Bovine spongiform encephalopathy: current status and possible impacts.

Bovine spongiform encephalopathy is an apparently new disease; first recognized in 1985, its pathological distinction was first reported in 1986. Bovine spongiform encephalopathy is a member of a group of transmissible encephalopathies that includes scrapie in sheep and Creutzfeldt-Jakob Disease in humans. Early indications of its epidemiology suggested that the disease was transmitted via cattle feed containing meat and bone meals from previously infected animals. The tissues most likely to contain infectious agents were considered to be nervous tissues and offal, and their inclusion in ruminant feed was banned in the United Kingdom in 1989; regulations were tightened in 1992. Subsequent diagnosis has indicated that this ban has been effective and that confirmed cases are predicted to decline from a peak in the United Kingdom of 37,490 in 1992, to 7417 actual cases in 1996, and then to virtual extinction in 2001. Subsequent culling of all nonproductive cattle more than 30 mo of age and culling of cohort animals of confirmed cases is likely to reduce the predicted numbers and times significantly. Current interest is in the means of transmission of bovine spongiform encephalopathy within species and possibly to humans. A new variant of Creutzfeldt-Jakob Disease, with 28 cases confirmed, is virtually certain to be bovine spongiform encephalopathy in humans. The outbreak of bovine spongiform encephalopathy has had major impacts on the United Kingdom dairy industry, including the loss of beef from dairy markets, the culling of more than 900,000 dairy bull calves, the removal of all cattle more than 30 mo of age from the human food chain, and now slaughter of cohort animals. Impacts on dairy marketing have yet to be properly assessed. Information and statistics for bovine spongiform encephalopathy can be found on the worldwide web at http:@www.maff.gov.uk/maffhome.html.