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

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

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

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

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

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

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A new study was recently published in the Journal of Veterinary Internal Medicine (Frederick et al. 2009) which looked at infectious agents found in the feces of foals with diarrhea. Specifically, they looked for rotavirus, Clostridium perfringens, C. difficile, Salmonella, parasite eggs and Cryptosporidium oocysts.

They found at least one infectious agent in the feces of 122 (55%) of the 233 foals in the study. That means, despite testing for a wide range of pathogens, they could not identify an infectious agent in 45% of the diarrheic foals. This is very similar to the situation typically found in adult horses with diarrhea. This could have happened for a number of reasons:

1. No test is perfect. It’s possible that in some of the cases one of the test results was a “false negative,” meaning it did not detect the infectious agent even though it was there.
2. A few cases may have been caused by other infectious agents that were not included in the diagnostic panel.  For example, Rhodococcus equi is a common cause of respiratory disease in foals, but it has also been associated with diarrhea in some cases.
3. The diarrhea was caused by an agent of which we are unaware, and for which we have no test. Researchers are constantly looking for other bacteria, viruses or parasites that may be capable of causing or contributing to diarrhea in foals and adult horses.
4. The diarrhea was not caused by an infectious agent. For example, the authors failed to discuss foal heat diarrhea as a cause of clinical diarrhea in very young foals. This is a well recognized cause of foal diarrhea, but no infectious agents are involved.

The most commonly identified pathogens were rotavirus (20% of cases), Clostridium perfringens (18%), Salmonella (12%) and C. difficile (5%). Overall 191 (87%%) of the foals survived, and survival was not associated with any pathogen identified in the feces (i.e. in this study, foals were not more likely to die if they had one particular pathogen in their feces than another). This must be interpreted very cautiously, however, because the study does not account for other kinds of illness in these foals, or even whether diarrhea was the primary problem for which they were referred to the hospital. Diarrhea, especially in very young foals, can be very serious because they can dehydrate very quickly and are very susceptible to shock of various kinds.

There were a few other issues with this study that are important to keep in mind as well:

1. The group of foals they looked at ranged in age from newborns to 10-months old. The digestive tract of a foal undergoes drastic changes in the first year of life, and it is well known that certain infectious agents only cause disease in foals of particular ages. For example, different parasites may take weeks to months to develop within the intestine of a foal, so even if a foal is infected as soon as it’s born, these parasites cannot cause disease for quite some time. For this reason, it would have perhaps been more useful to look at the data separately for different age groups.
2. There was no control group in this study. Most of the time, if an animal has diarrhea and the test you perform tells you there is a known diarrhea-causing pathogen in the feces , you assume the diarrhea is due to that agent. This is not necessarily always the case. Some pathogens are carried around by totally normal animals, who may get diarrhea for a completely different reason. So what we really need to know now is: if the authors tested 233 foals with normal feces (and the same ages), how common would each of these pathogens be?

While the data may be interesting to look at, this paper doesn't really tell us anything new that will change the way we treat or manage foals with diarrhea in general.  Nonetheless, the information may still be useful for helping to design and interpret future research studies about these pathogens and diarrheal disease in foals.

Image source: www.bbc.co.uk (credit: George Ring)

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

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

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

Fortunately, clostridial myonecrosis is relatively uncommon. Avoiding this disease involves decreasing the chances of creating the anaerobic environment in which clostridial spores can grow:

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

More information about clostridial myonecrosis is available on the equIDblog Resources page.

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

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

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

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

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

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

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

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

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

What should we take home from this report?

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

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

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Diarrhea is a relatively common problem in foals. It can range from very mild to fatal, and sick foals can get worse (i.e. "crash")  very fast. Outbreaks of diarrhea in foals can also occur.  So while most cases of foal diarrhea are mild, the implications of this condition for both the foal and the farm can be huge.

There are a variety of potential causes of diarrhea in foals. One is Clostridium difficile, a bacterium which can be found in the intestinal tract of a small percentage of healthy adult horses and foals, but which can also cause disease under certain conditions. Clostridium is a type of spore-forming bacterium - it produces spores that are able to survive for a very long time (i.e. years) in the environment, and that are resistant to most disinfectants. Most cases of C. difficile infection in foals are single, sporadic cases, but outbreaks on breeding farms can occur and can be very difficult to control. Typically such outbreaks start out with a few individual (sporadic) cases of foal diarrhea early in the foaling season, with a gradual increase in the number of cases over the following weeks to months. Often it gets to the point that  all foals born later in the season develop diarrhea. You cannot tell the difference between diarrhea caused by C. difficile and that caused by other infectious agents just by examining the foal - diagnostic tests are needed to make the diagnosis (watch for an upcoming post for more information about this kind of testing).

There is little information about control measures for C. difficile infection that have been proven to work. However, our understanding of the organism and what it does in horses and other species lets us make some general recommendations:

• Only use antibiotics when it's really necessary. "Routine" use of antibiotics in foals (which some people use to try to compensate for poor management practices) is not needed, and may increase the risk of C. difficile.
• Use good general hygiene practices, particularly around the time of foaling and in areas where neonatal foals live or often are. Clostridium difficile is spread by the fecal-oral route, meaning foals swallow the C. difficile from manure contamination in their immediate environment.
• Isolate all horses (foals and adults) with diarrhea so that they are less likely to spread it to other horses.
• Do not try to treat healthy horses or foals to try to get rid of C. difficile. There's no evidence that it works and it could actually make it more likely that the horse/foal will get sick.
• Let your veterinarian run the appropriate diagnostic tests to identify the cause of diarrhea in any adult horses or foals, particularly on farms where more foals are expected to arrive. It's better to find out early with what you are dealing, in case specific preventive or early treatment measures can be used to help stop an outbreak from occuring.
• Make sure you have a good infection control program for your farm.

No vaccine for C. difficile is currently available, nor will one be available in the near future. Other techniques for preventing this disease are being evaluated but none are yet proven.

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

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There's something ironic about traveling to a conference to speak about infectious diseases and coming down with food poisoning.  As I lay in bed in Orlando in a relatively non-functional state Friday, I had lots of time to contemplate the good and bad points of vomiting. As much as it is unpleasant, the ability to vomit is useful, and it is something horses lack. As one of the many anatomical quirks that horses possess, horses are essentially unable to vomit, regardless of what in happening farther down the intestinal tract. This is serious problem, because unlike people who can relieve the pressure of a distended stomach by vomiting, the only thing a horse's stomach can do is get bigger and bigger until it finally bursts. Stomach rupture is fatal and kills numerous horses every year - it causes massive infection in the abdomen (peritonitis) due to the spillage of the bacteria-laden intestinal contents.

Stomach rupture typically occurs secondary to obstruction of the small intestine, which usually requires surgery to fix. It can also result from a condition called duodenitis/proximal jejunitis or anterior enteritis. This disease has been an enigma for years, with no clearly identifiable cause. Recently, the bacterium Clostridium difficile was implicated as the cause of this syndrome, at least in Ontario.  This bacterium was found commonly in stomach fluid from horses with anterior enteritis, but not in that of horses with gastric distension from other causes.  More study is needed to determine if these results are repeatable over time and in other regions, but it may be an important insight into this uncommon but potentially life-threatening condition.

More information about Clostridium difficile can be found on the equIDblog Resources section.

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The discovery of antibiotics was one of the most important medical advances in history, and these drugs have had an immense impact on human and animal health. While antibiotics have saved countless lives, their use can also be associated with some very serious side effects and complications.  For example, in horses, antibiotic-associated diarrhea (colitis) is a major issue.

By the nature of their intestinal tract, horses at among the highest risk species for developing serious diarrhea associated with antibiotic use.  The intestinal tract of a horse is full of billions of bacteria of different types. These bacteria are important for normal digestion, and also help to prevent infection by "bad" bacteria such as Salmonella and Clostridium difficile.  Antibiotics can disrupt the balance of this complex bacterial population.  The imbalance itself can cause problems, and can also make it easier for bad bacteria to move in, grow and cause disease.

Here are some important points to remember about antibiotics, particularly in horses:

• Antibiotics can only kill bacteria. They should not be used when a bacterial infection is not present and not likely to occur. Antibiotics are too commonly misused for viral infections in horses, which puts the animals at unnecessary risk.
• Any antibiotic can cause diarrhea, but some drugs are considered higher risk. Erythromycin and tetracyclines are considered high-risk in most areas of North America. Certain drugs, such as lincomycin and oral penicillins, are such high risk that they should never be used in adult horses.
• Both oral and injectable antibiotics can also cause diarrhea. Drugs that are injected can still reach the intestinal tract and affect the bacteria there. Some drugs, like tetracycline, are actively pumped into the intestinal tract from the bloodstream, resulting in relatively high concentrations in the intestine, even if the drug was given by injection.
• While some antibiotics can be purchased over the counter in some areas, antibiotics should never be given without the direct recommendation of a veterinarian.
• If your horse is being treated with antibiotics and develops diarrhea, contact your veterinarian immediately.
• There is no known way to reduce the risk of antibiotic-associated diarrhea in horses, other than to avoid unecessary use of antibiotics. Some people treat horses with probiotics or yogurt, but currently there is no evidence that this is beneficial (but it probably doesn't hurt, at least in adult horses).

Another major concern with antibiotic use is the development of antibiotic resistance in bacteria, but that's a topic for another post (or two, or three or more!).

More information about Clostridium difficile and probiotics in horses can be found 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.

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