Abstract
To assess the potential threat of the novel H3 subtype Avian Influenza Virus (AIV) to the poultry industry and human health, whole-genome sequencing and phylogenetic tree and homology analysis were conducted on four H3N3 viruses and one H3N8 virus isolated from three different regions. Representative strains were selected for the study of pathogenicity and transmissibility in Specific Pathogen Free (SPF) chickens, BALB/c mice, and Hartley guinea pigs. Phylogenetic tree and homology analyses indicate that the eight gene segments of the four H3N3 viruses are derived from reassortments involving H3N8 virus (HA gene), H10N3 virus (NA gene), and H9N2 virus (internal genes). Additionally, the gene segments of one H3N8 strain are the result of reassortment between H3N8 virus (HA and NA genes) and H9N2 virus (internal genes). Multiple mammalian-adaptive mutations were detected in the gene fragments, including amino acid substitutions and alterations in glycosylation sites. Animal experimental results indicate that the B166 (H3N3) and K245 (H3N8) isolates were pathogenic to SPF chickens and BALB/c mice, and were also capable of infecting Hartley guinea pigs. Both strains transmitted among chickens, with B166 displaying slightly lower transmissibility than K245. However, only K245 was transmissible via direct contact in Hartley guinea pigs. This highlights the potential public health risks of H3 subtype viruses, posing a threat to the poultry industry and human health, which makes ongoing monitoring and further research crucial.