Rabies-induced spongiform change and encephalitis in a heifer.

A 1-year-old mixed breed heifer was presented to the Veterinary Medical Teaching Hospital at the University of Illinois with a 3-day history of abnormal mentation and aggressive behavior. Based on the history and clinical examination, euthanasia and necropsy were recommended. The differential diagnosis included rabies, pseudorabies, and a brain abscess. The brain was removed within 60 minutes of death, and the section submitted for fluorescent antibody testing was positive for rabies virus antigen. Residual brain tissue was immersion fixed in 10% neutral buffered formalin. Histologic examination revealed a marked perivascular and meningeal lymphocytic meningoencephalitis and locally extensive spongiform change of the gray matter affecting the neuropil and neuron cell bodies. The most severely affected regions with spongiform change were the thalamus and cerebral cortex. No Negri bodies were found in any sections. Since the outbreak of bovine spongiform encephalopathy (BSE) in the United Kingdom, there has been an increased surveillance of bovine neurologic cases in an effort to assess if BSE has occurred in the USA. In areas where rabies virus is endemic, rabies should be included as a possible differential diagnosis in cases of spongiform changes of the central nervous system.