Abstract
BackgroundSo-called atypical scrapie was first identified in Great Britain (GB) in 2002 following the introduction of wide-scale scrapie surveillance. In particular, abattoir and fallen stock surveys have been carried out in GB since 2002, with a total of 147 atypical positives identified by the end of 2006. The results of these surveys provide data with which to assess temporal trends in the prevalence of atypical scrapie in sheep in Great Britain between 2002 and 2006.ResultsUsing the results of abattoir and fallen stock surveys, the prevalence of atypical scrapie (percentage of samples positive) was estimated. The prevalence in the abattoir and fallen stock surveys, for all years combined, was 0.09% (95% confidence interval (CI): 0.08%–0.11%) and 0.07% (95% CI: 0.05%–0.11%), respectively. There were no significant temporal trends in either survey. Comparing the surveys' results, there were no significant differences in annual prevalence or the prevalence within PrP genotypes. For the abattoir survey, the PrP genotype with the highest prevalence was AHQ/AHQ, which was significantly higher than all other genotypes, except ARR/AHQ, AHQ/ARH and ARH/ARQ.ConclusionThe estimated prevalence of atypical scrapie was similar in both the abattoir and fallen stock surveys. Our results indicate there was no significant temporal trend in prevalence, adding to evidence that this atypical form of scrapie may be a sporadic condition or, if it is infectious, that the force of infection is very low.
Highlights
-called atypical scrapie was first identified in Great Britain (GB) in 2002 following the introduction of wide-scale scrapie surveillance
SFuigrvueriella1nce data on atypical scrapie in Great Britain (GB) Surveillance data on atypical scrapie in Great Britain (GB). (a) Number of animals tested within the abattoir surveys by year and diagnostic test. (b) PrP genotype distribution of samples which were positive for atypical scrapie each year in the abattoir surveys. (c) Number of animals found dead on farm tested between 2003 and 2006. (d) PrP genotype distribution of samples which were positive for atypical scrapie each year in the fallen stock surveys
Within this research we investigated temporal trends in the occurrence of atypical scrapie using the results of the abattoir and fallen stock surveys, initially examining the overall prevalence, but stratifying by sampling year and the three main codons (136, 154 and 171) on the PrP gene associated with classical scrapie
Summary
-called atypical scrapie was first identified in Great Britain (GB) in 2002 following the introduction of wide-scale scrapie surveillance. Abattoir and fallen stock surveys have been carried out in GB since 2002, with a total of 147 atypical positives identified by the end of 2006 The results of these surveys provide data with which to assess temporal trends in the prevalence of atypical scrapie in sheep in Great Britain between 2002 and 2006. Following the introduction of wide scale scrapie surveillance throughout the European Union in 2002, a number of anomalous positive results were identified in abattoir surveys in several countries [1,2,3,4]. (b) PrP genotype distribution of samples which were positive for atypical scrapie each year in the abattoir surveys. (d) PrP genotype distribution of samples which were positive for atypical scrapie each year in the fallen stock surveys. A further polymorphism at codon 141 (substitution of leucine (L) to phenylalanine (F), in the ARQ haplotype) has been linked with increased susceptibility to atypical disease [15,16,17,18]
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