Prevalence of drug-resistant gastrointestinal nematodes in an organized sheep farm

Aim: The present study was aimed to determine the resistance against albendazole, fenbendazole, levamisole and closantel in gastrointestinal (GI) nematodes of sheep. Introduction: Anthelmintics are used traditionally as an integral part of helminthic control strategies for grazing livestock to prevent production losses from parasitic infections. The continuous and indiscriminate use of the same anthelmintics over years together as the sole means of control are now failing due to the emergence of resistance strains of helminths. Resistance to the commonly used anthelmintics in GI nematodes of sheep has become an increasingly widespread problem throughout the world. Materials and Methods: Fifty-five naturally infected Madras Red lambs of 6-12 months of age were selected and distributed randomly into five treatment groups of 11 animals each. Four groups were treated orally with albendazole (5 mg/kg), fenbendazole (7 mg/kg), levamisole (7.5 mg/kg) and closantel (10 mg/kg) respectively, whereas the fifth group served as untreated control. Fecal samples were collected per rectum of each lamb just prior to treatment (pre-treatment) and on 7, 14, 21 and 28 days post-treatment. The anthelmintic resistance was evaluated by in vivo fecal egg count reduction test (FECRT), post-treatment larval culture and in vitro egg hatch assay. Results: In the FECRT, albendazole reduced the faecal egg count by 86.50%, 84.81%, 85.28% and 84.47% respectively for 4 weeks after treatment. Fecal egg count reduction using fenbendazole was 92.64, 93.04, 90.80 and 90.06% respectively for 4 weeks after treatment. The percent efficacy for levamisole and closantel was more than 95%. The post-treatment larval culture contained only Haemonchus contortus. In the in vitro egg hatch assay, the ED50 value for benzimidazole was 0.299 μg albendazole/ml and levamisole showed an ED50 value of 0.283 μg/ml. Conclusion: Our study confirmed the resistance of H. contortus to benzimidazole in sheep.