Incidental mosquitocidal effect of an ivermectin mass drug administration on Anopheles farauti conducted for scabies control in the Solomon Islands.

Christian Kositz,Jason Diau,Carlos Chaccour,Rowena Asugeni,Cheryl Whitehorn,Michael Marks,Jeptah Talina,David Mabey

doi:10.1093/trstmh/trx025

Abstract

BackgroundThe Solomon Islands is targeting elimination of malaria by 2030. The dominant vector is the predominantly exophagic, exophilic Anopheles farauti sensu strictu. This biting behaviour limits the efficacy of conventional vector control tools and highlights the need for new strategies. When administered to humans ivermectin has been shown to have a mosquitocidal effect. Mass drug administration (MDA) with ivermectin is an emerging strategy in the control of scabies. In this study we explored any incidental effect of ivermectin MDA conducted for scabies control on mosquitoes.MethodsMDA for scabies was conducted in three villages. We performed human landing catches and measured 5-day mortality amongst Anopheles mosquitoes caught before and after MDA. Cox regression was used to calculate hazard ratios (HR) for mortality between mosquitoes caught before and after MDA.ResultsThere was a significant increase in 5-day mortality in anopheline mosquitoes caught post-MDA which was highest on the day of MDA itself (HR 4.2 95% CI 1.8 to 10.1, p=0.001) and the following day (HR 4.4 95% CI 1.8 to 10.8, p=0.002) compared to mosquitoes caught before MDA.ConclusionsThis study shows a possible mosquitocidal effect of ivermectin MDA conducted for scabies control. Studies with a larger sample size with clinical as well as entomological outcomes should be conducted in this population.

Highlights

WHO has set an ambitious goal to eliminate malaria from 35 countries by the year 2030.1 The Solomon Islands is one of the countries targeted by WHO for malaria elimination
Prior to the Malaria Eradication Programme (MEP) in the 1970s three species of Anopheles mosquitoes were involved in the transmission of malaria in the Solomon Islands
An. koliensis appears to have been eliminated following the MEP and An. punctulatus is no longer considered a major vector having been controlled through the use of indoor residual spraying (IRS) and long-lasting insecticide treated bed nets (LLINs) in the 1990s

Summary

Introduction

WHO has set an ambitious goal to eliminate malaria from 35 countries by the year 2030.1 The Solomon Islands is one of the countries targeted by WHO for malaria elimination. The MEP was based predominantly on a strategy of indoor residual spraying (IRS) combined with mass drug administration.[5] An. koliensis appears to have been eliminated following the MEP and An. punctulatus is no longer considered a major vector having been controlled through the use of IRS and long-lasting insecticide treated bed nets (LLINs) in the 1990s.6. The dominant vector is the predominantly exophagic, exophilic Anopheles farauti sensu strictu. This biting behaviour limits the efficacy of conventional vector control tools and highlights the need for new strategies. Mass drug administration (MDA) with ivermectin is an emerging strategy in the control of scabies. In this study we explored any incidental effect of ivermectin MDA conducted for scabies control on mosquitoes

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