Mites, Mange & Sheep Scab
In sheep, mite infestations cause skin irritation leading to oozing (exudation) and skin thickening. The intense irritation will lead to disruption of feeding patterns.
The most important mite infestation of sheep is sheep scab, caused by Psoroptes ovis.
Sheep scab is caused by the mite Psoroptes ovis. Psoroptes are non-burrowing, surface-feeding mites, up to 0.75mm long and oval in shape.
Sheep scab was believed to have been eradicated from Great Britain in 1952, but was re-introduced during the 1970s. Subsequent national control measures included compulsory summer and autumn plunge dipping of all sheep for 1 minute and the statutory restriction of movement of sheep out of infected areas.
Sheep scab control (Sheep Scab [National Dip] Order 1990) was deregulated in July 1992 and, by autumn 1993, the disease was diagnosed in flocks throughout the UK, highlighting its highly contagious nature.
The severity of the disease is influenced by the stage of infection, the virulence of the strain of P. ovis involved, the time of year, fleece length, sheep age, sheep breed and the individual host’s immune response.
Sheep scab is characterised by intense itchiness.
Clinical signs are generally more severe in lambs and yearling sheep than in ewes.
Sheep scab can be introduced to a flock by carrier sheep, including purchased animals, sheep returning from grazing and strays. The other route of introduction is by exposure to mites in the environment, including contaminated fields, handling facilities, shared equipment, sheep transport and clothing.
Most sheep scab outbreaks occur during winter and spring months, when fleece length and environmental humidity combine to provide optimal conditions for the multiplication and development of P. ovis mites.
In young and growing lambs, P. ovis infestation can result in rapid weight loss, debilitation and death. Low birthweights and high mortality rates in lambs born to ewes with severe sheep scab during pregnancy probably result from an excessive loss of body condition in the ewes.