Infectious Diarrhea in Horses: Determining the Cause

Multiple clues can help a practitioner determine the cause of infectious diarrhea or colitis in adult horses, including the farm's history of previous outbreaks, geographic location, and season, said Thomas J. Divers, DVM, Dipl. ACVIM, ACVECC, of Cornell University, at the 2010 Western Veterinary Conference, held Feb. 14-18 in Las Vegas, Nev.

"Regardless of whether we are talking about salmonellosis, clostridiosis, or Potomac horse fever, almost all adult colitis looks the same," said Divers. "When I look at a horse with colitis, I can't tell the difference among the diseases by clinical exam alone. They all have fever and diarrhea, and all of them are toxemic."

A veterinarian will do diagnostic testing to see if the horse needs to be isolated, and to better target the treatment and understand the epidemiology of the infection.

The main culprits of infectious diarrhea in adults are Salmonella, Clostridium difficile, Clostridium perfringens, and Potomac horse fever. Salmonellosis is an equal opportunity organism; it can affect a horse at any age or any time of year. Potomac horse fever occurs in warmer weather and only in certain areas of the country. C. difficile diarrhea usually occurs during or following a course of antibiotics in adult horses. C. perfringens Type A is the most difficult infectious cause to understand and prove. Other infectious causes of diarrhea exist but are uncommon, he said.

Even with testing, the cause of the diarrhea might remain elusive, Divers noted. In those cases, metronidazole (an antimicrobial), Bio-Sponge, and supportive therapy, such as rehydration and electrolytes and appropriate anti-inflammatories, would be recommended. Unless the horse is colicky, forage might help get the gastrointestinal track back in shape.

Practitioners must also work to prevent laminitis in horses with infectious diarrheas. Divers recommended instituting cryotherapy until the horse improves.

About the Author

Marie Rosenthal, MS

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