The efficacy of insecticide-treated window screens and eaves against Anopheles mosquitoes: a scoping review

Background Female mosquitoes serve as vectors for a host of illnesses, including malaria, spread by the Plasmodium parasite. Despite monumental strides to reduce this disease burden through tools such as bed nets, the rate of these gains is slowing. Ongoing disruptions related to the COVID-19 pandemic may also negatively impact gains. The following scoping review was conducted to examine novel means of reversing this trend by exploring the efficacy of insecticide-treated window screens or eaves to reduce Anopheles mosquito bites, mosquito house entry, and density. Methods Two reviewers independently searched PubMed, Scopus, and ProQuest databases on 10 July, 2020 for peer-reviewed studies using insecticide-treated screens or eaves in malaria-endemic countries. These articles were published in English between the years 2000–2020. Upon collection, the reports were stratified into categories of biting incidence and protective efficacy, mosquito entry and density, and mosquito mortality. Results Thirteen out of 2180 articles were included in the final review. Eaves treated with beta-cyfluthrin, transfluthrin or bendiocarb insecticides were found to produce vast drops in blood-feeding, biting or mosquito prevalence. Transfluthrin-treated eaves were reported to have greater efficacy at reducing mosquito biting: Rates dropped by 100% both indoors and outdoors under eave ribbon treatments of 0.2% transfluthrin (95% CI 0.00–0.00; p < 0.001). Additionally, co-treating window screens and eaves with polyacrylate-binding agents and with pirimiphos-methyl has been shown to retain insecticidal potency after several washes, with a mosquito mortality rate of 94% after 20 washes (95% CI 0.74–0.98; p < 0.001). Conclusions The results from this scoping review suggest that there is value in implementing treated eave tubes or window screens. More data are needed to study the longevity of screens and household attitudes toward these interventions.

Impact of increased ventilation on indoor temperature and malaria mosquito density: an experimental study in The Gambia

In sub-Saharan Africa, cooler houses would increase the coverage of insecticide-treated bednets, the primary malaria control tool. We examined whether improved ventilation, using windows screened with netting, cools houses at night and reduces malaria mosquito house entry in The Gambia. Identical houses were constructed, with badly fitting doors the only mosquito entry points. Two men slept in each house and mosquitoes captured using light traps. First, temperature and mosquito density were compared in four houses with 0, 1, 2 and 3 screened windows. Second, carbon dioxide (CO 2 ), a major mosquito attractant, was measured in houses with (i) no windows, (ii) screened windows and (iii) screened windows and screened doors. Computational fluid dynamic modelling captured the spatial movement of CO 2 . Increasing ventilation made houses cooler, more comfortable and reduced malaria mosquito house entry; with three windows reducing mosquito densities by 95% (95%CI = 90–98%). Screened windows and doors reduced the indoor temperature by 0.6°C (95%CI = 0.5–0.7°C), indoor CO 2 concentrations by 31% between 21.00 and 00.00 h and malaria mosquito entry by 76% (95%CI = 69–82%). Modelling shows screening reduces CO 2 plumes from houses. Under our experimental conditions, cross-ventilation not only reduced indoor temperature, but reduced the density of house-entering malaria mosquitoes, by weakening CO 2 plumes emanating from houses.

Novel control strategies for mosquito-borne diseases

Mosquito-borne diseases are an increasing global health challenge, threatening over 40% of the world's population. Despite major advances in malaria control since 2000, recent progress has stalled. Additionally, the risk of Aedes -borne arboviruses is rapidly growing, with the unprecedented spread of dengue and chikungunya viruses, outbreaks of yellow fever and the 2015 epidemic of Zika virus in Latin America. To counteract this growing problem, diverse and innovative mosquito control technologies are currently under development. Conceptually, these span an impressive spectrum of approaches, from invasive transgene cassettes with the potential to crash mosquito populations or reduce the vectorial capacity of a population, to low-cost alterations in housing design that restrict mosquito entry. This themed issue will present articles providing insight into the breadth of mosquito control research, while demonstrating the requirement for an interdisciplinary approach. The issue will highlight mosquito control technologies at varying stages of development and includes both opinion pieces and research articles with laboratory and field-based data on control strategy development. This article is part of the theme issue ‘Novel control strategies for mosquito-borne diseases'.

Factors associated with access to Insecticide-Treated Nets and use of house modification in Bagamoyo and Ulanga districts, Tanzania

ABSTRACTBackgroundInsecticide-treated Nets (ITNs) and house modifications are proven vector control tools, yet full coverage has frequently not been achieved. This study investigates factors associated with ITN access and use of house modification in Tanzania.MethodsBaseline data from cross-sectional surveys was analysed from 7,240 households in Bagamoyo (60km north of Dar es Salaam) and 1,241 households in Ulanga (a remote rural area), from previous studies on spatial repellants and indoor residual spray evaluation. We estimated the associations between the outcomes: population access to ITNs, ITN per sleeping spaces, presence of window screens and closed eaves, and the covariates household size, age, gender, pregnancy, education, mosquito entry (doors and windows), house modification (window screens & closed eaves), mean distance to mosquito breeding sites and wealth using regression models.ResultsPopulation access to ITNs (households with one ITN per two potential people that stayed in the house the previous night of the survey) was 64% (56 - 71) and ITNs per sleeping spaces (households with enough ITNs to cover all sleeping spaces used the previous night of the survey) was 63% (54 - 72) in Bagamoyo, three years after the last Universal Coverage Campaigns (UCC). These findings are both lower than the 80% coverage target of the Tanzania National Malaria Strategic Plan (Tanzania NMSP). In Ulanga, population access to ITNs was 84% (78 - 91) and ITNs per sleeping spaces was 93% (89 - 97), one year after the last UCC. Household size was significantly associated with lower access to ITNs even shortly after UCC. House modification was common in both areas. In Bagamoyo, screened windows were more common than closed eaves (61% vs 14%) whereas in Ulanga more houses had closed eaves than window screens (55% vs 12%). Households in the poorest quintile were less likely to adopt window screening and closing eaves in Bagamoyo, this contrasts with Ulanga district where a greater proportion of poorer households blocked eaves with mud but were less likely to adopt screening.ConclusionPopulation access to ITN was substantially lower than the targets of the Tanzania NMSP after three years and lower among larger households after one year following ITN campaign. House modification was common in both areas, motivated by wealth. Improved access to ITNs and window screens through subsidy, especially among larger households, uptake of a combination of these two interventions may be maximized.

Evaluating effectiveness of screening house eaves as an intervention for integrated vector management for malaria control in Nyabondo, Western Kenya.

BackgroundMosquito-proofing of houses with appropriate screens fixed at potential mosquito entry points is gaining greater recognition as a practical intervention for reducing malaria transmission indoors. The study aimed at evaluating the effectiveness of house eaves screening in preventing mosquito entry and malaria prevalence in Nyabondo, western Kenya. Methods160 houses were selected for the study, with half of them randomly chosen for screening at the eaves with fibre-glass coated wire mesh (experimental group) and the other half left without screening (control group). Randomization was carried out by use of computer-generated list, in permuted blocks of ten houses and 16 village blocks in the study site, with treatments in the ratio of 1:1. Cross-sectional baseline entomological and malaria parasitological data were collected before house eave screening. After the baseline period, series of sampling of indoor adult mosquitoes were conducted once a month in each village using CDC light traps. Three cross-sectional malaria parasitological surveys were also conducted at three month intervals after installation of the screens. The primary outcome measures were indoor Anopheles mosquito density and malaria parasite prevalence. ResultsA total of 15,286 mosquitoes were collected over the two years period using CDC light trap in 160 houses distributed over 16 study villages (mean = 4.35, SD = 11.48). Of all mosquitoes collected, 2,872 were anophelines (2,869 An. gambiae s.l., 1 An. funestus and 2 other anopheles). Overall, among An. gambiae collected, 92.6% were non-blood fed, 3.57% were blood fed and the remaining 0.47% were composed of gravid and half gravid females. Overall more mosquitoes were collected in the control than experimental arms of the study. Results from four cross-sectional prevalence surveys showed that screened houses recorded relatively low malaria prevalence rates compared to the control houses. Overall, malaria prevalence was 5.6% (95%CI: 4.2-7.5) N=1,918, with baseline survey recording 6.1% prevalence (95%CI: 3.9-9.4), n=481 and third follow-up survey recording 3.6% prevalence (95%CI: 2.0-6.8) n=494. At all the three follow-up survey points, house screening significantly reduced the malaria prevalence by 100% (p<0.001), 63.6% (p=0.026), and 100% (p<0.001) for first, second and third follow-ups surveys respectively. The house screening significantly reduced malaria prevalence by 54% (OR = 0.46, 95%CI: 0.24-0.87, p = 0.017). ConclusionsThe study demonstrated that house eave screening has potential to reduce indoor vector densities and malaria transmission in high transmission areas in Kenya.