BSE meat may be riskier to humans than first thought

New research suggesting that the risk of catching variant CJD from the meat of infected cattle and sheep may be higher than previously believed is to be examined by government scientific experts.

Professor Stanley Prusiner, the American scientist who first discovered prions, the proteins suspected of causing the fatal brain illness, has disclosed that mice infected with scrapie have been found to have unexpectedly high levels of prions in their muscles.

Professor Prusiner said this raised the "obvious worry" that cows and sheep could be similarly affected. Scrapie is a brain disease of sheep similar to BSE, which causes vCJD in humans.

The Department of Health said yesterday that all new research into vCJD and BSE was assessed by its committees of experts, principally the Spongiform Encephalopathy Advisory Committee. "We would ask them to assess the validity of any new findings, including tests, before we decide how we ought to respond to them," a spokeswoman said.

Until now, levels of prions in infected cow and sheep meat and muscle tissue were always believed to be low enough to make them safe. Dangerous levels are only normally found in the brain and spinal cords of animals.

However, the new tests being pioneered at the University of California in San Francisco are far more sensitive and have discovered higher concentrations than have previously been found. While describing the findings as significant, Professor Prusiner has stressed that the levels are still a hundredfold less than those found in brains. But as the scientist who received the Nobel prize for his discovery of prions, Professor Prusiner's work will be treated with considerable respect.

There is no clear scientific evidence yet that, however high the prion level is, the meat and muscle tissue is likely to infect consumers. Others tests where different types of infected animal body parts are injected into rats have shown that while brain and spinal cord does cause the animals to develop vCJD, meat and muscle tissue does not.

Professor Prusiner also called for testing of everyone in Britain to establish the true extent of the disease, which has killed 117 people since 1995. Some estimates have put the eventual death toll at 100,000. He also argued for testing of all cows and sheep entering the food chain, since many were being slaughtered before they showed any symptoms.

Currently, the only accurate tests for vCJD are on brain and spinal tissue and can only be made after death. Scientists are working on blood tests to enable mass screening, but these are still some way from being confirmed for use.

The Government would tread carefully before launching a mass screening programme. Although resolving the uncertainty at the heart of the vCJD controversy would help health service planning, it would cause alarm among those found to be incubating a disease that can take up to 40 years to develop and could lead to compensation claims. Tests would help to prevent those with the disease from infecting others through surgical instruments or blood donations.