Investigating the Epidemiology of Haemonchus contortus, Using Traditional Faecal Diagnostics Supported by Deep-Amplicon Sequencing, in an Outbreak of Haemonchosis in a Scottish Pedigree Sheep Flock.

This case report describes an investigation of an outbreak of haemonchosis in a Scottish pedigree sheep flock. The case occurred in a small lowland flock of pedigree Spotted Dutch sheep (n = 16) grazing pasture previously grazed by alpacas and horses. In 2024, despite routine anthelmintic treatments, clinical signs in the sheep led to suspicions and subsequent confirmation of acute haemonchosis. As part of clinical investigations, traditional faecal parasitology was combined with species identification using peanut agglutinin staining of GIN eggs and ITS-2 deep-amplicon genomic sequencing of first-stage larvae. Using these techniques, Haemonchus contortus was identified as the predominant GIN, and FAMACHA scoring was used to assess the level of anaemia for targeted selective treatment of affected animals. Additionally, ITS-2 deep-amplicon genomic sequencing described the GIN species profile of different animal management groups to further understand H. contortus epidemiology and inform control practices against future outbreaks. This case highlights the benefits of combining traditional faecal egg count diagnostics with GIN species identification techniques to better understand H. contortus epidemiology, thereby promoting sustainable control practices against haemonchosis.