Mange in Pigs

Sarcoptic mange, caused by infestation with Sarcoptes scabieisuis, is of primary importance in pigs worldwide. Unless pigs originated from specific pathogen-free (SPF) colonies or after mange eradication programs, all pig herds must be considered potentially infested even if acaricides are used routinely.

S scabieisuis in a herd typically becomes established after introduction of infested breeding stock. Transmission of S scabieisuis can occur rapidly via direct contact between infested and naive pigs and from sow to piglets, with pruritus occurring in piglets as young as four days old. Transmission also is possible via contact with fomites contaminated with S scabieisuis. Exposure to contaminated pens for as little as 24 hours can result in transmission of the mite.

Laboratory experiments indicate that S scabieisuis survival time off of the host is dependent on temperature, with survival being > 96 hours at temperatures < 25°C and < 1 hour at temperatures > 30°C. The potential of fomite transmission and off-host survival times should be considered when addressing outbreaks and developing herd eradication programs.

Lesions due to infestation with S scabieisuis usually start on the head, especially the ears (resulting in head shaking), then spread over the body, tail, and legs. Itching can be intense and associated with an allergic hypersensitivity reaction to the mites. Hypersensitivity mange results in raised papules, erythema, and intense itching and occurs more frequently in fattening pigs.

In a small number of older pigs, hyperkeratotic mange develops, which, while less pruritic, results in gray to white patches on the skin and in the ears. Infestations are negatively correlated with daily weight gains and feed conversion in pigs.

Experimental studies of S scabieisuis in pigs have demonstrated that infestation alters the microbial community on the skin. Comparing the microbiome of bacteria on pigs without S scabieisuis versus that of infested pigs showed that noninfested pigs had low relative abundances of Staphylococcus, whereas the relative abundance of Staphylococcus increased greatly on pigs with S scabieisuis during the course of infestations. Specifically, the staphylococci population shifted from S hominis to that of the more pathogenic S chromogenes as scabies progressed.

S scabieisuis diagnosis is best performed by combining different approaches, including:

• dermatitis score recorded at slaughter

• scratching index

• observation of clinical signs of mange

• ear or skin scrapings for microscopic examination

• ELISA for detection of specific antibodies

The usefulness of each criterion may vary according to the age of the animals. This global approach is particularly useful during an eradication campaign.

Control programs focus on treatment of sows prior to entering farrowing pens and treatment of growing pigs using acaracide sprays or injectable macrocyclic lactones. Eradication is feasible in many production facilities. Different eradication programs have been used, but all rely on three key factors:

• culling severely infested breeding stock

• treating all animals (adults, growing pigs, neonates) at the facility within the same time frame

• environmental treatments, including removal of bedding, if applicable

Leaving one pig untreated or introducing clean animals to a contaminated pen can result in reinfestation of the whole herd.

In eradication programs, injectable macrocyclic lactones are typically used with treatment intervals ranging from 10 to 14 days. A challenge in eradication programs is the meat withdrawal periods; hence, grower-finisher pigs might need to be removed prior to commencing an eradication program. If a facility has embarked on an eradication program, all new stock should be quarantined and treated (regardless of clinical signs) before introduction to the herd.

Injectable doramectin and ivermectin are labeled for use against S scabieisuis and are considered highly effective treatments. In some instances, a second dose of macrocyclic lactone 14 days later may be necessary for complete resolution, and a two-dose approach is normally used in eradication programs.

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; however, 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.

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 clinical signs of 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.