Fatal parasite-induced enteritis and typhlocolitis in horses in Southern Brazil.

Diseases related to the alimentary system are the main cause of death in horses. This retrospective study aimed to describe the pathological findings of fatal parasite-induced enteritis and typhlocolitis caused by cyathostominae, Eimeria leuckarti, Balantidium coli, and Strongyloides westeri in horses. The records of parasite-induced intestinal lesions in horses necropsied in Southern Brazil between 2005 and 2017 were reviewed. Ten horses had fatal parasitic enteritis and/or typhlocolitis, and the main causes were: cyathostominae typhlocolitis (6/10), E. leuckarti enteritis (1/10), S. westeri enteritis (1/10), B. coli colitis related to cyathostominae (1/10), and infection by multiple agents (1/10). Cyathostominae typhlocolitis showed marked mucosal thickening, with multifocal elevated nodules containing tangled filiform parasites. Microscopic examination revealed that the mucosa and submucosa had encysted parasitic structures surrounded by eosinophilic and granulomatous inflammation. E. leuckarti enteritis was microscopically characterized by macrogamonts, microgamonts, and oocysts inside the host cells. S. westeri enteritis showed microscopic atrophy of the villi with numerous mucosal encysted parasitic structures. B. coli typhlocolitis showed severe diffuse mucosal reddening, with microscopic superficial mucosal necrosis associated with multiple protozoan trophozoites. Fatal parasite-induced enteritis and typhlocolitis are important causes of death in horses in Southern Brazil.