The efficacy of levamisole, and a mixture of oxfendazole and levamisole, against the arrested stages of benzimidazole-resistant Haemonchus contortus and Ostertagia circumcincta in sheep

Sheep were allowed to graze pasture that had been seeded with benzimidazole -resistant Haemonchus contortus and Ostertagia circumcincta in order to acq uire a burden of arrested larvae. Following housing, sheep were dosed orall y with either oxfendazole at a dose rate of 4.7 mg/kg (to confirm the benzi midazole-resistant status of the species of nematode), levamisole at a dose rate of 7.5 mg/kg, or an oxfendazole/levamisole mixture at a dose rate of 4.6 mg/kg oxfendazole and 8.1 mg/kg levamisole. The efficacies of the treat ments were assessed by estimation of the arrested larval burden in the abom asum of each sheep, either at 10 or 11 days (oxfendazole and oxfendazole/le vamisole mixture), or 12 or 13 days (levamisole), after treatment. Compared to the untreated controls, the protection afforded by a single dos e of either levamisole or the oxfendazole/levamisole mixture was >99% again st the arrested stages of both Haemonchus contortus and Ostertagia circumci ncta. Treatment with oxfendazole confirmed the benzimidazole-resistance sta tus of the two species. (C)2000 Elsevier Science B.V. All rights reserved.