Many scientists are becoming worried that bovine spongiform encephalopathy (BSE), commonly known as mad-cow disease, may cause Creutzfeldt-Jakob disease (CJD) in humans. BSE is a disease caused by prions (See BIOLOGY 4/e: prions on p. 651 and S. Prusiner on prion-caused diseases on p. 644). In March of 1996 the outbreak of mad-cow disease in Britain, with many thousands of cattle apparently affected, created widespread concern that the disease may pass to humans. BSE first appeared in British cattle in the 1980s, and reached its peak in 1993. Even now, 300 new cases of BSAE are confirmed each week. The disease, a degeneration of the brain caused by prions, appears to have entered the British cattle herds from sheep! Sheep are subject to a prion disease called scrapie, and the disease is thought to have passed from sheep to cows through feed pellets containing ground-up sheep brains (in Britain it was -- until banned six years ago -- common practice to add ground-up animal parts to feed pellets to increase protein content). It is this passage of the prion from one species to another that has British scientists worried: The death of four dairy farmers in Britain from CJD in the last four years suggests that the prion may be able to pass from cows to people! The case for a connection between eating British beef and CJD is by no means clearcut, but there appears to be legitimate cause for caution. Because the incubation period for CJD can be anything from 15 to 45 years, the link between meat-eating and disease may not become apparent until many people have been affected.
Source: "Mad Cow Epidemic Puts Spotlight On Puzzling Human Brain Disease", by Lawrence K. Altman, M.D. New York Times, April 2, 1996