Anthelmintic resistance in strongylids (Nematoda: Strongylidae) parasitizing wild and domestic equids in the Askania Nova Biosphere Reserve, Ukraine.

Resistance of strongylids in domestic horses to benzimidazole anthelmintics (BZ) has been detected worldwide; however, information on the presence of BZ-resistance in wild equids has not been published to date. The purpose of this study was to analyze the manifestations of the BZ resistance in strongylids in domestic and wild equids kept in the Askania Nova Biosphere Reserve, Ukraine. Four species of equids: domestic horses and Shetland ponies (Equus caballus), donkeys (E. asinus), plains zebras (E. burchelli) and Grévy’s zebras (E. grevyi) kept under semi-free conditions were examined using the Fecal Egg Count Reduction Test (FECRT) in order to detect the presence of resistance to the BZ anthelmintics. Analysis of long-term data (2009–2019) revealed a decrease in the efficacy of BZ drugs against strongylids in these four species of equids from 97.6% in 2009 to <75% in 2019. The efficacy of anthelmintic treatments was low in all species of equids: in plains zebras – 69.4%, Grévy’s zebras – 72.7%, horses – 66.4%, ponies – 61.1% and donkeys – 45.2%. Ten species of cyathostomins (Cyathostomum catinatum, Cylicocyclus nassatus, C. ashworthi, C. leptostomus, Cylicostephanus calicatus, C. goldi, C. longibursatus, C. minutus, Coronocyclus labiatus, C. labratus) were found after horse deworming with albendazole. Our results are the first detection of BZ-resistance in strongylids of wild equids kept under semi-free conditions in the Reserve.