The carcass of a BSE-infected cow being burnt in a Dorset field. BSE (bovine spongiform encephal- opathy), or mad cow" disease, progressively destroys the brains of infected cattle. The disease first appeared around 1985 and, so far, has only been identified in Britain. It is thought to have arisen from a similar disease, scrapie, which infects sheep and to have been transmitted to cattle via processed feed containing infected sheep carcasses. The infective agent responsible for BSE is not a virus or bacterium, but a virus- like protein known as a prion. Similar diseases affecting humans include Kuru, Creutzfeldt- Jakob disease & Gerstmann-Straussler syndrome."