Abstract Background The northern fowl mite (NFM), Ornithonyssus sylviarum , is one of the most important external parasites of commercial poultry in the USA. NFM feeds on blood, causing irritation and stress to infested birds and potentially reducing egg production in flocks with high levels of mite infestation. Fluralaner is a systemically active insecticide and acaricide. We report on two studies that evaluated the efficacy of fluralaner administered to layer chickens in medicated drinking water through two single doses of 0.5 mg fluralaner per kg chicken body weight at 7 days apart for control of NFM. Methods In two separate studies, white Leghorn chickens ( Gallus gallus domesticus ) were exposed to NFM so that they developed mite infestations. The first study was a dose confirmation study ( n = 64 pullet birds per treatment group). The second study was a field efficacy study ( n = 400 layer birds per treatment group). Once infested with NFM, birds were assigned to Medicated or Control treatment groups. In the Medicated group, a fluralaner solution was administered through medicated drinking water on study day 0 and again on day 7. The Control group received only unmedicated drinking water. NFM present in the vent region of birds were recorded prior to treatment (day −7 for dose confirmation and day −5 for field efficacy studies) and post-treatment on days 2, 8, 14, 19, and 28. In each study, product efficacy was determined by comparison of mite counts on Medicated and Control birds. Results The number of mites was significantly reduced on Medicated group birds relative to Control group birds by day 2. At day 2 post-treatment, 99% control efficacy (> 99% for geometric mean) was achieved in the dose confirmation study and > 96% (> 99% for geometric mean) control efficacy was achieved in the field efficacy trial. Control efficacy in both studies exceeded 99% from day 8 to day 28. There were no adverse health impacts observed in birds treated with fluralaner. Conclusions This study confirms the effectiveness of fluralaner for control of NFM when administered to chickens through drinking water as two single doses of 0.5 mg/kg chicken body weight at 7 days apart. Graphical Abstract
Gerry et al. (Wed,) studied this question.