Bovine spongiform encephalopathy and Creutzfeldt-Jakob disease: facts and uncertainties underlying the causal link between animal and human diseases.

Following an outbreak of bovine spongiform encephalopathy (BSE) in dairy cows in the United Kingdom (UK), 153 definite and probable human cases of new variant Creutzfeldt-Jakob disease (nvCJD) have been reported, almost exclusively in the UK. Although exposure to the BSE agent is the most plausible interpretation for the occurrence of nvCJD, the causal link between the BSE prion and nvCJD is still debated. This review discusses the pros and cons of nvCJD as a separate nosographic entity, the scientific basis for a correlation between BSE and nvCJD, the validity of the current diagnostic criteria for CJD and nvCJD, the contribution of epidemiology to the detection of a causal relation between BSE and nvCJD, and the present and future directions of the epidemiological research on BSE, CJD and nvCJD.