Tests show BSE caused by infected sheep

Government scientists have found direct evidence to support the theory that the BSE epidemic was originally caused by feeding cattle the rendered carcasses of sheep infected with scrapie.

Government scientists have found direct evidence to support the theory that the BSE epidemic was originally caused by feeding cattle the rendered carcasses of sheep infected with scrapie.

The theory was dismissed last year as "fallacious" by the BSE inquiry, but preliminary results of an experiment to test it have revealed that cows injected with sheep scrapie fall ill with what appears to be bovine spongiform encephalopathy. Results of the experiment were passed this week to the Government's spongiform enceph-alopathy advisory committee (Seac), but further work is needed before the evidence can be considered conclusive.

Knowing the precise origin of BSE is important because it would reassure scientists that the measures introduced to prevent a recurrence are watertight. The experiment involved either feeding or injecting scrapie into calves to see whether they were susceptible to the disease. Two calves have so far succumbed to BSE-type symptoms. Their brains are the subject of post-mortem tests.

Scientists from the Veterinary Laboratories Agency near Weybridge in Surrey began their investigation after criticism by Seac in 1996 that research into the origins of BSE was sorely lacking. Ten calves have been injected intracerebrally with material from the brains of sheep that died of scrapie before 1975, when it was thought there would be no risk of the sheep being cross-contaminated with BSE.

Another 10 calves were similarly injected with scrapie material from sheep that died after 1990. Since the experiment was started in July 1999, one calf in each group has succumbed to BSE-like symptoms.

Another experiment, started last September, has involved feeding scrapie material to separate groups of calves to see if the sheep disease can be transmitted orally to cattle, as the "scrapie hypothesis" predicts. Danny Matthews, the head of molecular biology at the Veterinary Laboratories Agency, said that even if the cattle fed on scrapie developed similar symptoms to cattle with BSE, it would take many years of further tests on mice before that could be confirmed.

The BSE inquiry dismissed the scrapie hypothesis largely because many other countries had also rendered sheep carcasses into cattle feed and had not suffered a BSE epidemic.

The inquiry suggested a spontaneous mutation in a gene for the prion protein implicated in BSE and scrapie. The inquiry concluded: "BSE probably originated from a novel source early in the 1970s, possibly a cow or other animal that developed the disease as a consequence of a gene mutation."

However, Dr Matthews criticised the inquiry's dismissal of the scrapie hypothesis. He said: "It's crazy that they should have come up with that conclusion ... I think the evidence for spontaneity is pretty thin."

Other research into the origins of BSE is being done by Professor Gabriel Horn, of Cambridge University, who has been asked by the Department of Health and Ministry of Agriculture to investigate the idea that the epidemic was caused by the rendering of a zoo animal carrying an endemic form of the brain disease.

Professor Horn said: "It is important to know the origins of BSE because if we get some real insight that turns out to be surprising it might alert us to a way we might act in the future to prevent such a calamity."