Treatment of sarcoptic mite infestation and mite hypersensitivity in pigs with injectable doramectin

Thirty-two pigs were infested experimentally with Sarcoptes scabiei var suis and allocated randomly to a medicated group (injected intramuscularly with 300 μg doramectin/kg) or an unmedicated group (injected intramuscularly with 1 ml saline/33 kg). They were observed daily for 15 minutes for signs of pruritus, and the ear lesions were assessed and skin scrapings examined for mites on days 7, 14, 21 and 28 after treatment. In the 16 pigs treated with doramectin the ear lesions resolved completely within 14 days, no mites were recorded on 15 of them on day 7 or on any of them on days 14, 21 and 28; pruritus was greatly reduced from day 7 onwards (range 0 to 0.62 rubbing episodes per pig per day) and papular skin lesions were absent from 15 of the pigs at slaughter on day 28. In comparison, the ear lesions in the 16 unmedicated pigs failed to resolve in 15 of them. Mites were present on 15 of them at different times during the experiment; the numbers of rubbing episodes ranged from 0 88 to 4.65 per pig per day and all the pigs had papular skin lesions at slaughter. In the unmedicated pigs, both the degree of pruritus and the presence and severity of papular skin lesions at slaughter were greater in those with zero or low mite counts than in those with high mite counts.