Characterization of emerging H3N3 avian influenza viruses in poultry in China

Avian influenza viruses continue to challenge poultry and human health; therefore, careful surveillance and evaluation of emerging viruses are important for animal disease control and human influenza pandemic preparedness. In this study, we detected a series of H3N3 subtype avian influenza viruses in chickens, pigeons, and ducks during our routine surveillance and diagnosis between September 2022 and May 2023. We performed extensive analyses to fully understand the origins of these viruses and their risk to animals and humans. We found that the viruses were complex reassortants; the viruses from chickens and pigeons carry genes mainly derived from H3N8 viruses and H10N3 viruses, whereas the two duck viruses were reassortants of duck and wild bird viruses. The chicken and pigeon, but not duck, viruses replicated in multiple organs of chickens and were shed for up to 13 days, but none caused disease or death. Six of the viruses tested all bound to both avian- and human-type receptors. Seventeen viruses were tested in mice and most replicated efficiently but were not lethal. Six viruses were tested in guinea pigs, and four of them transmitted efficiently via respiratory droplets. Our study thus identified novel H3N3 avian influenza viruses and revealed their zoonotic potential, thereby emphasizing the importance of careful monitoring and control of H3 viruses in animals.