Thousands may have CJD

Concern was growing today about a potential mad cow disease timebomb as experts warned thousands of Britons are unknowing carriers of the human form.

Specialists now warn that those people present a continuing risk of passing the disease to others through contaminated surgical instruments, blood transfusions or organ donation.

Fears of a possible vCJD epidemic had faded in recent years as new infections appeared to decline.

Today the scientific community warned of the "urgent" need to establish the true extent of the problem. The research, published in the Journal of Pathology, involved examining 12,674 stored appendix and tonsil samples and used three "bearing signs" to identify those infected.

Professor John Collinge, head of the Medical Research Council Prion Unit at St Mary's Hospital, Paddington, explained the research may have underestimated the number of vCJD carriers by analysing more appendix samples, which were much less sensitive to vCJD infection than tonsils.

He said: "In addition, no test is going to be 100 per cent effective and you don't know at what stage in the incubation period the test will be positive."

He added the Government should look again at the question of using disposable surgical instruments for operations which might involve a risk of vCJD transmission. "Some surgeons are very worried about it," he said.

Professor James Ironside, senior pathologist at the National CJD Surveillance Unit in Edinburgh, took part in the study.

"There would seem to be more positive than you would expect given the known number of vCJD cases and the fact that they seem to be declining.

"That may be because of genetic differences and susceptibility but it may also be that you can have a subclinical infection which never progresses to produce symptoms - a ' carrier state'. The findings do have to be taken seriously."

Professor Pat Troop, chief executive of the Health Protection Agency, is overseeing a vCJD screening project using 100,000 fresh tonsil samples. He hopes his research will provide " better estimates" of the number of people infected.