Page 317 - TBE_Book_V2_2019

Chapter 12b

TBE in Japan

Kentaro Yoshii

History and Current Situation

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In Japan the Japanese encephalitis virus (JEV), predominant ticks in the area. Sequence and
one of mosquito-borne flaviviruses, has been phylogenetic analysis classified the TBEV
widely endemic on the main and on the isolates as Far-Eastern subtype.
southern islands with more than 1,000
Japanese encephalitis (JE) cases reported Ever since this first confirmed TBE case in
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annually in the late 1960s. In contrast, until 1993, only four additional cases of TBE were
1993, no TBE case had ever been reported and reported from Japan (in 2018), although
it was considered that there was no endemic endemic foci of TBEV were detected in various
focus of TBEV. parts of Japan, especially in Hokkaido. It is
possible that TBE patients are missed in Japan.
In 1993, a case of viral encephalitis in Hokuto One major problem is the low awareness for
city, in the southern part of Hokkaido, was the disease in Japan, even among physicians.
diagnosed as TBE. The patient had suffered Another problem is that tests for diagnostic
from fever, headache, and neurological confirmation of TBEV are not generally
symptoms such as seizures. Hemagglutination available due to the low awareness and
inhibition (HI) test against JEV showed restrictions to handle TBEV under high bio-
significant increase in HI antibodies. However, safety level (BSL 3). In Japan, no TBE vaccine is
2-mercaptoethanol-sensitive HI antibodies licensed, and it is an urgent medical need to
were not detected, and it was unlikely that JEV conduct serological survey in residents in TBEV
infection occurred in Hokkaido, where JEV was -endemic area and to establish preventive
not endemic. Furthermore, blood-sucking measures for residents and for travelers to
vector mosquitoes were not active in the end Europe and Russia.
of autumn in the area. Further serological
analysis was conducted against other Overview of TBE in Japan
flaviviruses. IgM-ELISA and neutralization tests
revealed very low antibody titer against JEV Only five confirmed cases of TBE have been
while high titers of antibodies were detected reported from Japan to date. The first patient
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by neutralization test against TBEV. was a 37-year-old female in 1993 , and the
second patient was a male person in his 40s
Because the patient was a dairy farmer with (2016). The third and fourth patients were
no history of overseas travel, it was concluded male in their 70s (2017). The fifth patient was
that she had been infected with TBEV by a tick a female in her 40s (2018). Retrospective
in her living area in Hokkaido. Epizootiological survey revealed infection with TBEV in one
surveys were conducted in Hokkaido, Lyme disease-suspected patient with
antibodies against TBEV were detected in meningoencephalitis and two asymptomatic
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dogs, horses and wild rodents in the central to cases Japan Self-Defense Forces members in
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the southern parts of Hokkaido. TBEV was Hokkaido.
isolated from dogs, wild rodents and from
Ixodes ovatus ticks, which are the

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