※ [本文转录自 politics 看板] 作者: ivanos (common sense) 看板: politics 标题: [情报] Mad cow threat: How bad is it? 时间: Thu Oct 29 20:14:07 2009 http://www.organicconsumers.org/madcow/testing21704.cfm Mad cow threat: How bad is it? February 17, 2004 Sacramento Bee by JON ORTIZ As scientists study mad cow disease, a malady known and studied for only 20 years, some findings are challenging the conventional wisdom that shapes U.S. regulations aimed at combating the fatal illness. Does the disease reside strictly in the brain and spinal column? Is the only means of transmission through eating tainted beef? Are cattle below the age of 30 months sure to be free of the deadly infection? The U.S. Department of Agriculture - an agency that both monitors beef safety and promotes the product - has assured the public that the answers to these questions are "Yes." In frequent, reassuring pronouncements, the agency has joined the beef industry in telling Americans that mad cow disease poses virtually no threat to public health. This rigid stance ignores an expanding body of data and research in a field of study that is still young, scientists and consumer advocates say. Among the recent findings: - The researcher who won the Nobel Prize for showing how mad cow disease works watched the disease expand into the muscle tissue of mice infected with it. - British doctors found that one individual infected with the human form of the disease transmitted it to another person through a blood transfusion. - Japanese labs that test millions of cattle annually found the disease in animals under the age of 30 months. "There's plenty we don't know. But the USDA takes the science that will cause the beef industry the least trouble and basically ignores the rest," said Michael Hanson, a scientist with Consumers Union, the organization that publishes Consumer Reports magazine. Yet from the start of the mad cow scare, the USDA has asserted that prions, the misshapen, brain-eating proteins that cause the bovine and human diseases, do not invade muscle meat. On Dec. 31, nine days after an infected cow surfaced in Washington state, USDA Secretary Ann Veneman said, "We have taken actions ... that include very aggressive matters, including (banning) certain parts of the head and the spinal column - the most at-risk materials - that were taken out of the food chain." The move, the USDA officials have said in news conferences and media releases, will keep the beef supply safe. Bovine spongiform encephalopathy, the medical name for mad cow disease, can take years to develop in cattle. Symptoms of its human version, new variant Creutzfeldt-Jakob disease, sometimes don't appear for decades. Recent studies of mad cow disease have suggested that the disease can migrate to muscle tissue. The first proof came when Stanley Prusiner, the San Francisco scientist who won the Nobel for his work on mad cow and similar diseases, infected mice with prions. In a paper published by the National Academy of Sciences in 2002, Prusiner reported finding "quite high" levels of prions in the rodents' muscles. Follow-up studies in Germany a year later confirmed that mice, at least, could end up with contaminated muscles after ingesting prions. "It's clear that the disease can spread outside the brain and spinal cord, even though the USDA says otherwise," said Michael Greger, a Scarborough, N.Y., doctor who has written about mad cow. "If there's one thing you know when you study this disease and its short history in Europe, it's that you can't make absolute statements like, 'Muscle meat cannot be infected.' " But Gary Weber, executive director for regulatory affairs at the National Cattlemen's Beef Association, says the experiment hasn't been repeated using cows. "You can't extrapolate that experiment to beef - and scientists have tried," Weber said. "And the World Health Organization has concluded that beef muscle does not represent any risk even if it comes from an animal with full-blown BSE." Critics such as Greger also question government's policy that allows brains and spinal cord from cattle younger than 30 months old to be sold for human consumption. USDA officials say the best science shows that even if a younger cow is carrying the disease, the illness hasn't developed enough to be passed. That notion came under fire earlier this month in a report by an international panel of experts commissioned by the USDA to review how the department handled the Washington mad cow case. In one section of the report, the panel recommended lowering the current cutoff for selling cow brains, spinal cords, skulls and intestines to 12 months. The USDA has banned the sale of those parts from cattle 30 months and older. "A cutoff of 12 months represents a recognition of the fact that some cattle under 30 months of age may be slaughtered with infectivity present in (those tissues)," the report said. The USDA has said little about the report, other than that it is considering how it will respond. But Greger and other critics point out that the government's assertion about the 30-month threshold in cattle may be more of a comment on the science behind U.S. test techniques, which take up to a week to confirm the presence of the disease. Other countries, such as Japan and Great Britain, use tests that can spot the presence of prions within hours and are considered far more sensitive than tests used here. The results of those tests became a point of controversy when Japan, which checks for mad cow in all slaughtered cattle, reported finding the disease in a 21-month-old bull and a 23-month-old cow. Scientists are divided over the integrity of those tests, however, because Tokyo did not send samples for confirmation to the leading mad cow laboratory in Weybridge, England. That lab administers a verifying test that is considered the world's "gold standard." "The problem with rapid tests is that they'll turn up a number of false positives," said Weber of the beef association. For years, the USDA had resisted using rapid test techniques similar to those used by Japan, preferring an older method that takes one week to get results. That changed after a punishing salvo of criticism of delays that allowed the diseased Washington Holstein to be ground into hamburger and sold in restaurants and stores. The department sought bids from rapid test manufacturers and may adopt new testing techniques soon. That could mean that more U.S. mad cow cases will surface, Hanson said, because more sensitive testing will probably ferret out infection that has gone undetected using current methods. "You get what you look for," he added. "History shows that once a country moves to rapid testing, the number of cases found goes up." --

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