Abstract
The tick-borne encephalitis virus (TBEV) is a flavivirus transmitted to humans, usually via tick bites. The virus causes tick-borne encephalitis (TBE) in humans, and symptoms range from mild flu-like symptoms to severe and long-lasting sequelae, including permanent brain damage. It has been suggested that within the population of viruses transmitted to the mammalian host, quasispecies with neurotropic properties might become dominant in the host resulting in neurological symptoms. We previously demonstrated the existence of TBEV variants with variable poly(A) tracts within a single blood-fed tick. To characterize the role of the poly(A) tract in TBEV replication and virulence, we generated infectious clones of Torö-2003 with the wild-type (A)3C(A)6 sequence (Torö-6A) or with a modified (A)3C(A)38 sequence (Torö-38A). Torö-38A replicated poorly compared to Torö-6A in cell culture, but Torö-38A was more virulent than Torö-6A in a mouse model of TBE. Next-generation sequencing of TBEV genomes after passaging in cell culture and/or mouse brain revealed mutations in specific genomic regions and the presence of quasispecies that might contribute to the observed differences in virulence. These data suggest a role for quasispecies development within the poly(A) tract as a virulence determinant for TBEV in mice.
Highlights
The Eu-Tick-borne encephalitis virus (TBEV) strain Neudoerfl has the longest known TBEV genome, and it contains a 30–250 nt poly(A) tract[5]
Characterization of the rescued viruses revealed substantial differences in their replication kinetics in cell culture and in their virulence in mice. Viruses derived from these infectious clones were passaged in cell culture or mice followed by sequencing with generation sequencing (NGS) and Sanger sequencing to understand the genetic determinants that are important for virus replication in diverse cellular environments
To determine how the length of the poly(A) tract impacts Eu-TBEV replication and pathogenicity, we constructed an infectious clone based on Torö-2003
Summary
The Eu-TBEV strain Neudoerfl has the longest known TBEV genome, and it contains a 30–250 nt poly(A) tract[5]. We report the generation of two infectious clones – Torö-6A and Torö-38A – with short and long poly(A) tracts, respectively. Characterization of the rescued viruses revealed substantial differences in their replication kinetics in cell culture and in their virulence in mice. Viruses derived from these infectious clones were passaged in cell culture or mice followed by sequencing with generation sequencing (NGS) and Sanger sequencing to understand the genetic determinants that are important for virus replication in diverse cellular environments. NGS analysis identified genomic elements favoured by replication in cell culture and mouse, revealing host-specific genetic divergence
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