Intestinal lesions in a horse associated with eastern equine encephalomyelitis virus infection.

The primary lesions of eastern equine encephalomyelitis (EEE) virus infection in the horse are limited to the brain and spinal cord. Intestinal lesions in addition to the changes in the central nervous system were found in a 6-month-old male Tennessee Walking Horse. One week prior to death, this colt was vaccinated for EEE virus, western equine encephalomyelitis virus, influenza virus, equine rhinopneumonitis virus, and tetanus. The clinical signs consisted of ataxia and rear-end weakness, with a body temperature of 102.8 F. Gross lesions consisted of yellowish discoloration, swelling, edema, and hemorrhage of the brain stem and dark discoloration of the gray matter of the spinal cord. Microscopic lesions in the small intestine were mainly in the muscular layer and consisted of multifocal areas of myonecrosis and lymphomonocytic infiltration with a few focal areas of mild fibrous connective tissue proliferation. Occasional focal mild perivascular lymphocytic infiltration was observed in the submucosa. Lesions in the brain and spinal cord consisted of widespread areas of perivascular lymphomonocytic cuffing, focal areas of necrosis, neutrophilic infiltration, hemorrhage, neuronal degeneration, and gliosis. Hepatic changes consisted of periportal lymphocytic infiltration and mild vacuolar degeneration of hepatocytes. EEE virus was isolated from the intestine and detected by DNA in situ hybridization.