[The bovine spongiform encephalopathy in the UK and France: an epidemiological perspective]

Epidemiology is aimed at the study of the health status of human and animal populations. The present review shows how epidemiologists in the UK and France, contributed to a better knowledge of the bovine spongiform encephalopathy (BSE), its probable origin, and its associated risk factors. Following case studies and case-control surveys, the role of meat and bone meal (MBM) as the source of infection for cattle has been well established. Other epidemiological studies have shown the absence of horizontal transmission, but on the other hand a cohort study concluded to a possible vertical transmission. Backcalculation models, which intend to infer the characteristics of infection from the observations, agree on two results : first, the BSE infects young animals, under 2 years. Secondly, the peak of the French BSE epizootic, probably in the nineteen-eighties, was ignored. Successive measures concerningMBMfailed to completely abolish the epizootic. The analysis of born-after-the-ban (BAB) cases shows that their spatial distribution in France is not random, which argues against a sporadic origin. The French BAB cases may result from two nonexclusive events : residual contaminations of cattle by feed intended for pigs and poultry, and mother-to-calf prion transmission, likely at a low rate. If a total eradication of BSE is not obtained, it will be the task of epidemiologists in particular, to figure out the source of the residual infection.