A household randomized-control trial of insecticide-treated screening for malaria control in unimproved houses in Tanzania

(2025) 24:182 Odufuwa et al. Malaria Journal https://doi.org/10.1186/s12936-025-05434-2 Malaria Journal Open Access RESEARCH A household randomized‑control trial of insecticide‑treated screening for malaria control in unimproved houses in Tanzania Olukayode G. Odufuwa1,2,3,4*, Sarah Jane Moore1,2,3,5, Zawadi Mageni Mboma1,5, Rehema Mwanga1, Fatuma Matwewe1, Lorenz Martin Hofer2,3, Isaya Matanila1, Said Abbasi1, Mohammed Ally Rashid1, Rose Philipo1, Fadhila Kihwele1, Jason Moore1,2,3, Hien Nguyen6, Rune Bosselmann7, Ole Skovmand8, Jennifer C. Stevenson1,2,3, Joseph B. Muganga1 and John Bradley4 Abstract Background Installing insecticidal netting on open eaves, windows, and holes in walls of unimproved houses is a potential malaria control tool. It prevents mosquito house-entry, induces lethal and sub-lethal effects on malaria vectors, and may reduce malaria transmission. Therefore, a household epidemiological trial was conducted to assess the efficacy of insecticidetreated screening (ITS) on malaria infection and indoor vectors in Tanzania. Methods In Chalinze district, Tanzania, 421 households were randomized into two arms. In June-July 2021, one group of households’ houses was fitted with ITS (incorporated with deltamethrin and piperonyl butoxide) on eaves, windows, and wall holes, while the second group did not receive screening. After installation, consenting household members (aged ≥ 6 months) were tested for malaria infection using quantitative polymerase chain reaction after the long rainy season (June/July 2022, primary outcome) and the short rainy season (January/February 2022, secondary outcome). Secondary outcomes included indoor total mosquito per trap/night (June–July 2022), adverse effects after one month of ITS installation (August 2021), and chemical bioavailability and retention of ITS samples after one year of field use (June/July 2022). At the end of the trial, the control group received ITS. Results Malaria prevalence among residents in the ITS arm was 19.9% (50/251) and 28.3% (65/230) in the control arm after the long rains, however, this difference was not significant [adjusted odds ratio (OR) 0.67 (95% CI 0.35–1.28), p = 0.227]. Similarly, no protection was seen for ITS after the short rains, [OR 1.27 (95% CI 0.68–2.38), p = 0.452]. However, school-age children in the ITS arm had lower malaria after the long rains [OR 0.11 (95% CI 0.02–0.73), p = 0.022]. No serious adverse effects were reported. The mean number of female Anopheles mosquitoes caught per trap/night was not significantly different between arms [1.7 vs 2.4, crude relative risk: 0.71 (95% CI 0.16–3.09), p = 0.650]. ITS showed reduced chemical bioavailability and retention post-field use. The trial reported high household refusals (17–30%) in both arms in both surveys. Conclusion The trial was inconclusive because households’ refusal resulted in low power. A large cluster randomized trial of the intervention, preferably with screens treated with longer-lasting insecticides installed in houses, is needed. Trial registry: The trial was registered at ClinicalTrials.gov (NCT05125133) on October 2021 Keywords Insecticide-treated screening, ITS, Insecticide-treated nets, ITNs, Eave nets, Malaria prevalence, Mosquitoes, Trial, House modification, Tanzania *Correspondence: Olukayode G. Odufuwa Full list of author information is available at the end of the article © The Author(s) 2025. 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To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/. Odufuwa et al. Malaria Journal (2025) 24:182 Background Since 2020, the global malaria burden, particularly in subSaharan Africa (SSA), has increased [1], mainly driven by indoor malaria transmission [2]. Indoor malaria transmission, and mosquito densities in particular, are influenced by housing characteristics [3–7]. The main entry points for malaria vectors into a house are open eaves (gaps between the walls and roof ), unscreened windows, and holes in walls [8, 9]. Unimproved houses (houses built with traditional or natural materials, e.g., mud), very commonly have these features in Tanzania and SSA generally [10]. These houses are more commonly found in rural areas [11] and in areas of low socioeconomic status [10], which are frequently the areas with the greatest potential for malaria transmission [10, 12]. Although many people living in unimproved houses are provided with insecticide-treated nets (ITNs) [13], ITN coverage and use are often not optimal [14]. No demographic group is completely covered with nets [15], but some, such as school-age children, are particularly likely to be unprotected [16]. Indoor residual spraying (IRS), i.e., spraying the interior walls of houses where mosquitoes rest, is another recommended vector control tool [17]. Although it does protect all groups equally (unlike ITNs) [18], it is being scaled down in SSA largely due to its operational cost [1]. Therefore, modifying houses to kill mosquitoes and prevent their entry, could fill a gap in vector control by providing a cost-effective method that provides equitable protection. There is some evidence that some forms of house modification can prevent malaria infection [3–6], and the World Health Organization (WHO) recommends house screening as a supplementary vector control tool [17]. Previous malaria elimination activities in the United States of America, Europe, and elsewhere where house improvements, including screening with netting without insecticide was an essential activity [6]. In addition, it does not need user compliance and has the potential to protect all occupants. Often, house modification involves closing mosquito entry points, especially the eaves, with local building materials [19–21]. While this can sometimes protect household members, randomized trials have not always found an epidemiological effect at a larger scale [22]. Furthermore, even if individual households are protected by closing mosquito entry points, without having a direct insecticidal effect means there is unlikely to be a population- (...truncated)