This is Gwen Outen with the VOA Special English Health Report.

Blood transfusions can save lives. But they can also spread diseases. Researchers believe this is how at least two people in Britain became infected with the human version of mad cow disease. They say the cases appears to confirm that eating beef from an infected cow is not the only way the disease can spread.

The first case was reported at the end of last year; the second was reported earlier this month in the magazine The Lancet. The second patient had received a blood transfusion five years ago. The unidentified person was one of seventeen known to have received blood from people who later developed vCJD. The full name is variant Creutzfeldt-Jakob disease.

The disease attacks the brain and central nervous system. But in this patient, the infection had not spread to those areas. In fact, the report says the elderly person never developed signs of the disease. The patient died of unrelated causes. Tests later found the infection in the spleen.

Scientists say the finding suggests that a larger population of people could become infected. And here is why:

The human genetic map comes in different versions called genotypes. This patient had the most common genotype in the British population. 150 deaths from the human form of mad cow disease have been reported worldwide. But so far, there have been no such cases in people with this common genotype.

James Ironside is an investigator with the CJD Surveillance Unit in Edinburgh. He says infections might take longer to appear in people with this genotype.

The evidence also suggests that people without signs of the disease could still carry the infection. And they may be able to pass it to others.

In cows, the official name of the disease is bovine spongiform encephalopathy. Holes form in the brain. Researchers say the disease is caused by prions, proteins that are deformed and infectious. No cure is known. But French scientists reported in The Lancet that they have identified a new way to clean prions off of medical devices.

Also, American scientists reported on a method used in Britain to try to make blood safer for transfusion. White blood cells are removed to lower the risk of the human form of mad cow disease. But the researchers say animal tests found that the risk is reduced by only about forty percent.

This VOA Special English Health Report was written by Cynthia Kirk. This is Gwen Outen.