ONLY 70 more people are likely to die from the human form of mad cow disease from infected beef, according to the most comprehensive study of the condition to date.

Britain’s outbreak of variant Creutzfeldt-Jakob disease (vCJD) has probably peaked and the 147 deaths so far make up two thirds of the final toll, scientists said yesterday.

The findings dispel fears of a vCJD timebomb, which were raised last year when research suggested that up to 3,800 people might be infected with the incurable brain disorder.

A more precise analysis of these results indicates that only a small fraction of this number will contract the disease and die. The study has cut the estimated number of those carrying the rogue prion proteins that cause vCJD to 3,000, and calculates that just 70 will develop the full-blown condition.

The rest — about 93 per cent of the total infected with prions by eating beef — will remain carriers but stay healthy. They might, though, transmit the disease by giving blood.

Even under the worst outcome, no more than another 363 clinical cases of vCJD contracted from BSE-infected beef are likely. More people could still develop the disease through contaminated blood transfusions.

The estimates, by Paul Clarke and Azra Ghani of Imperial Colledge, London, add to a growing consensus among epidemiologists and doctors that the human impact of the BSE crisis will be much smaller than initially feared.

When vCJD first appeared in 1995, projections suggested that it might kill 500,000 people. The number of deaths has declined sharply from a peak of 28 in 2000 to just eight recorded last year. A further five patients are still alive.

This trend had led experts to predict that the ultimate total would be numbered in hundreds rather than thousands, but research at Derriford Hospital in Plymouth published last May triggered concern that this could be an underestimate.

The study of appendix and tonsil tissue from more than 12,500 people found signs of vCJD in three of them, which when extrapolated to the entire population suggested that there could be 3,800 carriers.

Dr Ghani, who was part of the team that made that estimate, said that the figure was a “rough back-of-the-envelope calculation”, and that the new work is a much better reflection of the likely shape of the disease’s spread.

In the study, published in the journal Proceedings of the Royal Society, the researchers sought to explain the discrepancy between the projections from the tissue samples and current death trends.

They found that the best explanation was that most people infected with prions would not develop the disease.

“The most plausible reason is that a very, very high proportion of those who are infected would not develop the disease,” Dr Ghani said. “We have seen this happen in animal studies, and it is the explanation that best fits the data.”

Asked whether she thought that the outbreak had peaked, she said: “I think that’s the case for consumption of beef. There is still uncertainty about secondary transmission via blood transfusions, though.”

Every clinical case of vCJD reported has occurred in people with particular genetic attributes, and there is concern that people with different DNA profiles could be susceptible after a longer incubation period.

The study considered this possibility, but found that even if true the total number of future cases is likely to be just 363. “If other genotypes are susceptible, it could potentially increase the clinical cases fivefold, but it is still not on the scale of the appendix survey,” Dr Ghani said.

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