Evidence of transovarial transmission of Chikungunya and Dengue viruses in field-caught mosquitoes in Kenya.

Claire J Heath,Peter Siema,Uriel Kitron,Jesse J Waggoner,Malaya K Sahoo,Francis M Mutuku,Charles H King,Benjamin A Pinsky,Joel O Mbakaya,Elysse N Grossi-Soyster,A Desiree Labeaud,Bryson A Ndenga,Nayer Zahiri,Harun N Ngugi,Jimmy Hortion,Lyric C Bartholomay

doi:10.1371/journal.pntd.0008362

Abstract

Arboviruses are among the most important emerging pathogens due to their increasing public health impact. In Kenya, continued population growth and associated urbanization are conducive to vector spread in both urban and rural environments, yet mechanisms of viral amplification in vector populations is often overlooked when assessing risks for outbreaks. Thus, the characterization of local arbovirus circulation in mosquito populations is imperative to better inform risk assessments and vector control practices. Aedes species mosquitoes were captured at varying stages of their life cycle during different seasons between January 2014 and May 2016 at four distinct sites in Kenya, and tested for chikungunya (CHIKV), dengue (DENV) and Zika (ZIKV) viruses by RT-PCR. CHIKV was detected in 45 (5.9%) and DENV in 3 (0.4%) mosquito pools. No ZIKV was detected. Significant regional variation in prevalence was observed, with greater frequency of CHIKV on the coast. DENV was detected exclusively on the coast. Both viruses were detected in immature mosquitoes of both sexes, providing evidence of transovarial transmission of these arboviruses in local mosquitoes. This phenomenon may be driving underlying viral maintenance that may largely contribute to periodic re-emergence among humans in Kenya.

Highlights

Arthropod–borne viruses comprise some of the most important emerging pathogens due to their geographic spread and increasing impact on vulnerable human populations
This study provides some of the first evidence of transovarial transmission of chikungunya and dengue viruses in Aedes aegypti mosquitoes in Africa during interepidemic periods, which has important implications for local virus persistence and epidemic patterns
Transovarial transmission (TOT) is believed to be a mechanism by which arboviruses maintain a local presence during environmental conditions that are adverse for mosquito proliferation, e.g. during dry seasons and winter

Summary

Introduction

Arthropod–borne viruses (arboviruses) comprise some of the most important emerging pathogens due to their geographic spread and increasing impact on vulnerable human populations. Transovarial transmission (TOT) is a mechanism by which infective female mosquitoes pass the virus to their offspring via their eggs. Quiescence of vertically infected mosquito eggs in response to environmental conditions may contribute to viral persistence or re-emergence within a region [14]. A recent review of modeling studies suggests that, for DENV, TOT is likely not an important mechanism of viral propagation in Southeast Asia and the Americas, but rather asymptomatic infections in humans and the movement of people account for DENV persistence [15]. Comprehensive evidence exists demonstrating that TOT of CHIKV and DENV occurs in many distinct endemic regions, complex mechanisms and a lack of field data lead to an incomplete understanding of the contributions of TOT to viral persistence during interepidemic times. We further investigate the rate of TOT of these viruses to determine its possible contribution to viral maintenance in this endemic setting

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Conclusion