sheep-scab in Britain were at £8 million (US$12 million) annually in 2005. Transmission between hosts is readily accomplished by contagion during flocking contact and also on fomites such as scraps of sheep's wool because these relatively large and robust mites can survive for one to two weeks off their host. Psoroptes ovis infests the superficial layers of the skin. Irritation of the outer skin by the mite's mouthparts and saliva results in a complex form of cutaneous hypersensitivity and inflammatory exudation of serum and fresh cells. The mites feed on this moist exudate. The skin loses its hair (depilation) at the sites of infestation and this may be extensive. As a result of the movement of the mites into areas of fresh skin, large scabs accumulate on the raw skin left behind. The mites cause intense pruritus (itching). In cases of heavy infestations, the host grooms compulsively, aggravating the depilation, and it may become mentally distressed. Psoroptes ovis infests sheep worldwide and can be a serious welfare and animal-production problem for sheep farmers. Infestations of cattle with mites of the similar genus Chorioptes, in combination with Sarcoptes mite infestation, has been shown to cause a failure to gain body weight by over a two-month period compared to cattle without the mites. Psorergatic skin disease Psorergates bovis causes pruritus, but little clinical harm to cattle. In contrast, Psorergates ovis feeding on sheep induces inflammatory and hypersensitive reactions in the epidermis, resulting in intense pruritus and formation of scabs. Further damage to the skin and fleece of sheep occurs when the sheep groom compulsively. Economic loss is incurred by damage and depilation of the wool fleece. This species is prevalent in Australia, New Zealand, southern Africa, and the Americas. Sarcoptic skin disease Sarcoptic mites as adults are microscopic, nearly circular in outline, and their legs are short, adapted for burrowing. The females, after mating with males on the surface of their host's skin, burrow into the living layers of the epidermis (mainly the stratum spinosum). They make tunnels horizontal to the surface of the skin. Here, eggs are laid and development of larvae and nymphs occurs. The mites have low mobility and transmission between hosts occurs only during close contact. The feeding of the mites and their excretory products irritates and inflames the skin, causing intense pruritus. Dermal hypersensitivity reactions develop in the host. Chronic infestations lead to thickening of the skin