Age affected: All ages (especially sows, boars).
Causes: Mite - Sarcoptes scabei var suis.
Effects: Scratching, rubbing, red spots, scabs & thickened skin, dirty or blood-blistered ears, reduced growth.
Mange in pigs is caused by the mite Sarcoptes scabiei var suis which is 0.5 mm in diameter and is barely visible. The mite is circular and it can be distinguished from others by the pattern of sucker and bristle-bearing legs. The sexes can also be distinguished by this means, the male pattern being sucker-sucker-bristle-sucker and the female, sucker-sucker-bristle-bristle. The mite lives in galleries in the horny skin and feeds on epidermal cells. The female lays up to 50 eggs which hatch into larvae and then moult through 2 stages as nymphs to become adults, sometimes within 10 days, but more usually within 14-15 days. They can only multiply on the pig, but can survive for 2-3 weeks in moist cool conditions. Initial infestation is followed by multiplication of the mites and sensitisation of the host. The burrowing and feeding activities of the mites then cause intense pruritis (irritation) which causes scratching which in turn results in the rupture of small vesicles (blisters) near the burrows of the mites. The fluid released dries on the skin to block the mite burrows 6-7 weeks after infection and hyperkeratinisation (thickening) of the skin occurs and is greatest in older pigs.
Mode of transmission
Transmission is usually by direct contact between pigs and can be from the sow to piglets or after mixing. Indirect transmission can occur, as pen furniture may carry the eggs, nymphs or adults for up to 3 weeks where rubbing has taken place. Transmission between farms is usually by the introduction of infected pigs, but contaminated clothing or carriage of pigs from the farm in contaminated transport could also introduce infection.
The most obvious sign of mange in pigs is scratching. Affected pigs scratch constantly, especially in hot weather, rubbing against any fixed object. Pigs with mange often appear redder than their less severely affected pen-mates. On close inspection, small red spots can be seen and there is general reddening about the eyes, around the snout, on the inner surface of the ear flaps, between the legs and the body and on the front of the legs where the skin is thin. Scratching results in damage to the rubbed skin and the formation of brownish scabs on the damaged areas. Subsequently the skin become wrinkled, covered with crusty patches and thickened. The hair is rubbed off the flanks and, in badly-affected animals, the ears become thickened and distorted as a result of excessive head shaking which causes blood vessels in the ear to break and then heal by scarring. Reduction in productivity occur in infected herds due to the constant scratching. Weaning weights may be depressed 10%, sow feed use per piglet and per kg piglet are both increased by 5-10% and growth rates in finishing pigs are reduced by 5% or more. Reduction in sow condition may affect numbers born.
The constant scratching and rubbing, the presence of broken hairs on the flanks, crusts in the ears, crumpled ears and thickened, wrinkled skin all suggest mange. Mange is confirmed by finding mites in deep skin scrapings from the inside of the ears and the face (80% of cases) and the skin of the back foot 50% of cases. Mites can be made to leave crusts of skin or ear wax by vibration and heat and can then be seen using a hand lens. Recovery of mites is relatively easy in weaners, but more difficult in chronically affected sows. Serological tests can be used to detect antibody, but piglets less than 10 weeks of age may test false positive for infection because of colostral immunity. Serological tests can be used to confirm eradication, but sows may take up to a year to lose antibody after mites have been eliminated.
The changes described above may be seen at post-mortem examination. The changes may also be seen at slaughter, however, once scalding and scraping have taken place, wax deposits in the ears, all hairs and the surface layers of skin are missing. The presence of red, pinpoint lesions on the skin after scalding at slaughter are suggestive of mange and have been graded as Score 1 (mild lesions on the belly, head and buttocks) Score 2 (lesions over the flanks and back in low to moderate numbers) and Score 3 (several generalised lesions).
Treatment and prevention
Mange may be treated using a wide variety of insecticides, but those most commonly used at present are the avermectins. Ivermectin is given by subcutaneous injection or orally and kills mites in the ear and on skin. Animals with crusty lesions in the ears should be treated again within 14 days to eliminate mites. Mange can be controlled by treatment of the herd at intervals or at entry to housing (sows entering the farrowing house piglets at weaning and growing pigs at moving). Purchased pigs should be isolated and given a course of treatment topically, parenterally or in feed. An 8-10% improvement in daily live weight gain and feed conversion efficiency can be achieved if treated pigs are moved into clean accommodation. Compounds such as phosmet and amitraz are effective, but are not currently licensed in the EU. A single application of phosmet is effective, poured on the back with part of the dose placed in the ears. Amitraz solution can be sprayed gently over the pig and placed in the ears. A second treatment within 7-10 days will kill eggs and larvae.
Ivermectin, doramectin and phosmet have been used to eradicate mange from a farm. At least two treatments are usually given, 13 days apart and accommodation should be cleaned or sprayed with amitraz. Replacement stock should be from mange-free herds, but, if bought from infected herds, animals should be held in isolation, treated 13 days apart and then introduced to the herd. If lice are also present, coordinate mange and louse treatments.
The presence of mange on a farm affects its welfare status and may lead to downgrading or exclusion from quality assurance schemes.