A contagious pustular dermatitis caused by the orf virus, a DNA virus of the Parapoxvirus genus, which is related to the vaccinia-variola subgroup of poxviruses. Orf mainly affects lambs and occurs in the spring. The disease rarely occurs in humans. When it does, it is usually confined to a single pustular lesion on a finger, which encrusts and finally heals. Antibiotics are not indicated except for secondary bacterial infections.