Individual factors associated with L- and H-type Bovine Spongiform Encephalopathy in France

The median age at detection for L-BSE and H-BSE cases was 12.4 (range 8.4-18.7) and 12.5 (8.3-18.2) years respectively, with no significant difference between the two distributions. However, this median age differed significantly from that of classical BSE (7.0 (range 3.5-15.4) years). A significant geographical cluster was detected for L-BSE. Among animals over eight years of age, we showed that the risk of being detected as a L-BSE case increased with age at death. This was not the case for H-BSE.To the best of our knowledge this is the first study to describe the epidemiology of the two types of atypical BSE. The geographical cluster detected for L-BSE could be partly due to the age structure of the background-tested bovine population. Our regression analyses, which adjusted for the effect of age and birth cohort showed an age effect for L-BSE and the descriptive analysis showed a particular age structure in the area where the cluster was detected. No birth cohort effect was evident. The relatively small number of cases of atypical BSE and the few individual data available for the tested population limited our analysis to the investigation of age and cohort effect only. We conclude that it is essential to maintain BSE surveillance to further elucidate our findings.Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative prion disease of cattle. The disease was first identified in the United Kingdom in 1986 before spreading to most European countries. Since epidemiological studies demonstrated the role of contaminated meat and bone meal (MBM), animal feed was considered the main source of BSE infection in cattle. The implementation of control measures that led in 2001 to a total ban on the use of MBM in animal feed allowed the BSE epidemic in Europe to be controlled [1]. However, the origin of the BSE agent remains uncertain: could it be due to a spontaneous sporadic bovine disease recycled into MBM or an adaptation of another transmissible spongiform e