Scientists puzzled by sheep BSE tests
Unexplained results could take years to analyse
James Meikle, health correspondent
Thursday November 27, 2003
Scientists could take years to determine whether new BSE-like diseases really are occurring in sheep, it has emerged.
Monitoring of thousands of animals has thrown up 26 more unexplained results since the nightmare possibility that BSE had leapt from cattle to sheep was revealed by government officials in September.
At that time 28 results from samples of nearly 30,000 sheep brains tested up to March were troubling experts. But the puzzling results are continuing at roughly the same rate, scientists on the spongiform encephalopathy advisory committee (Seac) were told.
Government and EU scientists are trying to establish whether there is a problem with the testing method, and whether an unknown type of scrapie, a BSE-like disease in sheep which has never been known to be dangerous to man, or the far more lethal BSE is indeed in our flocks. Meanwhile, the Food Standards Agency is not advising against the consumption of lamb or sheep meat.
The unexplained results come from a rapid screening test which should produce results overnight. Indications of a scrapie-like disease have to be confirmed by another test that takes up to three weeks. In total 54 results have now not been confirmed but this might be because the quick test is better at detection.
Work on establishing the tests' reliability might take months, even after issues of commercial confidentiality over their exact components have been settled. But meanwhile scientists want to start feeding and injecting mice and sheep with brain material that provided the puzzling results.
But this could take months or years and still prove inconclusive. It is quite possible that the brain tissue of sheep has changed its "signature" from normal but is not clinically infected with disease and therefore would have no obvious effect on the laboratory animals. Some types of scrapie also do not transmit at all to mice.
Scientists hope they might get an indication of what might be happening from an experiment that is being conducted in Germany, using material from a sheep there that threw up a confusing result.
Chris Bostock, the Seac member heading the investigations, said: "We do not understand the basis for and significance of these samples." The report from his group presented at Seac yesterday said that the hypothesis that the samples represented pre-clinical BSE in sheep could not be ruled out on the available evidence. But the patterns revealed did not resemble those from sheep deliberately given BSE in the laboratory.
The scientists are seriously concerned by the lack of brain material they can use for further tests. This is because abattoirs have to safely dispose of heads of sheep before test results come back. This rule might have to be altered.
Even sheep supposedly resistant to scrapie have shown unexplained results, worrying for contingency planners already trying to get farmers to breed these types. Scientists have suggested that sheep known not to have scrapie should be tested but finding enough of these in Britain would be difficult.
Some sheep have been imported from scrapie-free New Zealand to use in BSE research but far larger numbers would be needed and it is far from certain that the authorities in scrapie-free countries could, or would want to, provide the numbers needed.