Pityriasis rosea is a dermatitis usually seen in four to twelve week old pigs and is characterized by 1- to 20-cm raised, reddened, ring-shaped lesions on the skin. Lesions first develop on the skin of the ventral abdomen but occasionally start in other areas. The cause is unknown. Papules first develop on the ventral abdomen and inner thighs. These early lesions expand to form circular, coalescing lesions with an expanding rim. Older lesions often have healed centers. Lesions heal in about four weeks without intervention. Pityriasis rosea is easily diagnosed by gross examination and does not require any treatment. The condition is not pruritic and seems to have no apparent effect on the health or growth rate of affected pigs.
Nearly all affected pigs recover completely.