A case-control study of atypical scrapie in GB sheep flocks

Wide-scale scrapie surveillance started in 2002 in the EU. As a result, a new form of scrapie was detected which has been referred to as atypical scrapie. Here we present a case-control study conducted on British sheep farms to increase our understanding of the disease and potential risk factors at holding level. Forty case and 120 control holdings were traced from the confirmed atypical results in the scrapie surveillance programme in Great Britain during the period 2002-2007. A detailed questionnaire was completed by interview to record data on holding-specific management variables. A combination of generalized additive, generalized linear and Bayesian models returned 3 variables clearly associated with an increase in the odds of atypical scrapie: presence of two sheep breeds (Welsh Mountain and Cheviot) and flock type (store/fattening flocks). A fourth variable, the number of visits by veterinarians to the holding exerted a protective effect. Various other variables were significantly associated with the outcome, but at a somewhat lower level of confidence; for example, the size of the holding and the presence on the farm of concentrates intended for animals other than sheep.