An African antelope imported into a British safari park in the 1970s was probably the origin of mad cow disease, says a New Zealand epidemiologist.
Roger Morris of Massey University has used computer modelling to analyse dozens of possible explanations for BSE. 鈥淭he one that comes out top of the list is the African antelope hypothesis,鈥� he says.
African antelopes are susceptible to spongiform encephalopathy, says Morris. He thinks a single infected animal used as feed for cattle could have triggered BSE. The BSE epidemic led to the slaughter of millions of cattle and the human form of the disease, vCJD, has killed more than 90 people so far.
Advertisement
鈥淭he area of Britain where BSE started is the area where safari parks started in the 1970s,鈥� Morris told AFP. 鈥淚鈥檝e got evidence that every step in the sequence could have occurred.鈥�
Spontaneous mutation
But other experts are not convinced. The main alternative suggestions blame scrapie-infected sheep being fed to cattle or a spontaneous genetic mutation in cattle.
The antelope theory 鈥渋s not the most likely hypothesis, given what happened with the BSE epidemic,鈥� says John Wilesmith, head of epidemiology at the UK鈥檚 Veterinary Laboratory Agency, who has worked with Morris. But he adds: 鈥淭here are lots of complex theories for BSE and they鈥檙e all worthy of examination.鈥�
Nora Hunter of the Neuropathogenesis Unit at the Institute for Animal Health in Edinburgh agrees the idea is interesting but says: 鈥淭here are numerous other possibilities and it will be very hard to prove.鈥�
Single strain
A wildlife source of BSE-causing prions would explain why the epidemic in the UK was unique and caused by a single strain of prion, Morris says.
The evidence 鈥渟trongly favours鈥� the idea that a wild animal of some kind was responsible, he says, and while an infected antelope is the most likely cause other animals, for example lions, can also develop a TSE (transmissible spongiform encephalopathy).
One difficulty with Morris鈥檚 theory is that a wild antelope suffering from a TSE has never been identified. But this is not surprising, he says, as an afflicted antelope would rapidly fall prey to lions or hyenas.
Counting sheep
Morris discounts the mutation hypotheses, which was favoured by the UK鈥檚 official inquiry into BSE, published last year. If a spontaneous mutation was to blame, 鈥測ou would expect BSE to have cropped up sporadically in the past in countries with much larger cattle populations,鈥� he told 快猫短视频 in November 2000.
The inquiry report rejected suggestions that changes to the way sheep are rendered allowed scrapie to cross to cattle and Morris agrees. Other countries have scrapie and similar rendering practices to Britain but none has had a native case of BSE, he points out.
However, Wilesmith favours the hypothesis. 鈥淭he factor that distinguishes Britain from lots of countries is that we have a large sheep population. Our ratio of sheep to cattle is uniquely high. A scrapie-like agent seems the most likely explanation,鈥� he says.
Pressure cooker
One legacy of the BSE epidemic is the difficult task of destroying the infectious prions from BSE-infected carcasses, but a Scottish company believes they have now found a way.
Prions resist standard sterilisation but Waste Reduction Europe has adapted a US technique, which involves pressure-cooking carcasses with sodium hydroxide to 1,500掳C.
This destroys the prions and converts the carcasses into an aqueous solution that can be safely disposed of in a sewer, the company says.