Detection of Insect-Specific Flaviviruses in Mosquitoes (Diptera: Culicidae) in Northeastern Regions of South Africa.

Milehna M Guarido,Antonio Paulo Gouveia Almeida,Maarten Schrama,Marietjie Venter,Kamini Govender,Basil D Brooke,Erin E Gorsich,Megan A Riddin

doi:10.3390/v13112148

Abstract

Mosquitoes in the Aedes and Culex genera are considered the main vectors of pathogenic flaviviruses worldwide. Entomological surveillance using universal flavivirus sets of primers in mosquitoes can detect not only pathogenic viruses but also insect-specific ones. It is hypothesized that insect-specific flaviviruses, which naturally infect these mosquitoes, may influence their vector competence for zoonotic arboviruses. Here, entomological surveillance was performed between January 2014 and May 2018 in five different provinces in the northeastern parts of South Africa, with the aim of identifying circulating flaviviruses. Mosquitoes were sampled using different carbon dioxide trap types. Overall, 64,603 adult mosquitoes were collected, which were screened by RT-PCR and sequencing. In total, 17 pools were found positive for insect-specific Flaviviruses in the mosquito genera Aedes (12/17, 70.59%) and Anopheles (5/17, 29.41%). No insect-specific viruses were detected in Culex species. Cell-fusing agent viruses were detected in Aedes aegypti and Aedes caballus. A range of anopheline mosquitoes, including Anopheles coustani, An. squamosus and An. maculipalpis, were positive for Culex flavivirus-like and Anopheles flaviviruses. These results confirm the presence of insect-specific flaviviruses in mosquito populations in South Africa, expands their geographical range and indicates potential mosquito species as vector species.

Highlights

Eleven of these were in Aedes mosquitoes (11/17, 64.7%), while the remaining six were from Anopheles mosquitoes (6/17, 35.3%)
Five positive pools identified in Aedes clustered closely with published mosquito flavivirus (HQ676625.1) but on a separate branch to those identified in Anopheles, while three An. coustani-positive pools clustered with Culex flaviviruses and on a separate branch, suggesting a phylogenetic distinction according to the vector species
For most sequences of insect-specific flaviviruses (ISFV) detected in this study, we were unable to amplify larger fragments of the non-structural protein 5 (NS5) gene, except for one pool detected as mosquito flavivirus and four pools detected as cell-fusing agent virus (CFAV)

Summary

Introduction

Members of the genus Flavivirus are emerging arthropod-borne viruses that have a great impact on global health. Important mosquito-borne viruses belonging to this genus include West Nile, yellow fever, dengue and Zika viruses. In areas where these viruses occur, it is important to carry out mosquito surveillance as a tool to understand the dynamics of arboviral circulation. One strategy to quantify arboviral circulation is to use RT-PCR, RT-PCR with consensus primers, followed by sequencing to identify arboviruses at the species and genotype level [1]. While providing in-depth information on circulation of known arboviruses, this strategy has enabled researchers to identify previously unknown viruses, including apparent insect-specific flaviviruses (ISFV)

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Conclusion