Impact of Removing the Monitoring Requirements for Holdings with Atypical Scrapie in Great Britain

Atypical scrapie (AS) is a transmissible spongiform encephalopathy (TSE) that affects sheep and goats. Low within-flock incidence suggests that AS is not transmissible between animals, and testing of all animals that exit positive flocks for two years following detection (i.e., intensified monitoring) used to be carried out in the EU to provide data to test this. This intensified monitoring stopped in 2021 but continues in Great Britain (GB). The aim of this study was to predict the number of AS cases missed if this monitoring were also stopped in GB, using a combination of statistical and transmission modelling. The number of AS cases estimated to be missed if the intensified monitoring was stopped was low relative to the number of AS cases detected in other active surveillance streams (e.g., fallen stock and abattoir surveys), at approximately 1 case every 3 years (0.34 per year, 95% CI: 0.18-0.54) compared to 10 per year (95% CI: 4-17) in the active surveillance stream. This suggests that stopping the intensive monitoring of AS would have relatively little impact on AS surveillance and on the power of the available AS data to infer whether AS is contagious.