Speaker
Description
Flavivirus infection causes >100,000 annual cases of encephalitis and meningitis worldwide, with case fatality rates of 20-50%. Encephalitic flaviviruses include West Nile virus, which caused widespread outbreaks in Europe and the US in 2025, and Japanese Encephalitis virus, which entered temperate Australia in 2022 and became endemic within a single season. These highly pathogenic flaviviruses infect native mosquito species and their animal hosts, utilising pre-existing transmission pathways for rapid spread. Such transmission pathways may be exposed by studying the evolution and vector associations of related endemic viruses.
Edge Hill virus (EHV) is a less-pathogenic flavivirus of the Yellow Fever Group, endemic to Australia and frequently detected in the most populous state, New South Wales (NSW). Genomic data on EHV is scarce, with only 2 complete and 16 partial genomes published, and none since 2010. To understand flavivirus transmission pathways, we investigated the spatiotemporal genetic diversity of EHV and its associated mosquito vectors. Over 120,000 mosquitoes collected in 2021-2024 by the NSW Arbovirus Surveillance Program were pooled by date and location and sequenced using COSMOS, a targeted metagenomics method that combines virus sequencing with vector species identification. EHV was detected in 36 pools, of which 32 produced complete genomes. Phylogenetic reconstruction based on whole genomes and the NS5 region, which enabled inclusion of historic sequences, revealed two contemporary EHV genetic lineages, with evidence of lineage replacement since 2010. Seven traps contained both lineages, indicating ongoing co-circulation. EHV was significantly associated with coastal Aedes vigilax mosquitoes (OR=7.8), However, inland detections in traps without Ae. vigilax strongly suggests additional involvement of Culex annulirostris, the Australian vector of encephalitic flaviviruses. EHV genomes collected west of the Great Dividing Range were non-monophyletic and interspersed with genomes from coastal locations, indicating rapid dispersion across >1200 km during breeding seasons, and exposing existing routes of flavivirus transmission.
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