Emergence of behavioural avoidance strategies of malaria vectors in areas of high LLIN coverage in Tanzania

K S Kreppel,M Viana,G C Lanzaro,F C Meza,P C D Johnson,D Maliti,Y Lee,H M Ferguson,N J Govella,B J Main

doi:10.1038/s41598-020-71187-4

Abstract

Despite significant reductions in malaria transmission across Africa since 2000, progress is stalling. This has been attributed to the development of insecticide resistance and behavioural adaptations in malaria vectors. Whilst insecticide resistance has been widely investigated, there is poorer understanding of the emergence, dynamics and impact of mosquito behavioural adaptations. We conducted a longitudinal investigation of malaria vector host choice over 3 years and resting behaviour over 4 years following a mass long-lasting insecticidal nets (LLINs) distribution in Tanzania. By pairing observations of mosquito ecology with environmental monitoring, we quantified longitudinal shifts in host-choice and resting behaviour that are consistent with adaptation to evade LLINs. The density of An. funestuss.l., declined significantly through time. In tandem, An. arabiensis and An. funestuss.l. exhibited an increased rate of outdoor relative to indoor resting; with An. arabiensis reducing the proportion of blood meals taken from humans in favour of cattle. By accounting for environmental variation, this study detected clear evidence of intra-specific shifts in mosquito behaviour that could be obscured in shorter-term or temporally-coarse surveys. This highlights the importance of mosquito behavioural adaptations to vector control, and the value of longer-term behavioural studies.

Highlights

Malaria remains a major public health concern in Africa despite a vast reduction in cases and deaths over the last decade[1, 2]
Data on the indoor and outdoor resting and indoor host-seeking malaria vectors Anopheles arabiensis and Anopheles funestus s.l. was collected in 4 villages over the course of 4 years
This study demonstrated a systematic temporal shift in two epidemiologically-relevant mosquito behavioural traits over the 4 years following a mass long-lasting insecticidal nets (LLINs) distribution in Tanzania

Summary

Introduction

Malaria remains a major public health concern in Africa despite a vast reduction in cases and deaths over the last decade[1, 2]. Primarily using long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), remains the primary strategy for reducing malaria transmission. Both these strategies rely on exploitation of the behavioural predisposition of many African vector species to feed on humans (anthrophagy) and rest inside houses (endophily)[4]. Behavioural adaptations may arise within vector species as a result of selection or phenotypic p lasticity[22, 23] Both inter- and intraspecific changes in vector behaviour pose challenges for eliminating residual malaria transmission, but evolutionary changes are concerning because they may increasingly erode the effectiveness of current vector control measures and not be solvable by replacing existing insecticides with new ones. Evidence for within-species behavioural adaptations following interventions is less convincing

Objectives

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Results

Conclusion