Individual Factors Associated with L- and H-Type BSE in France

L-type (L-BSE) and H-type (H-BSE) atypical Bovine Spongiform Encephalopathy (BSE) were identified in 2003 in Italy and France, respectively, before being identified in other countries worldwide, according to Carole Sala of ANSES and co-authors there and at INRA-Theix, both in Lyon, France.

In a paper to be published in BMC Veterinary Research, the researchers explain that around 60 atypical BSE cases have currently been reported in 13 countries, with over one–third in France. While the epidemiology of classical BSE (C-BSE) has been widely described, atypical BSEs are still poorly documented but appear to differ from C-BSE.

The Lyon-based group analysed the epidemiological characteristics of the 12 cases of L-BSE and 11 cases of H-BSE detected in France from January 2001 to late 2009 and looked for individual risk factors. As L-BSE cases did not appear homogeneously distributed throughout the country, two complementary methods were used: spatial analysis and regression modelling. L-BSE and H-BSE were studied separately as both the biochemical properties of their pathological prion protein and their features differ in animal models.

The median age at detection for L-BSE and H-BSE cases was 12.4 years (range: 8.4–18.7) and 12.5 years (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, which is 7.0 years (range: 3.5–15.4) years).

A significant geographical cluster was detected for L-BSE. Among animals over eight years old, the risk to be detected as a L-BSE case increased with age at death. This was not the case for H-BSE.

This is the first time that a study has addressed the epidemiology of the two types of atypical BSE, according to Sala and co-authors. The geographical cluster detected for L-BSE could be partly due to the age structure of the background-tested bovine population.

They concluded that the model, adjusted for the 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 revealed.

The small number of cases of atypical BSE included in the study and the few individual data available limited the analysis to the investigation of age and cohort effect only. In this context, it appears essential to maintain the surveillance of BSE to consolidate our initial findings and improve knowledge of these diseases, concluded Sala and co-authors.

Reference

Sala C., E. Morignat, N. Oussaid, E. Gay, D. Abrial, C. Ducrot and D. Calavas. 2012. Individual factors associated with L– and H–type Bovine Spongiform Encephalopathy in France. BMC Veterinary Research, 8:74. doi:10.1186/1746-6148-8-74