title: Host Range Restriction of Insect-Specific Flaviviruses Occurs at Several Levels of the Viral Life Cycle.
abstract: The genusFlaviviruscontains emerging arthropod-borne viruses (arboviruses) infecting vertebrates, as well as insect-specific viruses (ISVs) (i.e., viruses whose host range is restricted to insects). ISVs are evolutionary precursors to arboviruses. Knowledge of the nature of the ISV infection block in vertebrates could identify functions necessary for the expansion of the host range toward vertebrates. Mapping of host restrictions by complementation of ISV and arbovirus genome functions could generate knowledge critical to predicting arbovirus emergence. Here we isolated a novel flavivirus, termed Niénokoué virus (NIEV), from mosquitoes sampled in Côte d'Ivoire. NIEV groups with insect-specific flaviviruses (ISFs) in phylogeny and grows in insect cells but not in vertebrate cells. We generated an infectious NIEV cDNA clone and a NIEV reporter replicon to study growth restrictions of NIEV in comparison to yellow fever virus (YFV), for which the same tools are available. Efficient RNA replication of the NIEV reporter replicon was observed in insect cells but not in vertebrate cells. Initial translation of the input replicon RNA in vertebrate cells was functional, but RNA replication did not occur. Chimeric YFV carrying the envelope proteins of NIEV was recovered via electroporation in C6/36 insect cells but did not infect vertebrate cells, indicating a block at the level of entry. Since the YF/NIEV chimera readily produced infectious particles in insect cells but not in vertebrate cells despite efficient RNA replication, restriction is also determined at the level of assembly/release. Taking the results together, the ability of ISF to infect vertebrates is blocked at several levels, including attachment/entry and RNA replication as well as assembly/release.IMPORTANCEMost viruses of the genusFlavivirus, e.g., YFV and dengue virus, are mosquito borne and transmitted to vertebrates during blood feeding of mosquitoes. Within the last decade, an increasing number of viruses with a host range exclusively restricted to insects in close relationship to the vertebrate-pathogenic flaviviruses were discovered in mosquitoes. To identify barriers that could block the arboviral vertebrate tropism, we set out to identify the steps at which the ISF replication cycle fails in vertebrates. Our studies revealed blocks at several levels, suggesting that flavivirus host range expansion from insects to vertebrates was a complex process that involved overcoming multiple barriers.
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Junglen
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany.
authors.forename: Marvin
authors.initials: M
authors.lastname: Korries
authors.affiliation: Robert Koch Institute, Berlin, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Grasse
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany.
authors.forename: Janett
authors.initials: J
authors.lastname: Wieseler
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Kopp
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany.
authors.forename: Kyra
authors.initials: K
authors.lastname: Hermanns
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany.
authors.forename: Moises
authors.initials: M
authors.lastname: León-Juárez
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany; German Centre for Infection Research (DZIF), partner site Bonn-Cologne, Bonn, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Drosten
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Bonn, Germany.
authors.forename: Beate Mareike
authors.initials: BM
authors.lastname: Kümmerer
keywords: host range restriction; infection barriers; insect-specific flavivirus