Prevention of Cutaneous Myiasis Caused by Screw Worm Larvae (Cochliomyia hominivorax) Using Ivermectin

During March of 1991 and 1992, four trials were carried out in the central area of Argentina to evaluate the efficacy of ivermectin in the prevention of myiasis caused by Cochliomya hominivorax larvae. In the first trial 24 steers were artificially wounded, in the second and third trial, 36 and 20 bull calves were castrated while in the fourth trial, 30 newborn calves were used. On day 0, half of the animals of each trial was treated with ivermectin (200 micrograms/kg) and the rest remained as untreated controls. None of the treated animals sustained a screw-worm larva infestation, but 3 of 12 (25%), 8 of 18 (44%), 5 of 10 (50%) and 8 of 15 (53%) of the controls developed active myiasis in trials 1 to 4 respectively.