Salmonellosis affects humans, horses, most mammals, and birds. It can cause debilitating–and even deadly–diarrhea. Salmonella bacteria can affect both foals and adults, and they spread easily by horse-to-horse contact and by fomites (shared tools, water buckets, hands, etc., on which bacteria can “hitch a ride” to the next victim). Seemingly well horses can harbor the bacteria, and when stressed, they can shed it or become ill. “The environment can be contaminated by birds, rodents, or other wild animals shedding the organism in feces, including contaminating feed for horses,” says Simon Peek, DVM, MRCVS, PhD, Dipl. ACVIM, clinical assistant professor of large animal internal medicine, theriogenology, and infectious disease in the department of large animal internal medicine at the University of Wisconsin. Salmonella has received attention lately due to several outbreaks of nosocomial disease (infections picked up at a hospital by an animal that did not have that infection upon entrance) in various teaching hospitals.

Peek says there are more than 2,000 types of Salmonella, including several that affect horses. Most common is S. typhimurium, a type that also infects cattle and people. All types are zoonotic (affect animals and humans) except for one type that only infects humans.

“These Gram-negative bacteria cause a variety of problems–most commonly gastrointestinal disease and diarrhea,” says Peek. “Salmonella can also cause abortion, but not as often in horses as cattle. The infection can cause septicemia; in foals it can cause generalized sepsis–bacteria in the blood spreading to multiple organs. In adult horses, bacteria are more likely to be confined to the GI tract, particularly the colon. It is much rarer in mature horses for bacteria to get out of the GI tract and into the bloodstream.”

A foal with septicemia is dull and depre