How to cite this article: Vet. Res. (2008) 39:15
DOI: 10.1051/vetres:2007053

Review

Review on the epidemiology and dynamics of BSE epidemics

Christian Ducrot¹, Mark Arnold², Aline de Koeijer³, Dagmar Heim⁴ and Didier Calavas<sup>5

1</sup>  INRA Unité d'Épidémiologie Animale, 63122 Saint-Genès-Champanelle, France
²  VLA Sutton Bonington, The Elms, College Road, Sutton Bonington, Loughborough, LE12 5RB, England
³  Division of Infectious Diseases, Animal Sciences Group, Wageningen, University and Research Center, PO Box 65, 8200 AB Lelystad, The Netherlands
⁴  Office vétérinaire fédéral, Schwarzenburgstrasse 155, Case Postale 3003, Bern, Suisse
⁵  AFSSA Lyon, Unité Épidémiologie, 31 avenue Tony Garnier, 69364 Lyon Cedex 07, France

Received 24 April 2007; accepted 23 October 2007 ; published online 11 January 2008

Abstract - The paper describes how the comprehensive surveillance of bovine spongiform encephalopathy (BSE) and studies carried out on these data has enhanced our knowledge of the epidemiology of BSE. Around 7 000 BSE cases were detected through the screening of about 50 million cattle with rapid tests in Europe. It confirmed that the clinical surveillance had a poor capacity to detect cases, and also showed the discrepancy of this passive surveillance efficiency between regions and production types (dairy/beef). Other risk factors for BSE were being in a dairy herd (three times more than beef), having a young age at first calving (for dairy cattle), being autumn-born (dairy and beef), and being in a herd with a very high milk yield. These findings focus the risk on the feeding regimen of calves/heifers. Several epidemiological studies across countries suggest that the feedborne source related to meat and bone meal (MBM) is the only substantiated route of infection — even after the feed ban —, while it is not possible to exclude maternal transmission or milk replacers as a source of some infections. In most European countries, the average age of the cases is increasing over time and the prevalence decreasing, which reflects the effectiveness of control measures. Consistent results on the trend of the epidemic were obtained using back-calculation modelling, the R₀ approach and Age-Period-Cohort models. Furthermore, active surveillance also resulted in the finding of atypical cases. These are distinct from previously found BSE and classified in two different forms based on biochemical characteristics; their prevalence is very low (36 cases up to 1st September 2007), affected animals were old and some of them displayed clinical signs. The origin and possibility of natural transmission is unknown.

Key words: BSE / epidemiology / modelling / review / control

Corresponding author: ducrot@clermont.inra.fr

© INRA, EDP Sciences 2008