N Ikonen1, L Kinnunen, T Forsten, R Pyhälä. 1. Influenza laboratory, National Public Health Institute, Mannerheimintie 166, 00300 Helsinki, Finland.
Abstract
BACKGROUND: Influenza B virus evolution is currently in a unique situation having two cocirculating main lineages B/Yamagata/16/88 (YM/88)-like and B/Victoria/2/87 (VI/87)-like viruses. Continuation of this bifurcation would mean development towards distinct forms resembling the HA subtypes of influenza A viruses. OBJECTIVE: We wanted to examine both intraepidemic heterogeneity and recent evolution in these two lineages. The initial purpose was to determine the geographic distribution of the two sublineages of the VI/87-like viruses in Europe in 1989-1990 under circumstances of low epidemic activity. Due to the outbreaks of YM/88-like viruses since 1991, the study was extended to contain the evolution of these viruses and their genetic relationship with the vaccine strains of that time. STUDY DESIGN: The HA1 gene sequences of 33 influenza B strains isolated in ten European countries since 1989 were determined and compared with those available through databases or personal contacts. RESULTS: The two main lineages, YM/88-like and VI/87-like viruses, both continued to circulate. In both lineages, changes in the potential glycosylation sites were observed. Two sublineages of the VI/87 lineage cocirculated during the 1989-1990 season with somewhat different geographic distributions. A high degree of intraepidemic heterogeneity was observed, as well as examples of conserved nucleotide sequences. CONCLUSIONS: It is important to follow the evolution and circulation of VI/87-like viruses. Current vaccines give poor or no protection against VI/87-like viruses in immunologically unprimed children or even in primed adults (Levandowski et al., 1991, Pyhala et al., 1994). Changes in the potential glycosylation pattern in the latest virus isolates of both main lineages have occurred and it is interesting to see the significance of these changes to viral evolution.
BACKGROUND:Influenza B virus evolution is currently in a unique situation having two cocirculating main lineages B/Yamagata/16/88 (YM/88)-like and B/Victoria/2/87 (VI/87)-like viruses. Continuation of this bifurcation would mean development towards distinct forms resembling the HA subtypes of influenza A viruses. OBJECTIVE: We wanted to examine both intraepidemic heterogeneity and recent evolution in these two lineages. The initial purpose was to determine the geographic distribution of the two sublineages of the VI/87-like viruses in Europe in 1989-1990 under circumstances of low epidemic activity. Due to the outbreaks of YM/88-like viruses since 1991, the study was extended to contain the evolution of these viruses and their genetic relationship with the vaccine strains of that time. STUDY DESIGN: The HA1 gene sequences of 33 influenza B strains isolated in ten European countries since 1989 were determined and compared with those available through databases or personal contacts. RESULTS: The two main lineages, YM/88-like and VI/87-like viruses, both continued to circulate. In both lineages, changes in the potential glycosylation sites were observed. Two sublineages of the VI/87 lineage cocirculated during the 1989-1990 season with somewhat different geographic distributions. A high degree of intraepidemic heterogeneity was observed, as well as examples of conserved nucleotide sequences. CONCLUSIONS: It is important to follow the evolution and circulation of VI/87-like viruses. Current vaccines give poor or no protection against VI/87-like viruses in immunologically unprimed children or even in primed adults (Levandowski et al., 1991, Pyhala et al., 1994). Changes in the potential glycosylation pattern in the latest virus isolates of both main lineages have occurred and it is interesting to see the significance of these changes to viral evolution.