EFFICACY OF INJECTABLE DORAMECTIN IN THE THERAPY AND CONTROL OF DERMATOBIA-HOMINIS INFESTATIONS IN LATIN-AMERICA

Three studies were conducted in Latin America, one in Brazil, one in V enezuela and one in Argentina, using a common protocol to investigate the efficacy of a single subcutaneous injection of doramectin at 200 m u g kg(-1) (1 ml per 50 kg) for the treatment and control of Dermatobi a hominis infestations in cattle raised under commercial conditions, I n each study, two groups of 20 animals each were allocated on the basi s of D. hominis nodules present 24 h before treatment to a treated gro up (T1), or to a control group (T2) which received saline solution at 1 ml per 50 kg of live weight. All cattle were injected in the mid-dor sal cervical region and examined on treatment day and 2, 7, 15 and 30 days post-treatment (p.t.). At each observation day the number of D. h ominis nodules was counted and the viability of the larvae inside them was assessed and recorded. Treatment with doramectin was 100% effecti ve in eliminating D. hominis larvae and in controlling the re-establis hment of the parasite under field conditions of continuous reinfestati on. During the first 48 h p.t., dead larvae of different ages were fou nd outside or partially outside the nodules in animals of the doramect in groups, After 48 h p.t., no live larvae were found inside existing nodules, nor did new nodules develop in animals of the doramectin grou ps in any of the three studies. When compared with nodule counts in th e control group on the same observation day or with parasite burdens o n the same animal before treatment, doramectin-treated animals began t o eliminate parasitic nodules at 48 h p.t. Efficacy reached 100% at 7 days p.t. and remained at 100% on subsequent observation days (P<0.05) . None of the doramectin-treated animals exhibited any clinical signs of adverse reaction to medication.