Creating mosquito-free outdoor spaces using transfluthrin-treated chairs and ribbons
Authors: Masalu John Paliga , Finda Marceline , Killeen Gerry F. , Ngowo Halfan S. , Pinda Polius G. , Okumu Fredros O. 
Published: February 2020

Background: Residents of malaria-endemic communities spend several hours outdoors performing different activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. These behaviors compromise effectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efficacies of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin and respectively fitted to chairs and outdoor kitchens, against mosquitoes.

Methods : Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efficacies of locally-made transfluthrin-emanating chairs and hessian ribbons were tested in outdoor environments of 28 households in dry and wet seasons, using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Field-collected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24h-mortality. Finally, WHO insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages.

Results : Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peri-domestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70-85%, while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 77-81% reduction in the general peri-domestic area. Almost all the field-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfluthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl & bendiocarb) but resistant to pyrethroids commonly used on LLINs (deltamethrin & permethrin).
Conclusion: Most houses had actively-used peri-domestic outdoor spaces where exposures to mosquitoes occur. Both the transfluthrin-treated chairs and ribbons reduced outdoor-biting malaria vectors in the peri-domestic spaces, and elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two prototype formats, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne diseases in areas with significant peri-domestic activities.
Keywords : Peri-domestic spaces, transfluthrin-treated chairs, eave ribbons, transfluthrin, spatial repellents, outdoor-biting, malaria vectors, Ifakara Health Institute.