Tokyo

Japan is considering a tough new rule to prevent the spread of new-variant Creutzfeldt–Jakob disease (vCJD), the human equivalent of mad cow disease.

If the rule passes when an advisory committee addresses it again in a few months' time, it would ban anyone who spent even a single day in Britain or France between 1980 and 1996 from giving blood. This would further tighten current restrictions, which bar people who have spent more than one month in those countries, and is expected to hugely reduce the number of eligible donors.

Other countries have taken similar, if less cautious, measures. The United States, for example, does not allow people who have lived in Britain for several months to give blood. But Japan's new rule, proposed by an advisory committee to the ministry of health on 7 March, is the most stringent yet. “We are taking the safest possible measure until the risk is further determined,” says Daisaku Sato, deputy director of the ministry's blood and blood-products division.

The proposed change reflects fears that arose after ministry officials announced the first confirmed case of vCJD in Japan in early February: the man was thought to have been infected during a stay of less than a month in Britain around 1990. He began to show symptoms in 2001, and died in December last year.

About 160 people have died from vCJD around the world, mostly in Britain. Until now, most fatalities have occurred among people who had lived in the country for at least a few years. The disease is thought to be caused mainly by eating meat infected with rogue proteins called prions, but there have been at least two cases of probable infection from blood transfusions.

Government officials and scientists are keen to determine how many people are carrying the disease without symptoms, and what the chances are that such people may transmit the disease through transfusions or surgery. In Britain, steps have been taken to reduce the risk — such as removing white blood cells from transfusion products. British blood banks are also considering filtering blood for prions, or restricting donors to low-risk age groups. But these options are expensive and severely limit blood supplies.

The Japanese Red Cross Society estimates that the new rule would cost it hundreds of thousands of potential donors. “The damage would be significant,” says a spokesman.

And Masahito Yamada, a prion-disease specialist at Kanazawa University, says that the ministry's efforts may have a limited effect as Japan relies on imports for many blood products. This poses concerns that contaminated blood could still enter Japan. “It is really important to establish a safe global distribution system for blood products,” Yamada says.