Inspection of wool lots at sales as a diagnostic test for louse infestation

The accuracy of visual inspection of wool lots for lice as a test for louse infestation was estimated using information provided by 178 woolgrowers in Queensland, Australia. The estimated sensitivity of inspection was 36% (95 % confidence interval, 19-58%) and the specificity was 95% (95% CI, 88-98%) . Accuracy was influenced by timing, after shearing, of pesticide applicati on for louse control and by class of pesticide last applied after shearing. Visual inspection was less sensitive (29%) if pesticides were applied >3 m onths after shearing and less sensitive (21%) if an insect growth regulator was the class of pesticide last used after shearing. Based on 36% sensitiv ity, it was estimated that 16 inspections would have to be conducted to red uce the false negative test rate to <20% in the study population. We sugges t that visual inspection of wool lots could be used to efficiently monitor the prevalence of louse infestations in Queensland sheep hocks. Positive in spection results are more likely to represent real louse infestations, rath er than a false test result, in flocks grazed in the more extensive regions of Queensland. (C) 2000 Elsevier Science B.V. All rights reserved.