In spite of the emergence of populations of drug-resistant cyathostomines worldwide, little is known of parasite species responsible for ‘early egg shedding’ in cohorts of horses subjected to treatment with widely used anthelmintics, e.g. ivermectin (IVM). In this study, we determined the cyathostomine egg reappearance period (ERP) after IVM treatment in a cohort of yearlings from a large Thoroughbred (TB) stud farm in the United Kingdom, and identified species of cyathostomines with reduced ERP using a combination of fundamental parasitology techniques coupled with advanced molecular tools. Individual faecal samples were collected from TB yearlings with cyathostomine infection prior to IVM treatment, as well as at 14, 21, 28, 35, 42 and 49 days post-treatment. Faecal egg counts (FEC) were performed for each individual sample for determination of ERPs. In addition, individual larval cultures were performed and representative numbers of third-stage larvae (L3s) harvested from each culture were subjected to molecular species identification via PCR-Reverse Line Blot (RLB). Prior to IVM treatment, 11 cyathostomine species were detected in faecal samples from TB horses enrolled in this study, i.e. Cyathostomum catinatum, Cylicostephanus longibursatus, Cylicostephanus goldi, Cylicocyclus nassatus, Cylicostephanus calicatus, Cyathostomum pateratum, Cylicocyclus radiatus, Paraposteriostomum mettami, Coronocyclus labratus, Cylicocyclus insigne and Cylicocyclus radiatus variant A. Of these, eggs of Cya. catinatum, Cys. longibursatus, Cyc. nassatus and Cyc. radiatus could be detected at 28 days post-treatment, while from day 42 onwards, cyathostomine species composition reflected data obtained pre-IVM treatment, with the exception of eggs of Cor. labratus and Cyc. insigne which could no longer be detected post-IVM administration. This study provides valuable data on the occurrence of IVM-resistance in cyathostomines in the UK. Nevertheless, further investigations are needed to shed light on the prevalence and incidence of drug-resistance in this country, as well as other areas of the world where equine trade is substantial.
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.
Abstract A plethora of data points towards a role of the gastrointestinal (GI) microbiota of neonatal and young vertebrates in supporting the development and regulation of the host immune system. However, knowledge of the impact that infections by GI helminths exert on the developing microbiota of juvenile hosts is, thus far, limited. This study investigates, for the first time, the associations between acute infections by GI helminths and the faecal microbial and metabolic profiles of a cohort of equine youngstock, prior to and following treatment with parasiticides (ivermectin). We observed that high versus low parasite burdens (measured via parasite egg counts in faecal samples) were associated with specific compositional alterations of the developing microbiome; in particular, the faecal microbiota of animals with heavy worm infection burdens was characterised by lower microbial richness, and alterations to the relative abundances of bacterial taxa with immune-modulatory functions. Amino acids and glucose were increased in faecal samples from the same cohort, which indicated the likely occurrence of intestinal malabsorption. These data support the hypothesis that GI helminth infections in young livestock are associated with significant alterations to the GI microbiota, which may impact on both metabolism and development of acquired immunity. This knowledge will direct future studies aimed to identify the long-term impact of infection-induced alterations of the GI microbiota in young livestock.
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