Thousands May Have Human Form of Mad Cow Disease

May 21, 2004

LONDON (AFP) - Some 3,800 people in Britain could be harbouring the human form of mad cow disease without knowing it, government-funded research suggests.

Scientists who examined 12,674 stored appendix and tonsil samples said they had identified three bearing signs of the agent that causes variant Creutzfeldt-Jakob disease (vCJD).

Applying their findings to the entire population of the United Kingdom, which is 60 million, they estimated that about 3,800 people would test positive for the illness.

Some 141 people are known to have died in Britain from vCJD, a spongy deterioration of the brain causing personality change, loss of body function, and eventually death.

Scientists think the findings -- which at first sight appeared to be at odds with declining rates of vCJD -- might indicate that people can carry the disease without developing symptoms.

They would still be able to spread the disease to others, however, via contaminated surgical instruments, blood transfusions or organ donation.

"Our findings need to be interpreted with caution, but cannot be discounted," said David Hilton, of Derriford Hospital in Plymouth, southern England, who led the study published in the Journal of Pathology.

Fears for the safety of British beef emerged in 1986 when mad cow disease, or bovine spongiform encephalopathy, was first discovered in a cow on a farm in West Sussex.

It was only 10 years later, however, that the government announced that a probable link had been established between BSE and vCJD.

The latest research involved examining thousands of appendix and tonsil samples removed during routine operations and stored at hospitals. Most were from people aged 20 to 29, the peak age for developing vCJD.

The scientists looked for accumulations of the abnormal prion protein molecules believed to trigger both BSE and vCJD.

One positive appendix sample was the subject of much publicity when preliminary results from the study were released in 2002.

The two others, also from appendix operations, show an unusual pattern of prion accumulation unlike that seen in known vCJD cases.

But the scientists have carried out tests which appear to discount the possibility that they are "false positives".

Despite a slight jump last year, the numbers of vCJD cases have appeared to be on the decline. But experts cannot be sure more will not emerge in the future as the disease reaches the end of its incubation period in people with different genetic make-ups.

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 given the known number of vCJD cases and the fact that they seem to be declining."

"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'."

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

A Department of Health spokesman said: "There is still much to learn about vCJD and this study is important for future research."

"The results reinforce the need for a continued precautionary approach to minimise people's exposure to BSE and vCJD. The Department of Health has already put in place measures to reduce any risk of possible transmission of the disease via blood products and surgical instruments."

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