Orf is a farmyard pox, a type of zoonosis. It causes small pustules in the skin of primarily sheep and goats, but can also occur on the hands of humans. A pale halo forms around a red centre. It may persist for several weeks before crusting and then either resolves or leaves a hard lump. There is usually only one lesion, but there may be many, and they are not painful. Sometimes there are swollen lymph glands.

It is caused by a Parapoxvirus. It can occur in humans who handle infected animals or contaminated objects. One third of cases may develop erythema multiforme. Once resolved, a person can still be infected again.

Generally, treatment options are limited. Injecting the lesion with cidofovir or applying imiquimod has been tried. It is sometimes necessary to cut them out. The vaccine used in sheep to prevent orf is live and has been known to cause disease in humans.

The disease is endemic in livestock herds worldwide. A recent outbreak emerged in southwest Ethiopia between October 2019 and May 2020.