[Source: PLoS Neglected Tropical Diseases, full page: (LINK). Abstract, edited.]
OPEN ACCESS / PEER-REVIEWED / RESEARCH ARTICLE
Vertical transmission of naturally occurring Bunyamwera and insect-specific flavivirus infections in mosquitoes from islands and mainland shores of Lakes Victoria and Baringo in Kenya
Yvonne Ukamaka Ajamma, Thomas Ogao Onchuru , Daniel O. Ouso , David Omondi, Daniel K. Masiga, Jandouwe Villinger
Published: November 19, 2018 / DOI: https://doi.org/10.1371/journal.pntd.0006949 / This is an uncorrected proof.
Many arboviruses transmitted by mosquitoes have been implicated as causative agents of both human and animal illnesses in East Africa. Although epidemics of arboviral emerging infectious diseases have risen in frequency in recent years, the extent to which mosquitoes maintain pathogens in circulation during inter-epidemic periods is still poorly understood. This study aimed to investigate whether arboviruses may be maintained by vertical transmission via immature life stages of different mosquito vector species.
We collected immature mosquitoes (egg, larva, pupa) on the shores and islands of Lake Baringo and Lake Victoria in western Kenya and reared them to adults. Mosquito pools (≤25 specimens/pool) of each species were screened for mosquito-borne viruses by high-resolution melting analysis and sequencing of multiplex PCR products of genus-specific primers (alphaviruses, flaviviruses, phleboviruses and Bunyamwera-group orthobunyaviruses). We further confirmed positive samples by culturing in baby hamster kidney and Aedes mosquito cell lines and re-sequencing.
Culex univittatus (2/31pools) and Anopheles gambiae (1/77 pools) from the Lake Victoria region were positive for Bunyamwera virus, a pathogenic virus that is of public health concern. In addition, Aedes aegypti (3/50), Aedes luteocephalus (3/13), Aedes spp. (2/15), and Culex pipiens (1/140) pools were positive for Aedes flaviviruses at Lake Victoria, whereas at Lake Baringo, three pools of An. gambiae mosquitoes were positive for Anopheles flavivirus. These insect-specific flaviviruses (ISFVs), which are presumably non-pathogenic to vertebrates, were found in known medically important arbovirus and malaria vectors.
Our results suggest that not only ISFVs, but also a pathogenic arbovirus, are naturally maintained within mosquito populations by vertical transmission, even in the absence of vertebrate hosts. Therefore, virus and vector surveillance, even during inter-epidemics, and the study of vector-arbovirus-ISFV interactions, may aid in identifying arbovirus transmission risks, with the potential to inform control strategies that lead to disease prevention.
The East African region is endemic to diverse mosquito-transmitted arboviruses, though little is known about the role of vertical transmission in maintaining these viruses within mosquito vector populations during inter-epidemic periods. We sampled mosquito larvae from the Lake Baringo and Lake Victoria regions of Kenya and reared them to adults in the laboratory before screening them for mosquito-associated viruses by multiplex RT-PCR-HRM, cell culture, and sequencing. From the Lake Victoria region, we detected the arbovirus, Bunyamwera, which can cause febrile illness in humans, in Culex univittatus and vector competent Anopheles gambiaemosquitoes. We also identified diverse insect-specific flaviviruses in Aedes aegypti, Aedes luteocephalus, Aedes spp. and Culex pipiens mosquitoes. From the Lake Baringo region, we detected Anopheles flavivirus in An. gambiae mosquitoes. These findings demonstrate that naturally occurring vertical transmission potentially maintains viruses in circulation within the sampled vector species populations. Therefore, mosquitoes may potentially transmit a pathogenic arbovirus during their first bite after emergence. Because various insect-specific flaviviruses have recently been found to either inhibit or enhance replication of specific arboviruses in mosquitoes, their vertical transmission, as observed in this study, has implications as to their potential impact on both horizontal and vertical transmission of medically important arboviruses.
Citation: Ajamma YU, Onchuru TO, Ouso DO, Omondi D, Masiga DK, Villinger J (2018) Vertical transmission of naturally occurring Bunyamwera and insect-specific flavivirus infections in mosquitoes from islands and mainland shores of Lakes Victoria and Baringo in Kenya. PLoS Negl Trop Dis 12(11): e0006949. https://doi.org/10.1371/journal.pntd.0006949
Editor: Michael J. Turell, INDEPENDENT RESEARCHER, UNITED STATES
Received: May 3, 2018; Accepted: October 26, 2018; Published: November 19, 2018
Copyright: © 2018 Ajamma et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All ISFV sequences are available from the GenBank nucleotide database (accession MG372051-MG372060, MK015647- MK015648).
Funding: This work was supported by the Swedish International Development Cooperation Agency (Sida) (www.sida.se), grant number 75000529 to YUA as an African Regional Postgraduate Programme in Insect Science (ARPPIS) scholar; and institutional financial support from UK Aid (www.ukaiddirect.org) from the UK Government; Sida; the Swiss Agency for Development and Cooperation (SDC) (www.eda.admin.ch/sdc); and the Kenyan Government (www.mygov.go.ke). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The views expressed herein do not necessarily reflect the official opinion of the donors.
Competing interests: The authors have declared that no competing interests exist.
Keywords: Arbovirus; Flavivirus; Orthobunyavirus; Bunyamwera Virus; Mosquitoes; Culex spp.; Anopheles spp.; Kenya.