Reduced Efficacy of Fenbendazole and Pyrantel Pamoate Treatments against Intestinal Nematodes of Stud and Performance Horses

Abstract

Nematodes are an important cause of disease and loss of performance in horses. Changes in the parasitic fauna of horses have occurred in the past few decades, making cyathostomins the major parasites in adult horses, while large strongyles have become less prevalent. Parascaris spp. remains the most important parasite infecting foals and weanlings. Anthelmintic resistance is highly prevalent in cyathostomins and Parascaris spp. worldwide and it must be factored into treatment decisions. To assess anthelmintic efficacy in Northern Italy, we sampled 215 horses from 17 sport and horse-breeding farms. Fecal egg count reduction tests (FECRT) were used to assess anthelmintic efficacy. Copromicroscopic analysis was performed using MiniFLOTAC before treatment with fenbendazole, pyrantel pamoate or ivermectin, and repeated 14 days post-treatment. Strongyle-type eggs were detected in 66.91% of horses (CI95% 61.40–73.79%), while Parascaris spp. was detected in 2.79% (CI95% 1.94–5.95%). Reduced efficacy against cyathostomins was observed for fenbendazole in 55.56% of the treated animals (CI95% 41.18– 69.06%), and for pyrantel pamoate in 75% of animals (CI95% 30.06–95.44%). Ground-based actions must be set in place to promote the uptake of state-of-the-art worm control plans that will prevent clinical disease while minimizing the selection pressure of resistant parasites.

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

“…Similarly, cyathostomin resistance to OFZ + PYR was found in 15 (out of 18) FECRTs at 2 weeks post-treatment and this reduction in FECs of animals treated with OFZ + PYR could be due to the effectiveness of PYR as anthelmintic products containing PYR alone are not available in Australia. However, resistance to a single active anthelmintics, BZs and THPs, have been consistently reported in cyathostomins worldwide ( Traversa et al, 2012 ; Canever et al, 2013 ; Lester et al, 2013 ; Sallé et al, 2017 ; Bellaw et al, 2018 ; Morris et al, 2019 ; Butler et al, 2021 ; Zanet et al, 2021 ). In early 2000, a study reported treatment failure of MOR against strongyles in Australia on two properties ( Pook et al, 2002 ).…”

Comparison of FECPAKG2, a modified Mini-FLOTAC technique and combined sedimentation and flotation for the coproscopic examination of helminth eggs in horses

“…egg is found [ 11 , 22 , 57 ]. In contrast, for a faecal egg count reduction test (FECRT) to identify drug-resistant nematode populations, a sensitive and precise quantitative method is required, and the Mini-FLOTAC method has been repeatedly shown to perform very well in FECRT studies [ 63 – 65 ], including studies on horses [ 32 , 66 – 68 ]. Reasons to consider when choosing a test based on convenience include access to the laboratories that offer tests and acceptable turnaround times for results.…”

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

“…leptostomus, CY. insigne, CT. longibursatus, CT. goldi, CT. calicatus, CT. minutus) has been recognized that comprises up to 99% of the cyathostomin burden in horses [ 4 , 13 , 54 , 55 , 56 , 57 , 58 , 59 ]. While the methods used in this study cannot measure the species composition of the parasite burden of individual horses, we did observe that five species of the ‘core’ group ( CT. longibursatus, CS.…”