A study of sheep scab in Northern Ireland including detection and identifying barriers to control

Sheep scab, caused by the highly infectious Psoroptes ovis mite, is considered to be endemic in Northern Ireland, although little investigation has been reported. A pilot project was undertaken to engage farmers, confirm cases with diagnostic methods and identify specific barriers to control, with the aim of informing future control programmes.

Through farmers self-reporting suspected outbreaks, on-farm risk assessments and clinical investigations were carried out by the farm's veterinary surgeon, who utilised light microscopy and serological testing to diagnose scab. Treatment was then provided and where macrocyclic lactones (MLs) were utilised, follow-up testing was attempted.

Sheep scab was identified in 60 flocks across all six counties of Northern Ireland. Serological testing proved essential in uncovering scab infestation where light microscopy failed to identify mites, or where no suitable lesions existed to scrape. Where MLs were used, follow-up was incomplete. Furthermore, four of six resampled flocks still showed a positive result. Barriers to better scab control included poor quarantine arrangements and preventative treatment strategies that ultimately proved ineffective.

The project demonstrated that farmers were willing to engage in control efforts, they appreciated the support provided in managing outbreaks and they recognised the need for a coordinated effort to control scab. Greater awareness of biosecurity is needed among farmers. Facilitation of farmer-driven scab control activities is urgently needed, alongside greater understanding of the scale of the disease and the impact that ML treatment failure can have on scab dissemination through the national Northern Ireland flock.