Analysis of infection and NA molecular evolution of avian H9N2 in different hosts in Yunnan province

7 901 samples collected from poultry and swine in the Yunnan province between 2006 and 2007 were detected with RT-PCR,HA,HI,ELISA,and NA genes in representative positive samples were cloned and analyzed.The results suggest that H9N2 subtype influenza virus was epidemic in 14 administrative division of Yunnan province and swine and goose infected with H9N2 subtype influenza virus were confirmed in Yunnan province first time.The homology of NA genes of 19 strains from different districts in Yunnan province was between 89%-100% and homology of deduced amino acid was 96.1%-99.6%.The 14 strains(including 1 goose source strain) have became predominant sublineages of which are 95% homology of NA gene(1 407 bp nucleotides,encoding 469 amino acids).Four strains(three duck,one gooes and one swine source strains)of NA gene homology 99% is another sublineages,the deletion of three-amino-acids at 61-63aa in NA consisted of 466 amino acids is a characteristic difference with predominant sublineages.NA genes of H9N2 subtype of avian influenza virus in Yunnan province exists a polymorphism with other strains of domestic and abroad.