Speaker
Description
The process of reassortment plays a crucial role in driving the transmission dynamics of influenza viruses across species barriers. Since 2020, the H5 Highly Pathogenic Avian Influenza (HPAIV) panzootic has caused significant outbreaks in poultry, wild birds and marine mammals. Extensive reassortment of the virus's eight gene segments have occurred across populations, disseminating extensive viral diversity at local and intercontinental scales. Notwithstanding the significance of reassortant viruses in the acquisition of virulence factors and alterations in host tropism, the patterns of reassortant emergence in different regions remain poorly understood.
In this study, we analysed over 250 unique reassortant types identified from a dataset of publicly available H5 sequences. These data were supplemented with >90 newly obtained HPAIV genomes from systematic surveillance in China between 2020 and 2023. We applied phylodynamic and statistical learning methods to phylogenies of all eight genomic segments to compare the patterns of reassortant emergence across regions. Specifically, we compared their frequency, location, host, and subtypes of origin; rates of evolution, dispersal and relative fitness.
Our investigation highlights Europe's role in seeding reassortants with enhanced fitness and transmissibility. These variants, originating from distant locations, are perpetuated and further reassorted in wild birds for broader dissemination. In contrast, Asia, particularly East Asia, serves as the centre for generating diverse reassortment types, but often resulting in reassortant viruses with low persistence and transmissibility. Reassortment events in East Asia are more likely to occur in mixed populations compared to other continents, especially involving reassortments with locally circulating subtypes in poultry subtypes. The observed "reassortment chatter" pattern in these regions is influenced by a complex interplay of ecological factors, including exceptional biodiversity, overlapping agricultural land cover and habitats, and human intervention.
