Effect of infection with, and treatment of, sensitive and resistant strains of teladorsagia circumcincta on the ovine intestinal microbiota

Nematodes are one of the main impactors on health, welfare and productivity of farmed animals. Teladorsagia circumcincta is arguably one of the most globally important nematode species in sheep. Control of these nematode infections is essential and heavily reliant on chemotherapy (anthelmintics), but this has been complicated by the development of anthelmintic resistance. In mammals the composition of the intestinal microbiota has been shown to have a significant effect on overall health. The interactions between host, microbiota and pathogens are complex and influenced by numerous factors. In this study, the interactions between T. circumcincta infections and microbial composition and abundance were investigated. In a preliminary study the intra-and inter-individual diversity and composition of the microbiota of grazing sheep was assessed in two distinct regions of the ovine intestinal tract, the terminal ileum (TI) and rectal contents. Additionally, the effects of experimental infection of sheep with two strains of T. circumcincta (anthelmintic resistant or sensitive) on the microbiota were assessed with and without anthelmintic (monepantel) administration. The inter-animal variability was greater in the TI compared to the rectal samples. However, the alpha-diversity (species richness) was significantly lower in the TI samples. In the experimental study, clear differences were observed between successfully treated animals and those sheep that were left untreated and/or those carrying resistant nematodes. Differences in microbiota between the four different experimental conditions were observed and potential predictive biomarkers were identified. In particular, a restoration of potentially beneficial Bifidobacteria sp. in successfully-treated animals was observed.