Commonly known as "mad cow disease," BSE is a slowly progressive, incurable disease affecting the central nervous system of cattle, first diagnosed in Britain in 1986. Consumption by cattle of BSE-contaminated ruminant proteins in animal feed has been cited as one possible means of transmission. Scientists have confirmed a link between BSE in cattle and several dozen recent European cases of a human variant of BSE, Creutzfeldt-Jacob disease. More than 77,000 cattle suspected of having been exposed to the disease have been slaughtered in Great Britain, and a ban on ruminant protein-containing feeds was imposed in 1988. To date, no BSE has been found in U.S. cattle, although other BSE-like animal diseases are found in the United States, including scrapie in sheep and goats. USDA banned the importation of live cattle from Great Britain in 1989, and imposed a partial ban on using ruminant protein in animal feed in 1997.