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KNOXVILLE, Tenn. — 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.

If that is true, it would be “the biggest prion disease incident ever known,” New said.

“The only upside of the situation is that it could help us learn more about prions, which we know very little about.”

New said prions are more difficult to study than viruses, bacteria and other disease-causing agents.

“They’re not viruses, so we can’t apply virus tests to them,” New said. “You can’t take them out of tissue and grow them in a laboratory.”

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.

Some scientists believe prions cause mad cow disease and may cause brain disease in humans that eat infected beef.

“We can show that virus and bacteria jump species, but we don’t have the technology to investigate whether prions do,” 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.

Lack of knowledge about prions is contributing to hysteria in Britain, New said.

“The unknown is scary, and there are a lot of unknowns about prions,” New said. “That’s what the (British) public is focusing on right now rather than the scientific facts.”

Contact: Dr. John New (423-974-5576)