Characterization of avian influenza A (H4N2) viruses isolated from wild birds in Shanghai during 2019 to 2021

The H4 subtype of avian influenza viruses has been widely distributed among wild birds. During the surveillance of the avian influenza virus in Shanghai from 2019 to 2021, a total of 4,451 samples were collected from wild birds, among which 46 H4 sub-types of avian influenza viruses were identified, account-ing for 7.40% of the total positive samples. The H4 subtype viruses have a wide range of hosts, including the spot-billed duck, common teal, and other wild birds in Anseriformes. Among all H4 subtypes, the most abun-dant are the H4N2 viruses. To clarify the genetic charac-teristics of H4N2 viruses, the whole genome sequences of 20 H4N2 viruses were analyzed. Phylogenetical analysis showed that all 8 genes of these viruses belonged to the Eurasian lineage and closely clustered with low patho-genic avian influenza viruses from countries along the East Asia-Australia migratory route. However, the PB1 gene of 1 H4N2 virus (NH21920) might provide its inter-nal gene for highly pathogenic avian influenza H5N8 viruses in Korea and Japan. At least 10 genotypes were identified in these viruses, indicating that they under-went multiple complex recombination events. Our study has provided a better epidemiological understanding of the H4N2 viruses in wild birds. Considering the muta-tional potential, comprehensive surveillance of the H4N2 virus in both poultry and wild birds is imperative.

Automated summary

The H4 subtype of avian influenza viruses is widely distributed among wild birds. This study conducted surveillance and genetic analysis of H4N2 viruses in Shanghai. The results showed that H4N2 viruses have diverse genotypes and genetic characteristics in wild birds, highlighting the importance of comprehensive monitoring in both poultry and wild birds.