Surveillance for lesions of bovine spongiform encephalopathy in US cattle.

The appearance of bovine spongiform encephalopathy (BSE) as a new disease of cattle in 1985-1987 increased worldwide interest in various aspects of human and animal spongiform encephalopathies. In the United States, a part of the surveillance effort has been directed toward prospective examination of bovine brain specimens for lesions of BSE. One focus area has been to obtain specimens from cattle that (1) are two years of age or older, (2) have documented signs of neurologic disease, and (3) have received protein supplement as a substantial part of the i.v. ration. Another focus area has been to examine rabies-suspect cases that were rabies-negative. A third area has been to obtain the results of bovine neuropathology examinations being conducted at other state and regional laboratories. Specimens have been obtained by direct submission and by referral from other public health and veterinary diagnostic laboratories. Many of the cases have been classified as having (1) inflammatory lesions such as listeriosis, pseudorabies, brain abscesses and inflammation of undetermined cause, (2) degenerative lesions such as polio-encephalomalacia, lead poisoning, Wallerian degeneration, siderocalcinosis, and lipofuscinosis, (3) neoplastic lesions such as meningioma and Schwannoma, and (4) no significant findings. Other case results were reported as inflammation or no significant findings. Of the 459 cases reported here none has contained lesions with the characteristics and distribution typical of BSE.