Anthelmintic resistance of horse strongyle nematodes to ivermectin and pyrantel in Lithuania

Abstract

With intensive use of anthelmintic drugs over the past decades, anthelmintic resistance (AR) in horse nematodes is becoming a growing issue in many countries. However, little information is available about the parasites, treatment practices or AR in the horse population in Lithuania. The aim of this study was to assess the current situation of AR on horse farms in Lithuania. The study was conducted in 25 stables. On each farm a faecal egg count reduction test (FECRT) was performed after deworming tests with ivermectin (IVM), (Bimectin 0,2 mg/kg, Ireland) and pyrantel (PYR), (Embotape 19 mg/kg, Ireland). This study showed that strongyle infections were highly prevalent in horses residing in stud farms in Lithuania, with high infection intensities according to an over dispersed distribution pattern. Of all tested subjects (n=707) 93% exceeded the value of 200 strongyle EPG, which is considered the cut-off limit with in the new equine strongyle control strategy based on targeted selective treatment. The efficacy of IVM was comparatively high: 98.8% of 250 horses had a zero egg count 14 days after treatment. Resistance to PYR was present on five stables (20% of all tested herds). Egg count had a significant (p<0.01) difference between treatment and control groups. This in vivo study showed that horse farms in Lithuania already had problems with AR, with resistance to pyrantel. Our findings should guide the implementation of more sustainable management of strongyles infestation among horses in Lithuania.