A survey of macrocyclic lactone efficacy in Australian cyathostomin populations

Abstract

The macrocyclic lactone (ML) drugs are central to the control of equine strongyles but recent international reports raise concerns about reduced efficacy of these drugs against cyathostomins. The objectives of the present study were firstly, to evaluate the efficacy of ML drugs against cyathostomins on a cross-section of Australian horse farms, and secondly, to determine the egg reappearance period (ERP) following treatment of horses with MLs. A total of 419 horses on 43 properties were treated orally with ivermectin, abamectin or moxidectin, at recommended dose rates and drug efficacy was determined using the faecal egg count reduction test. Efficacy of 100% at 14 days post-treatment was reported on all of the 43 farms. ERP following ivermectin treatment was 6 weeks on two properties and ERP following moxidectin treatment was 12 weeks on a third property. These ERPs are shorter than those reported at the time of commercial release of these drugs which likely reflects changing drug susceptibility of the cyathostomin populations tested. Ongoing surveillance of drug efficacy and ERPs should be part of an integrated management approach to equine worm control that prioritises the preservation of anthelmintic efficacy.

Systematic review of gastrointestinal nematodes of horses from Australia

“…Furthermore, moxidectin was found effective in reducing strongyle (cyathostomins, Gyalocephalus spp., Triodontophorus spp.) burdens below 90% for as long as 12 weeks post-administration [17, 23, 78]. The longer anthelmintic treatment interval required for moxidectin could be highly valuable in reducing treatment frequency, and consequently selection of AR [9].…”

A questionnaire study of parasite control in Thoroughbred and Standardbred horses in Australia

“…Widespread resistance of cyathostomins to BZs has developed and resistance to THPs has been documented . Further, emerging resistance of cyathostomins to MLs has been reported in Australia and other countries recently . Parascaris populations are commonly resistant to MLs and resistance to BZs and THPs has been described .…”

Efectividad de tres principios antihelmínticos comúnmente usados contra nematodos gastrointestinales en caballos colombianos

“…En general, el control de parásitos intestinales en equinos se realiza bajo esquemas prefijados o en forma esporádica, siendo poco utilizados los análisis coprológicos como criterio base para la terapéutica (Anziani y Ardusso, 2017). A esto se suma la administración rutinaria de antihelmínticos de amplio espectro, siendo esta práctica considerada como el factor determinante para el desarro-llo de resistencias (Scott et al, 2015; Scheuerle et al, 2016; Tzelos y Matthews, 2016; Godéski et al, 2017), y el motivo por el que actualmente una gran parte de los principios antihelmínticos disponibles son poco eficaces; situación que se agrava debido a las pocas posibilidades de que nuevos productos estén disponibles en un futuro cercano (Scott et al, 2015;Beasley et al, 2017).…”

“…La resistencia a los antihelmínticos se genera a partir de una presión de selección sobre los parásitos, modificando dinámicas genéticas que se produce lentamente en el tiempo, luego de las cuales los parásitos sobrevivientes al tratamiento trasmiten alelos que confieren un fenotipo resistente a su progenie (Vidyashankar et al, 2012; Anziani y Fiel, 2015; Anziani y Ardusso, 2017). El fenómeno de resistencia antihelmíntica se ha convertido en un problema creciente en muchos países (Fischer et al, 2015), siendo agravado por el movimiento frecuente de equinos a nivel nacional e internacional (Beasley et al, 2017).…”