Isolation of Campylobacter fetus subspecies fetus in a two-year-old quarterhorse with chronic diarrhea of an undetermined etiology.

A 2-year-old quarterhorse was evaluated for chronic diarrhea and weight loss of 5 weeks duration after numerous diagnostic tests failed to identify an underlying cause. Historically, the horse was housed at pasture where human household waste vehicles were routinely cleaned and the effluent could run onto the field. Physical examination revealed poor body condition and frequent high-volume diarrhea. Diagnostic testing for Salmonella spp., endoparasites, Cryptosporidium spp., Clostridium spp., and diffuse infiltrative bowel disease were negative. Rectal tissue histopathology failed to identify Mycobacterium spp., spirochetal organisms, or submucosal infiltration with cells. Rectal tissue biopsy and a fresh fecal sample identified numerous Campylobacter organisms with microaerobic culture. Molecular testing revealed the species as Campylobacter fetus subsp. fetus as a possible organism associated with large bowel disease in this filly. The organism was sensitive to fluoroquinolone antimicrobials in vitro. The filly responded transiently to therapy, forming discrete fecal balls after 72 hr of treatment. At 5 months follow-up, the horse had gained weight, was alert and responsive, but reverted back to having soft "cow-pie" feces. Reculture of the feces at 9 months failed to identify any Campylobacter organisms. To the authors' knowledge, this is the first report to identify C. fetus subsp. fetus from feces and tissue of a horse with the use of molecular methods. This organism could play a role in the etiology of chronic diarrhea in horses.