Control and management of sheep mange and pediculosis in Great Britain.

The patterns of insecticide use for the prevention and control of sheep lice and Psoroptes mites, in England, Wales and Scotland, in 2003-2004, were examined using data from a retrospective questionnaire. Overall, 375 of the 966 (39%) farmers who responded said that they treated at least once to prevent louse infestation. For scab, 426 of the 966 (44%) farmers who responded said that they had treated prophylactically to prevent the disease. There were no significant differences between regions in the number of times farmers treated to prevent lice (chi(2)=0.54, P>0.1) or scab (chi(2)=0.16, P>0.1). Among the farmers who applied prophylactic treatment 23% had a subsequent outbreak of lice and 17% had an outbreak of scab. The majority of sheep farmers who used preventative treatment did so in June and July. Where a second treatment was given it was largely in October. For lice, 52% of farmers used pyrethroids to prevent and 70% to treat louse infestation. For scab prophylaxis, most farmers said that they used either the macrocyclic lactones (41%) or organophosphates (36%) as a preventative. For the therapeutic treatment of scab outbreaks, macrocyclic lactones (largely doramectin) were used on 58% of sheep farms. The high national prevalence of sheep scab and pediculosis indicates that current control methods are failing to contain these ectoparasites. The results of this study suggest that a large proportion of insecticide applications take place at times of year when they might expect to be relatively ineffective, and the use of inappropriate compounds for the parasites in question is common. The widespread use of macrocyclic lactones in particular for scab prevention and control is of concern, because of the additional use of these compounds in parasitic worm control and the potential that their overuse will hasten the development of resistance.