New evidence of BSE-CJD link

Scientists have produced the most compelling evidence yet that mad cow disease can affect humans.

Scientists have produced the most compelling evidence yet that mad cow disease can affect humans.

Experiments with mice showed that the cattle disease Bovine Spongiform Encephalopathy and new variant CJD are almost certainly caused by the same infectious agent.

The scientists said last night the findings increased concern that "a large section of the United Kingdom population may be at considerable risk".

Most experts think the sudden appearance of new variant Creutzfeldt Jakob Disease in 1996 - a new form of the human brain disease with distinct characteristics - was the result of people eating BSE-infected beef.

It is thought that both diseases are caused by rogue "prion" proteins that may have jumped the species barrier into humans.

However the hypothesis has never been conclusively proved, and since the scare began scientists have sought hard evidence to back the theory.

Today researchers at the University of California in San Francisco and the National CJD Surveillance Unit at Western General Hospital, Edinburgh, reported findings that firmly establish a link between BSE and nvCJD.

The scientists, led by Michael Scott at the University of California and Dr Robert Will at the CJD Surveillance Centre, conducted experiments with mice genetically engineered to produce the same prions naturally found in cows.

They discovered, not unexpectedly, that there was no "species barrier" between the mice and cows. Diseased brain tissue injected into the mice produced symptoms in 250 days, the same incubation period experienced by cattle with BSE. A second group of mice given prions from the first group became sick in virtually the same period of time.

The big surprise came when human brain tissue infected with the prions that cause new variant CJD was injected into the mice.

Again there was no apparent sign of a species barrier. New variant CJD had the same incubation period in the mice as BSE, and produced an identical pattern of brain damage.

The results, reported in the journal Proceedings of the National Academy of Sciences, suggest that BSE and nvCJD are interchangeable. Introduced into transgenic mice, nvCJD prions assumed an identity "indistinguishable from BSE prions".

The scientists wrote: "That human nvCJD prions so precisely duplicate the properties of native bovine BSE prions in their behaviour on transmission into Tg(BoPrP)Prnp (transgenic) mice creates a compelling argument for an etiological link between BSE and nvCJD.

"Although earlier proposals of an etiological link between BSE and nvCJD were disquieting, the investigations reported here raise greater concern that a large section of the United Kingdom population may be at considerable risk."

The mice were also highly susceptible to infection with the sheep prion disease scrapie, although this produced a different biological pattern.

Scientists suspect BSE may have originated in cattle as a result of feeding them sheep remains infected with scrapie.

In the report the researchers suggest that transgenic "bovine prion" mice could be used to check the potential of scrapie to produce BSE in cattle.