Anthelmintic resistance in gastrointestinal nematodes of sheep and goats in Fiji

There are two classes of anthelmintic (levamisole and benzimidazoles) have been used to control gastrointestinal nematodes of goats and sheep on smallholder and commercial farms in Fiji for more than 40 years. Given the potential this provides for the development of anthelmintic resistance (AR). A study was conducted to determine the level of AR on eleven farms across the Western and Northern divisions of Fiji. Efficacy was determined by faecal egg count reduction tests (FECRT) following administration of levamisole (LEV), albendazole (ALB), levamisole + albendazole combination (LEV+ALB), ivermectin (IVM), moxidectin (MOX) and the Haemonchus specific closantel (CLO). At day 14 following administration, resistance (FECRT < 95%) to ALB was found 6 of 7 farms tested, while levamisole resistance was observed on 1 of 4 goat farms and 2 of 3 sheep farms. Full susceptibility (FECRT > 95%) to IVM was found in all 3 sheep farms and 3 of 4 tested goat farms while MOX was fully effective on the 7 farms tested. The combination of LEV+ALB was effected on all 4 goat farms and 2 of 3 sheep farms. There was evidence of reduced efficacy of CLO against Haemonchus contortus on goat but not sheep farms. Reduced efficacy of ALB and LEV against both Haemonchus contortus and Trichostrongylus colubriformis was observed with overall average efficacy percentages being LEV (91.6%), ALB (65.3%), LEV + ALB (94.4%), IVM (97.4%), and MOX (98.7%). Moxidectin exhibited persistent efficacy to day 28 on 50% of goat farms and up to 42 days against Haemonchus contortus on sheep farms. CLO exhibited sustained efficacy against Haemonchus contortus for 28 days in both goats and sheep.