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Friday, 20 September, 2002, 06:29 GMT 07:29 UK
'Fewer than feared' at risk of vCJD
Prions under microscope
Prions can be spotted in tonsil tissue
Fewer people than once feared may be incubating vCJD in Britain - but the toll could still run into several thousands, say experts.

The latest prediction - based on tests on tonsil and appendix tissue taken out in the 1990s, suggested that approximately 7,000 people could be at high risk of developing vCJD.

Now the government plans an even wider programme of tests, setting up a national tissue archive for scientists to examine.


Ultimately, we need a blood test for CJD - but none is available at the moments

Professor Peter Smith, SEAC

However, scientists say the prediction - in the British Medical Journal - is still not completely reliable, and the final outcome could be a much greater, or smaller epidemic. Large sections of the population were undoubtedly exposed to the contaminated beef thought to cause vCJD during the 1980s and 1990s.

However, scientists have found it difficult to predict with any accuracy how many people will fall ill, mainly because they do not know how long the disease "incubates" in the body before symptoms emerge.

To try to improve predictions, researchers from Derriford Hospital and the CJD Surveillance Centre in Edinburgh examined more than 8,300 tissue samples taken during routine operations between 1995 and 1999.

Contaminated meat

Although some were taken from young children unlikely ever to have been exposed to contaminated meat, many were from much older patients who could be harbouring "prions" - thought by most scientists to be the cause of vCJD.

Tonsils, and to a lesser extent appendices, are part of the lymphatic system and probably the places where prions are most likely to accumulate.

So people with high levels of prions in these tissues are thought to be at higher risk of developing vCJD.


We need larger scale studies particularly of tissue from recently removed tonsils so that we can obtain a more reliable picture of the possible numbers of people who may develop vCJD

Dr David Hilton, Derriford Hospital
When doctors look at tonsils and appendix tissue from patients who have actually got, or died from vCJD, most have high numbers of prions within them.

However, out of the thousands of samples taken from apparently "healthy" patients, only one showed signs of prion accumulation.

If this rate was the same for the entire population, it would mean that for every million people, 120 would have this higher risk.

This would mean a total of 7,000 or so at risk of the disease, a far lower estimate than some of the "worst case scenarios" published by scientists.

Larger-scale testing

However, the authors of the research suggest that larger-scale testing is needed to form any sort of reliable prediction.

Dr David Hilton, a consultant neuropathologist, told the BBC's Today programme: "We do not know a lot about the reliability of the test.

"There is quite a large margin for error.

"We need larger scale studies involving tens of thousands of samples particularly of tissue from recently removed tonsils so that we can obtain a more reliable picture of the possible numbers of people who may develop vCJD."

Peter Smith
Professor Peter Smith: "More research needed"
This is likely to happen after Sir Liam Donaldson, England's chief medical officer, announced on Friday that a new "archive of tonsils" would be created.

He said: "The archive will allow prospective studies to be done on the largest possible number of tonsils so that we can get better estimates of the size of the vCJD epidemic."

Professor Peter Smith, the chairman of the Spongiform Encephalopathy Advisory Committee (SEAC) - which helps set government policy on vCJD - said that while the study provided some reassurance, a larger epidemic was still possible.

He said: "These tests offer a potential way of assessing how many people there might be incubating vCJD.

"Larger surveys involving more tissue samples would be useful.

"Ultimately, we need a blood test for CJD - but none is available at the moments."

See also:

19 Sep 02 | Europe
27 Feb 02 | England
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