Abstract：H3N8 influenza viruses have a broad host range, which are commonly found in wild birds and domestic poultry, and have been isolated from some mammals. Moreover, H3N8 influenza viruses have the ability to occasionally infect and transmit among other species. In recent years, avian influenza surveillance data indicates that the number of isolated H3N8 subtype Avian influenza virus (AIV) has a tendency to increase year by year. To understand the biological characteristics of the H3N8 AIV, two H3N8 viruses (A/duck/Guizhou/S1092/2013(H3N8)(DK/GZ/S1092/2013) and A/duck/Guizhou/S1145/2013(H3N8)(DK/GZ/S1145/2013)) were isolated from Guizhou province at 2013 for phylogenetic analysis, infectious experiment in mice (Mus musculus) and receptor-binding specificity analysis. The phylogenetic analysis results indicated that the 2 viruses displayed obviously genetic diversity, and all genome of the viruses had different origins except for hemagglutinin (HA) gene. The mice study suggested that the 2 viruses could effectively replicate in the lung and nasal turbinate of mice without pre-adaptation. The virus titers of DK/GZ/S1092/2013 in lung and nasal turbinate were 4.00 and 5.50 log10EID50/mL (EID50: Fifty percent embryo infection doses), respectively, and the virus titers of DK/GZ/S1145/2013 in lung and nasal turbinate were 4.25 and 3.58 log10EID50/mL, respectively. In addition, the 2 H3N8 influenza viruses displayed low virulence to mice, and mice did not display obvious clinical symptoms after infection with the viruses. In the observation period, DK/GZ/S1092/2013 only caused 1.8% bodyweight loss and DK/GZ/S1145/2013 only caused 0.8% bodyweight loss. The receptor-binding specificity analysis demonstrated that the 2 viruses had the ability to bind both sialic acid (SA) α2,3-Gal receptor from poultry and SA α2,6-Gal receptor from human, which indicated that the 2 H3N8 subtype AIV posed potential threat to infect human. In conclusion, this study systematically researched the biological characteristic of the 2 H3N8 subtype AIV, and the results indicated that the H3N8 influenza viruses posed potential risk to infect mammals. This study plays an important role in the prevention and control of H3N8 subtype AIV.
