Human Strain of Clostridium Difficile Reported in Quarter Horse

The same strain of Clostridium difficile that causes illness and death in human hospitals was reported in a 14-year-old Quarter Horse, according to a paper published in May issue of the Journal of Veterinary Diagnostic Investigation. Clostridium difficile bacteria can proliferate in the intestines and produce toxins that can damage the intestinal lining of horses, humans, and production animals such as cattle and swine.

In this case, the sick horse showed clinical signs of colic for 48 hours before treatment. Suspecting a Salmonella infection, veterinarians treated the patient with antibiotics, but the horse failed to respond to treatment and was euthanized.

Clostridium difficile

Clostridium difficile

The necropsy revealed large numbers of white blood cells and C. difficile bacteria in the horse's hind gut. Molecular testing methods confirmed that the strain of the bacterium from the horse was the same as that causing human C. difficile disease.

According to report co-author J. Glenn Songer, PhD, of the University of Arizona Department of Veterinary Science and Microbiology, C. difficile infection is often associated with antimicrobial treatment in adult horses, as was seen in this particular case.

"The infection can occur in veterinary teaching hospitals where healthy animals are exposed in the hospital--or the horse may be already colonized when it enters the hospital," Songer said. "Once inside the horse, C. difficile will multiply a bit, but it can't establish itself because of the other (helpful established) bacteria inhabiting the intestinal tract. The colonization begins, then ends, and begins again--never causing disease unless the organisms proliferate."

The trouble starts when clinicians treat a horse with antimicrobial drugs (for example, for or pre- or post-surgical infection prevention). For reasons that are not entirely clear, the bacterium is then able to establish itself in the gut and produce the toxins that cause diarrhea, colic, and an acute set of clinical signs sometimes called colitis X. Foals can also get the disease in the first few days of life, when C. difficile moves into an intestinal tract that does not yet have an established normal bacterial flora.

The disease can occur in both horse and human populations.

"We think it may have arisen in animal populations and spread to humans worldwide," Songer said. "However, this is still a hypothesis that needs further investigation."

Authors of the paper, "Equine colitis X associated with infection by Clostridium difficile NAP1/027," included Songer, HT Trinh, SM Dial, JS Brazier, and RD Glock.

About the Author

Nancy Zacks, MS

Nancy Zacks holds an M.S. in Science Journalism from the Boston University College of Communication. She grew up in suburban Philadelphia where she learned to ride over fields and fences in nearby Malvern, Pa. When not writing, she enjoys riding at an eventing barn, drawing and painting horses, volunteering at a therapeutic riding program, and walking with Lilly, her black Labrador Retriever.

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