Thousands carrying hidden CJD timebomb

Concealed infection could be passed on by blood or surgery

May 21, 2004, Friday
The London Times
Nigel Hawkes, Health Editor

BRITAIN is facing a variant-CJD timebomb with research published today suggesting that thousands of people across the country unknowingly carry the killer disease.

In the largest study into potential effects of vCJD, scientists predict that up to 4,000 people may be infected by the agent responsible for the degenerative brain disease, which is the human form of mad cow disease.

Some may already be passing it on through blood transfusions and contaminated surgical instruments, so that the disease may continue to kill for decades. Last night experts gave warning that the government-funded study, published today in the Journal of Pathology, might even have underestimated the threat.

Pathologists who examined more than 12,500 specimens of tonsils and appendix removed in operations found evidence in three cases of the prion protein responsible for vCJD.

If that proportion is repeated across the country, about 3,800 people would be carrying the infective agent -far more than the 141 who have died of it so far.

The samples were anonymous, so it is impossible to identify the three who tested positive.

Most came from people aged between 20 and 29, the peak age for developing vCJD.

"I find these results very concerning," Professor John Collinge, head of the Medical Research Council Prion Unit at St Mary's Hospital, London, said. "Our experience is that looking at appendix samples will underestimate the true picture. In addition, no test is 100 per cent effective, and you don't know at what stage in the incubation period the test will be positive."

Professor James Ironside, senior pathologist at the National CJD Surveillance Unit in Edinburgh, who took part in the research, said: "There would seem to be more positives than you would expect. 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'.

"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."

When vCJD first appeared in 1996, estimates of the number who might be infected ranged as high as 500,000. But as the number of cases has risen only slowly, the projections have fallen to somewhere between a few hundred and a few thousand.

That people may be unwittingly carrying vCJD infection does not mean that they will get the disease. But even if it remains permanently in a sub-clinical state, there are alarming implications for surgery and blood transfusions.

Carriers might pass on the infectious prion to those who are more susceptible through contaminated instruments or blood. Alternatively, the ultimate toll may rise higher because only those most susceptible have so far developed full symptoms.

People with a particular genetic pattern are most susceptible to the disease and so far all the victims come from this group. But others may get it after a longer incubation period.

Dr David Hilton, of the Department of Histopatho-logy at Derriford Hospital, Plymouth, who led the study, said: "Our findings need to be interpreted with caution, but cannot be discounted. 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 Collinge said that he thought the Government should look again at using disposable surgical instruments for operations that might involve a risk of transmission. A recommendation for the use of such instruments introduced in England was withdrawn about two years ago because of safety fears.

The Department of Health said: "There is still much to learn about vCJD and this study is important for future research. The Department has put in place measures to reduce any risk of possible transmission of the disease via blood products and surgical instruments."