The Use of Molecular Profiling to Track Equine Reinfection Rates of Cyathostomin Species Following Anthelmintic Administration

Abstract

Cyathostomins are a multispecies parasite ubiquitous in Equids. Cyathostomins have developed resistance to all but one class of anthelmintics, but species-level sensitivity to anthelmintics has not been shown. This study measured reinfection rates of cyathostomin species following the administration of three commercial dewormers. Nine treated horses were compared with 90 untreated controls during June-September 2017–2019. Ivermectin (IVM) (n = 6), Moxidectin (MOX) (n = 8) or Pyrantel (PYR) (n = 8) were orally administered. Fecal samples were collected every 14 d for 98 d. Fecal egg count reductions (FECR) were calculated using a modified McMaster technique. Nineteen cyathostomin species were identified by 5.8S-ITS-2 profiling using amplicon sequencing. Data were analyzed in QIIME1 and R statistical software using presence/absence methods. MOX had the lowest numbers of species present over the time course, followed by PYR then IVM (7.14, 10.17, 11.09, respectively); however, FECR was fastest for PYR. The presence of seven species: Coronocyclus labiatus, Cyathostomum catinatum, Cyathostomum tetracanthum, Cylicocylus elongatus, Cylicodontophorus bicoronatus, Cylicostephanus minutus, and Cylicostephanus goldi were unaffected by treatment (p > 0.05) points to species-specific differences in dewormer sensitivity and environmental persistence. Identifying resistance patterns at the species level will enable mechanistic understandings of cyathostomin anthelmintic resistance and targeted approaches to control them.

A national survey of anthelmintic resistance in ascarid and strongylid nematodes in Australian Thoroughbred horses

“…Recently, a high-throughput next-generation sequencing (NGS) tool, targeting the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA and a partial mitochondrial cytochrome c oxidase subunit I (COI), has been developed to determine the species composition of nematodes in horse faecal samples and/or parasite material ( Mitchell et al, 2019 ; Poissant et al, 2021 ; Courtot et al, 2023 ). While such approaches have been used in few initial studies ( Johnson and Biddle, 2021 ; Nielsen et al, 2022b ; Sargison et al, 2022 ; Abbas et al, 2023b ), additional improvements have been suggested for both markers. However, the DNA pool extracted from strongylid eggs can be reliably used for metabarcoding and bioinformatics analyses ( Courtot et al, 2023 ).…”

Moringa oleifera as a Natural Alternative for the Control of Gastrointestinal Parasites in Equines: A Review

“…In horses, gastrointestinal parasitism is often associated with poverty in developing countries [23], but this is not the only factor influencing parasite incidence. In general, all equines are at risk of gastrointestinal parasitism [24], even from the first hours of life, due to a weak immune system [25,26], although animals that are under grazing conditions are more susceptible [27] since pastures can provide adequate conditions for the development of parasite larvae that are expelled by animals through feces [28], so these animals tend to have higher infection rates [26].…”

“…Four possible mechanisms by which equine parasites increase their resistance to anthelmintics have been identified: (i) activation of pre-existing alleles for resistance to toxic compounds, (ii) spontaneous mutations before or at the time of anthelmintic exposure, (iii) frequent mutations for the reappearance of alleles that provide resistance, and (iv) host migration of resistant alleles spread through new populations [12,26,77,78]. However, it is not ruled out that anthelmintic resistance may be the result of the selection of a parasite subpopulation that is capable of resisting the toxicity of drugs that were previously lethal to it and that this subpopulation selects specific genes that allow it to survive, which are believed to mutate and are responsible for the development of resistance [79].…”

Patterns of Equine Small Strongyle Species Infection after Ivermectin Intervention in Thailand: Egg Reappearance Period and Nemabiome Metabarcoding Approach

“…Cyathostomins encompass a remarkably large number of species co-infecting equine hosts. However, limited information is currently available regarding species-specific ERP values, and the sensitivity of individual species to anthelmintic drugs, since it is unlikely that the 50 species would display a uniform resistance pattern [40,41]. A previous study identified four cyathostomins (Cyathostomum catinatum, Cylicocyclus (Cyc.)…”