Author: Mark Duffill MBChB FRCP, Department of Dermatology, Health Waikato, 2001.

What is orf?

Orf is a virus infection of the skin contracted from sheep and goats.

Orf is caused by a virus called the parapox virus, which infects mainly young lambs and goats who contract the infection from one another or possibly from persistence of the virus in the pastures. Human lesions are caused by direct inoculation of infected material.

Who is affected?

Orf is not uncommon among sheep farmers, shearers, freezing workers, vets and farmers' wives or their children who bottle-feed lambs. Children may also acquire it from playing on infected pasture. Butchers, meat porters and housewives are sometimes infected from carcasses, especially sheep heads. A similar condition, caused by a related virus, occurs in dairy farmers and is called Milkers' Nodule.

What does it look like?

After an incubation period of 5 or 6 days a small, firm, red or reddish-blue lump enlarges to form a flat-topped, blood-tinged pustule or blister. The fully developed lesion is usually 2 or 3 cm in diameter but may be as large as 5 cm. Characteristically, although there appears to be pus under the white skin, incising this will reveal firm, red tissue underneath. The orf lesion is sometimes irritable during the early stages and is often tender. Orf lesions are generally solitary or few in number. They occur most commonly on the fingers, hands or forearms but can appear on the face. Red streaks up the lymph channels with enlargement of the lymph glands on the inner side of the elbow and/or under the arm are not uncommon. There may be a mild fever.

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What are the complications of orf?

Patients whose immunity is reduced for some reason may develop larger or unusual orf lesions. Rarely widespread small blisters may occur, suggesting blood stream spread of the orf virus, but resolve after a few weeks.

A secondary allergy rash to the presence of the orf virus, erythema multiforme, occasionally develops, typically 10-14 days after the onset of orf, to give small blistery red ring-like lesions on the arms and legs. Less distinctive red rashes, 'toxic erythemas' also occur and rarely the blistering disorder pemphigoid.

Treatment of orf

No specific treatment is necessary in most cases, as orf usually clears up by itself in about 6 weeks. The lesion may be covered to prevent contaminating the environment or other people, although person-to person spread is very uncommon. Any secondary bacterial infection should be treated. Large lesions can be removed by shave excision.

Imiquimod cream has been reported to be effective in a few cases of orf.

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