Origins of BSE traced to herds of the African plains

Mad cow disease may have originally been brought to Britain in a shipment of infected animal remains from Africa, according to a growing body of scientific evidence.

Though this contradicts the Government's line, stringently maintained for the past decade, that the disease originated in diseased British sheep which were recycled into cattle feed, it fits a wealth of data which was not available when the diagnosis was first made in 1985.

If correct, it means that many precautions now being taken at great expense by the Government - for example, destroying sheep offal - are unnecessary, because scrapie would not pose a risk to humans or cattle. It also has implications for imports of foodstuffs from foreign countries where unusual diseases may occur, and precautions needed to stop their spread.

But John Wilesmith, the government scientist who in 1987 pinpointed infected cattle feed as the means by which BSE was spreading, said last night: "I think as events have gone on, the scrapie hypothesis still bears the test of time." He added that he was worried that any concentration on alternative sources of the epidemic could distract from introducing controls on recycling animal offal in Europe. "If they aren't, there could be more cases [of BSE]," he said.

Key in the new evidence is a written Parliamentary answer given by the Government yesterday, showing that between 1970 and 1980 the UK imported thousands of tonnes of meat and bone meal from various African countries, including South Africa, south western Africa and Botswana - which has a significant cattle industry. The imports effectively stopped afterwards.

Previously, scientists have shown that many African game animals such as cheetah, kudu, nyala, gemsbok, eland and oryx can catch BSE - increasing the chance that it originated among them. Some wild animals like elk and deer develop BSE-like diseases spontaneously, but it has never been observed in cattle before the epidemic, which began in 1985.

The new hypothesis will not alter predictions for the final number of people who may die from the "new variant" of the fatal brain disorder Creutzfeldt-Jakob Disease (CJD), which has so far affected 19 people. They almost certainly got it by eating BSE-infected cattle products.

Other evidence not available when scrapie, the equivalent in sheep of BSE, was blamed for the epidemic, also points to an origin outside this country.

Previously, the takeoff of BSE in 1985 was blamed partly on deregulation by the incoming Thatcher government in 1979 of the rendering industry (which strips useful elements from cattle and sheep carcasses).

It was claimed that rule changes allowed lower cooking temperatures, which did not destroy the BSE disease agent. That was then fed back to cattle as infected bone meal. But subsequent investigation has shown that rendering practices were unchanged from the late 1960s. Dr Wilesmith agreed: "Rendering hadn't changed - that's rubbish."

Thus the system to "amplify" BSE by recycling dead, infected carcasses was in place throughout the 1970s. Yet scrapie-infected sheep were entering the rendering system. If scrapie were the cause of the BSE epidemic, it could have started in the 1970s or early 1980s.

Other research shows that scrapie has a different molecular "fingerprint" from BSE. And separate studies have shown that cows inoculated with scrapie die of a disease like BSE - but which on detailed examination differs significantly.

Diseases that emerged from the Dark Continent

If BSE really does have its origins in Africa, then it joins a long list of dangerous disease to have emerged from the "dark continent". Among the best known is HIV, the Human Immunodeficiency Virus, which causes Aids. It is widely believed to have been passed to humans by a mutation from SIV, the Simian Immunodeficiency Virus, which is found among monkeys in the central African jungles.

Green monkey disease, or Marburg disease, was identified among workers with monkeys in laboratories, but traced back to their African source. Similarly, Lassa fever, Rift Valley fever and Congo Haemorrhagic Fever all originate in Africa. While such exotic diseases can have horrifying effects, they all - with one exception - are self-limiting. Any infectious disease that kills its host rapidly will fail to spread, because the victims will not survive long enough to transmit it.

HIV is the exception, because it takes so long to destroy the body's defences that it can be passed on and infect another person while the original host is still alive. But epidemic science suggests that the combination of evolutionary pressure and advancing medical science will eventually tame even this killer from the jungle.