A NOBEL prize-winning scientist says the entire British population should be tested for variant CJD, the human form of mad cow disease, amid fears that the number of cases may be greater than previously feared.

Professor Stan Prusiner, who discovered the cause of BSE, said the impact of the epidemic could be bigger than so far recognised. CJD has killed 117 people in Britain since 1995 and another 11 are known to be dying from the disease. Some experts suggest the death toll could reach more than 100,000.

“A million cattle infected with BSE entered the British food chain so almost everyone in the country will have been exposed to the infectious prion proteins that cause variant CJD,” said Prusiner. “Every Briton should be tested so that if they are developing the disease it can be spotted before symptoms appear.”

There is no cure for any form of CJD although some therapies are undergoing early trials. Tests would help prevent people who are incubating the disease from infecting others through surgical instruments, blood donations or other procedures. Instruments contaminated with CJD cannot be sterilised because the prions are resistant to high temperatures and chemicals.

Prusiner, a professor at the University of California, San Francisco, awarded the Nobel prize for medicine in 1997, was in Britain to discuss research into the disease. He warned that thousands of cows and sheep infected with BSE and related diseases were still being sold for human consumption because they were being killed before they developed symptoms. “The government should be testing every cow and sheep entering the food chain,” he said. “Nobody should be being exposed to prions in any way.”

Last week research by scientists at University College London indicated that the number of CJD cases caused by eating BSE-infected meat might be greater than previously thought. Researchers found evidence that BSE, in addition to causing variant CJD, may also be responsible for some cases of “sporadic” CJD, a strain of the disease that tends to affect older people. Since 1990, 588 cases of sporadic CJD have been reported in Britain.

Prusiner’s comments come as scientists at the government’s Veterinary Laboratories Agency are evaluating five potential tests for prion disease. So far the only validated tests need brain or spine tissue only available after death. At least two of the new tests have been shown to work with blood, so samples could be taken from living animals or people. Once the new tests are validated, possibly next year, they would allow mass screenings of livestock and people.

A national testing scheme could have political consequences. Multi-million-pound compensation claims might be launched by people told they are incubating the disease.

Scientists have found it hard to predict the scale of any epidemic. The number of variant CJD cases remains relatively small but prion diseases can lay hidden for up to 40 years.

Despite widespread public belief that BSE has been eradicated from British livestock, about 800 cows have been diagnosed with the disease this year. Studies have also shown that infected sheep and cattle have prions in their blood for years before they show signs that they are ill.

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