Anthelmintic resistance and novel control options in equine gastrointestinal nematodes

Abstract

Control of equine nematodes has relied on benzimidazoles (BZs), tetrahydropyrimidines and macrocyclic lactones. The intensive use of anthelmintics has led to the development of anthelmintic resistance (AR) in equine cyathostomins and Parascaris equorum. Field studies indicate that BZ and pyrantel resistance is widespread in cyathostomins and there are also increasing reports of resistance to macrocyclic lactones in cyathostomins and P. equorum. The unavailability of reliable laboratory-based techniques for detecting resistance further augments the problem of nematode control in horses. The only reliable test used in horses is the fecal egg count reduction test; therefore, more focus should be given to develop and validate improved methodologies for diagnosing AR at an early stage, as well as determining the mechanisms involved in resistance development. Therefore, equine industry and researchers should devise and implement new strategies for equine worm control, such as the use of bioactive pastures or novel feed additives, and control should increasingly incorporate alternative and evidence-based parasite control strategies to limit the development of AR. This review describes the history and prevalence of AR in equine nematodes, along with recent advances in developing resistance diagnostic tests and worm control strategies in horses, as well as giving some perspective on recent research into novel control strategies.

Single cell resolution landscape of equine peripheral blood mononuclear cells reveals diverse immune cell subtypes including T-bet+B cells

“…could expand this population. While viral exposure burdens are likely to be largely similar to burdens experienced by humans, horses in the northeastern U.S. are also frequently exposed to Borrelia burgdorferi (agent of Lyme disease) (69) and Sarcocystis neurona (agent of Equine protozoal myeloencephalitis) (70), and are continuously infested with or re-exposed to gastrointestinal nematodes (71). The horses in this study did not show signs of active infection or inflammation, as they all had normal complete blood count, serum amyloid A, iron indices, and globulins.…”

A survey of the level of horse owner uptake of evidence-based anthelmintic treatment protocols for equine helminth control in the UK

“…Current recommendations are that a FECRT be performed each year to avoid using ineffective anthelmintics (Tzelos and Matthews, 2016). Going forward, considering the levels of anthelmintic resistance reported in cyathostomins and in P. equorum (Raza et al, 2019), improved knowledge transfer from prescribers to horse owners needs to highlight the benefit of efficacy testing.…”

Systematic review of gastrointestinal nematodes of horses from Australia

“…A recent study from Queensland has demonstrated that the 95% inhibitory concentration (IC95) is a more consistent measure of the larval response than the IC50 in the larval migration inhibition test (in a 96 well format) for the detection of ML-resistant cyathostomins [76]. A number of studies have shown promising results from in vitro methods used in ruminants for the estimation of anthelmintic sensitivity and AR, but further studies are required to evaluate the usefulness of these methods in horses [88, 96, 97].…”