More people could be harbouring traces of vCJD than previously thought, according to new research.

A study of 12,674 appendix and tonsile samples by Plymouth's Derriford hospital and the CJD surveillance unit found that three showed signs of the disease.

Extrapolated across the whole population, it is now estimated that as many as 3,800 people could be "carriers".

"Our findings need to be interpreted with caution, but cannot be discounted," said lead researcher David Hilton.

"There is still much to learn about vCJD and presence of the protein in these tissue samples does not necessarily mean that those affected will go on to develop vCJD."

Professor James Ironside of the National CJD Surveillance Unit said patients may carry vCJD prions without showing any symptoms.

"That may be because of genetic differences and susceptibility, but it may also be that you can have a sub-clinical infection which never progresses to produce symptoms - a 'carrier' state'," he said.

"I think the findings do have to be taken seriously.

"Generally, one has to be cautious about interpreting these data, but they may indicate that there are people who are not infected in the normal way, but could represent a source of infection."

Transmission risk

The results have led to calls for the government to reconsider the use of disposable instruments in operations where there may be a risk of transmission.

However, a Department of Health spokesman said it had "already put in place measures to reduce any risk of possible transmission of the disease via blood products and surgical instruments".

It was announced in March that anyone who has had a blood transfusion since 1980 will be banned from becoming a blood donor, after a patient contracted CJD after receiving blood from a donor who later died from the condition.

A similar study in 2002 prompted ministers to establish a national tissue archive to allow researchers to continue testing.

It is hoped that 100,000 tonsile samples can be collected and tested on an anonymous basis, which head of the Health Protection Agency Professor Pat Troop hopes will give scientists a better indication of how many people are likely to be carrying vCJD.

But she added: "We must continue to take all the precautions that are there."