Assessing anthelmintic resistance on small ruminant farms in a tropical production system

Imidazothiazoles and benzimidazole are the only classes of anthelmintic drugs that have been used over the past 40 years in Fiji. Recently, concerns have arisen that anthelminthic resistance could be widespread and affect animal health and productivity in Fiji. The present study was designed to evaluate the current anthelmintic resistance status in Fiji's small ruminant farms. The study included 11 farms from the two (Western and Northern divisions) most relevant areas of small ruminant production in Fiji. The anthelmintic treatments tested were levamisole (LEV), albendazole (ALB), levamisole + albendazole combination (LEV+ALB), ivermectin (IVM), moxidectin (MOX), closantel (CLO) and a negative control (CON). The anthelmintic's efficacy was tested using faecal egg count reduction (FECR) tests and copro-cultures on days 14, 28, and 42 after treatment administration. The lowest mean FECR on day 14 was observed for ALB (65.2 %) followed by LEV (91.6 %), ALB + LEV (94.3 %), IVM (97.4 %) and MOX (98.8 %). The most relevant genera of GIN encountered were Haemonchus and Trichostrongylus spp., with no distinct pattern of resistance to drug groups between the two populations. None of the tested drugs (MOX and CLO) presented FECR over 95 % on days 28 and 42. Overall, the level of anthelmintic resistance observed was lower than hypothesised for this study. The combination of LEV+ALB has proven effective and presents an appealing treatment option for managing anthelmintic resistance and worm burden reduction in Fiji.