RESUMO
To demonstrate the phylogenetic evolution, the molecular characteristics of the motif of HA protein cleavage site and the varieties at the receptor binding sites of the hemagglutinin gene of the duck-origin H9N2 subtype avian influenza viruses, sequence alignment and phylogenetic analysis were performed by MEGA 4.1 Neighbor-Joining method.. The results revealed that the duck-origin H9N2 AIV viruses originated from CK/BJ/1/94-like and North-Ame-like, all the duck-origin H9N2 AIV viruses from mainland China belonged to CK/BJ/1/94-like and formed multiple genotypes through complicated re-assortment, while other duck-origin H9N2 AIV, isolated from other countries in Aisa, American and European such as Korea, Japan, Alberta, Austria, Switzerland, Iran, belonged to the North-Ame-like phylogenetic lineage. The amino acids at positions 183, 190, and 226 of the receptor binding sites of North-Ame-like group isolates had highly conserved H, E and Q respectively. In contrast with duck-origin H9N2 AIV viruses isolates from mainland China, the amino acids had N at positions 183, A, T, or V at 190, L or Q at 226, which was the same as the chicken-origin H9N2 AIV from mainland China. Most newly isolated chicken-origin H9N2 AIV in Fujian Province in Southern China had L at position 226 emphasized the higher risk of cross-infection between the chicken-origin and duck-origin H9N2 AIV in China.