Genetic characterization of haemagglutinin 1 domain of influenza B viruses isolated in Korea during 1988-1999

Abstract

Although Korean influenza virus isolates have been genetically associated with the vaccine strains of the corresponding year, influenza B viruses have prevailed almost every year in Korea during the past decades. We have analyzed the genetic characteristics and evolutionary patterns of the haemagglutinin (HA) 1 domains of influenza B viruses isolated during 1988-1999 using direct RT-PCR and sequencing. Phylogenetic analysis of influenza B viruses isolated in Korea indicated that antigenically and genetically distinguishable strains of the lineage II and lineage III variants had been cocirculated. Variants prevailed in early 1990s are represented in 1996/97 and 1998/99 and some different variants have been cocirculated geographically and prevailed concurrently in Korea. All HA1s of Korean isolates have amino acid substitutions mainly in the region between position 124 and 310, which was previously proposed an immunodominant region. Insertion-deletion patterns of the HA gene revealed that Korean influenza B viruses were evolved from Lee40 with different manner between lineage II and III viruses. Lineage III viruses were also divided into two groups as conserved group and inserted group, in relation to Lee40. But lineage II viruses had evolved with directional pattern. Antigenic index proposed that influenza B isolates prevailed since 1996/97 seasons might had emerged from the antigenic variants of a Seo1697-like virus and that new variants might appear from the lineage II viruses resulting in persistent prevalence in Korea.