House modifications using insecticide treated screening of eave and window as a vector control tool: evidence from a semi-field system in Tanzania and simulated epidemiological impact

Abstract

Background Gaps in unimproved house structures, especially in eaves and windows, allow vector entry and facilitate indoor vector biting and disease transmission. Simple house modification tools that target unimproved houses have the potential to reduce human exposure to bites in the home. This study assessed the performance of Insecticide Treated Screening (ITS) for eaves and windows, incorporated with deltamethrin and piperonyl-butoxide (PBO) compared to a PBO Insecticide Treated Net (ITN) in Tanzania. Method A randomised Latin-square (4x4) design study was conducted in four experimental huts built in a large netting cage to allow recapture of mosquitoes inside and outside of the huts within a semi-field system (SFS). Four treatment arms were evaluated: 1) new ITS; 2) 12-months naturally-aged ITS; 3) 12 months field-used PBO ITNs (standard of care in Tanzania), and 4) no treatment. The study was performed for 32 nights using 30 mosquitoes per strain, per hut, and per night, i.e., 120 (4x30) mosquitoes per hut-night. Four laboratory-reared strains were used: vectors of malaria (Anopheles arabiensis and An. funestus), dengue (Aedes aegypti) and nuisance biting (Culex quinquefasciatus). Recaptured mosquitoes were assessed for mortality at 72 hours (M72), blood feeding and hut entry. A simulation exercise with a modified mechanistic model tracking Plasmodium falciparum malaria was used to illustrate the potential epidemiological impact from these products. Results Against all mosquito species tested relative to field-used ITNs, new-ITS induced higher M72 [OR:2.25(95%CI:1.65–3.06),p < 0.0001], and M72 was similar for aged-ITS [OR:0.80(95%CI:0.59–1.08),p = 0.141]. ITS reduced more mosquito blood feeding [new OR:0.02(95% CI:0.01–0.03) and aged OR:0.09(95%CI:0.05–0.14)] and hut entry [new IRR:0.10(95%CI:0.08–0.13) and aged IRR:0.25(95%CI:0.21–0.31)] (p < 0.0001). Transmission model estimates indicate epidemiological impacts of ITS may supersede those of PBO ITNs at the population level. The model results indicate that the potency of these impacts depends on assumed intervention percentage cover, durability and mosquito bionomics. Conclusions ITS is an efficacious tool for controlling vectors transmitting malaria, and dengue, and reducing nuisance biting, as assessed in a semi-field setting. Given the intervention’s simplicity, it should be considered as an additional or stand-alone tool for screening of unimproved houses.