Orf Infection of Sheep
Summary written by Colin McInnes BSc PhD MRCVS
Taken from Moredun Foundation Newsheet Volume 5 No 2 (May 2009)
- 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 lower legs of lambs.
- 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 occasionally with extensive lesions affecting the mouth resulting, in some instances, in death.
- Infection will only establish where the skin or gums have been damaged. Thus rough food or pasture may predispose to infection.
- 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 currently not licensed for the treatment of orf. 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 solid 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 a 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.
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