[Study on the mutations within the whole genome of influenza virus subtype A/H3N2 strains circulated in Zhejiang province from 1998 to 2009].

Objective: To analyze the consistency of evolution condition between HA gene and the whole genome of influenza virus subtype A/H3N2 strains isolated in Zhejiang province from 1998 to 2009, and to study the potential antigenic region on the whole genome.

Methods: The sequences of whole genome of 19 Zhejiang influenza virus isolates circulated from 1998 to 2009, which conserved by influenza laboratory of Zhejiang Provincial Centre for Disease Prevention and Control, were amplified using RT-PCR assays. The obtained sequences were used to conduct phylogenetic analysis with 10 contemporaneous vaccine strains. Three methods, including comparison of the amino acid substitutions, calculation of the entropy value and the filtering of positive selection sites, were used to confirm the mutable sites on each gene.

Results: The whole genome of influenza virus subtype A/H3N2 was 4466 amino acids in length, with 137 stable mutations. The 144, 158 aa of HA gene mutate four and three times respectively; 93, 143, 307, 370, 372 aa of NA gene and 450 aa of NP gene mutate twice, and there were 29% (12/41) and 77% (24/31) mutations of HA and NA genes occurred on the non-epitope regions respectively. Analysis of the entropy value suggest that many amino acid sites on the non-epitope regions were prone to mutation, including 3, 225, 361 aa of HA gene; 93, 143, 147, 150, 372 aa of NA gene; 113, 576, 586 aa of PB1 gene; 101,256, 382, 421, 437 aa of PA; 377, 450 aa of NP gene; 218 aa of M1 gene and 31 aa of M2 gene.

Conclusion: Based on the whole genome of influenza virus subtype A/H3N2 strains isolated in Zhejiang province in 1998 to 2009, there may be several unknown or new antigen sites existing on the non-epitope regions of HA and NA genes and parts of internal genes. The phylogenetic tree constructed based on the complete sequence was more comprehensive than on the HA gene to reflect the genetic relationship and law of evolution among the influenza virus strains.