H9N2 subtype influenza viruses have been detected in different species of wild birds and domestic poultry in many countries for several decades. Because these viruses are of low pathogenicity in poultry, their eradication is not a priority for animal disease control in many countries, which has allowed them to continue to evolve and spread. Here, we characterized the genetic variation, receptor-binding specificity, replication capability, and transmission in mammals of a series of H9N2 influenza viruses that were detected in live poultry markets in southern China between 2009 and 2013. Thirty-five viruses represented 17 genotypes on the basis of genomic diversity, and one specific "internal-gene-combination'' predominated among the H9N2 viruses. This gene combination was also present in the H7N9 and H10N8 viruses that have infected humans in China. All of the 35 viruses preferentially bound to the human-like receptor, although two also retained the ability to bind to the avian-like receptor. Six of nine viruses tested were transmissible in ferrets by respiratory droplet; two were highly transmissible. Some H9N2 viruses readily acquired the 627K or 701N mutation in their PB2 gene upon infection of ferrets, further enhancing their virulence and transmission in mammals. Our study indicates that the widespread dissemination of H9N2 viruses poses a threat to human health not only because of the potential of these viruses to cause an influenza pandemic, but also because they can function as "vehicles'' to deliver different subtypes of influenza viruses from avian species to humans.

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To establish the reverse genetics system of the H7N9 avian influenza virus(AIV),eight plasmid system of A/CK/Shanghai/S1053/2013(CK/53) was constructed and the rCK/53 was successfully rescued,of which the whole genome sequences were identical with the parental virus.In addition,the recombinant vaccine virus of CK53/PR8 was generated which contained HA and NA genes of CK/53 in the back ground of internal genes derived from the vaccine virus strain of A/PuertoRico/8/34(PR8).Comparison of the growth of rCK/53 and CK53/PR8 in MDCK and A549 cells showed that there was no significant difference of the viruses in A549 cells,but displayed obvious difference at 48 and 72 hours post-infection in MDCK cells.The results would provide a promising technique support for further study on the pathogenic and crossing host barrier mechanisms of the H7N9 avian influenza virus and on further immune protection experiment.

A newly emerged H7N9 virus has caused 132 human infections with 37 deaths in China since 18 February 2013. Control measures in H7N9 virus-positive live poultry markets have reduced the number of infections; however, the character of the virus, including its pandemic potential, remains largely unknown. We systematically analyzed H7N9 viruses isolated from birds and humans. The viruses were genetically closely related and bound to human airway receptors; some also maintained the ability to bind to avian airway receptors. The viruses isolated from birds were nonpathogenic in chickens, ducks, and mice; however, the viruses isolated from humans caused up to 30% body weight loss in mice. Most importantly, one virus isolated from humans was highly transmissible in ferrets by respiratory droplet. Our findings indicate nothing to reduce the concern that these viruses can transmit between humans.

On March 31, 2013, the National Health and Family Planning Commission announced that human infections with a previously undescribed influenza A (H7N9) virus had occurred in Shanghai and Anhui Province, China. To investigate the possible origins of the H7N9 viruses causing these human infections, we collected 970 samples, including drinking water, soil, and cloacal and tracheal swabs of poultry from live poultry markets and poultry farms in Shanghai and Anhui Province. Twenty samples were positive for the H7N9 influenza virus. Notably, all 20 viruses were isolated from samples collected from live poultry markets in Shanghai. Phylogenetic analyses showed that the six internal genes of these novel human H7N9 viruses were derived from avian H9N2 viruses, but the ancestor of their HA and NA genes is uncertain. When we examined the phylogenetic relationship between the H7N9 isolates from live poultry markets and the viruses that caused the human infections, we found that they shared high homology across all eight gene segments. We thus identified the direct avian origin of the H7N9 influenza viruses that caused the human infections. Importantly, we observed that the H7N9 viruses isolated from humans had acquired critical mutations that made them more "human-like". It is therefore imperative to take strong measures to control the spread of H7N9 viruses in birds and humans to prevent further threats to human health.

To control of the continuing accumulation of antigenic changes within Clade 7.2 highly pathogenic avian influenza viruses(HPAIVs), and the potential pandemic threat to poultry or even humans, it is necessary to update our vaccine stock according to the antigenic analysis based on surveillance. In this study, a reassortant virus, named rPR8-LN/S4092, was generated using reverse genetics. The virus contained modified HA and NA genes of an epidemic strain A/Chicken/Liao Ning/S4092/2011 in the background of internal genes derived form A/Puerto Rico/8/34(PR8). The reassortant virus was attenuated by removal of the multi-basic amino acid motif in the HA gene by mutation and deletion(from PQIEGRRRKR to PQRETR), which could be served as a candidate vaccine virus.