The prevalence of atypical scrapie in sheep from positive flocks is not higher than in the general sheep population in 11 European countries
1 AFSSA-Lyon, Unité Epidémiologie, 31 Avenue Tony Garnier, 69364 Lyon, France
2 INRA Clermont-Theix, Unité épidémiologie animale, F63122 Saint Genès Champanelle, France
3 Italian Reference Centre for Animal TSEs-Istituto Zooprofilattico Sperimentale del Piemonte, Liguria e Valle d'Aosta, Italy
4 Department of Disease Control and Epidemiology, SVA, National Veterinary Institute, 751 89 Uppsala, Sweden
5 Institute for Experimental Pathology, University of Iceland, Keldur v/Vesturlandsveg, IS-112 Reykjavík, Iceland
6 Sector de diagnóstico de EETs, Laboratório de Patologia - Unidade de Sanidade Animal, Laboratório Nacional de Investigação Veterinária, INRB, I.P., Estrada de Benfica 701, 1549-011 Lisboa, Portugal
7 AFSCA, DG Politique de Contrôle, Bd du Jardin Botanique, 55, 1000 Bruxelles, Belgium
8 Veterinary Virology, Finnish Food Safety Authority, 00790 Helsinki, Finland
9 DAFF Administration Building, Backweston Campus, Stacumney Lane, Young's Cross, Celbridge, Co. Kildare, Ireland
10 Section of epidemiology, National Veterinary Institute, PO Box 750 Sentrum, 0106 Oslo, Norway
BMC Veterinary Research 2010, 6:9 doi:10.1186/1746-6148-6-9Published: 7 February 2010
During the last decade, active surveillance for transmissible spongiform encephalopathies in small ruminants has been intensive in Europe. In many countries this has led to the detection of cases of atypical scrapie which, unlike classical scrapie, might not be contagious. EU legislation requires, that following detection of a scrapie case, control measures including further testing take place in affected flocks, including the culling of genotype susceptible to classical scrapie. This might result in the detection of additional cases. The aim of this study was to investigate the occurrence of additional cases in flocks affected by atypical scrapie using surveillance data collected in Europe in order to ascertain whether atypical scrapie, is contagious.
Questionnaires were used to collect, at national level, the results of active surveillance and testing associated with flock outbreaks in 12 European countries. The mean prevalence of atypical scrapie was 5.5 (5.0-6.0) cases per ten thousand in abattoir surveillance and 8.1 (7.3-9.0) cases per ten thousand in fallen stock. By using meta-analysis, on 11 out of the 12 countries, we found that the probability of detecting additional cases of atypical scrapie in positive flocks was similar to the probability observed in animals slaughtered for human consumption (odds ratio, OR = 1.07, CI95%: 0.70-1.63) or among fallen stock (OR = 0.78, CI95%: 0.51-1.2). In contrast, when comparing the two scrapie types, the probability of detecting additional cases in classical scrapie positive flocks was significantly higher than the probability of detecting additional cases in atypical scrapie positive flocks (OR = 32.4, CI95%: 20.7-50.7).
These results suggest that atypical scrapie is not contagious or has a very low transmissibility under natural conditions compared with classical scrapie. Furthermore this study stressed the importance of standardised data collection to make good use of the analyses undertaken by European countries in their efforts to control atypical and classical scrapie.