CJD blood fears heightened

Blood supplies are already treated to reduce any risk

Scientists have found the strongest evidence yet that blood transfusions could transmit the brain disease new variant CJD.

Their research also shows that blood taken before the disease itself emerges could still harbour the infection.

A sheep infected with the brain disease BSE passed on the disease to another sheep through a blood transfusion.

But the experts involved say that blood stocks in the UK are already treated to reduce the risk - and that the benefits of transfusions are likely to far outweigh any risks.

The single case was reported in the medical journal The Lancet and involved a sheep given BSE-infected cattle brain to eat.

When the sheep's blood was transfused into another sheep, the second animal fell ill with a BSE-like disease - even though the first had yet to display any symptoms.

Professor Chris Bostock, director of the Institute for Animal Health in Edinburgh, which helped carry out the research, said that the experiments in sheep were the closest possible to human tests.

Infection precautions

"In scientific terms, we don't normally send out a report on a single case - but we feel it's very significant," he told BBC News Online.

The institute's study was done in sheep

"It suggests there is a risk from blood transfusion in the human population."

But he added: "The benefits of having a blood transfusion will greatly outweigh any risks."

While scientists have long acknowledged a theoretical risk of humans with undiagnosed vCJD passing on the infection through blood transfusions, no cases have actually been recorded.

Despite this, the National Blood Service already takes precautions to minimise any chance of infection.

It filters out some of the components of blood which experts believe are most likely to transmit the infection.

Statisticians are still having great difficulty predicting how many people will eventually fall ill with vCJD.

White cells removed

If large numbers are still incubating the disease without symptoms, the potential risk of blood transfusion transmission would be higher.

In an accompanying commentary to the research, US expert Paul Brown said that there was little more that the UK authorities could do.

"No further measures would seem possible - short of a draconian decision to shut down the whole UK blood donor system," he said.

A government spokesman said: "The research points out that whole blood is not used for human blood transfusions in the UK.

"White cells are now removed from blood for transfusion (leucodepletion) and all blood products used in the UK are made from plasma imported from countries where there is no evidence of vCJD."