Continued Evolution of H5Nx Avian Influenza Viruses in Bangladeshi Live Poultry Markets: Pathogenic Potential in Poultry and Mammalian Models

Highly pathogenic avian influenza A(H5N1) viruses have circulated continuously in Bangladesh since 2007, and active surveillance has detected viral evolution driven by mutation and reassortment. Recently, three genetically distinct A(H5N1) reassortant viruses were detected in live poultry markets in Bangladesh. Currently, we cannot assign pandemic risk by only sequencing viruses; it must be conducted empirically. We found that the H5Nx highly pathogenic avian influenza viruses exhibited high virulence in mice and chickens, and one virus had limited capacity to transmit between ferrets, a property considered consistent with a higher zoonotic risk.