The anthelmintic efficacy of fenbendazole against thiabendazole-resistant strains of Haemonchus contortus and Trichostrongylus colubriformis in sheep
Hogarth-Scott, R.S.; Kelly, J.D.; Whitlock, H.V.; Ng, B.K.; Thompson, H.G.; James, R.E.; Mears, F.A.
Research in Veterinary Science 21(2): 232-237
The anthelmintic efficacy of fenbendazole (methyl 5-(phenylthio)-2-benzimidazole carbamate) was tested in sheep against standardized strains of H. contortus and T. colubriformis, known to be resistant to thiabendazole. Fenbendazole at dose rates of 5, 10 and 20 mg/kg per os reduced total worm counts in H. contortus infected sheep by 66, 90 and 100%, respectively, with similar reductions recorded for worm egg outputs. For the thiabendazole resistant strain of T. colubriformis, fenbendazole reduced total worm counts in infected sheep by 4, 44 (40-48), 79 (75-83), 96 and 100% at dose rates of 5, 10, 20, 40 and 80 mg/kg per os. Significant suppression of worm-egg production by thiabendazole resistant T. colubriformis was obtained with fenbendazole at dose levels of 5 mg/kg and above. The implications of these results are discussed in the light of the increasing occurrence of strains of trichostrongylid nematodes resistant to currently available benzimidazole anthelmintics.