Jpn. J. Infect. Dis., 54 (1), 1-11, 2001
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Review
Epidemiology of Tick-Borne Encephalitis (TBE) and Phylogenetic Analysis of TBE Viruses in Japan and Far Eastern Russia
Ikuo Takashima*, Daisuke Hayasaka, Akiko Goto, Hiroaki Kariwa
and Tetsuya Mizutani
Laboratory of Public Health, Department of Environmental Veterinary
Scineces, Graduate School of Veterinary Medicine, Hokkaido University,
Kita-18, Nishi-9, Kita-ku, Sapporo 060-0818, Japan
(Received January 30, 2001. Accepted March 1, 2001)
CONTENTS: Summary Introduction Epidemiology of TBE and isolation of TBE virus in Hokkaido, Japan 1. Clinical findings and virus isolation 2. Genetic characterization of the virus isolates Phylogenetic analysis of TBE viruses from Japan and Far Eastern Russia 1. Relatedness of TBE virus, Hokkaido strain and Far Eastern Russian strains 2. Divergence of TBE virus, Hokkaido strain from Khabarovsk strains Pathogenicity of TBE virus, Hokkaido strain and protection from infection by European vaccine 1. Pathogenicity of the Hokkado isolates 2. Evaluation of European TBE vaccine
SUMMARY: In Oshima, the southern part of Hokkaido, a tick-borne
encephalitis (TBE) patient was found in 1993; in addition TBE
virus was isolated from the blood samples of sentinel dogs, ticks
pools, and rodents spleens in 1995 and 1996 by suckling mice.
To identify when these TBE viruses emerged in Hokkaido, the times
of divergence of TBE virus strains isolated in Oshima and Far
Eastern Russia were estimated. TBE virus was isolated in Khabarovsk
in 1998, and the nucleotide sequences of viral envelope protein
genes of isolates from Oshima and Khabarovsk were compared. Based
on the synonymous substitution rates of these virus E-protein
genes, the lineage-divergence times of these TBE virus strains
were predicted phylogenetically to be approximately 260-430 years
ago. Furthermore, the virulence of TBE virus isolates from Oshima
and Khabarovsk were compared in a mouse model. The results showed
that the isolates possessed very similar virulence in mice. European
TBE vaccine was found to be effective in TBE virus, Hokkaido strain.
This review provides evidence that the Oshima strains of TBE virus
in Hokkaido emerged from the Far Eastern Russia a few hundred
years ago, which explains why the virulence of these strains is
similar to that of TBE viruses isolated in Russia. Practical
application of the vaccine should be considered in Japan.
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