H9N2 is a subtype of the species Influenza A virus, whereas the PB1 and PB2 genes are closely related to those of the H5N1viruses and a quailH9N2 virus A/quail/Hong Kong/G1/97 (Qa/HK/G1/97) suggesting that many of the 1997chicken H9 isolates in the markets were reassortants.