AN INTERNATIONAL panel of scientists says the US should test around 200,000 cattle a year for BSE to work out the prevalence of the disease. The US had planned to test only a fifth that number.
Highlighting how little we still know about prion diseases, the call last week was followed by a report from Italy that suggests there may be a second, hitherto unknown form of BSE in cattle.
Shortly after the US discovered its first known case of BSE last December, it asked a group of scientists from Switzerland, the UK, the US and New Zealand to assess its control efforts.
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Last week the group recommended the US employ many of the same measures to prevent the disease spreading that it suggested last year to Canada 鈥� in particular, testing all animals found dead, unable to stand or that need emergency slaughter. In Europe, testing has shown these 鈥渄owners鈥� are 10 times more likely to be infected with BSE than apparently healthy cattle.
The US has an estimated 200,000 downers a year. It had planned to start testing up to 40,000 cattle, mainly downers, a year. But 鈥渘ow that it has been established that the BSE agent is circulating in North America, the US surveillance programme must be significantly extended in order to measure the magnitude of the problem鈥�, the scientists insisted.
Coincidentally, last week a group of scientists advising the US Food and Drug Administration on prion infection in food, drugs and cosmetics, also called for more testing to quantify the extent of the BSE problem in the US. The US Department of Agriculture had not responded to either call as New 杏吧原创 went to press.
Canada has taken some of the international panel鈥檚 advice. In January it announced it would test 8000 high-risk animals this year, but will increase that to 30,000 a year, probably including most of the country鈥檚 downers, by 2009.
The international panel also recommended that all high-risk tissue from cattle, such as brain and spinal cord, is removed from all animal feed, and that no mammalian or poultry remains are fed to ruminants. Neither the US nor Canada has so far taken those steps, even though Europe found they were necessary to stop the spread of BSE.
The panel hoped that, now BSE has become an American problem, serious research will be done to answer outstanding questions, for example, how soon after an animal ingests the rogue prions do its various tissues become infected, and at what stage does BSE become detectable by different tests. The UK has done only limited work in this area.
The work could be complicated by the discovery that there may be a second kind of prion disease in cattle. Salvatore Monaco and colleagues at the University of Verona in Italy found that two older cattle which tested positive for BSE last year had prions that behaved unusually compared with those found in most BSE-infected cattle identified by the test used in European abattoirs. The prion deposits also appeared in different areas of the brain, and in a different form, from the usual BSE pattern (Proceedings of the National Academy of Science, DOI: 10.1073/pnas.0305777101).
Markus Moser of the Swiss firm Prionics, which makes the rapid test that spotted the two cattle, says that before anyone can say this is truly a new prion disease, more cases must be found, and the prions must behave differently from classic BSE after they are injected into mouse brains, the definitive test.