Infection Kinetics and Transmissibility of a Reanimated Dengue Virus Serotype 4 Identified Originally in Wild Aedes aegypti From Florida.

Jasmine B Ayers,Caroline J Stephenson,Heather Coatsworth,Christy M Waits,Pei-Yong Shi,Rhoel R Dinglasan,Xuping Xie

doi:10.3389/fmicb.2021.734903

Abstract

Dengue virus is the most prevalent mosquito-borne virus, causing approximately 390 million infections and 25,000 deaths per year. Aedes aegypti, the primary mosquito vector of dengue virus, is well-established throughout the state of Florida, United States. Autochthonous transmission of dengue virus to humans in Florida has been increasing since 2009, alongside consistent importation of dengue cases. However, most cases of first infection with dengue are asymptomatic and the virus can be maintained in mosquito populations, complicating surveillance and leading to an underestimation of disease risk. Metagenomic sequencing of A. aegypti mosquitoes in Manatee County, Florida revealed the presence of dengue virus serotype 4 (DENV-4) genomes in mosquitoes from multiple trapping sites over 2years, in the absence of a human DENV-4 index case, and even though a locally acquired case of DENV-4 has never been reported in Florida. This finding suggested that: (i) DENV-4 may circulate among humans undetected; (ii) the virus was being maintained in the mosquito population, or (iii) the detected complete genome sequence may not represent a viable virus. This study demonstrates that an infectious clone generated from the Manatee County DENV-4 (DENV-4M) sequence is capable of infecting mammalian and insect tissue culture systems, as well as adult female A. aegypti mosquitoes when fed in a blood meal. However, the virus is subject to a dose dependent infection barrier in mosquitoes, and has a kinetic delay compared to a phylogenetically related wild-type (WT) control virus from a symptomatic child, DENV-4H (strain Homo sapiens/Haiti-0075/2015, GenBank accession MK514144.1). DENV-4M disseminates from the midgut to the ovary and saliva at 14days post-infection. Viral RNA was also detectable in the adult female offspring of DENV-4M infected mosquitoes. These results demonstrate that the virus is capable of infecting vector mosquitoes, is transmissible by bite, and is vertically transmitted, indicating a mechanism for maintenance in the environment without human-mosquito transmission. These findings suggest undetected human-mosquito transmission and/or long-term maintenance of the virus in the mosquito population is occurring in Florida, and underscore the importance of proactive surveillance for viruses in mosquitoes.GRAPHICAL ABSTRACTIn order to better assess the public health risk posed by a detection of DENV-4 RNA in Manatee County, FL Aedes aegypti, we produced an infectious clone using the sequence from the wild-caught mosquitoes and characterized it via laboratory infections of mosquitoes and mosquito tissues.

Highlights

Dengue virus (DENV) is a single stranded, positive-sense RNA arthropod-borne virus in the flavivirus family, which is predominantly transmitted in human populations by the bite of infected female Aedes aegypti mosquitoes
The four fragments were directionally assembled into the pCC1BAC that was pre-linearized by NotI and ClaI, resulting in the full-length infectious clone pCC1-DENV-4M FL
Gaining retrospective insight into arbovirus transmission dynamics and disease risk in a local setting is especially important considering that the original DENV-4M virus was detected from A. aegypti collected from a tourist corridor in Manatee County across 2 consecutive years and in the absence of dengue virus serotype 4 (DENV-4) human index cases (Boyles et al, 2020; Mosquito-Borne Disease Surveillance, 2021)

Summary

Introduction

Dengue virus (DENV) is a single stranded, positive-sense RNA arthropod-borne virus in the flavivirus family, which is predominantly transmitted in human populations by the bite of infected female Aedes aegypti mosquitoes. DENV causes dengue fever, the most common arboviral disease in humans with approximately 40% of the world’s population at risk of infection Imported (i.e., travel-related) cases of dengue occur in Florida every year, and locally acquired cases have been increasing over the past decade with 73 locally acquired cases in the state in 2020 alone (Mosquito-Borne Disease Surveillance, 2021). Travel associated cases of all four serotypes of DENV have been reported in Florida, but no locally acquired cases of DENV-4 have ever been reported (Mosquito-Borne Disease Surveillance, 2021)

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