British health officials are breathing a sigh of relief — for now. Initial results from a survey to assess the extent of infection with the human form of bovine spongiform encephalopathy (BSE) have drawn a blank.

Organ survey: the appendix, at the bottom of this false-colour X-ray, provides a test for vCJD. Credit: LUNAGRAFIX/SPL

Analyses of more than 3,000 clinical samples, mostly of appendixes removed from patients in the late 1990s, have failed to reveal any signs of the prion protein responsible for new variant Creutzfeldt–Jakob disease (vCJD). Just a handful of positive results would have suggested an epidemic of tens, or even hundreds, of thousands of cases.

But it's a case of no news rather than good news. A sizeable epidemic cannot be ruled out on the basis of these results alone. Technical limitations of the survey, plus uncertainty about the progression of vCJD in infected people, make it difficult to make predictions.

Researchers at the National CJD Surveillance Unit in Edinburgh and Derriford Hospital in Plymouth are analysing some 18,000 appendix and tonsil samples, using immunohistochemical methods to test for prions. They hope to gauge the extent of vCJD infection in the British population. But while previous research on tissues from vCJD victims has shown that the prion accumulates in appendixes and tonsils, no one knows how early in the course of infection it appears.

Leszek Borysiewicz of the University of Wales College of Medicine in Cardiff, who chairs the scientific committee overseeing the studies, stresses the limitations of the study. “This sample size is small,” he says. The tissue was also preserved with fixative chemicals that could make traces of prion hard to spot.

John Collinge of Imperial College, London, is now conducting a study of some 2,000 freshly collected tonsil samples, and will use a western blot test to detect the vCJD prion. This may yield better information. But by the time these results are available, researchers led by Roy Anderson at the Wellcome Trust Centre for the Epidemiology of Infectious Disease in Oxford claim they may already have defined an upper limit for the eventual size of the vCJD epidemic.

In January, the team published a paper in Proceedings of the Royal Society B (267, 23; 2000) predicting that, if the rate at which new cases of vCJD appear remains at its current level until the end of this year, then the upper limit for the epidemic would be 14,000 cases. So far, at least, there are no signs of an increase in the rate of new cases.