Britain's ''mad cow'' disease is caused by a mysterious, disease-causing microorganism that is hard to kill and even harder to study, a University of Tennessee epidemiologist said Tuesday. Dr. John New said mad cow disease is caused by a class of organisms called prions. Some scientists say 10 people in Britain recently died from a brain illness caused by eating beef from cattle with mad cow disease. An incubation period in which animals may be infected for years before getting sick or showing any symptoms makes prion study lengthy and expensive, New said.
Prions also are heat resistant.
Cooking kills deadly bacteria such as E. coli but is not as effective on prions, New said. Britain plans to kill millions of cattle in an effort to wipe out the disease, quell panic and restore beef sales. The United States has not imported British beef since 1985. The U.S. Department of Agriculture has found no sign of the disease in American cattle, but says it will increase cattle testing as a precaution. The U.S. Centers for Disease Control and Prevention is considering starting a national surveillance of the brain disease which caused the deaths in Britain.