The pandemic potential of H9N2 avian influenza viruses

Since their introduction into land-based birds in 1988, H9N2 avian influenza A viruses have caused multiple human infections and become endemic in domestic poultry in Eurasia. This particular influenza subtype has been evolving and acquiring characteristics that raise concerns that it may become more transmissible among humans. Mechanisms that allow infection and subsequent human-to-human transmission of avian influenza viruses are not well understood.