ABSTRACT
To elucidate the molecular characteristics of the hemagglutinin (HA) genes of H5N1 subtype of avian influenza viruses in the boundary region of Yunnan province. Of 420 samples were collected from the foreign poultry in boundary region of Yunnan province during 2003 to 2008 and these samples were subjected to screening by H5/N1 subtype-specific and multiplex RT-PCR. testing. The HA genes of H5N1 viruses from positive samples were amplified by RT-PCR and cloned into vector pMD18 T for subsequent sequencing. The alignment with sequences of the known reference strains and phylogenetic analysis were then performed. The genes from 21 representative positive samples with 4 different sequences at the cleavage site were obtained and all of them possessed the molecular characteristic of highly pathogenic avian influenza virus. The mutation of key amino acids had been found among receptor-binding sites, potential glycosylation sites and neutralizing epitopes.-Phylogenetic analysis showed those positive samples could be divided into 5 distinct clades, including clade 1, 2.4. 2.3.2, 2.3.4 and 7. It is evident that H5N1 viruses from the foreign boundary region of Yunnan province in 2003 to 2008 show genetic divergence and clade 2,3,4 is the dominant clade in this region.