Orf - a Serious disease affecting livestock and man
Published on 26 July 2010 in Food, health and wellbeing
Introduction
Orf is a highly contagious viral disease that causes painful scabby lesions on the lips and nostrils of affected animals. It is a significant welfare problem for both sheep and goats not just in the UK but worldwide and is regarded as being in the top 20 most important viral diseases affecting the rural poor in developing countries.
It mainly affects younger animals in their first few months of life andcan retard their growth as severely affected lambs and kids may not be able to feed for several days, becoming weakened and prone to other diseases. Orf is therefore not only a welfare problem for the animals, but also has severe economic effects as it delays finishing for market.
An additional hazard is that the disease is zoonotic (i.e. can be transmitted to humans) posing a substantial occupational risk to farmers, shepherds, vets and carcass processors. A study in a farming community in Wales suggested that as many as 30% of people may suffer orf lesions at some time in their life with 15% of those requiring time off work, with some even requiring hospitalisation.
The scabs caused by the orf virus in and around the mouth and lips od infected animals normally heal without treatment in 4-6 weeks however the lesions can become extensive and spread to other parts of the body and secondary bacterial infections are not uncommon. If the affected animal is still suckling there is also the danger of transmission to the ewe’s udder, which in turn can lead to acute mastitis.
Similar diseases occur in cattle, namely pseudocowpox and papular stomatitis. Although generally considered milder in cattle than orf in sheep, more severe forms of these diseases also occasionally occur.
Key Points
- Although there is a vaccine against orf available, it is a fully virulent virus that can cause disease in its own right. For that reason its use is limited to farms which a known problem with the disease and cannot be given to sheep 7-8 weeks before they are due to lamb.
- Although the vaccine against orf is useful in reducing the effects of the disease on farms which have a history of orf, they do not provide long lasting solid immunity to orf and may contribute to the environmental pool of infection.
- Thorough disinfection of farm buildings is very important in the control of this disease as it is generally considered that the year to year spread and persistence of orf in sheep is based on animals becoming infected with virus shed into the environment from previously infected animals
Orf is a zoonotic infection (can spread from animals to humans) so it also poses a significant health risk to humans who come in contact with infected animals.
- Some anti-viral drugs have been shown to be effective in killing the orf virus, but these are currently not licensed for the treatment of this disease. The topical application of antiseptics, however, may reduce bacterial contamination of the lesions and help prevent secondary complications.
- The symptoms of orf are very similar to those of foot and mouth disease virus and blue tongue virus, so orf is an important differential diagnosis for other pathogens like these.
Research Undertaken
Research at Moredun has concentrated on three areas;
- understanding how orf virus interacts with the sheep host to cause the disease that it does;
- developing improved diagnostics for orf; and
- developing improved control strategies for orf including improved vaccines.
The current orf virus vaccine is a virulent virus that causes a lesion to form and which can also contribute to the environmental pool of the virus. Our focus therefore has been to attempt to get a higher degree of protection from a safer form of the virus. We have been working with one viral protein in particular that may prevent efficient recognition of the virus by the sheep immune system. Work is underway to determine whether vaccines that exploit the properties of this protein may provide a positive way forward.
Policy Implications
Orf is endemic both in the UK and worldwide wherever sheep and goats are farmed. It is regarded as being in the top 20 most important viral diseases affecting the rural poor in developing countries.
A recent sero-survey conducted across Scotland has suggested that few farms in this country have not been affected by orf, although the true cost of the disease is unknown.
Orf is a serious zoonotic infection and poses a significant health risk to humans. A study in a farming community in Wales suggested that as many as 30% of people may suffer orf lesions at some time in their life with 15% of those requiring time off work, with some even requiring hospitalisation.
Author
Dr Colin McInnes colin.mcinnes@moredun.ac.uk
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