Sheep scab, caused by Psoroptes ovis mites, results in intense itching for affected sheep. Repeated rubbing and skin damage leads to wool breakage and eventual complete loss of patches of fleece. Interruptions to feeding leads to dramatic weight loss and the irritation can be so bad that some sheep display fitting behaviour. The disease spreads rapidly through the flock and poses a significant welfare issue.
A history of control measures
Official control measures for sheep scab have been in place in various forms since 1870 and eradication was finally achieved in the 1950’s. Re-introduction of the disease in the 70’s and steady deregulation and relaxation of control measures led to numbers of sheep scab cases rising year on year. Anecdotal evidence suggests that the incidence of disease is still rising and in 2010 Scotland took the first step towards achieving eradication again by reintroducing sheep scab as a notifiable disease.
Sheep scab appears to be rife in the north east of Scotland at the moment, but as can be seen from the map below, there is a real hotspot here in Ayrshire too. With the fast approaching winter months being the typical season for sheep scab, there are concerns about further spread.
Spread is via direct contact, but the mites can also live in lumps of wool that are lost by repeated rubbing for up to 17 days. Contaminated clothing and shears are another source of infection. Other mites and lice can cause similar symptoms, so prompt diagnosis by a vet is important if you suspect an outbreak.
Treatment and Prevention
Whilst there are no official control measures in place across the UK today, there are actions that farmers can take to prevent sheep scab on their farm. Studies have shown that a single injection of Doramectin (Dectomax®) is effective for the treatment, and more importantly, prevention of infestation with Psoroptes mites. All animals in a group should be treated, regardless of whether they are showing signs of the disease or not. The mites are more active in the winter months, so a sensible time to administer prophylactic treatment is just before tupping, tying in nicely with the worming dose often given at this time. Animals should not be moved until 17 days after dosing to allow any mites in the environment to die.
Certain management strategies can help reduce the risk of disease. Double fencing between neighbouring sheep fields means that there is less chance of any lumps of wool harbouring mites making it across the borders from one group to another. Make sure that any shared handling equipment, including that belonging to visiting shearers is cleaned well between groups. Avoiding any animals at sales with suspicious signs, however mild, can help stop the mites being bought in. That said, some animals have sub-clinical disease and can harbour mites without showing any clinical signs at all. It is a good idea to watch sheep carefully after purchase and mixing and act quickly if you suspect sheep scab is a problem.
Eradication in the UK has been achieved once and other countries, such as New Zealand, have maintained their status of being sheep scab free for over a century. With Scotland taking the initiative, but no sign yet of the rest of the UK following suit, it is up to farmers to take the initiative and be pro-active against sheep scab being the cause of production losses on their farms.
For more information on prevention and eradication, click on the link below to NADIS.