Infection with the sheep gastrointestinal nematode Teladorsagia circumcincta increases luminal pathobionts

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Abstract Background The multifaceted interactions between gastrointestinal (GI) helminth parasites, vertebrate host gut microbiota and the immune system are emerging as a key area of research within the field of host-parasite relationships. In spite of the plethora of data available on the impact that GI helminths exert on the composition of the gut microflora, whether alterations of microbial profiles are caused by direct parasite-bacteria interactions or, indirectly, by alterations of the GI environment (e.g. mucosal immunity), remains to be determined. Furthermore, no data is thus far available on the downstream roles that qualitative and quantitative changes in gut microbial composition play in the overall pathophysiology of parasite infection and disease. Results In this study, we investigated the fluctuations in microbiota composition and local immune microenvironment of sheep vaccinated against, and experimentally infected with, the ‘brown stomach worm’ Teladorsagia circumcincta, a parasite of worldwide socio-economic significance. We compared gut microbial profiles with those obtained from groups of unvaccinated/infected and unvaccinated/uninfected animals. We show that alterations to the gut microbial composition are associated mainly with parasite infection, and that this involves the expansion of populations of bacteria with known pro-inflammatory roles that may contribute to the immunopathology of helminth disease. Using novel quantitative approaches for the analysis of confocal microscopy-derived images we also show that gastric tissue infiltration of T cells is driven by parasitic infection rather than anti-helminth vaccination. Conclusions Teladorsagia circumcincta infection leads to an expansion of potentially pro-inflammatory gut microbial species and abomasal T cells. This data paves the way for future experiments aimed at determining the contribution of the gut flora to the pathophysiology of parasitic disease, with the ultimate aim to design and develop novel treatment/control strategies focused on preventing and/or restricting bacterial-mediated inflammation upon infection by gastrointestinal helminths.

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