Orf, also known as contagious pustular dermatitis, ecthyma contagiosum, and sore mouth disease, is caused by a parapox virus that infects sheep and goats. Orf is transmitted to humans by direct contact, typically occurring in sheepherders or shearers, farmers, butchers, and veterinarians. Orf presents with one or more papule, pustule, or nodule on an area of the body that has been exposed to these animals or animal products. Mild fever (usually 3-4 days) and malaise are associated with infection. Secondary lymphangitis and local lymphadenopathy may be present. Autoinoculation leading to further lesions may occur, but human-to-human spread has not been documented. Spontaneous recovery usually occurs in 4-6 weeks.

Of note, erythema multiforme has been reported to occur in the setting of orf virus infection. In immunocompromised individuals, orf may be persistent and progressive (orf progressiva). Additionally, orf has been associated with the induction of autoimmune bullous disease in rare cases that may appear clinically as bullous pemphigoid, mucous membrane pemphigoid (MMP), or epidermolysis bullosa acquisita. Laminin 332 (a component of the basement membrane and target antigen of MMP) has been identified as the target antigen in 5 cases.