Mange in Pigs
Mange in pigs is principally due to infestation with Sarcoptes scabiei var suis. Rarely, infestation with Demodex phylloides has been reported to cause clinical disease in pigs.
Sarcoptic mange, caused by infestation with Sarcoptes scabiei var suis, is of primary importance in pigs worldwide. S scabiei var suis in a herd typically becomes established after introduction of infested breeding stock. Transmission of S scabiei var suis can occur rapidly through direct contact of infested and naive pigs. However, transmission to naive pigs is also possible through contact with fomites contaminated with S scabiei var suis. Survival of the mite eggs away from the host is limited. However, exposure for as little as 24 hr to contaminated pens that were recently vacated by infested pigs resulted in transmission of the mite. Laboratory experiments indicated that S scabiei var suis did not survive >96 hr at temperatures <25°C or >24 hr at 20°–30°C. Survival was <1 hr at temperatures >30°C. Unless pigs originated from SPF colonies or after mange eradication programs, all pig herds must be considered potentially infested even if acaricides are used routinely.
Lesions due to infestation with S scabiei var suis usually start on the head, especially the ears, then spread over the body, tail, and legs. Itching can be intense and associated with a hypersensitivity reaction to the mites. As the hypersensitivity subsides, typically after several months, the thickened, rough, dry skin is covered with grayish crusts. Infestations are negatively correlated with daily weight gains and feed conversion in pigs.
Experimental studies of S scabiei var suis in pigs have demonstrated that infestation alters the microbial community on the skin. Comparing the microbiome of bacteria on pigs without S scabiei var suis versus that of infested pigs showed that noninfested pigs had low relative abundances of Staphylococcus, whereas the relative abundance of Staphylococcus increased significantly on pigs with S scabiei var suis during the course of infestations. Specifically, the staphylococci population shifted from S hominis to that of the more pathogenic S chromogenes as scabies progressed.
Diagnosis is best performed by combining different approaches: dermatitis score recorded at slaughter, scratching index, observation of clinical signs of mange, ear or skin scrapings for microscopic examination, and ELISA for detection of specific antibodies. The usefulness of each criterion may vary according to the group age. This global approach is particularly useful during an eradication campaign.
Injectable doramectin and ivermectin are labeled for use against S scabiei var suis and are considered highly effective treatments. In some instances, a second dose of macrocyclic lactone 14 days later may be necessary for complete resolution. Hot lime sulfur is labeled for use against mange in swine. In swine, lime sulfur dips are repeated at intervals of 3–7 days to treat mange, unlike in other species in which they are repeated every 12 days. Label instructions must be followed closely, because there are three possible lime sulfur dilutions for use on swine. Unlike phosmet, lime sulfur spray can be applied to suckling pigs. Certain spray formulations of permethrin are labeled for use against mites on swine, but it is generally not considered the compound of choice. If permethrin is used, animals should be wet thoroughly with the product and re-treated in 14 days. Phosmet spray is approved for sarcoptic mange in swine at the species-specific dilution instructions on the label. A single treatment is usually effective, but a second treatment can be applied 14 days later if necessary. Phosmet should not be applied directly to suckling pigs. Coumaphos sprays are available for use on swine in the USA, but they are labeled only for control of lice.
Demodectic mange caused by infestation with Demodex phylloides is possible in pigs. Clinical signs of D phylloides infestation include reddening of the skin, pustules, and alopecia. Although rare in domestic pigs, D phylloides infestation can be common in wild boars without overt signs of clinical disease. In wild boars, the highest prevalence and greatest numbers of D phylloides were found in sebaceous glands in eyelids and cheeks. D phylloides can also be found around the eyes, mouth, snout, ventral neck, ventrum, and thighs. There is no reliable treatment.