Enteric Bacteria: Can Healthy Horses be Carriers?

Could a healthy horse in one’s own backyard be a disease risk for other horses?

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Many horse owners will agree that keeping their charges safe from disease risk is a top priority. But could a healthy horse in one’s own backyard be a disease risk for other horses? At the 2011 American College of Veterinary Internal Medicine Forum, held June 15-18 in Denver, Colo., Angelika Schoster, DVM, a DVSc candidate at the University of Guelph’s Ontario Veterinary College discussed novel epidemiologic features of several bacteria often related to diarrhea and colitis (inflammation of the colon) in horses. Schoster explained that some healthy horses might also carry these bacteria and act as potential reservoirs to infect others with gastrointestinal ailments caused by the organisms.

Schoster described a study in which researchers evaluated healthy horses for several enteric (intestinal) pathogens known to cause colitis, diarrhea, and other gastrointestinal ailments in equines: Clostridium difficile, Clostridium perfringens, Salmonella, and Escherichia coli. In addition, they examined the antibiotic sensitivity of commensal E. coli (nonpathogenic), as it can be a good indicator of antimicrobial sensitivity in the common pathogens.

Twenty five horses from five farms were examined monthly over the course of a year. None had any known gastrointestinal disease, nor had they received any medications at the time of enrollment into the study.

Researchers did not detect C. perfringens or Salmonella sp. in any of the horses. However, they did detect C. difficile in 44% of the horses and on 60% of the farms, and the bacteria detected was a toxigenic (produces a toxin) form of C. difficile. Schoster noted that researchers believe the toxigenic strain ribotype 078, which is similar to a strain becoming increasingly important in human enteric disease, is becoming more prevalent in horses. The study results suggest that C. difficile shedding occurred only for short durations. Simply put, while it’s not uncommon for healthy horses to carry bacteria, it’s relatively unlikely that they will actually infect other horses

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Written by:

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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