Partitioning the contributions of alternative malaria vector species.

Anne Deredec,Austin Burt,Samantha M O’Loughlin,Tin-Yu J Hui

doi:10.1186/s12936-016-1107-y

Abstract

BackgroundIn many locations malaria is transmitted by more than one vector species. Some vector control interventions, in particular those using genetic approaches, are likely to be targeted against a single species or species complex, at least initially, and it would therefore be useful to be able to predict the epidemiological impact of controlling a single species when multiple vector species are present.MethodsTo address this issue, the classical Ross-McDonald model of malaria epidemiology is expanded to account for multiple vector species, giving expressions for the equilibrium prevalence, sporozoite rates and reproductive number. These allow one to predict when control of just one vector species will lead to elimination of the disease. Application of the model is illustrated using published data from a particularly extensive entomological and epidemiological survey before the rollout of bed nets in eastern Kenya, where Anopheles gambiaes.l. and An. funestus were vectors.ResultsMeta-analysis indicates that sporozoite rates were 38 % higher in An. gambiaes.l. than in An. funestus, and, according to the model, this difference could be due to An. gambiae s.l. having a higher frequency of feeding on humans, a higher human-to-mosquito transmission rate, a lower adult mortality rate, and/or a shorter incubation period. Further calculations suggest that An. gambiaes.l. would have been sufficient to maintain transmission by itself throughout the region, whereas An. funestus would not have been able to support transmission by itself in Malindi District.ConclusionsPartitioning the contributions of different vector species may allow us to predict whether malaria will persist after targeted vector control.

Highlights

In many locations malaria is transmitted by more than one vector species
All mosquitoes were identified based on morphological characters, and mosquitoes in the Anopheles gambiae s.l. species complex were present at all 30 sites, while An. funestus was recovered from all but three sites
The heads and thoraces of all collected anophelines were tested for Plasmodium falciparum sporozoites using an enzyme-linked immunosorbent assay (ELISA)

Summary

Introduction

In many locations malaria is transmitted by more than one vector species. Some vector control inter‐ ventions, in particular those using genetic approaches, are likely to be targeted against a single species or species complex, at least initially, and it would be useful to be able to predict the epidemiological impact of control‐ ling a single species when multiple vector species are present. Many indirectly-transmitted or vector-borne diseases are transmitted by more than one vector species, even within a single locale [1]. This is true of malaria, which in many places is transmitted by several species of anopheline mosquito [2,3,4]. In this paper the classic Ross-McDonald model of malaria epidemiology [15, 16], modified to allow for super-infection and heterogeneity in propensity to be bitten [17, 18], is extended to allow for multiple vector species, leading to expressions for the equilibrium prevalence in humans, sporozoite rate in mosquitoes, and reproductive number. Application of the model is illustrated using a extensive survey of malaria and vectors in eastern Kenya [19]

Methods

Results

Conclusion