Abstract
Case study
A 28-year-old sheep farmer presents with a tender blood-tinged pustule on his little finger. The skin lesion started as a red–blue lump and has increased in size over a few days.
Biophoto Associates/Science Photo Library.
This is orf
Orf is a parapox viral infection of the skin contracted from sheep and goats. This curiously named disease spreads to humans by direct contact with an infected animal. In animals, the illness is known as ‘scabby mouth’, as it causes scabs around the nose, mouth and teats. Human to human spread is very rare. Predictably, orf is a risk for sheep farmers, shearers and anyone that bottle-feeds lambs. It can occur less predictably in a suburban population, for example after a school trip to the local farm.
Orf is usually a clinical diagnosis. Lesions are generally single or few in number. They usually occur on the hand or forearm. The index finger is the most common site affected. There may be a mild accompanying systemic upset with a lymphangitis (Primary Care Dermatology Society, 2015).
An incubation period of 5–6 days is followed by a firm, red–blue papule. This grows in size to form a blood-tinged blister or pustule. Lesions can be as large as 5 cm and are often painful. Orf lesions can appear target-like in character, with a red rim, a white middle and a red centre. Interestingly, although these lesions look to be pus-filled, incising the skin will uncover red tissue underneath. Secondary bacterial infection can occur. Immunocompromised patients are prone to larger, atypical lesions.
Lesions tend to resolve within 6 weeks, and there is no specific treatment for the disease. Patients will be conferred lifelong immunity. The lesions should be covered to prevent secondary infection. In some, imiquimod cream has been successful (Duffill, 2001).
ORCID iD
Dr Charlotte Sidebotham https://orcid.org/0000-0002-7269-2734