Optimizing low-technology metofluthrin emanators to extend active ingredient release while maximizing protection against malaria transmission

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We recently developed a low-technology emanator consisting of commonly available Hessian sacking impregnated with the widely-used volatile pyrethroid transfluthrin, which is slowly released into the air as a vapour. These emanators protected humans against behaviourally and physiologically resistant Anopheles arabiensis indoors and outdoors for over 2 years and killed the vast majority of mosquitoes that succeeded in feeding on protected humans. The disadvantage of transfluthrin is its relatively high melting point, which limits its vapour pressure and efficacy outside of low-altitude equatorial settings with very high night time temperatures. Fortunately, a similarly safe volatile pyrethroid called metofluthrin is also available from generic sources, which has a lower melting point so it remains volatile across the full range of temperatures relevant to malaria transmission.We therefore propose to repeat dose-optimization for this emanator prototype with metofluthrin, rather than transfluthrin, using a range of thicknesses of diffusion-retarding plastic coatings. Our primary objective is to identify the minimum dose, and optimal coating thickness at that dose, which confers at least 80% protection against exposure to biting An. arabiensis, as well as An. gambiae and An. funestus, for at least one year. Our secondary objective is to demonstrate that predicted maximum cost per year of protection is comparable with those for long-lasting insecticidal nets.If both objectives are achieved, this early phase study will be followed by an application to conduct the main study: a community-randomized controlled trial to assess impact upon malaria incidence among both users and non-users, supplemented with participatory social science studies of end-user perceptions. Both studies will be conducted in a relatively high altitude (1100m) region of west Kenya with moderate temperatures.