Objective: To characterize the genetic diversity of hemagglutinin (HA) and neuraminidase (NA) of influenza B viruses isolated in Zhejiang province during 1999 - 2010.
Methods: Respiratory specimens were collected from patients with flu-like syndrome during the influenza outbreaks or from the hospitals which carrying out influenza surveillance project in Zhejiang province. Samples were detected by real-time RT-PCR and isolated for influenza virus. HA(1) and NA genes of influenza B virus isolates were amplified and sequenced. Phylogenetic comparison and genetic diversity analysis were performed using the bioinformation software.
Results: A total of 34 influenza B viruses were evolved in this study including Victoria-like and Yamagata-like strains according to the results of the HI test. The mutation rate of Victoria-like HA(1) gene was 4.5% and Yamagata-like HA(1) gene was 3.4%, respectively. The Victoria-like influenza B isolates had appeared to be all reassortants having a Victoria lineage HA and Yamagata lineage NA since 2004. The predominant type of influenza virus isolates in 2010 was also influenza B virus after the H1N1 flu pandemic in Zhejiang province. The isolated strains were antigenically and genetically similar to B/Brisbane/60/2008-the vaccine strain proposed for 2009 - 2010. Many differences of HA(1) and NA amino acids existed in the current isolates when compared to previous influenza B strains.
Conclusion: Significant diversity was generated among influenza B virus isolated from 1999 to 2010 in Zhejiang province. Genetic re-assortment and antigenic drift seemed the main evolutionary mechanism on influenza B virus.