Anthelmintic resistance in gastrointestinal nematodes on communally reared sheep farms of the King Sabata Dalindyebo Municipality, South Africa

Anthelmintic drugs are readily accessible to farmers and have been widely used to control gastrointestinal nematode (GIN) infections in communally reared sheep in the Eastern Cape Province (ECP), South Africa. Indiscriminate and prolonged use of these drugs has inevitably contributed to the selection of resistant GIN populations. This study aimed to assess the anthelmintic resistance status of GINs in communally reared sheep farms in King Sabata Dalindyebo Local Municipality, ECP. A semi-structured questionnaire was used to collect data on farm characteristics and helminth control practices. Faecal egg count reduction tests were performed on 259 lambs selected from eight communal farms. Lambs with egg per gram count > 150 were treated with anthelmintics (co-formulation of albendazole + closantel, and levamisole) currently used on the farms as well as an alternative anthelmintic from a different drug class (ivermectin, and a co-formulation of levamisole + praziquantel). Several suboptimal helminth control practices were identified that may have compromised the accurate administration of anthelmintics and effective management of deworming. These include the advanced age (> 65 years) of farmers: failure to weigh sheep prior to drug administration, use of syringes (5 ml/10 ml) instead of drench guns, and absence of a drenching and shifting approach. Helminths eggs from the genera Moniezia, Strongyloides, Trichuris, and Haemonchus were identified in both pre-and post-treatment faecal samples. Coprological culture of post-treatment samples, followed by morphological and molecular identification of larvae, confirmed the presence of Haemonchus contortus. This GIN species exhibited resistance to all the anthelmintic formulations assessed in this study. These findings highlight the urgent need for improved management strategies to mitigate resistance and promote sustainable worm control in communal sheep farming areas of ECP.