Abstract

BackgroundIn sub-Saharan Africa, malaria interventions over the last decades have been successful in reducing both mortality and morbidity. In western Kenya however some areas experience contrasting outcomes of the ongoing interventions while the causes for this observation remains not yet clearly known.MethodsThe WHO insecticide (deltamethrin) susceptibility test of the common malaria vectors was studied. Multiple surveys on household use and hospital prescriptions of antimalarial drugs from 2003 to 2015 were done. Along with this, cross sectional surveys on their availability in the local drug dispensing outlets were also done in 2015. Monthly precipitations and air temperature data was collected along with systematic review on abundance and composition of common malaria vectors in the study area before and during interventions. The above factors were used to explain the possible causes of contrasting outcome of malaria interventions between the three study sites.ResultsAreas with malaria resurgence or sustained high transmission (Kombewa and Marani) showed higher composition of Anopheles funestus sensu lato (s.l.) than the previously abundant Anopheles gambiae sensu stricto (s.s.) and the later had higher composition to an area with a sustained infection decline (Iguhu). Anopheles gambiae s.l. from Kombewa showed highest resistance (50% mortality) upon exposure to WHO deltamethrin discriminating dosage of 0.75% while those from Marani and Iguhu had reduced resistance status (both had a mean mortality of 91%). Sampled An. funestus s.l. from Marani were also highly resistant to deltamethrin as 57% of the exposed vectors survived. An increasing of mean air temperature by 2 °C was noted for Marani and Iguhu from 2013 to 2015 and was accompanied by an increased rainfall at Marani. Community drug use and availability in selling outlets along with prescription in hospitals were not linked to the struggling control of the disease.ConclusionsThe malaria vector species composition shift, insecticide resistance and climatic warming were the likely cause of the contrasting outcome of malaria intervention in western Kenya. Surveillance of malaria parasite and vector dynamics along with insecticide resistance and vector biting behaviour monitoring are highly recommended in these areas.

Highlights

  • In sub-Saharan Africa, malaria interventions over the last decades have been successful in reducing both mortality and morbidity

  • The use of indoor residual insecticide spray (IRS) in combination with long-lasting insecticidal nets (LLINs) resulted to the observed reduction of disease burden [5, 6]

  • Trend of asymptomatic and clinical malaria and populations of indoor resting malaria vectors The first cycle (2006) of LLINs mass distribution in western Kenya resulted to a decline of both asymptomatic malaria and clinical cases

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Summary

Introduction

In sub-Saharan Africa, malaria interventions over the last decades have been successful in reducing both mortality and morbidity. In western Kenya some areas experience contrasting outcomes of the ongoing interventions while the causes for this observation remains not yet clearly known. Malaria has been the major public health concern in many tropical and subtropical countries but the interventions have greatly reduced both morbidity and mortality. The use of indoor residual insecticide spray (IRS) in combination with LLINs resulted to the observed reduction of disease burden [5, 6]. The massive application of IRS in western Kenya started in 2005 and by 2010 only 38% of households in epidemic prone areas were covered and even less in the recent years [4, 8]. About 92.8% of children with fever in 2015 were given ACT and only 1.4% used sulfadoxine–pyrimethamine (SP) [7]

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