Jpn. J. Infect. Dis" 55, 2002

Laboratory and Epidemiology Communications
Tick‑Bone Encephalitis Ⅵms within and outside Japan:

a Cause fわr Concem?

Michae1 Br6ker*
Chiron Behring GmbH & Co,

Post Box 1630, 35006 Marbtirg, Germany
Communicated by lchiro Kurane(Accepted April 25, 2002)

The tick‑bone encephalitis (TBE) Vims is an etiologic

implementation of the vaccination recommendations (7).

agent of serious illnesses including neuroinfections and is

SeroepidemiologlCal studies have shown that more than 90%

endemic in Europe and Asia. The TBE vims which belongsof the young adults were found to have protectlng antibody

to the family ofFlaviviridae is transmitted by ticks. Basedlevels and about 80% follow the official TBE vaccination

on serologlCal analyses, the TBE virus can be subdivided intor.ecommendations (8)I ln contrast to the success ofvaccina‑

the European and the Far Easternsubtypes. Human infection

tlOn in Austria, there has been an increase in TBE cases overis characterised by two clinical stages: after an incubation

the last 20 years in Czechoslovakia (now the Czech Republic

period of7‑14 days, the disease manifests itself as an innuenza‑and Slovak Republic) from a.round 100 to about 700 cas?s1ike syndrome with fever, headache, and vomltlng. After asymptom‑a.ee interval of 1 ‑3 weeks, 6‑20% of patients develop
menlngltlS, and lO% of the orlglnally infected patients go on
to develop encephalitis and myelitis, with sequelae occumng

yearly. This neighbounng region is comparable to Austria ln

in 3‑11% of cases; the mortality rate is 1‑2%･ A specificyear (Keizai Koho Center, personal com.munication)I Many

population density and TBE epidemiology, but TBE vaccina‑tion coverage is much lower.

About 2.3 million Japanese tourists travel to Europe every

therapy is not available (for a review, see reference 1 ).

of them favour attractive towns and locatlOnS Where the TBE

virus is endemic, e.g., SouthernGern1any (Heidelberg) or theIn 1993, a case ofTBE was reported in the southem part ofAlpine regiPn in Switzerland and Austria (more than 400,000

Hokkaido. To detemine the seroprevalence of the TBE vinュs,a seroepidemiologlCal suⅣey was perf♭med among humans

Japanese vISit Gemany and Austria). In 2001, a Japaneseand animalsknown to be susceptible for theviruS. Sera fromtourist became infected in Salzburg (Austria), where he wasgoats, dogs, and cattle were fわund to be antibody positive. Twovisiting his daughter, a music student in Hthe city of Mozart".

of24 residents in the case study area were TBE antibody

He fell severely ill in June 2001with the typical biphasic

positive, one of whom had suffered from severe encephalitis

course and died in September 2001 (9).

35 years ago. Moreover, the TBE virus was isolated fromunc.on fined dogs (2) and from small rodents (3) from thisIn Denmark, the TBE virus is found only on the island ofBomholm in the Baltic sea. Until 1999, no cases ofTBE had

reglOn･ Genomic sequence and phylogenetic analyses of one

been reported f♭r a period of40 years. In 1998, a resident ofcanine vims isolate revealed a close relationship with the Far

Bomholm developed menlngO‑enCephalitis, but the cause

Eastem subtype of the TBE vims (4). The TBE vims wasremained unidentified until his general practitioner, whoalso isolated from various tick species (5). While in Europe

happened to learnabout TBE during a refresher course,

the main host of the TBE virus is the tick lxodes ricinus, there‑examined the patient fわr T古E antibodies. Since then, threeprlnCIPal vector in Far EasternRussia is I. persulcatus. The
main host on Hokkaido was identified as I. ovatus (6). It may

TBE cases were reported in 1999 and one case each in 2000

and 2001 (1 0, and K. Kristiansen, personal communication).

SeroepidemiologlCal studies calTied out by hemagglutina‑

thus be concluded that the TBE vinュs is endemic in Japan, atleast on the island ofHokkaido.

tion and neutralization tests among forest workers fromThe TBE vims is widely distributed throughout EuropeBomholm showed that 30% were TBE vinュs positive (12/40)

and Asia･ TBE cases are reported from Northern Europe

and three had experienced symptoms ofTBE. Of508 adult(coastal areas of SouthernScandinavia) to south of the Alps
(some reglOnS in Northem Italy). The most westerly location

residents ofBomholm examined fわr TBE antibodies, 1.4%

where the TBE virus is endemic is the AIsa?e region (France)
and in an easterly direction the endemic reglOn extends across

TBE positive in 83% and new studies indicate that about 2%

were positive. In the 1960S, sera from deer were found to beof the ticks are infected by the TBE virus (10).

the Asian continental shelfas far as Siberia. Some highly

TBE had been virtually forgotten on Bornl10lmfor the last 40

endemic regions are Austria, Slovenia, the Czech Republic,
the Baltic countries, and Russia. Infectionwith the TBE virus

years. It is thus not surpnslng that TBE has not been diagnosed

can be controlled by vaccination, which is recommended inonly be identified if suitable surveys are performed,

for many years among its 45,000 residents, since causes canall endemic countries, In the pre‑vaccination era, more thanIt was conclusively demonstrated thaHhe TBE vinュs is

700 cases annually were reported in Austria, whereas now

endemic in Japan. Considering the level ofunde汀epOrtlng

only 50 to 70 patients annually are hospitalized fbllowlng

on Bomholm, it may bejustified to assume that the numberofTBE cases may also be underreported on Hokkaido and*Co汀eSpOnding author: Tel: +49‑642 1 ‑39‑29 12, Fax: +49‑642ト

possibly ln Other regions Of Japan. Physicians should take

39‑53 1 5, E‑mail: MichaeLBroeker@Chiron‑Behring,com

TBE more seriously as a possible cause ofviral encephalitis

55

Jpn. J. Infect. Dis., 55, 2002
sion cycle of tick‑bone encephalitis vims in Hokkaido.

and possibly distinguish it舟om Japanese encephalitis.

Travellers to TBE‑endemic regions in Europe (often theJpn. J. Vet. Res., 46, 2‑3.

most popular tourist areas, e.蛋., the wine一growlng reglOn

6. Takeda, TリIto, T., Chiba, M., Takahashi, K., Niioka, T.

around Heidelberg in Germany, Salzburg in Austria, etc.)

and Takashima, I. (1998): Isolation of tick‑borne

should be vaccinated against TBE. "Last minute" protection

encephalitisvirusfrom Ixodes ovatus (Acari: Ixodedae)

in Japan. J. Med. Entomo1., 35, 227‑231.

is possible thanks to newly developed TBE vaccines fわrchildren and adults offering a clinically proven and licensed
vaccination schedule on days 0, 7, and 21 (1 1,12). Furthermore,

7. Kunze, U., Bernhard, G., B6hm, G. and Groman, E.

the viral strains used to produce the vaccines approved in

vaccination: Status 2000. Wien. Med. Wochenschr., 150,

(2000): Tick‑borne encephalitis (TBE) and TBE‑

Europe also induce antibodies that confer neutralizing activity

2‑7,against isolates of the Far Eastem and Japanese subtypes c･f

8. Hainz, U., Aigner, K, Asch, E., Berger, P., B6hmer, F.,
Feldkircher, B., Horwarth, B., Jenewein, B" Kassal, H.,

the TBE vinュs and could therefわre be used f♭r residents of■orvisitors to TBE endemic areas in Eastem Asia (Hokkaido,Kistner, 0,, Mack, H., Pfeiffer, K/P., Pils, K., Plank, J"
Rermer, D., Salmein‑Teissl, M., Schwanzer, E., Trieb, K.

Siberia).

and Grubeck‑Loebenstein, B･ (2002): Do recommnIended
vaccination strategies give Sufficient protection inREFERENCES

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2. Chiba, M. (1996): A serological survey of tick‑bonesiumorganized by the Austrian Green Cross, Gmunden,ePcephalitis (TBE) in Hokkaido and isolation of the TBE
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Austria, October 5, 2001.
10. Kristiansen, K. (2002): TBE in Denmark‑in particular

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ll. Zent, 0., Banzhoff, A., Meriste, S., Sluzewski, W. andWittermann, C. (2002): Clinical evaluation. of a new

Takashima, I･ ( 1 999): Isolation of tick‑bone en?ephalitis

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4･ Takashima, I., Morita, K., Chiba, M" Hayasaka, D., Sato,T., Takezawa, C" Igarashi, A., Kariwa, H., Yoshimatsu,K., Arikawa, J. and Hashimoto, N. (1997): A case oftick‑(2002): Clinical evaluation of a polygeline‑free TBE

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56