Authors

Discussion

Parasitic gastroenteritis (PGE) is the primary production limiting disease of lambs in the UK, estimated to cost the industry £84 million pounds per annum. The primary pathogen in the UK is Teladorsagia circumcincta, an abomasal nematode which has rapidly developed resistance to the anthelmintics used in its treatment and control. The most commonly used anthelmintic is ivermectin, and once significant ivermectin resistance develops on a holding, future sheep production may no longer be economically viable. The long-term aim of this project is to find markers of ivermectin resistance in T. circumcincta isolated from UK farms, using genome-wide approaches. Firstly, in order to characterise and phenotype the parasite population on farm, faecal egg counts, resistance bioassays and speciation PCRs were performed throughout the season, culminating in a faecal egg count reduction test (FECRT) using three groups of lambs treated with a benzimidazole, levamisole or ivermectin. Next, pyrosequencing at the β-tubulin isotype-1 locus was undertaken to correlate the benzimidazole resistance phenotype from the egg hatch assay and FECRT, with the benzimidazole resistance genotype and assess the influence of counter selection with ivermectin. Data gathered from these assays show the complexity of species present on a farm and demonstrates that the strongyle species composition has a significant impact on both the ‘resistance’ status of the parasite population and the clinical relevance of this. As such, the importance of speciating a strongyle faecal egg count cannot be ignored in clinical practice when diagnosing PGE and/or anthelmintic resistance.