Epidemiological Investigation and Characterization of Avian Influenza A H3N8 Virus in Guangdong Province, China.

The H3N8 low pathogenic avian influenza virus (LPAIV) exhibits broad host tropism, infecting diverse avian and mammalian species, raising concerns about its zoonotic potential. Following the emergence of human infections with H3N8 LPAIV in China, including a fatal case, we investigated the epidemiological and virological characteristics of this virus in Guangdong Province. In 2022, a serological survey revealed H3N8 seroprevalence rates of 10.85% in farmed chickens and 7.97% in ducks. We isolated three H3N8 viruses, designated as A/chicken/Qingyuan/22/2022 (H3N8); A/chicken/Qingyuan/31/2022 (H3N8); and A/chicken/Qingyuan/15/2022 (H3N8), and found that these chicken isolates, like the human isolate A/Changsha/1000/2022, share the same E190 residue. This residue can synergize with sites such as Q226 and G228 to enhance binding affinity for SAα-2,6-Gal. Additionally, they harbor the three amino acid residues N193, W222, and S227. Among these, N193 has the potential to form hydrogen bonds with α2-6-linked glycans, while W222 and S227 may alter the conformational flexibility of the 220-loop. These two effects collectively endow the H3N8 isolates with dual receptor-binding properties. These findings suggest a shift in receptor specificity, potentially facilitating viral adaptation to mammalian hosts. Characterization of viral genome detection dynamics, and histopathology in animal models further elucidated the viral infection dynamics. Our study provides critical insights into the evolutionary trajectory and zoonotic potential of the H3N8 LPAIV.