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

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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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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An eight-year-old Quarter Horse gelding was presented for examination due to chronic weight loss over several months. Lately he’d also been lying down frequently and exhibiting increased breathing effort, so he was treated for what was suspected to be mild signs of colic, but failed to improve. He’d also collapsed once during mild exercise.

On examination, the gelding was quiet, alert and otherwise physically normal except for his poor body condition. However, on rectal palpation there was a large, firm, non-painful mass within the caudo-dorsal (i.e. upper rear) abdomen. revealed a large (42 centimeter) firm mass in the caudo-dorsal abdomen. The mass was further evaluated using ultrasound via the rectum. the mass was multi-lobulated (i.e. made up of many pockets on the inside) and had a large blood supply. It did not appear that the mass was directly attached to or growing in any abdominal organs (e.g. kidneys, intestine). Blood work showed a high white blood cell count (mature neutrophilia), moderate anemia, and high protein levels due to an abnormal increase in globulins (hyperglobulinemia).

These findings were highly suggestive of a large abdominal abscess, but a cancerous mass could not yet be ruled out. It was decided to take the horse to surgery the next day in order to better evaluate the mass, collect samples and remove it if possible. In surgery, the mass was found to be right at the root of the intestinal mesentery (the large membrane that carries the blood supply to the intestines), and there were a large number of adhesions between the mass and the base of the cecum, as well as to some loops of the small intestine. A needle and syringe were used to remove a sample of the mass’s contents in a sterile manner. The fluid retrieved had the appearance of thick pus, which further supported the tentative diagnosis of an abscess. Unfortunately, due to the location and size of the mass, as well as the number and size of adhesions, it could not be safely removed. The horse was therefore euthanized while still under anesthesia.

Necropsy examination confirmed that the mass was an abscess. The capsule of the abscess was extremely thick and tough, indicating that it had been developing over a very long period of time. A long-standing abscess such as this explained all of the gelding’s clinical signs – weight loss and moderate anemia due to chronic disease, high globulin levels due to constant stimulation of immune cells by the infectious focus, and recumbency and collapse due to discomfort caused by entanglement of the intestines in the adhesions associated with the abscess.

Culture of the fluid sample retrieved at surgery yielded a heavy, pure culture of Streptococcus equi subsp. equi – the bacterium that causes strangles. This horse had what’s known as “bastard strangles,” which is a recognized complication that occurs occasionally in horses that have had the classic upper respiratory infection. In these cases the S. equi invade beyond the respiratory tract and can end up anywhere in the body. Then, just as the bacterium does in the lymph nodes around the head and throat in classic cases, the S. equi can form abscesses. The abscesses may form in internal lymph nodes (which is likely what happened with this gelding) or in organs like the kidneys or even the brain. These abscesses tend to develop slowly and insidiously. Even if they can be identified, they are typically extremely difficult to treat effectively, and unfortunately euthanasia is often the end result. Other bacteria that can cause similar abscesses include Rhodococcus equi, Corynebacterium spp. and Arcanobacterium pyogenes.

Strangles is endemic in the horse population – whenever horses are mixed or brought together in large groups there is a risk of strangles transmission. We cannot eliminate the risk, but we can try to reduce it as much as possible using basic infectious disease control measures. More information about strangles is available on the equIDblog Resources page and in our archives.

Image: A Standardbred in poor body condition due to chronic debilitation as a result of large abdominal abscess, similar to the case described here (photo credit: M. Anderson).

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After a rather lengthy process, Hoosier Park (Anderson, Indiana) has lifted its strangles quarantine. A quarantine was implemented on September 12th after a horse on the premises began exhibiting signs of strangles. Fifty-four horses were placed under quarantine. When S. equi, the bacterium that causes strangles, was identified in a quarantined horses, officials decided to move all quarantined horses out of the track facility. Presumably, once it was clear that the quarantine was not just a matter of waiting for confirmation that all horses were actually negative, they decided that the risk of having potentially infectious horses living at the track was unacceptable (pretty logical thought process). Now that those horses have been removed and no other cases have been found in the approximately 1000 other horses housed in the other track barns, they are back to business as usual. The quarantined barn is being disinfected and will not be used for the rest of the 2009 racing season.

This incident demonstrated a very aggressive but apparently effective response to strangles. They have presumably ended this latest outbreak and hopefully won't have to deal with it again. However, infectious diseases and outbreaks are inherent risks in the racing industry (as well as other competitive horse industries). The way we manage race horses, moving them around, mixing them, having various (and sometimes minimal) preventive medicine programs, having minimal measures to keep sick horses off the track, and a financial disincentive (i.e. people lose money) to keep horses away, means that infectious disease risks are not going to go away. It's not a question of whether there will be another strangles outbreak on a racetrack. It's a question of when and where.

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Another strangles scare has resulted in a trio of horse trainers being banned from racing in New Zealand until October 7.  New Zealand Thoroughbred Racing (NZTR) is taking a hard line with this particular outbreak, especially with the upcoming Kelt Capital Stakes premier raceday on October 3.  While they're trying to do the right thing to protect the larger racing population, there are a few things going on that simply don't quite add up.

All horses from the affected farms are banned from racing facilities for 21 days after the last known case had run its course (reportedly September 16): That's great, but... 21 days is the isolation period typically used to detect clinical cases of strangles (i.e. exposed horses that get sick will usually do so within 21 days).  However, some horses, particularly those recovering from being sick, can shed the strangles bacterium for much longer than this.  In order for such a ban to really be effective, horses from the property should also be tested to ensure they are not shedding Streptococcus equi subsp equi before being allowed in more public facilities.

In a press release issued by NZTR on September 23, it is stated that "An isolation period of six weeks is usually necessary to ensure that the disease is not still incubating before ending the isolation.": Why would they make such a statement and then only isolate these properties for three weeks?

The same press release states "...controls have been put in place, as recommended, and this should ensure that the risk of further spread will be effectively controlled."  If the NZTR thinks that banning horses from the affected farm and the neighbouring properties from the track is going to eliminate the risk of strangles, they're deluding themselves.  As we've said before, strangles is an endemic disease in the horse population, and there are certainly other horses in New Zealand that are carrying strangles.  Any time a large group of horses get together there is risk.    The best way to reduce the risk is to ensure that simple, practical infectious disease control measures are in place, and followed, every day.  Statements like this just give people a false sense of security.

Strangles was initially identified in a horse from a sale that was brought onto the farm over a month earlier.  The horse was isolated on September 8 for being sick, and diagnosed sometime in the following week:  There are a few good points here.  First of all, it demonstrates a classic example of a "normal" carrier animal (the "trojan horse" if you'll forgive the pun) from a sale (making it high risk for carrying infectious diseases) that was brought onto a farm and likely not isolated and tested, ultimately resulting in an outbreak on the farm which is now affecting the ability of all the horses there to race.  Classic.  Furthermore, this horse from the sale arrived on a truck with several other horses which were delivered to three other properties in the area.  There is no indication that these other horses have been tested to see if they are carriers, nor that the other properties have been inspected.  Based on the ban that has been slapped on the currently affected property and its neighbours, I could see trainers and owners being reluctant to report any new cases, or even horses with a fever, for fear of the same thing happening to them.  Also, I have to wonder, if there was a known strangles case on the index farm since at least last week, why did it take until September 23 for the NZTR to issue the ban? 

"...once strangles was diagnosed, all the horses on the Cottle property - minus the infected ones - were vaccinated [for strangles].": Vaccination in the face of an outbreak is actually not recommended according to the strangles consensus statement from the American College of Veterinary Internal Medicine.  Particularly with a known carrier having been on the farm for a month, by that time all the other horses were likely already exposed, and vaccinating them at that point merely puts another drain on their systems.

"The barn yard was disinfected but the bedding was not replaced.":  I've never seen nor heard of a barn yard that could actually be effectively disinfected.  It would have to made entirely of sealed wood/concrete or metal, and even then it would be a momentous task and likely still impossible.  I don't doubt they gave the area a thorough cleaning, but it was not disinfected.  The fact that the bedding was not replaced surprises me - this seems like one of the simpler, easier things to do.  While it also can't guarantee a strangles-free stall, any horse that is shedding the bacterium is likely to have highly contaminated bedding, and removing it at least decreases the environmental pathogen burden.  The article also states that "the bacteria can survive in bedding and soil for at least eight months."  Perhaps under ideal sheltered conditions this may be possible, but a study presented last year showed that in the "real world" S. equi probably only survives in the environment for a few days.

Both the article and the press release do make a few sound recommendations in the end, including adopting hygiene guidlelines such as replacing bedding, disinfecting water troughs and feed buckets and other equipment, avoiding mixing and moving horses, being aware that people are a potential source of cross-contamination, and of course our favorite: "As with any contagious
disease, handwashing is a simple and effective tool."

More information on strangles is available on the equIDblog Resources page and in our archives.

Image: Banned trainer/owner Tim Symes, with his horse Molly O'Reilly (source: www.hawkesbaytoday.co.nz)

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The Kentucky state veterinarian has banned horses kept at Hoosier Park racetrack (Anderson, Illinois) from barn areas of any Kentucky racing facility because of concerns about strangles. Two Hoosier Park horses were diagnosed with this highly infectious disease caused by the bacterium Streptococcus equi, and 57 horses have been quarantined. Horses from Hoosier Park that have been isolated and monitored for 21 days may enter Kentucky facilities.

The idea behind the 21 day quarantine is that within 21 days, most horses that have been exposed to strangles will develop signs of disease within that time period. However, the problem is that horses that have been infected with strangles can get over the infection and look great for 21 days (or much, much longer) but still carry S. equi in their throats or guttural pouches. So, while this is a reasonable approach, it by no means guarantees that S. equi will be kept out of Kentucky. However, in reality there are never any guarantees when it comes to infectious diseases like this. While some cases of strangles get a lot of attention, it's an endemic disease that is circulating in the horse population, and certainly is present in some horses in Kentucky already. Responding to outbreaks and limiting the risk of outbreak-associated transmission is very important, but it's equally important to make sure that routine infection control practices are in place on tracks (and elsewhere) to reduce the risk of disease transmission every day.

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

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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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I received the following question the other day: "I have a friend who had chemo embolization on tumor on liver in late June. She is in hospital now, and an abscess was discovered on liver.  Pathology results said "equine strep".  Her brother visited immediately after procedure, and he works with horse full time."

Streptococcus is a group of bacteria that includes many different species. There are two main species in horses Streptococcus equi subsp. equi (aka S. equi, the cause of strangles) and Streptococcus equi subsp. zooepidemicus (aka S. zooepidemicus, a cause of various types of infections). As you can guess by the 'equi' name, their natural host is the horse. Strep infections are very common in people, but rarely involve these two species. Nonetheless, infections with either Streptococcus equi or S. zooepidemicus can be found in people, but S. zooepidemicus is most common. Usually, these infections develop in people who are already sick for another reason, have compromised immune systems, or in young children. Interestingly, not everyone that is infected reports direct or even indirect contact with horses.

Back to the question: it's hard to say what's going on here based on the the general term "equine strep", but presumably the person has an infection with S. equi or S. zooepidemicus. Whether horses are actually involved will be tough (or impossible) to determine. It's a tempting hypothesis that the patient's brother carried the bacterium from the farm to the hospital, but I'd be wary about making a definitive statement about the bacterium's origin solely based on that. There are ways to investigate this further, such as trying to isolate Streptococcus species from horses on the farm, typing them and comparing them to the strain that caused disease in the person, but this type of testing is very costly and almost never performed, as human infection with these species is so uncommon.

This should be a good reminder that people who are sick and in hospital are at higher risk for developing infections, and they can get infections from bacteria that rarely cause disease in healthy individuals. While there is no proof of a link to horses (at least in this case), good infection control practices should be used whenever anyone visits someone in the hospital. That would include not wearing barn clothes to the hospital and paying close attention to handwashing.

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Dr. Bob Wright of the Ontario Ministry of Agriculture Food and Rural Affairs has compiled a document with various pieces of information about disease occurences in horses in Ontario and Canada. While there's nothing too earth-shattering in it, it does give a nice synopsis of certain diseases and shows how Ontario is a pretty good place to be in terms of some nasty diseases. The report can be viewed by clicking here.

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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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 An outbreak of strangles has resulted in at least one death and the closing of one barn at Northlands Park in Edmonton. The 150 horse barn will be cleaned, disinfected and kept empty for three weeks, until March 23.  The article refers to the disease as equine distemper, which is another common name for strangles.  It should not be confused in any way with canine or feline distemper, both of which are caused by viruses.  Strangles (equine distemper) is caused by the bacterium Streptococcus equi subsp. equi.

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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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Microbiologists like to confuse people. The names of different bacteria are often changed as new information is discovered and species are grouped, separated or completely reclassified.  One can imagine that this eventually makes for some confusing situations.

One example of this is Streptococcus equi (aka Strep equi), the cause of the highly infectious disease strangles, and its close relative Streptococcus zooepidemicus (aka Strep zoo). Streptococcus zooepidemicus is commonly found in the respiratory tracts of healthy horses and can cause secondary infections, but it is not highly transmissible like Strep equi.  Technically, however, both of these organisms are actually Streptococcus equi. The S. equi that causes strangles is Streptococcus equi subspecies equi, while the other one is Streptococcus equi subspecies zooepidemicus. Usually, people just refer to them as S. equi and S. zooepidemicus for simplicity's sake, and in most situations, that's enough for people to understand what they're dealing with. However, sometimes there can be confusion if a diagnostic laboratory reports the full name of the organism and someone doesn't notice the "zooepidemicus" at the end, and panic ensues about a non-existent strangles case/outbreak until someone reads the report properly.  The take-home message here is read all diagnostic test results carefully and if in doubt, call for clarification.

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The latest version of the DEFRA/AHT/BEVA Equine Quarterly Disease Report has been released. This is a joint venture of three British organizations, and often contains some interesting infectious disease information. This edition contains brief information about diagnoses of selected diseases such as equine herpesvirus (EHV) -1 abortion, EHV-1 neurological disease and equine influenza. There is also a brief review of the eradication of equine infectious anemia (EIA) following the 2006 outbreak in Ireland, which was also discussed in a previous equIDblog post.

Another useful piece of information in this report is the data regarding strangles (Streptococcus equi subsp. equi) diagnoses. They report 280 positive S. equi culture results and 167 positive S. equi PCR test results during the last quarter. This shows once again that strangles is still a rather common disease. This is important to remember when considering routine infection control practices, because the risk of strangles exposure is ever-present, it is not just concern during outbreaks.   Also, people shouldn’t overreact to single cases of strangles (as they often do), since this disease is far from rare.

The full Equine Quarterly Disease Report can be downloaded by clicking here, or through the Animal Health Trust’s website.
 

Image from http://snapshot.parade.com/mainemb.php?g2_itemId=783542.

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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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A recent article from British Columbia, Canada, described the complaints of horse owners that they were not warned about cases of strangles (Streptococcus equi subsp equi infection) in the Maple Ridge, BC area. The issue revolves around a small number of cases of this highly infectious - but relatively common - equine disease.

One horse owner stated "If I had known it was out there, I would have done things differently." While I understand where she's coming from, it's important for all horse owners to remember than exposure to infectious diseases is an ever-present risk. Streptococcus equi, and various other infectious agents, are widespread in the horse population, and there is never a "no-risk" situation. For that reason, we should be taking practical measures to reduce the risk of disease transmission at all times, not just when we know there is an infectious disease in the area.

Increasing infection control measures during outbreaks or during particularly high risk periods is an important disease prevention measure, however too often, people only pay attention to infection control during high-profile events. While outbreaks get the most attention, most infectious diseases occur as sporadic events, not outbreaks. Focusing solely on outbreaks has a minimal impact on infectious diseases overall.

Addressing strangles infections is a tough and often controversial area. Frequently, cases of strangles are kept quiet because people are afraid of being stigmatized. That certainly doesn't help because it can facilitate spread of the infection. In contrast, sometime excessive (approaching paranoid) responses occur. Like most things, there needs to be a happy medium, where strangles cases are properly diagnosed, appropriate control measures are implemented and relevant people are notified, but without widespread panic and unnecessary restrictions or ostracism.

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

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I often get asked "My horse has been exposed to a horse with strangles. Can I treat him with antibiotics to prevent infection?" It's a reasonable question, but unfortunately there is no clear answer.

Strangles is an infection caused by the bacterium Streptococcus equi subsp equi, which is often simply called Strep equi or S. equi for short.   This pathogen is always circulating somewhere in the equine population, and it can cause sporadic cases of strangles in individual horses, or large  outbreaks in groups. It is transmitted mainly by nasal secretions and pus from infected horses when they come in contact with other horses.  The classical and most prominent feature of strangles is the formation of large abscesses in the lymph nodes between the jaw bones.

Treatment of strangles with antibiotics is typically frowned upon because antibiotics do not penetrate abscesses well. Draining the abscesses is the key to treatment in most situations. However, antibiotics can kill the S. equi if they are used before abscesses develop. Therefore, if a horse has been exposed to strangles and is in the very early stages of developing an infection, but it does not have any abscessed lymph nodes, then treatment with antibiotics could be useful.

The downside of this kind of treatment is, while it stops the immediate infection from developing, the horse does not develop immunity against S. equi like it would if its body had to fight the infection. This is not a problem if good infection control measures are in place to prevent further S. equi transmission. However, if transmission is not controlled, then the horse is at risk of being re-exposed, and could be infected again after the antibiotics are stopped.  This can lead to a vicious cycle of exposure-treatment-susceptiblity-exposure-treatment...  I've seen farms where this goes on for a long time with horses receiving multiple courses of antibiotics, and they often eventually getting the disease anyway.

Antibiotics can be useful in horses with early disease (i.e. fever, no lymph node enlargement) IF they are used as part of an overall infection control program that has a heavy emphasis on implementation of sound infection control measures. If potentially infected horses can be rapidly detected and isolated, thus minimizing the risk of exposure to other horses, then early antibiotic treatment of horses that are developing strangles can be useful. Antibiotic treatment alone, without concurrent use of good infection control measures, is bound to fail. While uncommon, antibiotics can be associated with adverse effects in horses, so we want to make sure that we are only using them when they are needed.

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

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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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Click on any of the highlighted links below for more information about these horse-related infectious disease topics. Topics that are not highlighted are in development and coming soon. New information will be added as it becomes available, so be sure to check this page regularly for the latest updates.

All information sheets found on this page can be freely downloaded, printed and distributed. The authors only request that this website (www.equIDblog.com) is acknowledged as the source.  The downloadable files on this page can be opened with Adobe® Reader®.  To get the latest version of Adobe® Reader® for free, click here.

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