Novel H7N7 avian influenza viruses detected in migratory wild birds in eastern China between 2018 and 2020

Wild birds are the natural reservoirs of avian influenza viruses, and surveillance and assessment of these viruses in wild birds provide valuable information for early warning and control of animal diseases. In this study, we isolated 19 H7N7 avian influenza viruses from wild bird between 2018 and 2020. Full genomic analysis revealed that these viruses bear a single basic amino acid in the cleavage site of their hemagglutinin gene, and formed four different genotypes by actively reassorting other avian influenza viruses circulating in wild birds and ducks. The H7N7 viruses bound to both avian-type and human-type receptors, although their affinity for human-type receptors was markedly lower than that for avian-type receptors. Moreover, we found that the H7N7 viruses could replicate efficiently in the upper respiratory tract and caecum of domestic ducks, and that the H5/H7 inactivated vaccine used in poultry in China provided complete protection against H7N7 wild bird virus challenge in ducks. Our findings demonstrate that wild bird H7N7 viruses pose a substantial threat to the poultry industry across the East Asian -Australian migratory flyway, emphasize the importance of influenza virus surveillance in both wild and domestic birds, and support the development of active control strategies against H7N7 virus. (C) 2022 Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences. Published by Elsevier Masson SAS on behalf of Institut Pasteur.

Automated summary

Wild birds serve as natural reservoirs for avian influenza viruses, and monitoring and assessing these viruses in wild birds provide valuable information for early warning and control of animal diseases. This study isolated 19 H7N7 avian influenza viruses from wild birds between 2018 and 2020, which actively reassorted with other avian influenza viruses to form different genotypes. These H7N7 viruses could bind to both avian-type and human-type receptors, with a lower affinity for human-type receptors. Furthermore, they replicated efficiently in the upper respiratory tract and caecum of domestic ducks, and the H5/H7 inactivated vaccine provided complete protection against H7N7 wild bird virus in ducks. These findings highlight the substantial threat of wild bird H7N7 viruses to the poultry industry in the East Asian-Australian migratory flyway, emphasizing the importance of influenza virus surveillance in both wild and domestic birds and supporting the development of active control strategies against H7N7 virus.