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

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 and 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 * 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 simplicity of the intervention, 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. ### Competing Interest Statement OGO, SN, AB, IM, JBM, and SJM test vector control tools for private and public companies including Moon Netting., RB works for Moon Netting, and OS consults on design of vector control tools for private and public companies including Moon Netting. All authors declare no conflict of interest. ### Funding Statement The study is funded by the United Kingdom Medical Research Council Joint Global Health Trials (Grant number: MR/T0036771 & EPIDZR44). ESS is funded by a UKRI Future Leaders Fellowship from the Medical Research Council (MR/T041986/1). ESS and RJS acknowledge funding from the MRC Centre for Global Infectious Disease Analysis (reference MR/R015600/1), jointly funded by the UK Medical Research Council (MRC) and the UK Foreign, Commonwealth & Development Office (FCDO), under the MRC/FCDO Concordat agreement and is also part of the EDCTP2 programme supported by the European Union. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The approval to conduct the study was granted by the Ifakara Health Institute-Institutional Review Board (IHI/IRB/No: 19-2020), National Institute for Medical Research Tanzania (NIMR), Tanzania (NIMR/HQ/R.8a/Vol.IX/3473) and London School of Hygiene and Tropical Medicine (LSHTM) Observational / Interventions Research Ethics Committee (21639 - 1). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.