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Officials say Mad Cow Disease Doesn't Pose Threat to U.S.

May 21, 2003 -- The U.S. government has banned imports of Canadian beef after an 8-year-old cow in Alberta was found to have mad cow disease (also called bovine spongiform encephalopathy or BSE). Officials believe this is an isolated case of the disease that swept Great Britain a decade ago and does not pose a major threat to the food supply of the U.S. and Canada.

The mad cow disease outbreak that emerged in Great Britain in 1986 eventually spread to more than 36,000 cattle by 1992. It's a deadly neurological disease found only in animals, but a similar disease, known as new variant Creutzfeldt-Jacob disease (vCJD), is thought to occur in humans who consume contaminated beef products from cows with mad cow disease.

Canadian authorities say meat from the infected cow in Alberta never entered the food supply. The brain of the cow was tested for mad cow disease after the animal showed signs of illness, and its meat was declared unfit for human consumption. Officials are currently investigating where the cow came from, its movement between herds, and how its remains were processed.

It's only the second time mad cow disease has been found in North America. In 1993, an animal imported from Great Britain was found to have the disease and was destroyed along with its herd.

No cases of mad cow disease among cattle have ever been found in the U.S.

The mad cow disease epidemic in the U.K. was thought to be spread through the addition of infected animal protein in animal feed products given to cattle. Since then, many countries, including the U.S. and Canada, have banned the use of such products in animal feeds as a protective measure against mad cow disease.

But the incubation period of mad cow disease is up to eight years, and officials are looking into the possibility that the cow may have eaten contaminated feed before the Canadian ban was in place.

Although mad cow disease has not been shown to spread among cows in a herd, Canadian officials say the entire 150-cow herd in Alberta will be slaughtered, and neighboring herds will be quarantined or destroyed as additional precautions.

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