Sheep Scab: Assessing the Use of Commercial Diagnostic Data to Enhance Surveillance

Sheep scab is an economically damaging ectoparasitic disease caused by the Psoroptes ovis mite that poses a significant welfare concern for the sheep population in Great Britain (GB). Though sheep scab is endemic, resistance to common treatments has emphasised the importance of timely control. In 2017 a new diagnostic ELISA test for sheep scab was commercialised in GB. Different to the current clinical diagnosis via skin scraping, the sheep scab ELISA reliably detects infestation at the subclinical stage, limiting spread and economic loss. This study collated and analysed data from the sheep scab ELISA since commercialisation to examine its current use, identify risk factors for infestation, and to consider its value as a complementary source of surveillance data. As expected, the number of submissions increased substantially over time, with the highest number received in the last month of the study period (August 2019). The data consistently showed seasonal patterns, with the highest number of submissions in autumn and winter. While spatial analysis showed wide-spread uptake across England and Wales, fewer submissions originated from Scotland, potentially due to its notifiable status in Scotland. The recommended 12-sample submissions for estimation of serostatus at flock level were those most frequently submitted. Interestingly, the majority of submissions originated from itchy sheep, showing the test is also widely used to diagnose sheep with clinical signs. Among the risk factors, double fencing displayed a significant negative association to a positive serostatus submission.