Brain wasting disease protein prions in sheep

[Guest guest]

Hi All,

For the latest pseudo-scare regarding animal meats, see:

http://www.nytimes.com/2004/05/24/science/24sheep.html?th

Malformed Proteins Found in Sheep Muscle

By DONALD G. McNEIL Jr.

Published: May 24, 2004

Prions, the misfolded proteins that are widely believed to cause

brain-wasting diseases, have been found in sheep muscle, scientists

announced yesterday - the first time they have been discovered in

animal flesh that many humans normally eat.

But the scientists emphasized that the finding did not mean that lamb

or mutton posed a danger to humans.

" The risk of transmission from sheep to humans is very, very low, "

said Olivier Andréoletti, a prion specialist at the National

Veterinary School in Toulouse, France, and lead author of the study,

which was published yesterday in Nature Medicine.

The prions were found at one five-thousandth the concentrations that

are found in sheep brains, and therefore likely to be much less

infectious.

Also, the animals were infected with scrapie, a prion disease that is

not the same as bovine spongiform encephalopathy, or mad cow disease.

Although the symptoms of scrapie have been described in sheep for

centuries, and scientists believe that mutated scrapie prions may

have caused the British epidemic of mad cow disease of the 1980's, no

case of scrapie transmitted to humans has ever been found.

Moreover, according to Dr. Brown, a prion expert at the National

Institutes of Health, in nearly 40 years of trying, no researcher has

ever infected a healthy animal with a prion disease by injecting it

with liquefied muscle from a sick one - not even when the injection

was directly into the brain.

It is even less likely that a human could be infected by lamb or

mutton that has passed through the acidic process of digestion,

scientists said.

The study team, based at three French research institutes, found

prions in the leg muscles of sheep that were naturally infected with

scrapie and in sheep deliberately infected with it. In one naturally

infected sheep, they found scrapie eight months before the animal

showed any signs of the disease, which include itching that makes

animals scrape themselves against trees and fences (hence the name),

tremors, stumbling gaits and, eventually, lethargy and death.

Although he agreed that prion levels in the meat were low, Dr.

Giuseppe Legname, a prion expert at the University of California at

San Francisco, called the finding " a warning. "

Two years ago, in collaboration with Dr. Stanley Prusiner, who won a

1997 Nobel Prize in Medicine for his work in the field, Dr. Legname

found prions in the muscles of mice and showed that they could

replicate there. Since then, Swiss researchers have found prions in

the muscles of humans with sporadic Creutzfeldt-Jakob disease, a

degenerative brain disease that is thought to arise spontaneously in

one in a million humans.

That prions exist in the edible parts of livestock, Dr. Legname said,

suggests that the United States should screen livestock to minimize

the chances that Americans will be exposed to infected animals. The

United States Department of Agriculture, which tested about 20,000

cattle a year for mad cow disease before finding one positive for it

in December, has announced it will test more than 200,000 animals

starting this summer, but that is still only a small fraction of the

number of animals that Europe tests.

Dr. Brown, who spent decades on prion research, said he was not

surprised that they had been found in sheep muscle. " In the last few

years, the sensitivity of immunoblot tests has been ramped up so much

that people are beginning to find the protein all over the place, " he

said.

He ventured a prediction: " Within the next year, somebody will make a

big splash by finding it in the muscles of cattle, " he said, " and the

beef industry will go crazy. "

Nonetheless, he said it was still his instinct that beefsteak had not

been the culprit in transmitting mad cow disease from cattle to

humans in Europe.

" Mechanically recovered " meat, which is squeezed off chopped-up bones

under pressure, a process that in many cases mixes in spinal cord and

nerve tissue, was a " much better vehicle, " he said. Late last year,

spinal cord and nerve tissue from cows over 30 months old was banned

from human food.

Cheers, Al Pater