Sheep scab is one of the most contagious parasitic diseases of sheep in Great Britain and is now considered to be endemic. 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.
Mites can also exist off the sheep and are considered to be able to remain infective for up to sixteen days. Although transmission is usually sheep to sheep; transporters, fence posts used for rubbing, bushes, trees and contaminated clothes and equipment can be a source of infection. If left untreated this disease seriously affects the welfare of sheep and has a significant economic impact through its effect on the condition of ewes, reduced quality of sheepskins, the growth rate of lambs and damage to wool.
New controls to deal with the increasing incidence of sheep scab were introduced on 17 December 2010. This new 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 Divisional Veterinary Manager as soon as possible. These new measures will also enable enforcement action to be taken against those owners and keepers whose sheep are suspected of having scab, but who repeatedly fail to take the necessary action to treat, undermining the efforts of the majority to prevent the spread of the disease. Guidance on this Order is available.
The Order was amended by the Sheep Scab (Scotland) Amendment Order 2011 which came into force on the 14th March 2011.
Within the Shetland Isles the Sheep Scab (Shetland Isles) Order 2003 still applies.
Sheep scab was eradicated from the UK in 1952 but reappeared in 1973. In the period 1973 to 1984 there were numerous outbreaks of scab in the UK. In response to this, Government made it compulsory to dip sheep twice yearly. In 1989, following a policy review, Government moved to one compulsory dip in the autumn. This was done as part of a wider move towards deregulation and making the industry more responsible for treating the condition as and when it occurred. By 1993 all national measures for sheep scab control had been deregulated to the industry. Since deregulation the number of cases has risen and sheep scab is now found throughout the entire country. In an attempt to address this rise in scab cases the Sheep Scab Order 1997 was introduced. Government, industry and local authorities now recognise that this Order is not nearly robust enough to adequately control sheep scab.
In September 2003 the Scottish Sheep Industry launched the Scottish Sheep Scab Initiative. This was a 3 year initiative which ended in September 2006. This provided a structured framework of action to raise awareness of scab in Scotland and to promote and support best practice in the management and prevention of the disease itself.
In January 2007 the Scottish Sheep Scab Industry Working Group was established to work in partnership with Government to advise and steer the development of new legislation and associated measures that would seek to reduce the incidence of scab in Scotland.
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.