The human form of mad cow disease (BSE) may eventually kill thousands of people, but is unlikely to become an epidemic, researchers have said.

Professor Liam Donaldson, chief medical officer for England, has admitted that nobody knows how many people will fall victim to variant Creutzfeldt-Jakob disease (vCJD).

He has also refused to rule out the possibility that hundreds of thousands of people could be infected with the disease after eating beef products infected with BSE.

However, New Scientist magazine reports that the latest figures suggest that the final death toll is likely to be on the scale of thousands rather than millions.

Researchers at the Wellcome Trust Centre for the Epidemiology of Infectious Disease in Oxford have worked with statistics on how many infected cows were slaughtered, how much infected material entered the food chain and the course of the cattle epidemic.

From this, they have produced a model describing the likely course of Britain's vCJD epidemic.

Using figures on the number of cases in 1999 and 2000, they have predicted the maximum size of the epidemic.

Death rate vital

If 15 people or fewer died from vCJD in 1999, the model predicts that any epidemic will reach a maximum of half a million cases in total.

If there is no increase and a similar number die in 2000, then it predicts that any epidemic will peak at a total of 14,000 cases or fewer.

So far, nine deaths from vCJD have been confirmed for 1999, according to the national CJD Surveillance Unit in Edinburgh.

It is still too early to put a final figure on the year's toll, but the current figure is less than that reported for 1998 at this stage last year. In January 1999, 12 deaths had been confirmed for 1998, a figure that eventually rose to 17.

Christl Donnelly, a statistician on the team, said: "It's good news that we haven't seen so many cases so far.

"1999 may be a bit of a turning point."

The model assumes that only a certain proportion of the population is susceptible to vCJD.

All the known vCJD victims had two copies of a particular variant of the gene for a protein called PrP.

This trait is shared by about 40% of the British population.

However, it could be that other people are also susceptible, but will take longer to display symptoms.

A Department of Health spokesman said: "We are encouraged by the fact that vCJD is not yet an epidemic, but we do not know how many people it is going to effect, and we would be cautious about predicting a final figure."