Sheep scab is caused by a tiny, pearly-white mite (Psoroptes ovis) just visible to the naked eye. Mites live on the skin surface causing a skin allergy to their droppings.
Scab can be found throughout the year, but the majority of cases occur between October and March. Scab mites live their entire lives on the sheep, introduced into a flock through contact or purchase of infested stock. Mites can however live off the sheep for 16 to 17 days in tags of scabby wool, clothing, barns or livestock transport.