Mad cow disease in US?
2003-05-28 15:38
Paris - Mad-cow disease has probably infected some American cattle, despite proud claims that US herds are clean, the British weekly New Scientist reports in next Saturday's issue.
It asserts this on the basis that a cow with bovine spongiform encephalopathy (BSE) was found in Canada, which has an open trade border with the United States and shares many US farming practices and veterinary standards.
"If Canadian cattle are infected, it is likely that the disease is also present in the US," New Scientist says.
"The US and Canada test so few animals that low levels of BSE infection would not be detected... Other countries have found many more cases after increasing testing when the first infected cattle were reported."
Scientists working for the European Commission concluded in 2000 that BSE could be circulating in North America, but at low levels, the article says.
This was because British cattle, imported before 1990, were ground up into feed for other cows, a well-documented way of transmitting BSE.
The risk would have peaked between 1993 and 1997, when recycled animal protein was barred.
The Alberta cow at the centre of Canada's scare was born in 1995 and so presumably became infected by eating this feed - and other cattle may have done the same, New Scientist suggests.
Marcus Doherr of Switzerland's University of Bern, a leading BSE epidemiologist who took part in the Commission study, said the big worry was that both Canada and the United States do not carry out sufficient tests for BSE.
Doherr said that, typically, for every case that his team detected, as many as five more animals had been exposed to infection.
The test procedure in North America is to sample "high-risk" animals that are found dead or disabled on farms, or have neurological symptoms or have been rejected by the abattoir.
In Alberta's population of 2.5 million cattle over 18 months old, the target group for testing, only 1 655 animals have been tested for BSE, New Scientist says. The cow found to have BSE in fact had none of the disease's symptoms: it had been rejected because it had pneumonia.
"The situation is slightly better in the US, where nearly 20 000 cattle found dead on farms were tested for BSE last year. All were negative. But the sample is still too small to rule out the existence of BSE in the US herd."
Eating BSE-infected beef has been linked with a form of Creutzfeldt-Jakob disease, a fatal deterioration of the brain.
An outbreak of BSE could have "a huge economic impact on the massive $400bn North American beef industry," the article warns.