THE EFFICACY OF IVERMECTIN AGAINST NODULAR WORMS OF PIGS - THE RESPONSE TO TREATMENT USING 3 DIFFERENT DOSE LEVELS AGAINST OESOPHAGOSTOMUM-DENTATUM AND OESOPHAGOSTOMUM-QUADRISPINULATUM

Anthelmintic efficacies of 3 different doses of ivermectin (IVM) were evaluated in 3 isolates of nodular Norms in pigs, An isolate of Oesoph agostomum quadrispinulatum (OQ) was recently obtained from a commercia l farm where poor efficacy of IVM at the recommended dose (300 mu g.kg (-1) body weight) was detected, On this farm, IVM had been used for tr eatment of sows twice yearly for 6 years, Two other isolates, an O. de ntatum (OD) and a mixed Oesophagostomum dentatum and Oesophagostomum q uadrispinulatum isolate (ODQ) were obtained from a farm where anthelmi ntics had never been used, Efficacies of IVM against adult worms of th e OQ-isolate at dose rates of 150, 300 and 600 mu g.kg(-1) body weight ranged from 40.5-78.6%, Efficacies against larval stages (L3 and L4) were superior. Efficacies against the OD-isolate were 88.7, 96.1 and 9 9.6%, respectively. In the ODQ-isolate the efficacies of IVM against a dult stages furnished similar results. In conclusion, the efficacy of IVM against O, dentatum was: high but against both isolates of O, quad rispinulatum poorer. This suggests that IVM is intrinsically less effe ctive against O. quadrispinulatum and therefore not indicative of acqu isition of anthelmintic resistance in the OQ-isolate. Copyright (C) 19 96 Australian Society for Parasitology.