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Friday, 26 October, 2001, 01:35 GMT 02:35 UK
vCJD 'epidemic' might be waning
Beefburger, BBC
Exposure to BSE-infected beef may lead to vCJD
By BBC News science correspondent Pallab Ghosh

The total number of cases of vCJD in the UK caused by eating BSE-infected beef could be far fewer than previously thought, says a new study.

A research team from the London School of Hygiene and Tropical Medicine say their estimates show that the total numbers likely to die from vCJD may be no more than a few thousand - rather than the tens of thousands currently predicted.

Scientists are using models to try to forecast the development of vCJD in the UK population - but they concede there are still many unknown factors that make an accurate projection of future spread very difficult to achieve.

So far, just over 100 people in Britain are thought to have died from the variant form of the disease.

Thousands of victims

The best guess until now of an eventual death toll, by researchers at Imperial College in London, has been that as many as 100,000 could fall victim to the disease.

However, new research, published in the journal Science by a rival group, estimates the eventual number of deaths is likely to number only a few thousand at most.

Researchers at the London School of Hygiene have used a statistical method known as back calculation, which looks at how a disease is developing and then projects forward.

They point out that the number of cases of vCJD has risen very slowly year on year, and the total number of deaths is still relatively low.

The team believe that this pattern can best be explained if the incubation period - the time it takes for the symptoms of the disease to show - is very long.

Less consumption

In this case, those who may be infected are likely to die of other causes before symptoms show.

They suggest that an alternative explanation for the disease pattern is that relatively few people ate BSE-infected meat.

The Imperial team stand by their much higher estimates, saying that their rivals have underestimated the amount of BSE-infected meat to which the UK population was exposed.

However, both groups agree that any predictions are far from certain.

Both say there should be no relaxation in policy in protecting against the risk of cross-contamination through some surgical procedures and blood transfusions.

Nor should there be a let-up in efforts to find treatments for the disease.

Incubation periods

Professor Peter Smith, chairman of the government's advisory body on BSE, Seac, said: "When the disease was first recognised, there were fears there may be tens or hundreds of thousands of cases, or even more.

"As the epidemic has gone on there have not been the numbers of cases that might have occurred, and looking at their pattern so far, we think it is unlikely that the eventual size of the epidemic will be more than a few thousand.

"We cannot completely rule out larger epidemics, but they seem to us at this stage to be unlikely."

However, Professor John Collinge, head of the National Prion Clinic at St Mary's Hospital in London, said there were flaws in the new study.

He said there was likely to be a series of peaks in the number of cases of the disease over an extended period of time.

This was because vCJD had been linked to a series of different genes that made people susceptible to the disease.

Incubation periods may vary depending on the specific gene combination of each individual.

 WATCH/LISTEN
 ON THIS STORY
The BBC's Pallab Ghosh
"Scientists simply don't know enough about the disease"
Government advisor on BSE/CJD, Prof Neil Ferguson
"This study is a little over optimistic"
See also:

20 Oct 00 | Health
CJD - will there be an epidemic?
13 Sep 01 | Health
CJD warning 'misguided'
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