What is sheep scab? Sheep scab is an allergic dermatitis caused by a reaction to the faeces of the scab mite, Psoroptes ovis (P. ovis) (Figure 1) and is characterised by sheep itching and scratching against objects such as fence posts, gates or walls or nibbling and/or biting at their fleeces . It is a welfare issue as sheep can spend a considerable portion of their time scratching and can also result in increased mortality rates in young lambs that are born to affected ewes. Sheep scab is a notifiable disease. If sheep scab is suspected or confirmed in a flock, the Department of Agriculture, Food and the Marine must be notified through the Veterinary Inspector at the Regional Veterinary Office. What are the clinical signs? In the initial stages of infestation, animals often appear clinically normal or they may be restless, have a discoloured fleece and show increased scratching behaviours. In later stages, animals become severely itchy and the intense rubbing and scratching can result in wool loss, skin thickening, scabbing and wounds. The intense itching can also result in a loss of condition due to decreased feed intake and secondary infections. When does the condition usually occur? The condition mainly occurs during the autumn and winter months. However, cases have also occurred during summer months, with lambs being particularly affected. What is the life cycle? P. ovis is a non-burrowing mite which lives on the skin of its host (sheep). Over a period of approximately 40 days, female mites lay one to two eggs per day. The life cycle from an egg to an adult takes approximately 14 days to complete and each development stage involves a moult which lasts 12 – 24 hours, during which time that particular life cycle stage does not feed. The mite population grows rapidly within 6-8 weeks after infestation, resulting in the observed clinical signs as described above.
Figure 1 . Sheep scab mite recovered from a wool sample.
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