Lambs are affected year after year on some farms. It is the most common viral zoonosis in the UK and at least one RVC student is infected each year.

Pathogenesis:
Trauma leads to the development of lesions in non-woolled parts of the skin. Venereal lesions are also recorded. The proliferative lesions coalesce to form scabbed masses and heal in several weeks.

This is most serious for lambs whose mouth lesions stop them feeding.

In man papules/pustules develop (usually on the hands) within 10 days, enlarge and then regress in several weeks.