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

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)

• Email This
• Print
• Comments
• Trackbacks
• Share Link

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

• Email This
• Print
• Comments
• Trackbacks
• Share Link

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.

• Email This
• Print
• Comments
• Trackbacks (1)
• Share Link