Efficacy of injectable moxidectin against mixed (Psoroptes ovis and Sarcoptes scabiei var. ovis) mange infestation in sheep.

Field efficacy of injectable moxidectin was evaluated in sheep naturally infested with both Psoroptes ovis and Sarcoptes scabiei var. ovis mange. Three groups of 15 ewes were selected from the flock based on parasitological and clinical status. Group 1 remained as untreated controls; Group 2 animals received a subcutaneous injection of moxidectin at 0.2 mg kg-1 body weight on Day 1; Group 3 animals received 0.2 mg kg-1 moxidectin twice on Day 1 and Day 7. Efficacy was assessed by taking skin scrapings from each animal on Days -4, 0, 7, 14, 28 and 35 post-treatment and counting viable mite stages and species. In both treated groups the signs of itching disappeared within 7 days post-treatment. Rapid clinical improvement was associated with reduction in numbers of mites compared with initial score which was over 90%. However, in skin scrapings on Day 7 post-treatment several live mites of both species were present. The second injection of moxidectin removed all living mites, and skin scrapings from Group 3 animals were negative for all mites on Days 14, 28 and 35. The weight gain on average was 2.0 kg in Group 2 and 2.7 kg in Group 3 during the 35 days of trial. Untreated control animals lost on average 3.1 kg from their weight at the start of the trial. All untreated animals remained positive and suffered from intensive scratching, anorexia and moist, active skin lesions. They were given an emergency moxidectin treatment on Days 35 and 42, each animal receiving 0.2 mg kg-1 body weight, subcutaneously.(ABSTRACT TRUNCATED AT 250 WORDS)