Small-scale field evaluation of transfluthrin-treated eave ribbons and sandals for the control of malaria vectors in rural Tanzania

Background: Early-evening and outdoor-biting may compromise the efficacy of frontline malaria interventions, notably insecticide treated nets (ITNs). This study investigated the potential of low-cost insecticide-treated eave ribbons and sandals against mosquitoes indoors and outdoors in rural-Tanzanian villages where ITNs are widely used and malaria vectors have resistance to pyrethroids. Methods: Seventy-two (72) households were selected from three villages, (24 households per village), and upon consent recruited into the study. The households were divided into four study arms and assigned either transfluthrin-treated sandals (TS), transfluthrin-treated eave ribbons (TER), a combination of TER and TS or experimental controls. Each study arm had 18 households in total, all of which received new ITNs. Mosquitoes were collected using double net traps (to assess outdoor-biting), CDC-light traps (to assess indoor-biting) and Prokopack® aspirators (to assess indoor-resting). To evaluate the level of protection conferred by these tools, mosquito biting and resting densities were compared between treatment groups and control. Additional experiments were done in experimental huts to assess mortality of wild mosquitoes exposed to the treatments. Results: : TERs reduced indoor-biting, indoor-resting and outdoor-biting Anopheles arabiensis by 60%, 73% and 41% respectively, while TS reduced the densities by 18%, 40% and 42% respectively. When used together, TER & TS reduced outdoor-biting An. arabiensis by 57% and indoor-biting by 53%. Protection against Anopheles funestus ranged between 42 - 69% by TER and 57 - 74% by TER & TS combined, but protection against Culex mosquitoes did not exceed 32% even when TER and TS were combined. Mortality of field-collected mosquitoes exposed to TER, TS or both interventions ranged from 56 – 78% for An. arabiensis , 47 – 74% for An. funestus and 58 – 63% for Culex spp. Conclusion: Transfluthrin-treated eave ribbons and sandals or their combination can offer moderate household-level protection against common malaria vectors. Their efficacy is likely to be magnified by the transfluthrin-induced mortality, which was observed despite the prevailing pyrethroid resistance in the study area. Overall, the transfluthrin-treated eave ribbons were more efficacious than the sandals. Further studies are needed to improve the technologies and validate their potential as supplementary interventions against mosquitoes and mosquito-borne diseases.