EIGHT months ago, the village of Queniborough and its surroundings in Leicestershire gained dubious distinction as Britain's hot spot for variant Creuzfeldt-Jakob disease (vCJD), a fatal neurodegenerative condition related to bovine spongiform encephalopathy (BSE)—better known as mad-cow disease. Out of 95 cases of vCJD reported in Britain since 1995 (see chart) five occurred there.
This clustering of cases has proved a boon to epidemiologists trying to come to grips with the elusive origin and spread of vCJD. On March 21st, a team of government experts announced what it believes may lie at the heart of the Leicestershire vCJD outbreak: consumption of meat contaminated with BSE-infected brain tissue.
That may be no great surprise, but according to Gerry Bryant, one of the investigators, this is the first clear demonstration of an association between vCJD and BSE through diet. The authorities were able to rule out blood transfusions, vaccines and occupational exposure, as these were not shared by the five victims. They did find, however, that the victims had all bought meat from a handful of local butchers who either slaughtered cattle in their own back rooms or used small abattoirs nearby.
Unlike the large abattoirs employed by supermarkets, these operations practised “pithing”—ramming a rod through an animal's brain to squash the spinal cord. This rough and ready procedure (which has since been banned) allows bits of brain to leak out and contaminate other tissues.
Local slaughter houses also regularly removed the brains of beef cattle to sell to people who had acquired a taste for them, and then used the same knives for other butchery tasks—an obvious source of cross-contamination, albeit unwitting, since the butchers concerned could not have known the risks. The study has found that those with the disease were 15 times more likely to have bought and consumed beef from a butcher where such cross-contamination may have occurred than were those living in the same area who did not develop the disease.
The Leicestershire study also provides the first hard estimate of the incubation period of vCJD. The investigators reckon that between ten and 16 years passed between the victims' consumption of BSE-infected meat and the onset of their symptoms. As Robert Will, head of the National CJD Surveillance Unit in Edinburgh, points out, this number will help epidemiologists refine their estimates of the potential size of the epidemic. (These now range from hundreds to thousands of cases.)
The link between diet and vCJD will set alarms ringing across Britain. It will also worry people in the rest of Europe, which appears to be on the threshold of its own BSE epidemic. Already, three cases of vCJD have been reported in France. How many more will appear, and where, is hard to say. As Dr Will cautions, the Leicestershire findings are an important step forward in the study of vCJD, but they probably do not account for all the cases of the disease to date, given the other possible routes of exposure. When it comes to vCJD, researchers still have more questions than answers.