Occurrence of anthelmintic resistance in strongylid nematodes of sheep and horses in the Czech Republic

On selected farms of sheep, horses and cattle with naturally acquired strongylid infections levamisole, mebendazole, fenbendazole, albendazole, ivermectin and doramectin were tested for the prevalence of anthelmintic resistance. In vivo fecal egg counts reduction test (:FECRT) was used and in the case of the benzimidazole anthelmintics also in vitro egg hatch assay (EHA). Considerable resistance was found in equine small strongylids to mebendazole (8-10 mg/kg) with the FECR test values 61.5% and 70.4% and to fenbendazole (7.5 mg/kg) with 76% and 84.1%. The FECR test results in sheep proved the occurrence of resistant strains of Ostertagia spp, and Trichostrongylus spp. to levamisole (7.5 mg/kg) 67.8% and to fenbendazole (5 mg/kg) 83.7% and 85.4%. The resistance to benzimidazoles was confirmed by EHA in horses and sheep as well. Resistance to albendazole, ivermectin and doramectin was not found.