| H3N8 viruses have a broad host range, are commonly found in wild birds and domestic poultry, and have been isolated from dogs, horses, pigs, camels and seals as well. Moreover, H3N8 viruses have the ability to infect and transmit among other species occasionally. In recent years, national surveillance data indicates that the number of isolated H3N8 subtype avian influenza viruses has a tendency to increase year by year. In order to understand the epidemics and evaluate the risk of H3N8 avian influenza viruses(AIVs) to infect and transmit among poultry and mammals, we carried out systematiclly research about the biological charecteristics of 29 strains H3N8 viruses isolated from 2009 to 2013 in China.The results of genetic and phylogenetic analysis suggested that the H3N8 AIVs circulating in China currently displayed genetic diversity, and the 29 H3N8 viruses formed 27 different genotypes. In addition, there were extensive reassortment of internal genes between H3N8 viruses and the H4, H6, H7, H10 and H11 viruses isolated from wild birds or domestic ducks.In this study, the H3N8 viruses were mainly isolated from domestic ducks and seldom isolated from chickens. In order to evaluate the infectious risk of H3N8 avian influenza viruses to chickens, six H3N8 viruses isolated from ducks were choosed to challenge SPF chickens. It was demostrated that the six viruses could infect chickens without pre-adaptation. After inocubation, chickens didn’t display obvious clinical symptoms, and most inocubated chickens could shed viruses through orpharyngeal and cloacal routes. Moreover, four viruses could transmit from infected chickens to healthy chickens, which indicated that these viruses posed potential risk to become a novel epidemic virus in chickens.The mice study suggested that the most H3N8 viruses could replicate in the lung and nasal turbinate of mice effctively without pre-adaptation and displayed low virulence to mice. In addition, mice did not display obvious clinical symptoms after challenge the viruses. The receptor-binding specifity analysis demonstrated that all the 29 H3N8 viruses could bind to the α-2,6-linked sialic acids, although they retained high affinity for α-2,3-linked sialic acids. The transmission study revealed that the choosed eight viruses could transmit among guinea pigs by direct contact, and the six viruses replicated well in mice also could transmit efficiently among guinea pigs by direct contact, what’s more, two virues could transmit efficiently among guinea pigs by respiratory droplet as well. All those results demonstrated that the H3N8 AIVs posed potential risk to infect and transmit among humans.After the systematically biological characteristic study, we found two viruses(DK/JX/S3567/2012 and DK/HuB/SC455/2013), which had similar genetic background but had obviously different ability of replication and transmission in mammals. By reverse genetics manipulation, we found that the mutants K574 E and T588 A in PB2 could reduce the ability of DK/JX/S3567/2012 to replicate and transmit among mammals,and the role of K574 E mutant was very effective.In conclusion, the H3N8 AIVs in this study displayed genetic diversity and the viruses posed the potential risk to infect and transmit among both chickens and humans. Moreover, the PB2 mutants K574 E and T588 A played an important role in reducing the ability of H3N8 viruses to replicate and transmit among mammals, and the role of K574 E mutant was very effective. |
