Variable region of the 3′ UTR is a critical virulence factor in the Far-Eastern subtype of tick-borne encephalitis virus in a mouse model

Abstract

Tick-borne encephalitis virus (TBEV) is a major arbovirus that causes thousands of cases of severe neurological illness in humans annually. However, virulence factors and pathological mechanisms of TBEV remain largely unknown. To identify the virulence factors, we constructed chimeric viruses between two TBEV strains of the Far-Eastern subtype, Sofjin-HO (highly pathogenic) and Oshima 5-10 (low pathogenic). The replacement of the coding region for the structural and non-structural proteins from Sofjin into Oshima showed a partial increase of the viral pathogenicity in a mouse model. Oshima-based chimeric viruses with the variable region of the 39 UTR of Sofjin, which had a deletion of 207 nt, killed 100 % of mice and showed almost the same virulence as Sofjin. Replacement of the variable region of the 39 UTR from Sofjin into Oshima did not increase viral multiplication in cultured cells and a mouse model at the early phase of viral entry into the brain. At the terminal phase of viral infection in mice, the virus titre of the Oshima-based chimeric virus with the variable region of the 39 UTR of Sofjin reached a level identical to that of Sofjin and showed a similar histopathological change in the brain tissue. This is the first report to show that the variable region of the 39 UTR is a critical virulence factor in mice. These findings encourage further study to understand the mechanisms of the pathogenicity of TBEV, and to develop preventative and therapeutic strategies for tick-borne encephalitis.

MicroRNA-based control of tick-borne flavivirus neuropathogenesis: Challenges and perspectives

“…It is likely that replacement in the chimera of two LGTV genes for the corresponding genes of TBEV created LGTV-TBEV protein incompatibilities that compromised chimeric virus replication in vivo, altered virus-host interactions, and resulted in the reduction of neuroinvasiveness. Our data are in a good agreement with those observed by Sakai et al, 2014 for chimeric TBEV viruses constructed between TBEV Sofjin (highly pathogenic) and Oshima (low pathogenic) strains of TBEV (Sakai et al, 2014). Replacement of structural protein genes of Oshima genome with corresponding genes derived from Sofjin genome reduced chimeric virus replication in mouse neuroblastoma cells and exhibited neuroinvasiveness similar to that of the parental low-pathogenic Oshima strain”.…”

Functions of the 3′ and 5′ genome RNA regions of members of the genus Flavivirus

“…The longer VRs of natural isolates suggest increased length may have a selective advantage during infections in vector or host species. However, a shorter VR in a tick borne encephalitis genome was associated with higher virulence in a mouse model (Sakai, Yoshii et al 2014). The VR of mosquito-borne flaviviruses contains an A-U rich region that is thought to have evolved due to the RdRp stuttering on the UAA stop codon.…”

Virulence of tick-borne encephalitis virus is associated with intact conformational viral RNA structures in the variable region of the 3′-UTR

“…Virus titers were determined by plaque assay using baby hamster 98 kidney (BHK-21) cells as described previously (Sakai et al, 2014). Plaque assays in NA 99 cells showed that the mutant viruses had growth similar to that of Oshima-IC-pt, but 100 significantly lower than that of Sofjin-IC-pt (Fig.…”