Orf is a skin disease of sheep and goats characterised by the development of pustular or 'scabby' lesions around the mouth and nostrils of lambs. The infection may also affect the teats of ewes, and the lower legs of lambs. Although the disease can strike at any time of the year, infections are most commonly seen in young lambs and their ewes and in older lambs in the late Summer. Orf is not usually a severe disease, but the lesions can become secondarily infected.
The disease is under-reported since most farmers and veterinary surgeons recognise the condition and do not send samples to confirm the diagnosis. Since 2001 there have been an average of 40 animal diagnoses per year by Government laboratories. Vaccination may be used for the control of the disease in sheep.
More information on orf in sheep [external link].
Orf is most frequently diagnosed in those directly handling sheep, in particular those bottle-feeding lambs in the spring, and those involved in shearing and slaughtering sheep. Orf produces local lesions on the skin which are generally inconvenient but resolve without leaving a scar. Infection usually occurs through broken skin and leads to localised swollen, red areas which can be extremely painful.
Orf appears as a solitary lesion or as a few lesions, most commonly on the fingers, hands, or forearms. The lesion starts as a small, firm, red-to-blue papule that becomes hemorrhagic and flat-topped, and may have an umbilicated center. The fully developed lesion is typically 2-3 cm in diameter, but it may reach 5 cm. It is often tender and may bleed easily. Infection is usually uncomplicated. Secondary bacterial infection of orf lesions may cause complications, but these are usually controlled with antibiotic treatment.
Photographs of lesions are available in this report: - Human Orf Virus Infection from Household Exposures — United States, 2009–2011. MMWR 2012 [external link].
The vaccine used to control sheep disease is a live vaccine. It can cause disease in people who have an inoculation injury, or who are exposed to recently vaccinated animals.
Laboratory confirmation of Orf virus infection is made by electron microscopy. Patient samples may be sent to the Virus Reference Department at HPA Colindale, using the appropriate sample submission form (PDF, 87 KB). Please make careful note of sample collection guidelines.
The low number of cases reported is likely to represent only a small proportion of the total number of cases occurring; diagnosis of human orf infection is often made on the basis of clinical presentation and history, without laboratory confirmation. In addition, farmers familiar with the infection may not seek advice from their GP. Thus, parapox virus infections are generally under-reported. An annual average of 8 (range 1 to 25) cases of orf virus infection were identified between 1991 and 2006, but only 2 cases on average since 2005.