Japanese encephalitis virus (JEV) is a mosquito transmitted virus of public and animal health significance that occurs throughout southeast Asia and parts of Australia. It is the causative agent of Japanese encephalitis (JE). Between 2021 and 2022, outbreaks of JE occurred in Australia impacting both animals and humans. This outbreak was caused by a novel virus belonging to genotype (G) IV. The presence of GIV in Australia raised the need to understand the drivers of its spread into previously nonendemic areas and apparent displacement of the previous genotypes of JEV (GII and GI) that have been detected in northern Australia. This requires studies into the viral fitness of this novel Australian JEV GIV (NSW/22) compared to Australian isolates of GII (FU) and GI (TS00), and also to an earlier progenitor Indonesian isolate of GIV.
The goal of the project is to address gaps in the understanding of JEV GIV replication and evolution. This will involve identifying molecular determinants for its competitive spread over the other genotypes and understanding the genetic diversity of the Australian GIV through molecular characterization of quasispecies populations, to test the hypothesis that elevated levels of genetic diversity provide an improvement in viral fitness.
To address these questions a particular focus has been given to the Australian GIV, NSW/22. Two different NSW/22 virus stocks have been generated (one amplified in mosquito cells and one in mammalian cells) in order to replicate the enzootic cycle of the virus, which involve transmission between mosquitoes and vertebrates hosts and vice-versa. Virus stocks were molecularly characterised through bioinformatics analysis and metagenomic pipelines; viral kinetics was assessed through an in vitro growth comparative study in which selected mammalian and invertebrate cell culture systems were infected in order to understand the dynamics of replication of different cell derived NSW/22 virus stocks.