vCJD - predicting the future?

The recent emergence of variant Creutzfeldt-Jakob disease (vCJD) in the UK, and demonstration that vCJD is caused by the same prion strain that causes bovine spongiform encephalopathy, have led to concerns about the possibili ty of a human epidemic. Although only 79 cases of vCJD have occurred to dat e, it is likely that hundreds of thousands of infected cattle entered the h uman food chain in the late 1980s and early 1990s, and the average incubati on period of vCJD is unknown. Mathematical models have not yet been able to give useful predictions of future numbers of cases, and in the absence of a blood test for vCJD, current attempts to reduce uncertainties about futur e numbers of cases are based on the accumulation of PrPSc in lymphoreticula r tissues. Extensive lymphoreticular PrPSc accumulation has been seen in al l cases of symptomatic vCJD so far examined, and in one case 8 months prior to the onset of symptoms. Animal models of prion disease suggest that lymp horeticular involvement occurs early in the incubation period and reliably predicts future neurological disease. Based on these data, large scale anon ymous studies looking for PrP accumulation in surgically removed tonsillect omy and appendicectomy specimens are underway. Examination of the first 300 0 specimens has not revealed any positive samples, but at the moment the si gnificance of negative findings is uncertain. It is anticipated that by the time these studies are complete more data will be available on how early P rP can be demonstrated in lymphoreticular tissue in vCJD, which together wi th the results from examination of further samples, will allow some comment as to the likelihood of a large human vCJD epidemic.