Abstract
Background: Spatial repellents can provide personal and household protection against biting vector mosquitoes by volatising repellents into the air within a given area. Mosquito ShieldTM is a transfluthrin passive emanator undergoing evaluation for malaria control. Studies evaluating its entomological impact against different local malaria vector populations would help guide its deployment in endemic countries.
Methods: We performed a two-arm single-blinded small-scale household randomised entomological trial to assess the impact of Mosquito ShieldTM on the human landing rate of wild pyrethroid-resistant Anopheles gambiae sl vector mosquitoes in houses in the Ganhoua village of the Zakpota District of central Benin. From a total of 30 houses, 15 were randomly allocated to receive Mosquito ShieldTM while the remainder received a placebo product. The trial lasted through the life of the Mosquito ShieldTM product (32 days). Mosquito sampling was performed by human landing catches at baseline and at 6 timepoints post-intervention (days 0-1, 7-8, 14-15, 21-22, 28-29 and 31-32). Collections were performed for 2 days at each sampling time point. WHO cylinder bioassays were conducted during the trial with F1, An gambiae sl mosquitoes that emerged from larvae from the study area to assess the intensity of resistance to pyrethroids in the wild vector population.
Findings: The vector population in the study area showed a high intensity of resistance to pyrethroids. Baseline An gambiae sl human landing rates were similar in houses in both study arms before product application (11.53/person/night vs 11.67/person/night, p>0.05). A total of 5736 mosquitoes were collected in the placebo control arm and 3862 in the Mosquito ShieldTM arm post-intervention. Overall An gambiae sl human landing rates post-intervention were significantly lower in houses in the Mosquito ShieldTM arm 18.13/person/night) compared to the houses in the placebo control arm (26.84/person/night, IRR=0.658, p<0.001). Over the lifespan of the product, Mosquito ShieldTM provided a significant protective efficacy of 34.2% (22.1%-44.4%, p<0.001) against wild pyrethroid-resistant An gambiae s.l. vectors compared to the placebo. Human landing rates of other nuisance vector mosquito species (Culex and Mansonia) were also reduced in houses treated with Mosquito ShieldTM compared to the placebo.
Conclusion: Mosquito ShieldTM, a transfluthrin passive emanator, provided significant protection against pyrethroid-resistant malaria vectors to households in Benin. The spatial repellent shows potential to reduce malaria transmission by pyrethroid-resistant An gambiae sl vector mosquitoes and cover gaps in malaria control when deployed to complement existing vector control interventions.