Isolation of the Gram negative bacterium Serratia marcesens from the sheep scab mite Psoroptes ovis. Vet. Rec

THE astigmatid mite Psoroptes ovis is a globally distributed obli-gate ectoparasite of sheep, cattle and several other mammals. On sheep the mites live at the base of the fleece where they feed mainly on fluid exuded from the epidermis. Infestation with the mite leads to sheep scab which is characterised by intense pruritis, weight loss and hide damage. Untreated sheep scab is often life threatening. In the UK alone, around 50 million sheep are at risk from infestation and, until recently, the only efficient method of prevention and control was to submerge the sheep in a Ministry of Agriculture, Fisheries and Food approved pesticide. Misuse of organophosphate-based compounds (ops), the most effective agents against P ovis, and a range of other ectoparasites and fly-strike has been linked to ill health suffered by farm workers. Alternative compounds exist, but none offer the broad-spectrum activity of oPs and they often have other difficulties associate