Modified mosquito landing boxes dispensing transfluthrin provide effective protection against Anopheles arabiensis mosquitoes under simulated outdoor conditions in a semi-field system.

Marta Andrés,Lena M Lorenz,Sarah J Moore,Edgar Mbeleya

doi:10.1186/s12936-015-0762-8

Abstract

BackgroundEfforts to control malaria vectors have primarily focused on scaling-up of long-lasting insecticidal nets (LLINs) and indoor residual spraying. Although highly efficient against indoor-biting and indoor-resting vectors, these interventions have lower impact on outdoor-biting mosquitoes. Innovative vector control tools are required to prevent outdoor human–mosquito contacts. In this work, the potential of spatial repellents, delivered in an active system that requires minimal user compliance, to provide personal protection against exophagic mosquitoes active in the early evening was explored.MethodsA device previously used as an odour-baited lure and kill apparatus, the mosquito landing box (MLB), was modified to dispense the volatile synthetic pyrethroid, transfluthrin, as a spatial repellent. The MLB has an active odour-dispensing mechanism that uses a solar-powered fan and switches on at dusk to provide long duration dispensing of volatile compounds without the need for the user to remember to employ it. Two MLBs were located 5 m from a human volunteer to investigate the repellent effects of a transfluthrin ‘bubble’ created between the MLBs. Transfluthrin was emanated from polyester strips, hanging inside the MLB odour-dispensing unit. A fully randomized cross-over design was performed in a large, semi-field, screened cage to assess the effect of the repellent against laboratory-reared Anopheles arabiensis mosquitoes under ambient outdoor conditions. The knock-down capacity of the transfluthrin-treated strips was also evaluated at different time points up to 3 weeks after being impregnated to measure duration of efficacy.ResultsThe protective transfluthrin bubble provided 68.9% protection against An. arabiensis bites under these simulated outdoor conditions. Volatile transfluthrin caused low mortality among mosquitoes in the semi-field system. Transfluthrin-treated strips continued to knock down mosquitoes in laboratory tests, 3 weeks after impregnation, although this effect diminished with time.ConclusionModified MLBs can be used as efficient and long-lasting dispensers of volatile spatial repellents such as transfluthrin, thereby providing high levels of protection against outdoor-biting mosquitoes in the peri-domestic space. They have a potential role in combatting outdoor malaria transmission without interfering with effective indoor interventions such as LLINs.

Highlights

Efforts to control malaria vectors have primarily focused on scaling-up of long-lasting insecticidal nets (LLINs) and indoor residual spraying
LLINs are highly effective against indoor night-biting mosquitoes, while indoor residual spraying (IRS) is effective against mosquitoes that rest indoors and both are most effective against mosquitoes that mainly feed on humans [2]
According to the fitted, mixed effect, logistic regression, the volunteer under the protective transfluthrin bubble had an odds ratios (OR) of 0.17 for a mosquito landing compared to the control

Summary

Introduction

Efforts to control malaria vectors have primarily focused on scaling-up of long-lasting insecticidal nets (LLINs) and indoor residual spraying. Recent global malaria control efforts have substantially reduced malaria morbidity and mortality, thanks to the scaling-up of highly effective vector control strategies, mainly indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs), coupled with improved diagnosis and effective treatment with artemisinin-based combination therapy (ACT) [1]. Some Anopheles vectors exhibit outdoor-biting and resting behaviours, thereby effectively avoiding contact with LLINs and IRS. This has led to an increase in the relative abundance of outdoorbiting mosquitoes as compared to strictly indoor-biting mosquitoes in recent years, which continue to maintain a lower level of malaria transmission [4]. In the Mekong and Amazon regions, a large proportion of malaria transmission occurs outdoors or in the evening before people go to bed under bed nets [4, 8] and many vectors do not rest indoors [9, 10], limiting the efficacy of conventional indoor mosquito control interventions

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