Efficacy of ivermectin against ectoparasites of cattle in South Africa.

The efficacy of various formulations of ivermectin administered at the recommended dose rate of 200 micrograms/kg was evaluated in cattle infested with mange mites (Sarcoptes scabiei var. bovis.), lice (Linognathus vituli and Damalinia bovis) and ticks (Boophilus decoloratus, Amblyomma hebraeum, Rhipicephalus appendiculatus and Hyalomma spp.) in 8 trials conducted in South Africa. Mange mites (S. scabiei) were eliminated from animals treated subcutaneously, resulting in marked clinical recovery. Oral administration reduced the numbers of, but did not eliminate these mites. Sucking lice (L. vituli) were eliminated from animals treated orally or subcutaneously. Numbers of biting lice (D. bovis) were reduced but not eliminated, subcutaneous injection being more effective than oral drenching. Subcutaneous injection with ivermectin every 14 d over a period of 84 d significantly reduced numbers of engorged female R. appendiculatus and A. hebraeum. Numbers of Boophilus spp. and Hyalomma spp. were also reduced. A single subcutaneous injection resulted in significantly fewer engorged female B. decoloratus on treated animals for up to 28 d after treatment. In one trial significantly fewer A. hebraeum males occurred on treated animals for up to 28 d after treatment. Too few R. evertsi were present in these trials to evaluate the effect of ivermectin against this parasite.