Malignant catarrhal fever in bison.

Malignant catarrhal fever was diagnosed in 3 herds of American bison (Bison bison) in South Dakota from 1973 to 1976. Clinical signs included depression, nasal and ocular discharge, conjunctivitis and keratitis, and diarrhea. Herd morbidity ranged from 3 to 53.8%, and mortality was 100%. At necropsy, ulcerative lesions were found throughout the alimentary tract, trachea, and bronchi. Microscopically, necrotizing vasculitis without thrombosis was found in virtually every organ examined.