T. Nishi - Identification of genes involved in pathogenicity of FMD virus using two strains isolated in Japan with different viral features

Open Session of the EuFMD – 2018 – Increasing Global Security in the supply of effective vaccines – 29-31 October 2018 -Borgo Egnazia, Italy

Introduction
In 2000 and 2010, FMD outbreaks occurred in Japan and spread to 4 and 292 farms, respectively. Causative FMDV strains, O/JPN/2000 and O/JPN/2010, were isolated from affected cattle during each outbreak. In experimental infections, O/JPN/2000 showed only mild symptoms in cattle and goats, while O/JPN/2010 showed typical clinical signs in these animals. The difference in pathogenicity might cause the difference in severity of the two outbreaks; however, the molecular mechanisms underlying the pathogenicity of the virus are not well understood. In the present study, to identify genes involved in pathogenicity of the virus, we constructed chimeric recombinants of O/JPN/2000 and O/JPN/2010 and characterized the pathogenicity of those recombinants by animal experiments.

Materials and methods
The chimeric infectious cDNA clones were prepared by replacing the genetic regions of the full-length cDNA of O/JPN/2010 with corresponding PCR fragments amplified from O/JPN/2000. The recombined cDNA was introduced to a mammalian cell line, Cos-7, and chimeric recombinant viruses were recovered by using ZZR-127 cell cultures. These recombinant viruses, together with parental viruses, were intraperitoneally inoculated to suckling BALB/c mice (more than five mice per group) at the titer of 10 TCID50/head, and mortality rates in 7 days were observed.

Results
Totally 8 recombinant viruses were successfully recovered. Mortality rates of suckling mice which were inoculated with parental viruses, O/JPN/2000 and O/JPN/2010, were 0% and 100%, respectively. Strikingly, recombinant viruses of which one of VP1 or 3D was derived from O/JPN/2000 showed 0% mortality in suckling mice, on the other hand, other recombinant viruses showed 100% mortality.

Discussion
VP1 is outermost of virus particle and presumably responsible for interacting with cellular receptor or immune factors. 3D is RNA polymerase required for virus replication. Our results indicate that VP1 and 3D are individually involved in the pathogenesis of O/JPN/2010 in infected animals.

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