A new filter could reduce the likelihood of transmitting vCJD, the human equivalent of “mad cow” disease, in donated blood.

At least three people have already been infected by blood donations in Britain and an unknown number of donors could be incubating the disease without realising it. So a method of ensuring the safety of blood is urgently needed.

The answer, say a team writing in The Lancet, is a filter they have made that can remove enough of the prions respons-ible for vCJD from blood to ensure that it is no longer infectious.

In experiments using prions from scrapie, a related disease in sheep, they have shown that the filter can achieve this. When blood infected with scrapie was filtered and transfused into hamsters, the animals did not develop the disease.

Experiments have also shown that the filters can absorb prions from brain material taken from vCJD victims.

The filter consists of columns of resins containing a chemical that binds strongly to prions. Blood flowing through the columns emerges with the prions removed, so that it is no longer infective.

Peter Edwardson, of Pro- Metic BioSciences Ltd, one of the authors of the paper, said that filters are a better option than tests for blood infectivity. “Tests are never 100 per cent accurate,” he said.

The filter is the result of co-operation between ProMetic, based in Cambridge, the American National Red Cross and MacoPharma, an international supplier of blood filters.