Semi-field studies to better understand the impact of eave tubes on mosquito mortality and behaviour

Antoine M G Barreaux,Innocent Z Tia,Alphonsine A Koffi,Raphaël N’Guessan,N’Guessan Brou,Matthew B Thomas,Welbeck A Oumbouke

doi:10.1186/s12936-018-2457-4

Abstract

BackgroundEave tubes are a type of housing modification that provide a novel way of delivering insecticides to mosquitoes as they attempt to enter the house. The current study reports on a series of semi-field studies aimed at improving the understanding of how eave tubes might impact mosquito mortality and behaviour.MethodsExperiments were conducted using West African style experimental huts at a field site in M’be, Côte d’Ivoire. Huts were modified in various ways to determine: (i) whether mosquitoes in this field setting naturally recruit to eave tubes; (ii) whether eave tubes can reduce house entry even in the absence of screening; (iii) whether mosquitoes suffer mortality if they attempt to exit a house via treated eave tubes; and, (iv) whether screening and eave tubes might deflect mosquitoes into neighbouring houses without the intervention.ResultsNinety percent more mosquitoes (Anopheles gambiae sensu lato, and other species) entered huts through open eaves tubes compared to window slits. The addition of insecticide-treated eave tubes reduced mosquito entry by 60%, even when windows remained open. Those mosquitoes that managed to enter the huts exhibited a 64% reduction in blood feeding and a tendency for increased mortality, suggesting contact with insecticide-treated inserts prior to hut entry. When An. gambiae mosquitoes were deliberately introduced into huts with treated eave tubes, there was evidence of six times increase in overnight mortality, suggesting mosquitoes can contact treated eave tube inserts when trying to exit the hut. There was no evidence for deflection of mosquitoes from huts with screening, or screening plus eave tubes, to adjacent unmodified huts.ConclusionsEave tubes are a potentially effective way to target Anopheles mosquitoes with insecticides. That treated eave tubes can reduce mosquito entry even when windows are open is a potentially important result as it suggests that eave tubes might not need to be combined with household screening to have an impact on malaria transmission. The absence of deflection is also a potentially important result as coverage of eave tubes and/or screening is unlikely to be 100% and it is important that households that do not have the technology are not disadvantaged by those that do.

Highlights

Eave tubes are a type of housing modification that provide a novel way of delivering insecticides to mosquitoes as they attempt to enter the house
The approach used West African style experimental huts to investigate: (i) whether mosquitoes in this field setting naturally recruit to eave tubes; (ii) whether eave tubes can reduce house entry even in the absence of screening; (iii) whether mosquitoes suffer mortality if they attempt to exit a house via treated eave tubes; and, (iv) whether screening and eave tubes might deflect mosquitoes into neighbouring houses without the intervention
Impact of eave tubes on mosquito entry Insecticide-treated eave tubes reduced entry of An. gambiae mosquitoes by 46% relative to control huts fitted with untreated eave tubes (F1,23 = 18.302, p < 0.001) (Fig. 5)

Summary

Introduction

Eave tubes are a type of housing modification that provide a novel way of delivering insecticides to mosquitoes as they attempt to enter the house. The current study reports on a series of semi-field studies aimed at improving the understanding of how eave tubes might impact mosquito mortality and behaviour. The epidemiological impact of screening plus eave tubes is currently being evaluated in a large-scale cluster randomized trial (CRT) in 40 villages in central Côte d’Ivoire [8]. In parallel with this CRT, a number of smallscale studies are being conducted in Côte d’Ivoire to help better understand the functioning of screening and eave tubes and potentially assist in interpreting the ultimate impacts of the intervention on transmission. The approach used West African style experimental huts to investigate: (i) whether mosquitoes in this field setting naturally recruit to eave tubes; (ii) whether eave tubes can reduce house entry even in the absence of screening; (iii) whether mosquitoes suffer mortality if they attempt to exit a house via treated eave tubes; and, (iv) whether screening and eave tubes might deflect mosquitoes into neighbouring houses without the intervention

Methods

Results

Discussion

Conclusion