A cluster randomized, placebo control trial to evaluate the efficacy of a spatial repellent (Mosquito ShieldTM) against Aedes-borne virus infection among children ≥ 4–16 years of age in the Gampaha District, Sri Lanka

Spatial repellents (SRs) have been widely used for the prevention of mosquito bites but their efficacy in reducing ABV has never been tested rigorously in Asia at large scale. To address this knowledge gap, Sri Lanka was selected as a site to estimate the impact of the SR on ABV related outcomes in an area with high baseline dengue transmission. The study will be conducted in the Gampaha district of Sri Lanka across three Medical Officer of Health areas: Negambo, Wattala, Kelaniya. These areas have been selected due to their similar disease ecology, proximity to each other, and ease of access to the implementers of the trial. 

A total of 14,430 total subjects across 3,900 households will be enrolled for monitoring for active disease – ‘febrile surveillance cohort’. These households will form 30 clusters (15 intervention, 15 control), each containing ~187 houses. A subset of this cohort, 3,570 (110-120 per cluster) subjects aged ≥4-16 years that test seronegative (naïve) or positive to a previous single DENV infection (monotypic) at baseline sampling will also be enrolled for measuring DENV infection based on laboratory-confirmed seroconversion – ‘longitudinal cohort’. Persons identified positive for antibodies against multiple DENV serotypes (multi-typic) at baseline, indicating more than one previous infection, will be maintained for secondary analyses. Testing for ZIKV or CHIKV infection at baseline and during the intervention phase of the trial will be dependent on circulation history/detection in study area during study period.

Active ABV disease (symptomatic episodes among febrile surveillance participants) will be assessed through an enhanced passive-surveillance system with case ascertainment performed in designated healthcare facilities. Serum samples will be requested from longitudinal cohort participants within 1-2 weeks of when intervention is first deployed (Baseline sample: T0), with two additional follow up samples taken at ~12 (T1), and ~24 months (T2) from baseline sampling. This sampling scheme will coincide with two DENV seasons in Sri Lanka. DENV seroconversion and ABV active disease rates from pre-intervention and follow-up (post-intervention) samples will be compared between SR active intervention and control clusters. All participating houses in each cluster will be monitored entomologically over 3 months before deployment of the intervention and then monthly after the intervention is in place.

Entomological surveys will include monitoring of indoor Aedes aegypti and Anohpeles stephensi adult population densities. Blood-fed status of Ae. aegypti will also be assessed. The incidence of dengue in each cohort will be estimated and compared to determine the benefit of using an SR. Entomological measures will be measured to determine if there are entomological correlates of SR efficacy that may be useful for the evaluation of new SR products.

Vector Control

Jun 2022 — Jun 2024

$3.86M

Sri Lanka