Orf is a disease primarily of sheep and goats, but can also affect humans. It is caused by a parapoxvirus known as orf virus (ORFV) which has a worldwide distribution. Although it can affect animals of any age it is most prevalent around lambing time, affecting both lambs and ewes. Farmers, shepherds, veterinarians, abattoir workers and fleece handlers are at greatest occupational risk of contracting the disease, but others have been exposed through recreational use of the countryside.
The disease is characterised by scabby lesions that are often bloody, that form around the mouth and nares of the affected animals and in the ewe can often be found on the teats. In humans lesions are most commonly seen on the hands. If the disease affects nursing ewes they are often reluctant to allow lambs to suckle and equally, affected lambs often find normal feeding difficult. Together this can result in weakened lambs that do not thrive as well as others and can also be more susceptible to other infections. In extreme cases lamb finishing times can be prolonged.
- Orf is a common viral disease of sheep and goats characterised by the development of scabby lesions around the mouth and nostrils of lambs. On occasion it may also affect other parts particularly the teats of nursing ewes and the lower legs, around the corona. .
- Infection normally runs a course of four to six weeks and resolves with little or no intervention. However disease in young lambs is associated with poor growth during the period of infection. Serious disease may develop with extensive lesions affecting the mouth resulting, occasionally, in death.
- Previous infection with orf does not protect animals from becoming re-infected, but normally these subsequent infection should resolve over the course of 2-3 weeks.
- Infection will only establish where the skin or gums have been damaged. Thus rough food or pasture may predispose to infection. As a consequence thistle/nettle control is advised.
- The virus will not survive a winter outside but if protected from the elements it can persist in buildings for many years. Disinfection of buildings, pen divisions and feeding troughs is therefore important in the control of orf.
- Some anti-viral drugs have been shown to be effective in killing the virus, but these are only used for human infections. The topical application of antiseptics, however, may reduce bacterial contamination of the lesions and help prevent secondary complications.
- Vaccines against orf are useful in reducing the more detrimental effects of the disease, but do not provide long lasting immunity to orf and may themselves contribute to the environmental pool of infection. Although vaccinated animals may become re-infected with orf virus the resulting disease is milder and has a shorter course.
- The vaccine should never be applied to ewes less than 7-8 weeks before lambing and they should be kept away from the lambing area until the scabs, that contain large amounts of the virus, are shed.
- With the exception of pregnant ewes, animals can be vaccinated at any time and in particular if a problem with orf is encountered or if susceptible animals are to be mixed with infected animals.
- In no circumstances should the vaccine be used on farms that do not have an existing problem with orf.
- Humans can also become infected with orf virus resulting in localised swollen, red areas, which can be painful, and on occasion, result in severe systemic reactions.
Current interests and future aims:
- Finding alternative ways to deliver the orf virus vaccine.
- Developing combination vaccines against orf virus and other common diseases of sheep.