Phylogenetic and epidemiological characteristics of H9N2 avian influenza viruses in Shandong Province, China from 2019 to 2021

H9N2 avian influenza virus (AIV) has widely circulated in poultry worldwide and sporadic infections in humans and mammals. During our surveillance of chicken from 2019 to 2021 in Shandong Province, China, we isolated 11 H9N2 AIVs. Phylogenetic analyses showed that the eight gene segments of the 11 isolates were closely related to several sublineages of Eurasian lineage: BJ/94-like clades (HA and NA genes), G1-like clades (PB2 and M genes), and SH/ F/98-like clades (PB1, PA, NP and NS genes). The isolates showed mutation sites that preferentially bind to human-like receptors (HA) and mammalian fitness sites (PB2, PB1 and PA), as well as mutations in antigen and drug resistance sites. Moreover, studies with mice revealed four isolates with varying levels of pathogenicity. The average antibody titer of the H9N2 AIVs was 8.60 log2. Based on our results, the epidemiological surveillance of H9N2 AIVs should be

Automated summary

During surveillance in China, 11 H9N2 avian influenza viruses (AIVs) were isolated from chickens in Shandong Province. The isolates showed close genetic relationship with several sublineages of Eurasian lineage and had mutation sites associated with human receptor binding, mammalian fitness, antigenic variation, and drug resistance. Studies with mice revealed varying levels of pathogenicity among the isolates. The average antibody titer of the H9N2 AIVs was 8.60 log2. Epidemiological surveillance of H9N2 AIVs is crucial based on these findings.