September 20, 2002 Press Association by Julie Wheldon and Tim Moynihan
Figures suggesting that more than 7,000 people in Britain could be at
increased risk of the human form of BSE may be an
under-representation of the infection, it was warned today.
Scientists have estimated that 120 people per million could be at increased risk of developing variant Creutzfeldt-Jakob Disease (vCJD).
Based on the UK population of just under 60 million, this could mean 7,200 people are at increased risk of vCJD. But the director of the National CJD Surveillance Unit warned that the tests might be an under-representation of infection.
Professor James Ironside told the BBC2 Newsnight programme last night that the tests used were not sensitive enough to pick up all positives for human BSE.
He said: "Because of the nature of the specimens used in the study we have had to employ a technique that is not as sensitive as other methods that are currently available so in some ways even this finding might be an under-representation of the actuality in terms of infection with BSE."
And Professor John Collinge of the Institute of Neurology in London told the programme that he believed if the research had been done on tonsils using the latest techniques there could be four times as many positives.
The research, published in the British Medical Journal, is the first estimate of the number of people who could have pre-clinical vCJD.
Experts say the disease is almost certainly caused by the Bovine Spongiform Encephalopathy (BSE) agent.
The study, led by David Hilton of Plymouth's Derriford Hospital, was looking for the accumulation of prion protein, a known reliable marker of the disease in animals.
The researchers studied 8,318 samples from appendix and tonsil removal operations between 1995 and 1999.
They also looked at tissue removed during postmortems or surgery from patients later confirmed as having vCJD.
Of the samples removed in tonsil and appendix operations, they found prion protein in one of them.
Among specimens taken from patients who had vCJD but had not yet displayed any symptoms, two out of the three studied tested positive for prion protein.
For the samples removed during postmortems of people with vCJD who had died, the figure was positive for 19 of the 20 studied.
Based on the one positive case per 8,318 samples, the researchers estimate that 120 people per million could have a detectable accumulation of prion protein, though the margin of error for this estimated figure is high.
Dr Hilton said each time such an estimate was made the margin of error increased.
"Jumping to any conclusions on the basis of our findings would be dangerous," he warned.
"The margin of error is high and also we don't know if being positive will lead to the disease."
Large scale prospective screening was needed, he added.
The study is funded by the Department of Health and has another year to run.
Chief Medical Officer Sir Liam Donaldson announced plans yesterday to set up a new archive of tonsils so more research could be conducted.
The archive will be anonymous, which means individual patients will not be identified from their tissue samples.