Jennifer Clare Stevenson

Background: Gaps in unimproved house structures, especially in eaves and windows, allow mosquito entry, increasing indoor vector-borne disease transmission. Simple modifications to such houses may reduce human exposure, and insecticide treatment may kill mosquitoes, benefiting all community members. This study evaluated insecticide-treated screening (ITS) for eaves and windows, incorporated with deltamethrin and piperonyl butoxide (PBO), compared to a permethrin and PBO-treated bednet in Tanzania. Method: A randomised Latin-square design (4 × 4) was used in four experimental huts within a large netting cage to allow mosquito recapture inside and outside of huts. Four treatments were evaluated: (1) new (12-month stored) ITS; (2) 12-month naturally-aged ITS; (3) 12-month field-used pyrethroid-PBO bednet (standard of care in Tanzania), and (4) no treatment. The study was performed for 32 nights using 30 mosquitoes per strain, per hut per night. Four laboratory-reared strains were used: malaria vectors ( Anopheles arabiensis and An. funestus ), dengue vector ( Aedes aegypti ), and nuisance biting ( Culex quinquefasciatus ). Recaptured mosquitoes were assessed for mortality at 72 h, blood-feeding, and hut entry. A simulation with a modified mechanistic model tracking Plasmodium falciparum malaria was used to illustrate potential epidemiological impact from these products. Results: Against all mosquito species compared to 12-month aged pyrethroid-PBO-treated bednet, new ITS induced higher mortality [Odds Ratio:2.25(95%Confidence Interval:1.65–3.06), p < 0.0001], and aged-ITS was similar [OR:0.80(95%CI:0.59–1.08), p = 0.141]. Both new and aged ITS significantly ( p < 0.0001) reduced mosquito blood-feeding [new OR:0.02(95% CI:0.01–0.03); aged OR:0.09(95%CI:0.05–0.14)] and hut entry [new IRR:0.10(95%CI:0.08–0.13); aged IRR:0.25(95%CI:0.21–0.31)]. Transmission model estimates indicate epidemiological impacts of ITS may supersede pyrethroid-PBO-treated bednets at the population level. The model results indicate impact potency depends on assumed intervention percentage cover, durability, and mosquito bionomics. Conclusions: This study introduces a standardised semi-field bioassay to evaluate ITS, generating entomological data that, for the first time, enabled modelling of its potential impact on malaria transmission. ITS is an efficacious tool for public health as it kills substantial proportions of malaria and dengue vectors, and reduces nuisance biting. Given its simplicity, it should be considered an additional or stand-alone tool for screening unimproved houses.

Controlling mosquito-borne diseases is increasingly challenging due to factors such as outdoor and early biting mosquitoes and logistical or behavioral barriers, particularly in displaced populations where the use and efficacy of core interventions are inadequate. This study evaluated the impact of BiteBarrier, a transfluthrin-based spatial emanator, over eight weeks of aging against multiple mosquito species in semi-field system simulating both indoor and outdoor settings. We assessed the protective efficacy using both landing rate and feeding success methods across five mosquito species, including pyrethroid susceptible Anopheles gambiae sensu stricto (s.s.) and Aedes aegypti, An. gambiae s.s. with knock down resistance (KDR), and pyrethroid resistant An. funestus and Culex quinquefasciatus with upregulation of mixed function oxidases. The results show that the feeding endpoint provides more robust estimates of protective efficacy compared to the landing endpoint. The BiteBarrier provided over 93% (95% CI: 92 - 93) protection indoors and 80% (95% CI: 78 - 81) outdoors against mosquito bites and substantial mortality 47% (95% CI: 43 - 53) indoor and 26% (95% CI: 22 - 30) outdoors, regardless of mosquito species or resistance status. Overall, the BiteBarrier shows potential as a tool for reducing mosquito bites and vectorial capacity, offering protection over at least eight weeks of use for both indoor and outdoor environments.

Background: Despite extensive use of available vector control tools, the burden of malaria and dengue continues to increase throughout sub-Saharan Africa. Gaps in house structures, most especially in eaves and windows, allow vector entry and facilitate indoor vector biting and disease burden. Simple house modification tools that target these structures therefore have the potential to reduce human exposure to bites in the home. This study assessed the performance of Insecticide Treated Screening (ITS) comprising Eave Nets and Window Screens (ITENs & ITWS), incorporated with deltamethrin and piperonyl-butoxide (PBO) in Tanzania. Method: A randomised Latin square (4 X 4) was conducted in four experimental huts built in a semi-field system (SFS). Each hut within each of the chambers of the SFS was covered with a large netting cage to allow recapture of mosquitoes inside and outside of the huts. Four treatment arms were evaluated: 1) new ITS; 2) 12-months naturally-aged ITS; 3) estimated 12 months field-used Olyset® Plus ITNs (Standard-of-Care in Tanzania), and; 4) no treatment. The study was performed for 32 nights using a minimum of 30 mosquitoes per strain per night, that is, a total of 120 (4 x 30) mosquitoes per hut per night. Four laboratory-reared strains were used: transmitters of malaria ( Anopheles arabiensis and An. funestus ) and dengue infection ( Aedes aegypti ) and those known for nuisance biting ( Culex quinquefasciatus ). Recaptured mosquitoes were assessed for mortality at 72 hours (M72), blood feeding and hut entry endpoints. A simulation exercise with a modified mechanistic model tracking Plasmodium falciparum malaria was used to illustrate the potential epidemiological impact from these products. Results: New ITS induced higher M72 than field-used ITNs against all mosquito species tested [OR: 2.25 (95%CI: 1.65-3.06), p<0.0001], while M72 was similar between aged ITS and field-used ITNs [OR: 0.80 (95%CI: 0.59-1.08), p=0.141]. Both new, and aged ITS reduced more mosquito blood feeding and hut entry than field-used ITNs for all mosquito species tested (p<0.0001). Transmission model estimates indicate epidemiological impacts of ITS may supersede those of 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 those known for nuisance biting in a semi-field setting. Given the intervention’s simplicity, it should be considered as an additional (or stand-alone) tool alongside behavioural change educational efforts to encourage the repurposing of old ITNs for house screening.