Psoroptic mange: rising prevalence in UK sheep flocks and prospects for its control
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Psoroptic mange in sheep, known as scab, is caused by infestation by the astigmatid mite Psoroptes ovis (Hering). The disease has been widely prevalent and economically important in Europe for many hundreds of years. In the UK, intensive control measures over the first half of the twentieth century, involving compulsory treatment of infested flocks with organochlorine insecticides and movement controls, resulted in apparent eradication of the disease by 1952. However it was inadvertently reintroduced with imported stock in 1972. Twenty years of unsuccessful attempts to re-eradicate the disease then followed. Eventually, concern over the effects of the widespread use of acaricides on human health and the environment, and the failure of compulsory treatment programmes to control the disease, led in 1992 to deregulation of sheep scab and removal of compulsory national treatment programmes. Following this change, scab has very quickly become increasingly common and problematic. Nationally, there were estimated to be only 40 and 120 outbreaks per year in 1989 and 1992, but prevalence was estimated to have risen to 3,000 in 1997 and then 7,000 outbreaks by 2004. This has led to calls to re-impose eradication measures. Here, the biology of Psoroptes mites and the spread of the disease following reintroduction are described; the formidable obstacles to the success any proposed new eradication programme in the UK are then discussed.