Treatment failure of ivermectin for Oxyuris equi in naturally infected ponies in Czech Republic

Abstract

Nine ponies (20 months of age) with naturally acquired cyathostome and pinworm infections were treated orally with ivermectin at a dosage of 400 μg /kg. Ivermectin was highly effective on the cyathostome infection. However, adult Oxyuris equi were present in six horses. In recent years, anthelmintic treatment with macrocyclic lactones have not appeared to deliver the expected efficacy against equine pinworms (Oxyuris equi) in the USA. This is the first European study to demonstrate anthelmintic resistance in Oxyuris equi to macrocyclic lactones in naturally infected ponies (Czech Republic).

BEVA primary care clinical guidelines: Equine parasite control

“…A perception surrounding a lack of response to macrocyclic lactones has been reported in the United Kingdom based either on absence of improvement in clinical signs, 291,292 recurrence of faecal shedding of parasites 286,293 persistence of adult worms at necropsy 294 or early/persistent detection of perineal eggs by tape strip examination 295 . There is evidence for reduced efficacy of moxidectin 286 and there are anecdotal reports of resistance to pyrantel 296 .…”

Anthelmintic resistance in equine nematodes: Current status and emerging trends

“…Similar observations were made in New Zealand, where naturally infected horses were first administered ivermectin or abamectin and subsequently treated with oxfendazole, which resulted in expulsion of several adult O. equi ( Rock et al, 2013 ). In Europe, studies conducted in Germany ( Wolf et al, 2014 ), Czech Republic ( Scháňková et al, 2013 ), and France ( Sallé et al, 2016 ) have all documented resistance to macrocyclic lactones in O. equi . The German study documented a lack of efficacy of ivermectin as well as moxidectin ( Wolf et al, 2014 ), and all three European studies included recovery of adult O. equi from the treated horses, adding strength to the evidence.…”

“…Thus, X means that resistance was tested, but not found, and X-AR means that resistance was tested and found. Country Reference Benzimidazoles Pyrimidines Macrocyclic lactones Brazil Felippelli et al (2015) X-AR Czech Republic Scháňková et al (2013) X-AR France Sallé et al (2016) X X X-AR Germany Wolf et al (2014) X X-AR New Zealand Rock et al (2013) X X-AR USA Reinemeyer (2012) X X-AR …”

“…However, the studies summarized herein provided good examples of how good quality data can be generated. While a terminal study can provide the ultimate documentation of anthelmintic resistance as demonstrated by the study conducted by Fellipelli and colleagues (2015), several of the other studies made use of follow-up treatments with an effective anthelmintic and collected expulsed parasites in the feces ( Reinemeyer, 2012 ; Rock et al, 2013 ; Scháňková et al, 2013 ; Wolf et al, 2014 ; Sallé et al, 2016 ). However, this latter approach can become challenging if multi-drug resistance is suspected.…”

A survey of macrocyclic lactone efficacy in Australian cyathostomin populations

“…Furthermore, there is growing evidence of reduced ML efficacy against other equine nematodes. There are numerous reports of Parascaris equorum resistance to MLs (Schougaard and Nielsen, 2007;Lyons et al, 2008a;Veronesi et al, 2009;Armstrong et al, 2014;Bishop et al, 2014;Beasley et al, 2015), and growing concerns about ML efficacy against Oxyuris equi (Scháňková et al, 2013;Wolf et al, 2014;Felippelli et al, 2015). Combined, these events highlight the danger of suppressive treatment regimes, still widely practiced on Australian horse properties, and underline the importance of routine monitoring of drug efficacy across farms.…”