Genetic and biological characterization of two reassortant H5N2 avian influenza A viruses isolated from waterfowl in China in 2016

Two reassortant H5N2 viruses in which hemagglutinin (HA) was clustered into clade 2.3.4.4, were isolated from apparently healthy waterfowl in live poultry markets in Eastern China in 2016. We used specific pathogen-free chickens, mallard ducks, and BALB/c mice to evaluate the isolates' biological characteristics in different animal models. The newly isolated reassortant H5N2 viruses were able to cause severe disease in chickens and effective contact transmission, only at high doses. Our pathogenicity studies in ducks yielded an interesting result: the intravenous pathogenicity index (IVPI) indicated that isolate A/goose/Eastern China/1106/2016(1106) was low pathogenic and the other isolate A/duck/Eastern China/YD1516/2016(YD1516) was of highly pathogenicity in ducks. However, our 50% duck lethal dose (DLD50) experiment demonstrated that these viruses were all of low pathogenicity (DLD50 > 107.0 EID50) in ducks. Additionally, despite the fact that reassortant H5N2 were of low pathogenicity in mice, they could bind to both avian-type (SAα-2,3 Gal) and human-type (SAα-2,6 Gal) receptors, suggesting that these isolates still present a high risk for human infection. Therefore, it is of great importance to implement continual surveillance of avian influenza virus (AIV) to protect both veterinary and public health.