Scientists double estimate of BSE-infected cattle

Scientists have doubled their estimates for the number of British cattle infected with BSE during the epidemic in the Nineties.

A team at Imperial College London reported that nearly two million animals had been infected with bovine spongiform encephalopathy since the late 1980s. The previous estimate had been about 1.05 million animals.

But Christl Donnelly, an epidemiologist who worked on the study, said the higher total was unlikely to increase the number of cases of the fatal variant Creutzfeldt-Jakob disease (vCJD)– the human form of BSE – because the chance of infection from an individual animal was lower than scientists had thought. "You can't say there is zero risk, but it is certainly far lower than it has been for 20 years," she said.

More than 100 people have died since 1995 of vCJD and the latest estimates suggest the total will grow slowly over the next 20 to 40 years.

Fears that blood donations from people who are infected with vCJD but not showing symptoms could spread the disease more widely are, however, taken seriously.

A new screening system is being developed, which could distinguish infected blood by detecting subtle chemical differences from normal samples. The system, being developed in Germany, would use a computer-controlled analysis of infected and healthy samples of blood to determine whether the infectious "prions" are present. It has already been tested successfully on blood from hamsters infected with scrapie, a disease closely related to BSE.

Fears of spreading vCJD through blood transfusions have led the Government to remove white blood cells from all donated blood, while the United States has stopped accepting donations from anyone who has been in Britain.

New Scientist magazine reports today that the new screening system being developed by a team led by Dieter Naumann at the Robert Koch Institute in Berlin hopes to develop computer systems called "neural nets" which could perform high-speed analyses of blood samples to test for vCJD.