Mad cow disease unlikely in U.S., experts say

(CNN) -- Agricultural and health experts believe mad cow disease is not a threat in the United States.

"We have checked close to 12,000 brains of the highest risk cattle in the U.S. and found no evidence at all" of bovine spongiform encephalopathy, or BSE, said Dr. Linda Detwiler, a senior staff veterinarian for the U.S. Department of Agriculture.

Detwiler trains other veterinarians how to test cow brains for BSE, which has been linked to the development of the devastating Creutzfeldt-Jakob disease in humans. BSE has infected cattle in 13 European countries and killed about 90 people in the United Kingdom. Scattered infections also have been reported in Germany and France.

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The brain-wasting Creutzfeldt-Jakob disease usually involves psychiatric symptoms and behavioral changes, progressing to movement deficits, memory disturbances and other severe cognitive impairments. It is incurable, progressive and fatal. Symptoms can appear anywhere from 10 to 15 years following infection.

"We don't have mad cow disease," said Dr. Paul Brown, medical director of central nervous system studies at the National Institutes of Health. "We probably never will have mad cow disease, and therefore, it's a non-problem in the United States."

This is because the disease is believed to have come from contaminated bone-meal animal feed made from infected animal parts in England. BSE was first identified in that country in 1986.

But the United States banned importation of animal feed from the United Kingdom in 1989, and didn't import much even before that. In 1996, imports of animal feed from all European countries were banned.

In addition, imports of cattle or meat are prohibited, and the USDA monitors local herds carefully.

It is possible that U.S. tourists who become infected overseas could bring the disease back home, but even that, experts say, is unlikely to cause an epidemic.

"There's lot of bad news about this," said the NIH's Brown. But the good news is it's very difficult to transmit from one person to another."

CNN Medical Correspondent Elizabeth Cohen contributed to this report.

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