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incidence of the disease."
The Japanese experience is instructive, Dr. Prusiner said. Three and a half years ago, that country identified its first case of mad cow disease. The government then said it would begin testing all cows older than 30 months, as they do in Europe. Older animals presumably have a greater chance of showing the disease, Dr. Prusiner said.
Japanese consumer groups protested and the government then said it would test every cow upon slaughter, Dr. Prusiner said. The Japanese have 4 million cattle and slaughter 1.2 million of them each year. The United States has 100 million cattle and kills 35 million a year.
Early this fall, Japanese surveillance found two new cases of the disease in young animals, aged 21 and 23 months. "Under no testing regime except Japan would these cases ever be found," he said.
The 23-month-old cow tested borderline positive using two traditional tests. But the surveillance team then looked in a different part of the brain using an advanced research technique and found a huge signal for infectious material, Dr. Prusiner said. It was a different strain of the disease, possibly a sporadic case.
The only way to learn what the United States is facing is to test every animal, Dr. Prusiner said. Existing methods, used widely in Europe and Japan, grind up brain stem tissue and use an enzyme to measure amounts of infectious prions. Animals must have lots of bad prions to get a clear diagnosis.
Newer tests, by a variety of companies, are more sensitive, cheaper and faster. Dr. Prusiner said that his test could even detect extremely small amounts of infectious prion in very young animals with no symptoms. Sold by InPro Biotechnology in South San Francisco, a single testing operation could process 8,000 samples in 24 hours, he said.
British health officials will start using the test in February, Dr. Prusiner said. If adopted in this country, it would raise the price of a pound of meat by two to three cents, he said.
"We want to keep prions out of the mouths of humans," Dr. Prusiner said. "We don't know what they might be doing to us."
His laboratory is working on promising treatments for the human form of mad cow disease but preventing its spread is just as important, he said. "Science is capable of finding out how serious the problem is," he said, "but only government can mandate the solutions."
Published on Thursday, December 25, 2003 by the New York Times
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