Key quote "One possibility is that the incubation periods are very, very long and so they may occur at a later date. The worst-case scenario is that these individuals could infect other people through blood donation or surgery and we could get into a situation where vCJD is self-sustaining." - Professor James Ironside, of the National CJD Surveillance Unit
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TENS of millions more Britons are at risk of contracting the human form of mad cow disease than originally thought, raising fears over the safety of blood products and surgery.
Scientists had believed that only 40 per cent of the population with a specific gene type were susceptible to vCJD, the human form of the cattle disease BSE. But they recently discovered that the disease can lie dormant for decades in other people.
The evidence could mean that rather than dying out, as had been hoped, vCJD may go on to be self-sustaining.
Campaigners said it raised the possibility of more families suffering the consequences of vCJD, believed to have been passed from cattle to humans through eating meat infected with BSE during the 1980s and 1990s.
So far, there have been 161 definite or probable cases of vCJD in the UK. All of these have occurred in people of the genotype known as MM, which is shared by 40 per cent of the population. It was hoped this was the only susceptible group.
But scientists went on to find a dormant infection in someone of the MV genotype, which makes up 50 per cent of people.
Now they have found two dormant cases in patients of the VV genotype, making up the other 10 per cent of the population. This means everyone is at risk of being a carrier of the infection.
Professor James Ironside, of the National CJD Surveillance Unit at Edinburgh University, said it was the "final piece in the genetic jigsaw".
"The question is why we have not seen any patients with this VV genotype in the past ten years. One possibility is that the incubation periods are very, very long and so they may occur at a later date.
"The worst-case scenario is that these individuals could infect other people through blood donation or surgery and we could get into a situation where vCJD is self-sustaining."
The researcher said the two samples they examined came from three which tested positive in a group of over 12,600 appendix and tonsil samples checked for the prion protein - a marker for vCJD infection.
"The main thing our study seems to indicate is that the cases of infection with BSE may be more widespread than is apparent from the clinical cases.
"While we don't want to be alarmist about this we need to do more work to understand if there is a significant problem with subclinical infection."
The microbiologist Professor Hugh Pennington said it was a case of waiting and seeing what happened and whether cases of vCJD would increase.
"We do not know whether people who are carrying the prions will actually fall ill.
"If you were going to get other genotype people falling ill you would think there would have been at least one come through by now," he said.
Stan Lowther, a member of the Human BSE Foundation, whose daughter died of vCJD in 1996, said it was "very depressing" to think that even more people could fall victim to vCJD.
"We have always thought that there is this possibility that there could be a second wave of people developing vCJD in 15, 20 or 30 years' time," he said.
Don Simms, a member of the CJD Alliance, said they had always expected the worst but hoped for the best when it came to future cases of vCJD.
Mr Simms' son Jonathan is believed to be the longest-lived survivor with vCJD. He was diagnosed in 2001.
The family from Belfast won a legal battle for him to receive an experimental treatment, pentosan polysulphate, which appears to have helped.
"We don't know enough about the disease, despite all the millions that have been spent on research."
Dr Marc Turner, clinical director of the Edinburgh Blood Transfusion Division, said they had been mindful of the possibility of more people harbouring vCJD for some time.
But he said several measures had already been taken to reduce the risks to the blood supply.
Two-year decline and then wife died, aged just 29
MALCOLM Tibbert watched helplessly as his wife, Margaret, succumbed to vCJD at the age of just 29.
She was one of the first to fall victim to the human form of mad cow disease.
Her husband, from Eaglesham, near Glasgow, was left to explain to their eight-year-old son what had happened.
Mrs Tibbert's condition deteriorated rapidly and, after spending three months in the Prince and Princess of Wales Hospice in Glasgow, she died in 1996 - almost two years after she fell ill.
At the end of her illness, she suffered severe pneumonia, dementia and was unable to swallow.
Mr Tibbert has since helped set up the Human BSE Foundation to campaign for greater awareness of the condition.