Influenza B virus evolution: Co-circulating lineages and comparison of evolutionary pattern with those of influenza A and C viruses

Comparison of the HA genes of type B influenza viruses in herald waves and later epidemic seasons

“…This was constructed by giving priority to mainstream changes (changes inherited by most subsequent strains) over strain-specific changes and minimizing the chance that a strain-specific change shared by two viruses occurred independently. As reported by others [4][5][6], two evolutionary lineages (A, B in Fig. 3) of influenza B viruses co-circulated during this period as deduced from the evolutionary tree of the HA genes.…”

“…4 In this study, we showed that the influenza B viruses belonging to two evolutionary lineages independently caused epidemics until 1991. Herald viruses SI/64 [4], HK/73 [13], SI/79 [14], IK/85 [5], NS1/87 [5], YG16/88 [5], and AI5/88 [6] HA gene sequences were reported previously. The mark in the amino-acid column indicates a deletion.…”

“…The results showed that the spring isolates were in most cases genetically close to some of the winter isolates and they were considered to be the parental viruses for the following influenza seasons. Analysis of the HA genes of recent influenza B viruses has shown the existence of two co-circulating evolutionary lineages [4][5][6], and, therefore, clearcut results should be expected for the genetic relationship between herald and the later epidemic viruses. In the present study, we compared the HA gene sequences of influenza B viruses isolated during herald waves and later epidemic seasons in the same districts in Japan during 1987-90.…”

The evolution of human influenza viruses

“…The evolution of in£uenza B viruses is characterized by co-circulation of antigenically and genetically distinct lineages for extended periods of time (Yamashita et al 1988). Two lineages that are de¢ned by phylogenetic relationships of HA genes diverged in the early to mid-1970s, one represented by B/Victoria/2/87, the`B/Victoria lineage' and the other represented by the antigenic variant B/Yamagata/16/88, which emerged in 1988, thè B/Yamagata lineage' (¢gure 5 and table 3) (Kanegae et al 1990;Rota et al 1990 As might be expected, genetic reassortment between viruses of the co-circulating lineages is also a characteristic feature of the evolution of B viruses.…”

Evolution of influenza B/Victoria/2/87-like viruses: occurrence of a genetically conserved virus under conditions of low epidemic activity

“…Conserved viruses may serve as an important genetic reservoir for influenza B virus evolution, for new variants of epidemic significance rarely evolve from the previous epidemic variants (Yamashita et al, 1988;Kanegae et al, 1990;Rota et al, 1990), which can be seen as dead ends. Genomic conservation is a frequent phenomenon in influenza C viruses (Buonagurio et al, 1985) and in avian influenza A viruses (Kida et al, 1987).…”