Wednesday, December 31, 2003

Experts Try to Assess Risk From Diseased Cow:
"There are two fears that Americans seem to have in the wake of the discovery of mad cow disease in a Washington cow, and the science of assessing them is very different.

The first: Did my family eat any of that cow, and, if so, will it hurt them?

The second: Never mind that one cow — how many others are out there? "

Answering the first is really a matter of looking at the history of similar brain diseases in Britain and New Guinea.

Answering the second is, for the moment, largely a matter of statistics — but difficult, because the numbers are so vague.

It seems almost inevitable that some part of the cow was eaten. It was killed on Dec. 9, and ground up with about 20 others to make a batch of 10,000 pounds of hamburger that was shipped to groceries in eight states and Guam, although 80 percent went to Oregon and Washington, the Agriculture Department says.

The diseased cow was not found until Dec. 23, and a recall order was issued.

Dr. Gary Weber, a spokesman for the National Cattlemen's Beef Association, said he thought that, like most ground beef, the batch would have been frozen for transit. He had heard that 20 percent was found in storage, he said. But he said of the rest: "I'd hazard a guess that some of it has been consumed."

In Britain, nearly 200,000 cows were infected. Millions of people ate meat from those cows, including steaks, ribs, hamburger, neckbones, beef marrow and brains. Material from cows was used in a wide variety of items, including beauty products, polio vaccines and weightlifters' steroid substitutes. A lion in the Newquay zoo in England was found to have a form of the disease. Yet only about 150 Europeans have died of it. Early predictions of 100,000 to 200,000 British deaths did not come true.

Some research has indicated that not everyone is equally at risk, that some people have a genetic predisposition toward the disease.

Moreover, assuming the Agriculture Department was correct, and only muscle meat from the Washington cow was ground up, the risk is probably far lower. Although prions, the misfolded proteins that cause the disease, have been found in the muscles of hamsters, mice and humans infected with the disease, brain and nerve tissue is thought to be a million times more infectious.

But not all scientists agree. When young animals are infected, the disease does not show up in their brains for at least 30 months, said Dr. Stanley B. Prusiner, a neurologist at the University of California in San Francisco who won a Nobel Prize in medicine for his work on prion diseases. But it could be present in low levels in other tissues, including muscle, Dr. Prusiner said, and at higher levels in the lymph glands of calves. It is not clear that those levels would be enough to infect anyone, and federal officials have asserted that the muscle meat is safe.

Also, it is possible for brain tissue to be driven into or splattered on muscles in a slaughterhouse. Animals are usually killed with a blow from a hand-held jackhammer that slams a piston into the skull. The last few beats of the animal's heart can circulate the tissue. Also, sawing a carcass in half can splatter spinal cord tissue around, as can the use of high-pressure jets that strip meat from bone. Agriculture officials said they believed that such methods were not used on this carcass.

http://www.nytimes.com/2003/12/30/national/30ASSE.html?pagewanted=all&position=

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