Sheep scab is caused by a mite (Psoroptes ovis) and is transmitted by direct contact with infected sheep or objects. The scab mites live on the surface of the skin causing an allergy to their droppings-it is this allergic reaction that causes the sheep to scratch.
It can occur at any time of the year but flare ups within the flock often occur when the sheep are housed in winter.
The symptoms of sheep scab look very similar to symptoms caused by lice (Bovicola ovis). It is essential to get an accurate diagnosis before treating as not all products that treat scab are effective against lice and vice versa. In fact, the only treatment that will effectively treat both scab and lice is plunge dipping with an organophosphate (OP) dip. Other chemical treatments are available that will treat either scab or lice but not both together. Care must be taken to ensure you have the correct product to treat the correctly indentified parasite. The correct diagnosis can be obtained by asking your vet to take a wool sample and identifying the parasite under a microscope. For further information on how to treat scab and lice speak to your vet and refer to the leaflet on Licensed treatments for external parasites of sheep.
Further information on how to control ectoparasites(external parasites) in sheep can be found in the booklet- Effective control of ectoparasites in sheep.
Between November 2006 and March 2007 HCC, with support from Farming Connect and the British Wool Board, undertook a survey of Welsh sheep farms to get an indication of the prevalence of ectoparasites in Wales.
This survey showed that 11.6%, 57.5%, 11.1% and 15% of Welsh farms were affected by scab, flystrike, ticks and lice respectively.
Another finding of the survey was that not enough farmers are quarantining new stock brought onto their farms. Sheep can carry scab mites but not show any symptoms for several weeks so just because the new stock you have just bought are not scratching does not mean they do not have scab mites which could infect your flock. Isolate all incoming stock for 3 weeks and treat for scab regardless of whether they are showing signs of scab.
A full report outlining the findings of the survey is available here
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