Sheep scab: how to spot and report the disease

Sheep scab is one of the most contagious parasitic diseases of sheep in Great Britain.

The condition itself is a form of allergic dermatitis caused by the highly parasitic scab mite Psoroptes ovis. The female mite lays one or two eggs daily in the fleece of the sheep for about 40 days. Under ideal conditions, larval mites hatch from eggs and go through various development stages to become adults after two weeks.

The mites feed on the surface of the skin. The intense irritation they cause is believed to be a result of an allergic reaction of the sheep to the mite and its faeces. The severity of this reaction varies with the strain of the mite, between individual sheep and also between breeds.

Clinical signs

Sheep may be suspected as being infected with sheep scab if one or more of the following symptoms are exhibited:

• mild to excessive rubbing/scratching against fence posts, etc.
• mild to excessive nibbling and biting
• dirty areas of fleece due to rubbing and scratching - especially with the hindfeet behind the shoulder.
• 'nibble' (touch hypersensitivity) response, spontaneous or in response to handling or manipulation of a lesion
• tags of fleece on flanks due to biting or rubbing (similar to lice infestations)
• clean areas of fleece due to licking/biting at or near lesions*
• standing apart from flock, dull and depressed*

*Only when in combination with other symptoms described

During advances stages of disease:

• areas of wool loss and bare areas especially on shoulders and flanks
• poor body condition
• clumping or clotting of wool
• damaged moist red skin
• dry crusty scabs with moist red borders

In both early and advanced stages not all of the animals in the flock may show symptoms but you should assume all are infected.

How sheep scab is spread

Sheep scab is mainly spread by direct contact between sheep. The mites that cause the disease can also be picked up from fences, posts and trees that infected sheep rub against. Mites can also be spread on the clothing and equipment of sheep handlers.

Human health implications

Sheep scab only affects sheep. Humans are not affected.

Disease control

Given the prevalence of this disease and its economic and welfare impact it was identified under the Scottish Animal Health and Welfare Strategy in 2009 as a condition that required targeted action from both government and industry.

Legislation

The Sheep Scab (Scotland) Order 2010 places a legal obligation on any person who has reason to believe that sheep in their possession or care have sheep scab to notify their local Animal & Plant Health Agency (APHA) office as soon as possible.

The Order was amended by the Sheep Scab (Scotland) Amendment Order 2011. Within the Shetland Isles the Sheep Scab (Shetland Isles) Order 2003 still applies. Further information on Sheep scab notifications reported to the APHA is available.

Biosecurity

Biosecurity is about being aware of the ways disease can spread and taking every practical measure to minimise the risk of disease spreading. The advice details practical things you can do on your farm to help prevent the introduction and spread of sheep scab to and from your animals.