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Alabama Cow Has Mad Cow Disease

Cow Never Entered the Animal or Human Food Chains, U.S. Official Says
WebMD Health News
Reviewed by Louise Chang, MD

March 13, 2006 -- An Alabama cow has tested positive for bovine spongiform encephalopathy (BSE), commonly called mad cow disease.

The cow "did not enter the animal or human food chains," says John Clifford, DVM, chief veterinary officer for the U.S. Department of Agriculture (USDA), in a statement posted on the USDA's web site. "I want to emphasize that human and animal health in the United States are protected by a system of interlocking safeguards, and that we remain very confident in the safety of U.S. beef," Clifford says.

The cow is the third U.S. cow confirmed to have BSE. It was a "downer" cow, meaning it couldn't walk before a private veterinarian euthanized it and sent tissue samples to labs for testing. The BSE confirmation came after inconclusive results from earlier tests.

Herd of Origin Being Investigated

The USDA is investigating the cow's herd of origin. The cow's exact age isn't known, but it may have been more than 10 years old and only lived on the Alabama farm for less than a year, Clifford says.

"Experience worldwide has shown us that it is highly unusual to find BSE in more than one animal in a herd or in an affected animal's offspring," Clifford says. "Nevertheless, all animals of interest will be tested for BSE."

The cow's first tests, done at a Georgia lab with a USDA contract, were inconclusive. So the USDA followed up with two more tests done at the National Veterinary Services Laboratory in Ames, Iowa.

The first of those follow-up tests came back positive for BSE. The second test's results aren't in yet. "USDA considers an animal positive for BSE if either of the two confirmatory tests returns a positive result," Clifford says.

What Causes Mad Cow Disease?

BSE is a transmissible, slowly progressive, degenerative, and fatal disease affecting the central nervous system of adult cattle. It was first reported among cattle in the U.K. in 1986. Researchers believe that the infectious agent that causes mad cow disease is an abnormal version of a protein called a prion. For reasons still unknown, this protein becomes altered and destroys nervous system tissue -- the brain and spinal cord.

Cooking has not been shown to kill the BSE agent, according to information posted on the USDA's web site. Common methods to eliminate disease-causing organisms in food, like heat, do not affect prions.

There is no evidence to suggest that milk and dairy products carry the agent that causes BSE, states the USDA. Prions only seem to live in nervous system tissue.

Does Mad Cow Disease Affect Humans?

A human version of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD) is believed to be caused by eating beef products contaminated with central nervous system tissue, such as brain and spinal cord, from cattle infected with mad cow disease.

For this reason, the USDA requires that all brain and spinal cord materials be removed from high-risk cattle -- older cattle, animals that are unable to walk, and any animal that shows any signs of a neurological problem. These cow products do not enter the U.S. food supply. The USDA believes this practice effectively safeguards U.S. public health from vCJD.

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