Eosinophilic colitis and hepatitis in a horse with colonic intramucosal ciliated protozoa.

Tissues from a 9-year-old American Standardbred gelding with a history of anorexia, mild colic, and unexpected death were submitted to the Laboratories of Veterinary Diagnostic Medicine at the University of Illinois for histopathologic examination. Microscopic diagnoses were severe subacute, diffuse eosinophilic colitis with intralesional protozoa and a subacute to chronic eosinophilic portal hepatitis with granuloma formation. Two tissue-invading, ciliated protozoa were identified in large numbers within the colonic mucosa. The ciliates were Polymorphella ampulla and Cycloposthium sp., Phylum:Ciliophora. The eosinophilic colitis and portal hepatitis in association with the overpopulation and invasion by the ciliated protozoa suggests a causal etiology.