Trends in Flavivirus Infections in Japan.Although Japanese encephalitis acute disseminated encephalitis see under encephalomyelitis. equine encephalitis see under encephalomyelitis. hemorrhagic encephalitis that in which there is inflammation of the brain with hemorrhagic foci and perivascular exudate. has declined as an important cause
of illness and death in Japan, infection with other flaviviruses flavivirus /fla·vi·vi·rus/ (fla´vi-vi?rus) any virus of the family Flaviviridae.Flavivirus /Fla·vi·vi·rus/ (fla´vi-vi?rus) group B arboviruses: a genus of viruses of the family Flaviviridae, many members of which cause disease in humans and animals, including the agents of yellow fever, dengue, and St. Louis and other forms of encephalitis. has become a public health concern. Recently, reports of imported dengue dengue /den·gue/ (den´ge) an infectious, eruptive, febrile, viral disease of tropical areas, transmitted by Aedes mosquitoes, and marked by severe pains in the head, eyes, muscles, and joints, sore throat, catarrhal symptoms, and sometimes a skin eruption and painful swellings of parts. cases, as well as isolations of tick-borne encephalitis virus, have increased. The family Flaviviridae Flaviviridae /Fla·vi·vi·ri·dae/ (fla?vi-vir´i-de) the group B arboviruses: a family of RNA viruses with a single-stranded positive-sense RNA genome; there is a single genus, Flavivirus. consists of approximately 70 viruses, nearly 40 of which cause human disease (1). Japanese encephalitis virus (JEV) was an important cause of illness and death in Japan for many years, with [is greater than] 1,000 Japanese encephalitis (JE) cases reported annually in the late 1960s. The number of JE cases has decreased dramatically, and fewer than 10 cases have been reported annually since 1992 (2). Infection by other flaviviruses, including an increase in imported dengue cases and isolations of tick-borne encephalitis (TBE) virus, is becoming a public health threat. Imported Dengue Cases Dengue viruses are transmitted by infected mosquitoes, mainly Aedes Aedes /Ae·des/ (a-e´dez) a genus of mosquitoes, including approximately 600 species; some are vectors of disease, others are pests. It includes A. aegyp´ti, a vector of yellow fever and dengue. A·e·des ( aegypti and A. albopictus (3,4). The clinical manifestations of dengue virus infections range from asymptomatic infection to dengue fever Dengue hemorrhagic fever hemorrhagic fever n. , a severe form of the disease, can cause hemorrhage, shock, and encephalitis. It occurs when a person who has acquired immunity to one of the viruses that cause dengue fever is infected by a different dengue virus. It is a leading cause of death among children in Southeast Asia and in recent years has become increasingly prevalent in tropical America. There is no specific treatment for dengue fever except good nursing care. and
dengue hemorrhagic fever (5). Dengue epidemics caused by dengue virus
type 1 occurred in Nagasaki, Osaka, Kobe, and Hiroshima from 1942 to
1945 (6,7). No outbreaks of dengue virus infection have been reported
since then in Japan, and no domestic dengue virus infections have been
identified. However, during this period there have been imported dengue
cases (8,9) in persons who visited dengue epidemic areas, were infected
with dengue viruses, and became ill after returning to Japan. In
addition, some foreign visitors who were infected in their own countries
became ill with dengue while in Japan. A syndrome that occurs in perhaps 20 percent to 40 percent of infections by certain arboviruses and is marked by high fever, scattered petechiae, bleeding from the gastrointestinal tract and other organs, hypotension, and shock. Dengue virus infections were diagnosed in serum specimens of suspected dengue cases submitted from hospitals and clinics by IgM-capture enzyme-linked immunosorbent assay, hemagglutination he
inhibition tests, and reverse transcriptase-polymerase chain reaction.
Neutralization tests and virus isolation were also performed for some
specimens. Dengue cases were confirmed by these laboratory tests at the
National Institute of Infectious Diseases, Japan, from 1985 to 1999
(Table). The number of imported dengue cases has recently increased.
Only two dengue hemorrhagic fever cases were identified, one each in
1990 and 1991; all the other cases were dengue fever. Most of these
Japanese dengue patients became infected in Southeast Asia (Thailand,
India, Philippines, and Indonesia), although some patients became
infected in Central America and Africa in recent years. We believe that
these dengue cases account for only a fraction of the total imported
cases, although the exact number of imported cases is not known. Under a
new infectious disease control law, which took effect on April 1, 1999,
dengue fever/dengue hemorrhagic fever is a reportable disease. Thus, an
accurate annual number of imported dengue cases will be known in the
near future. mag·glu ti·nate v.Table. Cases of imported dengue and countries that persons visited before onset of symptoms, by year, Japan Countries '85 '86 '87 '88 '89 '90 No. of cases(a) 4 1 4 4 1 11(b) Asia Thailand 3 0 3 1 0 7 India 0 0 2 0 0 2 Philippines 2 1 1 1 0 1 Indonesia 0 0 0 1 0 0 Malaysia 0 0 1 0 0 2 Myanmar 0 0 0 0 0 0 Cambodia 1 0 0 0 0 0 Singapore 0 0 0 0 1 0 Nepal 0 0 1 0 0 0 Laos 0 0 0 0 0 0 Vietnam 0 0 0 0 0 0 Bangladesh 0 0 1 0 0 0 Maldives 0 0 0 0 0 1 Taiwan 0 0 0 2 0 0 China 0 0 0 0 0 0 Sri Lanka 0 0 0 0 0 0 Oceania/South Pacific Australia 0 0 0 0 0 0 Fiji 0 0 0 0 0 0 New Caledonia 0 0 0 0 0 0 Tahiti 0 0 0 0 0 0 Central America Dominica 0 0 0 0 0 0 Guatemala 0 0 0 0 0 0 Africa Nigeria 0 0 0 0 0 0 Liberia 0 0 0 0 0 0 Cote d'Ivoire 0 0 0 0 0 0 Countries '91 '92 '93 '94 '95 No. of cases(a) 6(b) 14 7 11 16 Asia Thailand 3 7 1 6 8 India 1 2 1 1 4 Philippines 3 1 3 1 1 Indonesia 0 3 1 2 2 Malaysia 0 0 0 0 1 Myanmar 0 0 0 0 1 Cambodia 0 0 1 0 1 Singapore 0 1 0 0 1 Nepal 0 1 0 1 0 Laos 1 0 0 1 0 Vietnam 0 0 0 1 0 Bangladesh 0 0 0 0 0 Maldives 0 0 0 0 0 Taiwan 0 0 0 0 0 China 0 0 0 0 0 Sri Lanka 0 0 0 0 0 Oceania/South Pacific Australia 1 0 0 0 0 Fiji 0 0 1 0 0 New Caledonia 0 0 0 0 1 Tahiti 0 0 0 0 0 Central America Dominica 0 1 0 0 0 Guatemala 0 0 0 0 0 Africa Nigeria 0 0 0 0 0 Liberia 0 0 0 0 0 Cote d'Ivoire 0 0 0 0 0 Countries '96 '97 '98 '99 Total No. of cases(a) 15 6 42 11 153 Asia Thailand 4 1 19 2 65 India 5 0 6 3 27 Philippines 1 1 8 1 26 Indonesia 3 1 5 0 18 Malaysia 2 0 1 1 8 Myanmar 0 0 3 4 8 Cambodia 0 0 3 1 7 Singapore 1 1 2 0 7 Nepal 0 1 1 0 5 Laos 0 1 2 0 5 Vietnam 0 1 2 0 4 Bangladesh 1 0 1 0 3 Maldives 0 0 1 1 3 Taiwan 0 0 0 0 2 China 0 0 2 0 2 Sri Lanka 0 0 1 0 1 Oceania/South Pacific Australia 0 0 0 0 1 Fiji 0 0 0 0 1 New Caledonia 0 0 0 0 1 Tahiti 0 1 0 0 1 Central America Dominica 0 0 0 0 1 Guatemala 0 0 1 0 1 Africa Nigeria 1 0 0 0 1 Liberia 0 0 1 0 1 Cote d'Ivoire 0 0 1 0 1 (a) Some patients visited more than one country. (b) in 1990 and 1991, one patient each year had dengue hemorrhagic fever. Tick-Borne Encephalitis Central European encephalitis and Russian spring-summer encephalitis (RSSE) viruses are TBE viruses prevalent in Eurasia (1). The presence of TBE virus in Japan was first confirmed when Negishi virus was isolated from an encephalitis patient in 1948. This virus was later determined by antigenic analysis to be TBE virus (10). No further cases of tick-borne encephalitis were identified in Japan until 1993, when Takashima et al. reported a tick-borne encephalitis case in Hokkaido, the northern island of Japan (11). The patient, a dairy farmer, had high fever, double vision, convulsions, and motor paralysis. The 6- and 43-day serum samples showed highest neutralizing antibody titer to RSSE virus, but the level of neutralizing antibody to Japanese encephalitis virus was low. Serologic tests indicated that the encephalitis was caused by TBE virus. Takashima et al. demonstrated that sentinel dogs were seropositive for RSSE virus (11). They then isolated viruses from the dogs' sera and demonstrated that the isolated virus was related most closely to RSSE virus by nucleotide sequencing. Takeda et al. isolated TBE virus from Ixodes Ixodes /Ix·o·des/ (iks-o´dez) a genus of parasitic ticks (family Ixodidae); some species are disease vectors. Ix·o·des (  k-s ovatus ticks collected
in the region and demonstrated that the isolated viruses were
antigenically close to RSSE virus (12). They also showed that captured
rodents had antibodies to TBE virus and that the viruses isolated from
the rodents were also antigenically close to RSSE virus (13). These
reports indicate that the TBE virus endemic in Hokkaido is closely
related to RSSE viruses. Further studies are necessary for understanding
the ecologic features of TBE virus in other islands of Japan.Dr. Kurane is director of the Department of Virology I, National Institute of Infectious Diseases, Tokyo, Japan. His research interests include human T-cell responses to dengue viruses and pathogenesis of dengue hemorrhagic fever. References (1.) Monath TP, Heinz FX. Flavivirus. In: Fields BN, editor. Fields virology. Philadelphia: Lippincott-Raven Publishers; 1996. p. 961-1034. (2.) Matsunaga Y, Yabe S, Taniguchi K, Nakayama M, Kurane I. Current status of Japanese encephalitis in Japan. J Jap Assoc Infect Dis 1999;73:97-103. (Japanese) (3.) Monath TP. Dengue: the risk to developed and developing countries. Proc Natl Acad Sci U S A 1994;91:2395-400. (4.) Henchal EA, Putnak R. The dengue viruses. Clin Microbiol Rev 1990;3:376-96. (5.) World Health Organization. Dengue haemorrhagic fever: diagnosis, treatment and control. Geneva: World Health Organization; 1997. p. 12-23. (6.) Hotta S. Dengue epidemic in Japan, 1942-1945. J Trop Med Hyg 1953;56:83. (7.) Fujita N, Yoshida K. Follow-up studies on dengue endemic in Nagasaki, Japan: detection of specific antibodies in the sera taken more than 30 years after a single attack of dengue. Kobe J Med Sci 1979;25:217-24. (8.) Yabe S, Nakayama M, Yamada K, Kitano T, Arai Y, Horimoto T, et al. Laboratory virological diagnosis of imported dengue cases. J Jap Assoc Infect Dis 1996;70:1160-9. (Japanese) (9.) Yamada K, Takasaki T, Nawa M, Nakayama M, Arai Y, Yabe S, et al. The features of imported dengue fever cases from 1996 to 1999. Jap J Infect Dis 1999;52:257-9. (10.) Ando K, Kuratsuka S, Arima S, Hironaka N, Honda Y, Ishii K. Studies on the viruses isolated during epidemic of Japanese B encephalitis in 1848 in Tokyo area. Kitasato Exp Med 1952; 24:49-61. (11.) Takashima I, Morita K, Chiba M, Hayasaka D, Sato T, Takezawa C, et al. A case of tick-borne encephalitis in Japan and isolation of the virus. J Clin Microbiol 1997;35:1943-7. (12.) Takeda T, Ito T, Chiba M, Takahashi K, Niioka T, Takashima I. Isolation of tick-borne encephalitis virus from Ixodes ovatus (Acari: Ixodidae) in Japan. J Med Entomol 1998;35: 227-31. (13.) Takeda T, Ito T, Osada M, Takahashi K, Takashima I. Isolation of tick-borne encephalitis virus from wild rodents and a seroepidemiologic survey in Hokkaido, Japan. Am J Trop Med Hyg 1999;60:287-91. Ichiro Kurane, Tomohiko Takasaki, and Ken-ichiro Yamada National Institute of Infectious Diseases, Tokyo, Japan Address for correspondence: Ichiro Kurane, Department of Virology 1, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640 Japan. Tel & Fax: +813-5285-1169. |
|
||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion