# Genetic and molecular characterization of a novel reassortant H3N2 influenza virus from a sick pig in Eastern China in 2019

## TL;DR

A new H3N2 influenza virus was found in a sick pig in China in 2019 and shown to have the potential to infect both humans and animals.

## Contribution

The study identifies a novel reassortant H3N2 SIV with mixed genetic origins and cross-species receptor binding capabilities.

## Key findings

- The virus has H3N2 HA and NA genes similar to human-like lineages but other genes similar to H1N1 SIVs from East Asia.
- ZJ-SW19 can bind to both human and avian receptors and replicate efficiently in various cell lines.
- The virus showed moderate virulence in mice and distinct antigenic properties from avian and human H3N2 viruses.

## Abstract

Swine influenza viruses (SIVs) cause clinical respiratory symptoms associated with high mortality rates among pigs. Because pigs can be a “mixing vessel” for influenza viruses, the SIV might pose a serious threat to animal and human health. In this study, an H3N2 SIV [A/swine/Zhejiang/19/2019(H3N2) (ZJ-SW19)] was isolated from a sick pig in Eastern China in 2019, and its molecular genetics were characterized. Phylogenetic analysis demonstrated the hemagglutinin (HA) and neuraminidase (NA) segments of ZJ-SW19 are highly homologous with those of H3N2 SIVs, belonging to human-like lineages; in contrast, the remaining six SIV segments (PB2, PB1, PA, NP, M, and NS) demonstrate the highest similarity with H1N1 SIVs isolated in East Asia during 2014–2020. The in vitro analysis of the virus’s growth kinetics revealed that ZJ-SW19 can replicate efficiently in various mammalian and avian cell lines (including MDCK, A549, and DF-1). The receptor-binding analysis results indicated that ZJ-SW19 can bind to human-like receptors (α-2,6-linked sialic acid) and avian-like receptors (α-2,3-linked sialic acid). Moreover, ZJ-SW19 demonstrated significant differences compared with avian- and human-origin H3N2 influenza viruses in the antigenic analysis. Finally, in the pathogenicity test, ZJ-SW19 effectively replicated in the mouse lungs with moderate virulence. Therefore, continuous circulation of novel reassortant H3N2 SIVs indicates the need for long-term, close surveillance of influenza viruses in pig herds.