Evaluating Interventions Targeting Outdoor-Biting Anopheles Mosquitoes and Implications for Malaria Control

This dissertation focuses on outdoor interventions for malaria control, mostly a volatile pyrethroid spatial repellent (VPSR) product which is a passive emanator of the pyrethroid compound transfluthrin. This strategy is designed to protect outdoor environments by creating a zone of protection around the device, which in many cases is well-suited to these environments due to the inherent difficulties in preventing mosquitoes from entering outdoor spaces. In some cases, structures which could be considered outdoor environments (here, open-walled kitchens and sleeping structures) may also be protected by covering the open spaces with a netting material, explored here in a more limited group of experiments. Before assessing these interventions, the first chapter details a general overview of malaria biology and transmission, especially the role of outdoor biting. Much of our understanding about biting behaviors of Anopheles species is tied to species identity, which can be determined by morphological and molecular methods with varying Timothy A. Burton degrees of success. Two regions of DNA used for discerning Anopheles species by DNA identity were assessed for their performance and ability to produce conclusive determinations of species. The remaining chapters focus on evaluating the VPSR and screening interventions. In Chapter two, a semi-field system in southern Zambia was used to compare host-seeking rates and other entomologically relevant endpoints. Additionally, considerations for improving the relevance of results generated from the system are presented and discussed, with the primary concern relating to the possibility of the system in over-exposing the mosquitoes to the intervention and preventing repellency action that may occur in nature. Chapters three and four assess the VPSR intervention in two small-scale field trials in diverse but generally lower malaria transmission environments which experience outdoor biting that is thought to contribute to transmission. The intervention was deployed to outdoor kitchens in Macha, southern Zambia and sleeping structures in Jambi, Sumatra, Indonesia, where host-seeking was assessed in comparison to control structures with placebo devices. A final, small scale direct comparison rotational trial compared the VPSR and screening intervention against a control. Various additional factors related to mosquito activity and intervention efficacy were explored to determine that temperature, among a few other factors, plays a significant role in the reduction of host-seeking activity.