OBJECTIVETo study the relationship between influenza epidemic and genetic characteristic on HA and NA regions of influenza virus subtype A3 isolates of Zhejiang province in the recent years.

METHODSRNA of 25 influenza virus subtype A3 isolates, circulated in Zhejiang province during 1998 to 2005, was extracted. HA1 and NA regions were amplified and sequenced. All the sequence data were analyzed using BioEdit.

RESULTSHA1 and NA regions of all the isolates belonged to 987nt and 1362nt, encoding protein of 329 and 454 amino acids respectively. Isolates shared amino acid homology of 90.9%-99.3% and 95.2%-99.5% on HA1 and NA regions, while divergence on HA1 was greater than that on NA region. During a period of 8 years, 30 amino acids on HA1 region were substituted and 14 of which refer to 4 antigenic determinant sites. Meanwhile,21 amino acids on NA region were substituted and 5 of which referred to 3 antigenic determinant sites. Significant divergences, both in HA1 and NA, were observed among isolates in 1998 and 2002, showing that they belonged to absolutely different branches. Additionally, influenza virus subtype A3 isolates identified in recent years, with 11 N-linked glyeosylation sites in HA1 region, had 5 sites more than early A/Aichi/2/68 strain. Since 1998,3 sites had been inserted in epidemic strains, indicating the accelerated trend of glyeosylation sites were increasing.

CONCLUSIONThere is a correlation between antigenic drift of influenza virus subtype A3 and the two epidemics in Zhejiang province in 1998 and 2002.