absolutely no surprise, but it's one more piece of evidence that we need to pay more attention to this routine infection control measure, in human hospitals, in veterinary environments, out in the barn, and even in households.

Remember, the 10 most important sources of infection are the fingers on your hands!

Click here for instructions on how to wash your hands properly.

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Many people in the horse world have heard the hype about methicillin-resistant Staphylococcus aureus (MRSA) in horses. MRSA can cause infection in horses, just like it can in people, dogs, cats and many other animals. It’s usually what we call an “opportunistic” pathogen, meaning it usually takes advantage of a person or an animal that is already sick or injured, like someone who’s in the hospital and has just had surgery. And because MRSA is resistant to many different antibiotics, the infection can be difficult to treat. The big concern with MRSA in recent years is that infections are now sometimes occurring in people who aren’t sick, and who don’t have wounds or incisions, which is where MRSA usually likes to move in. It’s very important to find out from the start if an infection is being caused by MRSA, so that it can be prevented from spreading to other people and animals, and so that it can (if necessary) be treated with the right kind of antibiotic.

Horses are a bit of a special case when it comes to animals and MRSA. When researchers look at the DNA of MRSA from a dog or a cat, it usually turns out to be one of the common human MRSA strains (usually called a “clone”) from the same area. This means that the dog or cat probably picked up the MRSA from a person somewhere.  When researchers look at the DNA of MRSA from horses, however, they often find a different clone, which seems to be more common in horses and people who work with horses than in people in general. A very similar situation has also been discovered in pigs. The worry is that this “horse MRSA clone” can survive in and be transmitted between horses better than the human MRSA clones. That means that in order to control MRSA, just controlling it in the people won't do the trick - we need to take steps to stop the spread of MRSA in horses specifically as well.

Here are some key points to help reduce the risk of your horse (and you!) getting MRSA:

• Always wash your hands with soap and water (or use an alcohol-based hand sanitizer) after handling a horse, and before handling another horse.
  • This is especially important if you have touched a horse’s nose, or any cuts or wounds that the horse may have.
  • Don’t go down the row of stalls in the barn and pet every horse on the nose! They love the attention, but this is a great way to spread MRSA if it’s there!
• New horses coming into the barn, or animals coming back from a hospital, should be kept separate from all the other animals and only dealt with after all the other horses, for 3-4 weeks.
  • This is an important measure for controlling many infectious diseases, not just MRSA.
• If your horse has a cut that looks infected, cover it with a bandage of some kind and contact your veterinarian. Your veterinarian can culture the wound to determine if it is an MRSA infection.

This equIDblog entry was originally posted on the Worms & Germs blog on 06-May-08.

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When people talk about prevention of infectious diseases on horse farms, they often use the term "biosecurity." I don’t.  I prefer to use the term "infection control." Here’s why:

• Biosecurity is a term often used in association with rearing of food animals, particularly chickens and pigs. In these types of facilities, new animals are rarely or never introduced to an established group, control of personnel access is very strict, and significant efforts are made to prevent exposure of animals to new infectious agents.
• In my opinion, we do not (and cannot) practice true biosecurity on horse farms because of the way horses are managed - the movement of horses on and off farms, movement of people that work with horses, and diseases that are always circulating in the horse population. The simplest daily, weekly or monthly activities - going to a show, buying a new horse, going off-site on a ride, bringing in visitors/farriers and other people that have had contact with horses - in combination with the fact that even healthy horses can carry  potentially harmful bacteria and viruses, means that there is always an risk of exposure to infectious agents on horse farms.
• We are not able to completely exclude infectious agents like bacteria and viruses from entering horse farms (i.e. making them "biologically secure"). However, what we need to strive for is to limit the problems that develop when these agents do enter the farm. For example, we know that the majority of horses carry equine herpesvirus in a dormant state in their bodies. We can’t eliminate it, but we try to reduce the risk of problems like herpesvirus abortion in mares by vaccinating mares while they're pregnant.

While it may be somewhat an issue of semantics, I think it’s important that horse owners have a realistic mindset. There is always, and will always be, infectious disease risks when dealing with horses in any situation. Some risks are avoidable while others are not.  The key is to implement measures to reduce the inevitable impact of infectious disease exposure on our horses.

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