The
anthelmintic efficacy of 6 non-
benzimidazole compounds and
thiabendazole against standardised,
benzimidazole resistant strains of H. contortus and T. colubriformis in sheep was determined using a controlled test. All compounds were administered intraruminally at their recommended therapeutic dose rates and 4 of the compounds were also assessed at half their recommended therapeutic dose rates. Levimisole at a dose of 6.4 mg/kg
body weight,
morantel at 4.4 mg/kg and 8.8 mg/kg,
naphthalophos at 6.25 mg/kg and 12.5 mg/kg,
rafoxanide at 7.5 mg/kg and
phenothiazine at 530 mg/kg were 98% or more effective in removing adult
infections of
benzimidazole resistant H. contortus.
Rafoxanide at 3.75 mg/kg,
phenothiazine at 265 mg/kg and
carbon tetrachloride at 0.05ml/kg were less effective, removing 80%, 73% and 72% respectively of the
benzimidazole resistant H. contortus worm burdens. Against the
benzimidazole resistant T. colubriformis
levamisole at 6.4 mg/kg, and
morantel at 4.4 mg/kg and 8.8 mg/kg removed 99%, 68% and 86% respectively of the adult
infections. All other
anthelmintics had little or no efficacy at the dose rates tested.
Thiabendazole at 44 mg/kg had no significant effect against these strains of H. contortus and T. colubriformis. Several non-
benzimidazole anthelmintics have shown high efficacy in this experiment and should be suitable for treating
infections with
benzimidazole resistant H. contortus. Of the
anthelmintics tested, only
levamisole and
morantel show high efficacy against
benzimidazole resistant T. colubriformis.