Objective To analyze the site mutations of the HA receptor binding domain (RBD) of chicken-originated H10N8 avian influenza virus, and investigate the virus replication efficiency in human respiratory cells and the pathogenicity in BALB/c mice.

Methods Full-genome sequencing was performed for two strains of chicken-originated H10N8 avian influenza viruses (A/CK/KM/12/2021 and A/CK/KM/20/2021), followed by screening for mutations at key amino acid sites. Virus receptor binding preferences were determined using a solid-phase direct binding assay. Additionally, H10N8 virus replication was assessed in Madin-Darby canine kidney (MDCK) cells, human respiratory cell lines (A549 and BEAS-2B), and pathogenicity was evaluated in BALB/c mice.

Results Two strains of chicken-originated H10N8 viruses exhibited mutations at HA sites A135T, S138A, P186S, Q220R, and D225G. These site-specific mutations enhanced the adaptability and virulence of the viruses in mammals (including humans). The H10N8 viruses predominantly bind to avian-type receptors (SAα-2, 3 Gal) with extremely weak affinity for human-type receptors (SAα -2, 6 Gal) (P < 0.001). Two strains replicated efficiently and exhibited robust growth kinetics in MDCK cells and human respiratory cells (A549 and BEAS-2B). Furthermore, two strains caused respiratory infectious diseases and even death in BALB/c mice after inoculation with viruses.

Conclusion The H10N8 subtype avian influenza viruses can efficiently replicate in human respiratory cells and cause respiratory infections in BALB/c mice without prior adaptation, indicating their potential to cross the species barriers and infect humans.