Assessing the relationship between vector indices and dengue transmission: a systematic review of the evidence.

Leigh R Bowman,P J Mccall,Silvia Runge-Ranzinger,Amy C Morrison

doi:10.1371/journal.pntd.0002848

Leigh R Bowman, P J Mccall + Show 2 more

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https://doi.org/10.1371/journal.pntd.0002848

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Abstract

BackgroundDespite doubts about methods used and the association between vector density and dengue transmission, routine sampling of mosquito vector populations is common in dengue-endemic countries worldwide. This study examined the evidence from published studies for the existence of any quantitative relationship between vector indices and dengue cases.Methodology/Principal FindingsFrom a total of 1205 papers identified in database searches following Cochrane and PRISMA Group guidelines, 18 were included for review. Eligibility criteria included 3-month study duration and dengue case confirmation by WHO case definition and/or serology.A range of designs were seen, particularly in spatial sampling and analyses, and all but 3 were classed as weak study designs. Eleven of eighteen studies generated Stegomyia indices from combined larval and pupal data. Adult vector data were reported in only three studies. Of thirteen studies that investigated associations between vector indices and dengue cases, 4 reported positive correlations, 4 found no correlation and 5 reported ambiguous or inconclusive associations. Six out of 7 studies that measured Breteau Indices reported dengue transmission at levels below the currently accepted threshold of 5.Conclusions/SignificanceThere was little evidence of quantifiable associations between vector indices and dengue transmission that could reliably be used for outbreak prediction. This review highlighted the need for standardized sampling protocols that adequately consider dengue spatial heterogeneity. Recommendations for more appropriately designed studies include: standardized study design to elucidate the relationship between vector abundance and dengue transmission; adult mosquito sampling should be routine; single values of Breteau or other indices are not reliable universal dengue transmission thresholds; better knowledge of vector ecology is required.

Highlights

Global dengue incidence has increased markedly over the past 50 years to the point where it is the most widespread mosquito-borne arboviral disease
Inclusion Criteria Any study where entomological surveillance of Aedes spp. was undertaken for .3 months in conjunction with number of reported dengue cases Any study type with all empirical data gathered within the same time period
Exclusion Criteria Studies with only one outcome of interest; Opinion papers; review articles; retrospective analyses comparing data generated at different time points Qualitative dengue reports

Summary

Introduction

Global dengue incidence has increased markedly over the past 50 years to the point where it is the most widespread mosquito-borne arboviral disease. Dengue is endemic throughout the tropics, and almost half of the world’s population are at risk of infection, 75% of whom live in the Asia-Pacific region [4]. Dengue has been confirmed in 128 countries worldwide [4,5] with major social and economic consequences [6,7,8,9,10]. Dengue is transmitted by Aedes mosquitoes, primarily by the highly urban-adapted vector Aedes aegypti, and a secondary vector Aedes albopictus [11]. Despite doubts about methods used and the association between vector density and dengue transmission, routine sampling of mosquito vector populations is common in dengue-endemic countries worldwide. This study examined the evidence from published studies for the existence of any quantitative relationship between vector indices and dengue cases

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