Since the lethal condition appeared in British cattle in the mid-1980s, mad cow disease has jumped the species barrier and killed more than 90 people in Europe. But some experts say thousands of humans could be afflicted. Meanwhile, hundreds of thousands of cattle -- sick or suspected of infection -- already have been destroyed in Europe. The precise cause of mad cow disease, or bovine spongiform encephalopathy (BSE), is a mystery, but scientists do know it is spread by feeding cattle with meat-and-bone meal from diseased animals. The European Union has imposed strict rules to prevent mad cow's further spread, including banning feed made from animals. While the United States has yet to detect a single case of mad cow disease, critics warn that government surveillance efforts and cattle-feed regulations are inadequate.

Mary H. Cooper specializes in environmental, energy and defense issues. Before joining CQ Researcher as a staff writer in 1983, she was a reporter and Washington correspondent for the Rome daily newspaper l'Unita. She is the author of The Business of Drugs (CQ Press, 1990). She also is a contract translator-interpreter for the U.S. State Department. Cooper graduated from Hollins College in English.