Evolutionary characteristics of influenza B virus since its first isolation in 1940: dynamic circulation of deletion and insertion mechanism |
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Authors: | R Nerome Y Hiromoto S Sugita N Tanabe M Ishida M Matsumoto S E Lindstrom T Takahashi K Nerome |
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Institution: | (1) Department of Virology I, National Institute of Infectious Diseases, Tokyo, Japan, JP;(2) Hoshi University, Tokyo, Japan, JP;(3) Epizootic Research Station, Equine Research Institute, Japan Racing Association, Tochigi, Japan, JP |
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Abstract: | Summary. New antigenic variants of B/Yamagata/16/88-like lineage which appeared in the season of 1997 as a minor strain tended to
predominate in the following season. Also, we could observe for the first time, three peaks of activity caused by H3N2 virus
and two variants of B influenza virus. Antigenic and phylogenetic analyses revealed that B/Victoria/2/87-like variants appeared
again in Japan in 1997 after a nine-year absence. Influenza B viruses evolved into three major lineages, including the earliest
strain (I), B/Yamagata/16/88-like variants (II), which comprised of three sublineages (II-(i), II-(ii), II-(iii)), and B/Victoria/2/87-like
variants (III). Evolution of influenza B virus hemagglutinin was apparently distinguishable from that of influenza A virus,
showing a systematic mechanism of nucleotide deletion and insertion. This phenomenon was observed to be closely related to
evolutionary pathways of I, II-(i), II-(ii), II-(iii) and III lineages. It was noteworthy to reveal that the nucleotide deletion
and insertion mechanism of influenza B virus completed one cycle over a fifty-year period, and that a three nucleotide deletion
was again observed in 1997 strains belonging to lineage II-( iii). It was evident that amino acid substitutions accompanying
nucleotide insertions were highly conserved.
Received December 4, 1997 Accepted March 10, 1998 |
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