Authors

L E Peachey¹; R A Molena¹; T P Jenkins¹; C Cantacessi¹;  ¹ University of Cambridge, UK

Discussion

Increasing evidence supports the occurrence a myriad of interactions between gastrointestinal (GI) helminths and the host gut commensal flora, with likely implications on host local and systemic immunity and metabolic potential. However, thus far, whether parasite-associated changes in the composition of the host gut microbiota are depending on the infection status (acute versus chronic) remains unclear. A better understanding of these mechanisms is nonetheless crucial, particularly in livestock species, as this knowledge will represent the basis for the development of novel parasite control methods based on the manipulation of the host gut flora. Therefore, in this study, we assessed the impact of acute and chronic infections by an important group of equine GI helminths (i.e. the cyathostomins) on the faecal microbiota of two cohorts of Thoroughbred (TB) horses from the same stud farm prior to and following treatment with a commonly used anthelmintic (i.e. ivermectin). The first cohort was composed of young-stock (between 12-16 months of age, ‘acute group’), whereas the second cohort was composed of broodmares (between 4 and 18 years of age, ‘chronic group’). Individual faecal samples were collected from all study animals at day 0 and ivermectin was administered immediately after sample collection. Sampling was repeated 2 and 14 days post-anthelmintic treatment. High-throughput sequencing of microbial 16S rRNA amplicons and subsequent bioinformatics and statistical analyses revealed global changes of the faecal microbiota that could be correlated with burden of infection (as estimated by faecal egg counts) in both yearlings and broodmares. For instance, higher infection burdens were associated with reduced microbial alpha diversity in yearlings, whilst the opposite was observed in broodmares. In addition, in yearlings, cyathostomin infection was associated with significant alterations of the relative abundance of major bacterial phyla with roles in carbohydrate and protein metabolism and GI inflammation. Conversely, in broodmares, helminth infection was associated with the expansion of lower level taxa with roles in methane metabolism and fibre digestion. The changes described above were reversed by anthelmintic treatment in the yearlings, but not in the broodmares. Observations from this study support the hypothesis that cyathostomin infection may be associated with dysbiosis in young animals with little acquired immunity to infection. The implications of this acquired knowledge on future studies aimed at reducing the pathology associated with cyathostomin infection via the manipulation of the gut microbiota will be discussed.