It can be distinguished from orf virus by DNA hybridization, though not by ultrastructural studies. Because immunity seems to be conferred by infection, lesions arise in those new to these occupations or those who have sporadic contact, such as pet owners. The disease is commonly known among agricultural workers to be benign, so it rarely is reported to doctors or other medical personnel in that setting. Sporadic cases and occasional epidemics occur. Lymphangitis, lymphadenitis, and fever may occur, which may last from a few days to a few weeks.
Patients typically have no previous history of milker's nodule.
Patients will have had recent contact with infected cows, calves, or viral fomites. The incubation period may be as brief as 4 days or as long as several weeks. Lesions are often solitary, and may be pruritic or painful. Some authorities divide the clinical course into 6 stages, each lasting roughly one week. Lesions are usually found on the fingers, hands, and forearms.