The relationships between faecal egg counts and gut microbial composition in UK Thoroughbreds infected by cyathostomins

L.E Peachey,R.A Molena,T.P Jenkins,A Di Cesare,D Traversa,J.E Hodgkinson,C Cantacessi

doi:10.1016/j.ijpara.2017.11.003

Abstract

A growing body of evidence, particularly in humans and rodents, supports the existence of a complex network of interactions occurring between gastrointestinal (GI) helminth parasites and the gut commensal bacteria, with substantial effects on both host immunity and metabolic potential. However, little is known of the fundamental biology of such interactions in other animal species; nonetheless, given the considerable economic losses associated with GI parasites, particularly in livestock and equines, as well as the global threat of emerging anthelmintic resistance, further explorations of the complexities of host-helminth-microbiota interactions in these species are needed. This study characterises the composition of the equine gut commensal flora associated with the presence, in faecal samples, of low (Clow) and high (Chigh) numbers of eggs of an important group of GI parasites (i.e. the cyathostomins), prior to and following anthelmintic treatment. High-throughput sequencing of bacterial 16S rRNA amplicons and associated bioinformatics and statistical analyses of sequence data revealed strong clustering according to faecal egg counts (P = 0.003). A trend towards increased populations of Methanomicrobia (class) and Dehalobacterium (genus) was observed in Clow in comparison with Chigh. Anthelmintic treatment in Chigh was associated with a significant reduction of the bacterial Phylum TM7 14 days post-ivermectin administration, as well as a transient expansion of Adlercreutzia spp. at 2 days post-treatment. This study provides a first known insight into the discovery of the intimate mechanisms governing host-parasite-microbiota interactions in equines, and sets a basis for the development of novel, biology-based intervention strategies against equine GI helminths based on the manipulation of the commensal gut flora.

Highlights

Cyathostomins are amongst the most important intestinal nematodes of horses globally (Love et al, 1999; Matthews, 2011; Stratford et al, 2011) with reported prevalence rates as high as89–100% in equine herds (Mfitilodze and Hutchinson, 1990; Collobert-Laugier et al, 2002; Hinney et al, 2011; Morariu et al., 2016)
Control of cyathostomin infections has traditionally relied on the regular administration of chemotherapeutic drugs; the frequent and uncontrolled use of these compounds has led to the global emergence of resistant populations of parasites (Nielsen et al, 2014; Peregrine et al, 2014)
Of 117 broodmares examined for cyathostomin infection, 36 matched the criteria outlined in Section 2.2. and were enrolled in this study

Summary

Introduction

Cyathostomins are amongst the most important intestinal nematodes of horses globally (Love et al, 1999; Matthews, 2011; Stratford et al, 2011) with reported prevalence rates as high as89–100% in equine herds (Mfitilodze and Hutchinson, 1990; Collobert-Laugier et al, 2002; Hinney et al, 2011; Morariu et al., 2016). Control of cyathostomin infections has traditionally relied on the regular administration of chemotherapeutic drugs (i.e. anthelmintics); the frequent and uncontrolled use of these compounds has led to the global emergence of resistant populations of parasites (Nielsen et al, 2014; Peregrine et al, 2014). Foci of multi-drug resistance have been recently reported in TB stud farms in the United Kingdom (Relf et al, 2014). This observation, coupled with the lack of novel anthelmintic compounds licenced for use in equids, represents a ‘Damocle’s sword’ for the UK (and global) equine industry. Alternative strategies for parasite control are urgently needed; in order to support the discovery of such strategies, a deeper understanding of the complex interactions occurring at the host-parasite interface, at the site/s of infection (i.e. the gut), is required

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