71 Physical and chemical house entry barriers to enhance odour-baited trapping for malaria control

Background: Odour-baited mosquito trapping is a promising new malaria intervention that lures, traps and kills mosquitoes. However, mosquitoes still bypass the trapping system and enter easily accessible African households through the open eaves. In this study, house screening and a spatial repellent were used as a physical and chemical house entry barrier to determine whether these interventions can protect people from malaria mosquitoes by decreasing mosquito house entry and simultaneously increasing odourbaited trapping efficacy. Methods: In an experimental greenhouse in Kenya, two semi-field experiments were conducted. In the first experiment, three physical house adjustment interventions were tested against using no intervention: house screening (block); odour-baited trapping (pull) and both interventions (block-pull). In the second experiment, three chemical interventions were tested against using no intervention: a cotton band around the eaves impregnated with the spatial mosquito repellant Delta-undecalactone (push); odourbaited trapping (pull) and both interventions (push-pull). The effects of interventions were evaluated by comparing mean trap catches of the odour-baited trap outside, and mean mosquito house entry. Results: In the first experiment (block-pull), the chance of a mosquito getting caught by an odour-baited trap more than doubled (OR=2.163) when complementing odour-baited trapping with house screening (P<0,001). All interventions significantly reduced mosquito house entry (p<0,001), with the strongest protective effect for the combined intervention of house screening and odour-baited trapping (OR=0.10). The interventions of the second experiment did not have a significant effect on odour-baited trap catches (p=0.584), nor mosquito house entry (p>0.172). Discussion: This study shows that house screening could be a valuable addition to odourbaited mosquito trapping for malaria control and confirmed the strong effect of house screening on mosquito house entry. In contrast to other studies, a chemical barrier of Delta-undecalactone did not improve the protection against malaria mosquitoes. However, push-pull strategies might still be a viable alternative to house screening, since the absence of an effect might have been caused by an interaction of the intervention with the experimental environment.