Search

Background: Spatial repellents that create airborne concentrations of an active ingredient (AI) within a space offer a scalable solution to further reduce transmission of malaria, by disrupting mosquito behaviours in ways that ultimately lead to reduced human-vector contact. Passive emanator spatial repellents can protect multiple people within the treated space and can last for multiple weeks without the need for daily user touchpoints, making them less intrusive interventions. They may be particularly advantageous in certain use cases where implementation of core tools may be constrained, such as in humanitarian emergencies and among mobile at-risk populations. The purpose of this study was to assess the efficacy of Mosquito Shield™ deployed in experimental huts against wild, free-flying, pyrethroid-resistant Anopheles arabiensis mosquitoes in Tanzania over 1 month. Methods: The efficacy of Mosquito Shield™ transfluthrin spatial repellent in reducing mosquito lands and blood-feeding was evaluated using 24 huts: sixteen huts were allocated to Human Landing Catch (HLC) collections and eight huts to estimating blood-feeding. In both experiments, half of the huts received no intervention (control) while the remaining received the intervention randomly allocated to huts and remained fixed for the study duration. Outcomes measured were mosquito landings, blood-fed, resting and dead mosquitoes. Data were analysed by multilevel mixed effects regression with appropriate dispersion and link function accounting for volunteer, hut and day. Results: Landing inhibition was estimated to be 70% (57–78%) [IRR 0.30 (95% CI 0.22–0.43); p < 0.0001] and blood-feeding inhibition was estimated to be 69% (56–79%) [IRR 0.31 (95% CI 0.21–0.44; p < 0.0001] There was no difference in the protective efficacy estimates of landing and blood-feeding inhibition [IRR 0.98 (95% CI 0.53–1.82; p = 0.958]. Conclusions: This study demonstrated that Mosquito Shield™ was efficacious against a wild pyrethroid-resistant strain of An. arabiensis mosquitoes in Tanzania for up to 1 month and could be used as a complementary or stand-alone tool where gaps in protection offered by core malaria vector control tools exist. HLC is a suitable technique for estimating bite reductions conferred by spatial repellents especially where direct blood-feeding measurements are not practical or are ethically limited. [ABSTRACT FROM AUTHOR]

Background: Methods for evaluating efficacy of core malaria interventions in experimental and operational settings are well established but gaps exist for spatial repellents (SR). The objective of this study was to compare three different techniques: (1) collection of blood-fed mosquitoes (feeding), (2) human landing catch (HLC), and (3) CDC light trap (CDC-LT) collections for measuring the indoor protective efficacy (PE) of the volatile pyrethroid SR product Mosquito Shield™ Methods: The PE of Mosquito Shield™ against a wild population of pyrethroid-resistant Anopheles arabiensis mosquitoes was determined via feeding, HLC, or CDC-LT using four simultaneous 3 by 3 Latin squares (LS) run using 12 experimental huts in Tanzania. On any given night each technique was assigned to two huts with control and two huts with treatment. The LS were run twice over 18 nights to give a sample size of 72 replicates for each technique. Data were analysed by negative binomial regression. Results: The PE of Mosquito Shield™ measured as feeding inhibition was 84% (95% confidence interval (CI) 58–94% [Incidence Rate Ratio (IRR) 0.16 (0.06–0.42), p < 0.001]; landing inhibition 77% [64–86%, (IRR 0.23 (0.14–0.36) p < 0.001]; and reduction in numbers collected by CDC-LT 30% (0–56%) [IRR 0.70 (0.44–1.0) p = 0.160]. Analysis of the agreement of the PE measured by each technique relative to HLC indicated no statistical difference in PE measured by feeding inhibition and landing inhibition [IRR 0.73 (0.25–2.12) p = 0.568], but a significant difference in PE measured by CDC-LT and landing inhibition [IRR 3.13 (1.57–6.26) p = 0.001]. Conclusion: HLC gave a similar estimate of PE of Mosquito Shield™ against An. arabiensis mosquitoes when compared to measuring blood-feeding directly, while CDC-LT underestimated PE relative to the other techniques. The results of this study indicate that CDC-LT could not effectively estimate PE of the indoor spatial repellent in this setting. It is critical to first evaluate the use of CDC-LT (and other tools) in local settings prior to their use in entomological studies when evaluating the impact of indoor SR to ensure that they reflect the true PE of the intervention. [ABSTRACT FROM AUTHOR]

Background: Vector mosquito biting intensity is an important measure to understand malaria transmission. Human landing catch (HLC) is an effective but labour-intensive, expensive, and potentially hazardous entomological surveillance tool. The Centres for Disease Control light trap (CDC-LT) and the human decoy trap (HDT) are exposure-free alternatives. This study compared the CDC-LT and HDT against HLC for measuring Anopheles biting in rural Tanzania and assessed their suitability as HLC proxies. Methods: Indoor mosquito surveys using HLC and CDC-LT and outdoor surveys using HLC and HDT were conducted in 2017 and in 2019 in Ulanga, Tanzania in 19 villages, with one trap/house/night. Species composition, sporozoite rates and density/trap/night were compared. Aggregating the data by village and month, the Bland–Altman approach was used to assess agreement between trap types. Results: Overall, 66,807 Anopheles funestus and 14,606 Anopheles arabiensis adult females were caught with 6,013 CDC-LT, 339 indoor-HLC, 136 HDT and 195 outdoor-HLC collections. Indoors, CDC-LT caught fewer An. arabiensis (Adjusted rate ratio [Adj.RR] = 0.35, 95% confidence interval [CI]: 0.27–0.46, p < 0.001) and An. funestus (Adj.RR = 0.63, 95%CI: 0.51–0.79, p < 0.001) than HLC per trap/night. Outdoors, HDT caught fewer An. arabiensis (Adj.RR = 0.04, 95%CI: 0.01–0.14, p < 0.001) and An. funestus (Adj.RR = 0.10, 95%CI: 0.07–0.15, p < 0.001) than HLC. The bias and variability in number of mosquitoes caught by the different traps were dependent on mosquito densities. The relative efficacies of both CDC-LT and HDT in comparison to HLC declined with increased mosquito abundance. The variability in the ratios was substantial for low HLC counts and decreased as mosquito abundance increased. The numbers of sporozoite positive mosquitoes were low for all traps. Conclusions: CDC-LT can be suitable for comparing mosquito populations between study arms or over time if accuracy in the absolute biting rate, compared to HLC, is not required. CDC-LT is useful for estimating sporozoite rates because large numbers of traps can be deployed to collect adequate mosquito samples. The present design of the HDT is not amenable for use in large-scale entomological surveys. Use of HLC remains important for estimating human exposure to mosquitoes as part of estimating the entomological inoculation rate (EIR). [ABSTRACT FROM AUTHOR]

Background: N,N-Diethyl-3-methylbenzamide (DEET) topical mosquito repellents are effective personal protection tools. However, DEET-based repellents tend to have low consumer acceptability because they are cosmetically unappealing. More attractive formulations are needed to encourage regular user compliance. This study evaluated the protective efficacy and protection duration of a new topical repellent ointment containing 15% DEET, MAÏA® compared to 20% DEET in ethanol using malaria and dengue mosquito vectors in Bagamoyo Tanzania. Methods: Fully balanced 3 × 3 Latin square design studies were conducted in large semi-field chambers using laboratory strains of Anopheles gambiae sensu stricto, Anopheles arabiensis and Aedes aegypti. Human volunteers applied either MAÏA® ointment, 20% DEET or ethanol to their lower limbs 6 h before the start of tests. Approximately 100 mosquitoes per strain per replicate were released inside each chamber, with 25 mosquitoes released at regular intervals during the collection period to maintain adequate biting pressure throughout the test. Volunteers recaptured mosquitoes landing on their lower limbs for 6 h over a period of 6 to 12-h post-application of repellents. Data analysis was conducted using mixed-effects logistic regression. Results: The protective efficacy of MAÏA® and 20% DEET was not statistically different for each of the mosquito strains: 95.9% vs. 97.4% against An. gambiae (OR = 1.53 [95% CI 0.93–2.51] p = 0.091); 96.8% vs 97.2% against An. arabiensis (OR = 1.08 [95% CI 0.66–1.77] p = 0.757); 93.1% vs 94.6% against Ae. aegypti (OR = 0.76 [95% CI 0.20–2.80] p = 0.675). Average complete protection time (CPT) in minutes of MAÏA® and that of DEET was similar for each of the mosquito strains: 571.6 min (95% CI 558.3–584.8) vs 575.0 min (95% CI 562.1–587.9) against An. gambiae; 585.6 min (95% CI 571.4–599.8) vs 580.9 min (95% CI 571.1–590.7) against An. arabiensis; 444.1 min (95% CI 401.8–486.5) vs 436.9 min (95% CI 405.2–468.5) against Ae. aegypti. Conclusions: MAÏA® repellent ointment provides complete protection for 9 h against both An. gambiae and An. arabiensis, and 7 h against Ae. aegypti similar to 20% DEET (in ethanol). MAÏA® repellent ointment can be recommended as a tool for prevention against outdoor biting mosquitoes in tropical locations where the majority of the people spend an ample time outdoor before going to bed. [ABSTRACT FROM AUTHOR]

Background: Long-lasting insecticidal nets (LLINs) are the most sustainable and effective malaria control tool currently available. Global targets are for 80% of the population living in malaria endemic areas to have access to (own) and use a LLIN. However, current access to LLINs in endemic areas is 56% due to system inefficiencies and budget limitations. Thus, cost-effective approaches to maximize access to effective LLINs in endemic areas are required. This study evaluated whether LLINs that had been stored for 5 years under manufacturer's recommended conditions may be optimally effective against Anopheles mosquitoes, to inform malaria control programmes and governments on the periods over which LLINs may be stored between distributions, in an effort to maximize use of available LLINs. Methods: Standard World Health Organization (WHO) bioassays (cone and tunnel test) were used to evaluate the bio-efficacy and wash resistance of Olyset® and DawaPlus® 2.0 (rebranded Tsara® Soft) LLINs after 5 years of storage at 25 °C to 33.4 °C and 40% to 100% relative humidity. In addition, a small scale Ifakara Ambient Chamber test (I-ACT) was conducted to compare the bio-efficacy of one long stored LLINs to one new LLIN of the same brand, washed or unwashed. LLINs were evaluated using laboratory reared fully susceptible Anopheles gambiae sensu stricto (s.s.) (Ifakara strain) and pyrethroid resistant Anopheles arabiensis (Kingani strain). Results: After 5 years of storage, both unwashed and washed, Olyset® and DawaPlus® 2.0 (Tsara® Soft) LLINs passed WHO bio-efficacy criteria on knockdown (KD60) ≥ 95%, 24-h mortality ≥ 80% and ≥ 90% blood-feeding inhibition in WHO assays against susceptible An. gambiae s.s. DawaPlus® 2.0 LLINs also passed combined WHO bioassay criteria against resistant An. arabiensis. Confirmatory I-ACT tests using whole nets demonstrated that long-stored LLINs showed higher efficacy than new LLINs on both feeding inhibition and mortality endpoints against resistant strains. Conclusions: Even after long-term storage of around 5 years, both Olyset® and DawaPlus® 2.0 LLINs remain efficacious against susceptible Anopheles mosquitoes at optimal storage range of 25 °C to 33.4 °C for temperature and 40% to 100% relative humidity measured by standard WHO methods. DawaPlus® 2.0 (Tsara® Soft) remained efficacious against resistant strain. [ABSTRACT FROM AUTHOR]

Background: A clear understanding of mosquito biology is fundamental to the control efforts of mosquito-borne diseases such as malaria. Mosquito mark-release-recapture (MMRR) experiments are a popular method of measuring the survival and dispersal of disease vectors; however, examples with African malaria vectors are limited. Ethical and technical difficulties involved in carrying out MMRR studies may have held back research in this area and, therefore, a device that marks mosquitoes as they emerge from breeding sites was developed and evaluated to overcome the problems of MMRR. Methods: A modified self-marking unit that marks mosquitoes with fluorescent pigment as they emerge from their breeding site was developed based on a previous design for Culex mosquitoes. The self-marking unit was first evaluated under semi-field conditions with laboratory-reared Anopheles arabiensis to determine the marking success and impact on mosquito survival. Subsequently, a field evaluation of MMRR was conducted in Yombo village, Tanzania, to examine the feasibility of the system. Results: During the semi-field evaluation the self-marking units successfully marked 86% of emerging mosquitoes and there was no effect of fluorescent marker on mosquito survival. The unit successfully marked wild male and female Anopheles gambiae sensu lato (s.l.) in sufficiently large numbers to justify its use in MMRR studies. The estimated daily survival probability of An. gambiae s.l. was 0.87 (95% CI 0.69–1.10) and mean dispersal distance was 579 m (95% CI 521–636 m). Conclusions: This study demonstrates the successful use of a self-marking device in an MMRR study with African malaria vectors. This method may be useful in investigating population structure and dispersal of mosquitoes for deployment and evaluation of future vector control tools, such as gene drive, and to better parameterize mathematical models. [ABSTRACT FROM AUTHOR]

Background: Many subsistence farmers in rural southeastern Tanzania regularly relocate to distant farms in river valleys to tend to crops for several weeks or months each year. While there, they live in makeshift semi-open structures, usually far from organized health systems and where insecticide-treated nets (ITNs) do not provide adequate protection. This study evaluated the potential of a recently developed technology, eave ribbons treated with the spatial repellent transfluthrin, for protecting migratory rice farmers in rural southeastern Tanzania against indoor-biting and outdoor-biting mosquitoes. Methods: In the first test, eave ribbons (0.1 m × 24 m each) treated with 1.5% transfluthrin solution were compared to untreated ribbons in 24 randomly selected huts in three migratory communities over 48 nights. Host-seeking mosquitoes indoors and outdoors were monitored nightly (18.00–07.00 h) using CDC light traps and CO2-baited BG malaria traps, respectively. The second test compared efficacies of eave ribbons treated with 1.5% or 2.5% transfluthrin in 12 huts over 21 nights. Finally, 286 farmers were interviewed to assess perceptions about eave ribbons, and their willingness to pay for them. Results: In the two experiments, when treated eave ribbons were applied, the reduction in indoor densities ranged from 56 to 77% for Anopheles arabiensis, 36 to 60% for Anopheles funestus, 72 to 84% for Culex, and 80 to 98% for Mansonia compared to untreated ribbons. Reduction in outdoor densities was 38 to 77% against An. arabiensis, 36 to 64% against An. funestus, 63 to 88% against Culex, and 47 to 98% against Mansonia. There was no difference in protection between the two transfluthrin doses. In the survey, 58% of participants perceived the ribbons to be effective in reducing mosquito bites. Ninety per cent were willing to pay for the ribbons, the majority of whom were willing to pay but less than US$2.17 (5000 TZS), one-third of the current prototype cost. Conclusions: Transfluthrin-treated eave ribbons can protect migratory rice farmers, living in semi-open makeshift houses in remote farms, against indoor-biting and outdoor-biting mosquitoes. The technology is acceptable to users and could potentially complement ITNs. Further studies should investigate durability and epidemiological impact of eave ribbons, and the opportunities for improving affordability to users. [ABSTRACT FROM AUTHOR]