ACTIVITY OF DORAMECTIN AGAINST NEMATODE AND ARTHROPOD PARASITES OF SWINE

The efficacy of doramectin, a novel avermectin, was assessed against b oth naturally-acquired and experimentally-induced infections of gastro intestinal roundworms, lungworms, kidneyworms, lice and mites in studi es conducted across North America and Europe. Twenty-two studies evalu ated efficacy against fourth larval and adult stages of the following nematode species: Hyostrongylus rubidus, Ascaris suum, Strongyloides r ansomi, Oesophagostomum dentatum, Oesophagostomum quadrispinulatum, Tr ichuris suis, Metastrongylus spp. and Stephanurus dentatus. Efficacy w as evaluated against the louse Haematopinus suis in six studies and ag ainst the mite Sarcoptes scabiei in four studies. A common study desig n was employed for each study type. In all studies, animals were allot ted at random to a doramectin-treated or a saline-treated group. The d oramectin-treated group received the drug at 300 mu g kg(-1) by intram uscular injection while the saline-treated group received saline by th e same route. In the nematode studies, worm burdens were determined fo r each animal at slaughter 14-16 days after treatment. Efficacy agains t each nematode species/stage was assessed on the basis of percentage reduction in geometric mean worm burden in doramectin-treated animals compared with saline-treated controls. In louse and mite studies, coun ts were made immediately before treatment and then at weekly intervals for four weeks, Efficacy was based on a comparison of the level of in festation on the day of treatment with that on the last day of test. D ata from individual studies were combined to derive a single estimate of efficacy against each of the parasite species represented in the st udy program. Efficacy of doramectin was 98% or greater against all nem atode species except T. suis for which the efficacy was 87% and 79% ag ainst adult and fourth larval stage, respectively. Efficacy was 100% a gainst both Haematopinus suis and Sarcoptes scabiei.