It might be difficult to imagine that a few tiny organisms can proliferate and cause an infection so serious it could result in the death or euthanasia of the host horse. For instance, one of the most dangerous organisms that can sicken horses is the bacterium Clostridium difficile. Scott Weese, DVM, DVSc, Dipl. ACVIM, associate professor at the University of Guelph's Ontario Veterinary College, discussed some of the recent advancements in understand and combating C. difficile at the 2011 American College of Veterinary Internal Medicine Forum, held June 15-18 in Denver, Colo.
"Clostridium difficile is an organism known to be a common cause of intestinal disease in both humans and animals," Weese explained.
As with humans, C. difficile causes colitis (an inflammation of the colon) and severe diarrhea in horses. This organism can persist as a spore in a dormant state for many years (i.e., not cause an active infection), all the while remaining resistance to antimicrobial drugs and disinfectants. Weese noted that recent mutations in some strains of C. difficile have increased its virulence (the ability to cause disease) through amplified expression of toxin genes.
Weese noted that researchers recently learned that C. difficile is present in the gastrointestinal tract of some healthy individuals. Not only does this create a carrier state, but it also increases the risk of a horse developing an overwhelming C. difficile infection due to a trigger such as antibiotic therapy.
Outbreaks tend to occur on breeding farms, particularly C. difficile diarrhea in foals during their first week of life. Weese stressed that good management practices that include regular cleaning and disinfection should decrease the number of spores that are dispersed in the environment.
Foaling mares outside and using antimicrobials sparingly could help prevent outbreaks as well. However, he noted, these techniques don't seem overly effective in containing the disease during the course of a large outbreak, probably due to the high level of contamination.
Weese recommended using oxidizing compounds (such as accelerated peroxide) as disinfectants to kill spores on barn surfaces. Disinfection can be challenging, however, due to the variety of difficult-to-reach surfaces on horse farms and organic debris such as manure that tends to inactivate disinfectants (bleach, in particular). There's no vaccine against C. difficile that horse owners can turn to, but a toxoid is currently being developed, Weese noted.
Owners and veterinarians have tried many prophylactic (preventive) approaches such as the use of di-tri-octahedral smectite (a natural clay that binds organic ions) to bind toxins, hyper-immune plasma to neutralize toxins, and probiotics to help keep the hindgut stabilized; however, none of these have been overly successful in preventing C. difficile infections.
Another preventive method some practitioners have considered is--while it might seem odd on the surface--preventive copraphagia (eating of manure) to help foals mature their gut flora more quickly. Weese explained that while this approach has not been used in horses, it would entail placing "healthy feces" (i.e., those not infected by C. difficile) into day-old foals' digestive tract in the face of an outbreak. There has been some success with this method in humans with recurrent C. difficile infections using a fecal enema, but researchers aren't sure if this technique can be extrapolated to horses, would be effective in horses, what route to administer the feces to the foal (via nasogastric tube or enema), and how much fecal matter to use.
As a zoonotic concern (i.e., a disease that can be transmitted to humans from horses, and vice versa), Weese commented that while the risk of human infection from exposure to an equine case of C. difficile is quite low, owners should still follow good infection control and hygiene practices when managing diarrheic horses.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.