Case‐control study on the use of pituitary‐derived hormones from sheep as a potential risk factor for the occurrence of atypical scrapie in Great Britain

Abstract

A case-control study was conducted in 2013 to investigate the use of pituitary-derived hormones from sheep as a potential risk factor for the presence of atypical scrapie in Great Britain sheep holdings. One hundred and sixty-five holdings were identified as cases. Two equal sets of controls were selected: no case of scrapie and cases of classical scrapie. A total of 495 holdings were selected for the questionnaire survey, 201 responses were received and 190 (38.3 per cent) were suitable for analysis. The variables 'use-of-heat-synchronisation/superovulation' and 'flock size' were significantly associated with the occurrence of atypical scrapie. Farms with atypical cases were less likely (OR 0.25, 95 per cent CI 0.07 to 0.89) to implement heat synchronisation/superovulation in the flock than the control group. Atypical cases were 3.3 times (95 per cent CI 1.38 to 8.13) more likely to occur in large holdings (>879 sheep) than in small flocks (<164 sheep). If the 'use-of-heat-synchronisation/superovulation' is a proxy for the use of pituitary-derived hormones, the significant negative association between having a case of atypical scrapie and the use of these practices rules out the initial hypothesis that using these drugs is a risk factor for the occurrence of atypical scrapie. Flock size was a significant risk factor for atypical scrapie, consistent with a previous generic case-control study.

Scientific report on the analysis of the 2‐year compulsory intensified monitoring of atypical scrapie

“…Three independent variables were associated with an increase in the odds of AS: the presence on the farm of two sheep breeds (Welsh Mountain and Cheviot) and flock type (store/fattening flocks) (Del Rio Vilas et al., 2010 ). Farms with AS cases were less likely to implement oestrus synchronisation/superovulation and cases were more likely to occur in large holdings (Marier et al., 2017 ).…”

Do we need to explain the occurrence of atypical scrapie?

“…In a paper summarised on p 403 of this issue, Marier and colleagues (2017) report the results of a case‐control study comparing 62 sheep case holdings that experienced at least one atypical scrapie affected animal between 2002 and 2012 with 128 control holdings either negative for or experiencing classical scrapie. Based on the characteristics of atypical scrapie, the authors wisely have addressed the iatrogenic hypothesis.…”