Creating mosquito-free outdoor spaces using transfluthrin-treated chairs and ribbons

Abstract

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. This compromises 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 efficacy against mosquitoes of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin, and fitted to chairs and outdoor kitchens, respectively.

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 24 h-mortality. Finally, The World Health Organization 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 only 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 and bendiocarb), but resistant to pyrethroids commonly used on LLINs (deltamethrin and permethrin).

Conclusion: Most houses had actively-used peri-domestic outdoor spaces where exposure to mosquitoes occurred. The transfluthrin-treated chairs and ribbons reduced outdoor-biting malaria vectors in these peri-domestic spaces, and also elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two new prototype formats for transfluthrin emanators, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne pathogens in areas where peri-domestic human activities are common.

Keywords: Eave ribbons; Ifakara Health Institute; Malaria vectors; Outdoor-biting; Peri-domestic spaces; Spatial repellents; Transfluthrin; Transfluthrin-treated chairs.

Fig. 1

Illustration of the location of Ulanga and Kilombero districts in the map of Tanzania (a), the location of Lupiro village in Ulanga district (b) and household location in Lupiro village showing both surveyed and those did not (c)

Fig. 2

Design and prototyping of the wooden chairs at the local carpentry (a), overview of the prototyped chair (b), fitting transfluthrin-treated hessian mat underneath the chair (c), one transfluthrin-treated chair with the DN-Mini trap positioned 0.5 m (d), two transfluthrin-treated chairs with DN-Mini trap installed 0.5 m (e); and outdoor kitchen fitted with transfluthrin-treated sisal ribbon with DM-Mini trap positioned 1.2 m (f)

Fig. 3

Illustration of houses with veranda extension physically characterized during survey (a), houses with built-up peridomestic space away from the main house commonly used for cooking (b) and houses with non-built-up peridomestic space physically characterized as under the tree (c)

Fig. 4

Picture of the first mosquito-free zone established at Ifakara Health Institute in January 2020. The chairs have transfluthrin-treated hessian mats underneath, but are layered with plastic sheeting to prevent rainfall and user contact