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  1. Fulltext The involvement of microtubules and actin during the infection of Japanese encephalitis virus in neuroblastoma cell line, IMR32
    Henry Sum MS
    Biomed Res Int, 2015;2015:695283.
    PMID: 25705678 DOI: 10.1155/2015/695283
    The role of the cytoskeleton, actin, and microtubules were examined during the process of Japanese encephalitis (JEV) infection in a human neuroblastoma cell line, IMR32. Cytochalasin D and nocodazole were used to depolymerise the cellular actin and microtubules, respectively, in order to study the effect of JEV infection in the cell. This study shows that depolymerisation of the actin cytoskeleton at early process of infection inhibits JEV infection in the cell; however infection was not inhibited when depolymerisation occurred at the later stage of infection. The microtubules, on the other hand, are required at 2 points in infection. The antigen production in the cells was inhibited when the infected cells were treated at time up to 2 hours after inoculation and there was no significant effect at later times, while the viable virus released continued to be affected until 10 hours after inoculation. In conclusion, infection of JEV in IMR32 cells required actin to facilitate early process in infection and the microtubular network is utilised as the transport system to the virus replication site and the release of mature virus.
    Matched MeSH terms: Encephalitis Virus, Japanese/genetics; Encephalitis Virus, Japanese/pathogenicity*
  2. The distribution of important sero-complexes of flaviviruses in Malaysia
    Kumar K, Arshad SS, Toung OP, Abba Y, Selvarajah GT, Abu J, et al.
    Trop Anim Health Prod, 2019 Mar;51(3):495-506.
    PMID: 30604332 DOI: 10.1007/s11250-018-01786-x
    Flaviviruses (FVs) are arthropod-borne viruses of medical and veterinary importance. Numerous species of FVs have been isolated from various host; mainly humans, animals, ticks, and mosquitoes. Certain FVs are extremely host-specific; at the same time, some FVs can infect an extensive range of species. Based on published literatures, 11 species of FVs have been detected from diverse host species in Malaysia. In humans, dengue virus and Japanese encephalitis virus have been reported since 1901 and 1942. In animals, the Batu Cave virus, Sitiawan virus, Carey Island, Tembusu virus, Duck Tembusu virus, and Japanese encephalitis viruses were isolated from various species. In mosquitoes, Japanese encephalitis virus and Kunjin virus were isolated from Culex spp., while Zika virus and Jugra virus were isolated from Aedes spp. In ticks, the Langat virus was isolated from Ixodes spp. One of the major challenges in the diagnosis of FVs is the presence of sero-complexes as a result of cross-reactivity with one or more FV species. Subsequently, the distribution of specific FVs among humans and animals in a specific population is problematic to assess and often require comprehensive and thorough analyses. Molecular assays such as quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and digital droplet RT-PCR (ddRT-PCR) have been used for the differentiation of flavivirus infections to increase the accuracy of epidemiological data for disease surveillance, monitoring, and control. In situations where sero-complexes are common in FVs, even sensitive assays such as qRT-pCR can produce false positive results. In this write up, an overview of the various FV sero-complexes reported in Malaysia to date and the challenges faced in diagnosis of FV infections are presented.
    Matched MeSH terms: Encephalitis Virus, Japanese
  3. Fulltext The current burden of Japanese encephalitis and the estimated impacts of vaccination: Combining estimates of the spatial distribution and transmission intensity of a zoonotic pathogen
    Moore SM
    PLoS Negl Trop Dis, 2021 10;15(10):e0009385.
    PMID: 34644296 DOI: 10.1371/journal.pntd.0009385
    Japanese encephalitis virus (JEV) is a major cause of neurological disability in Asia and causes thousands of severe encephalitis cases and deaths each year. Although Japanese encephalitis (JE) is a WHO reportable disease, cases and deaths are significantly underreported and the true burden of the disease is not well understood in most endemic countries. Here, we first conducted a spatial analysis of the risk factors associated with JE to identify the areas suitable for sustained JEV transmission and the size of the population living in at-risk areas. We then estimated the force of infection (FOI) for JE-endemic countries from age-specific incidence data. Estimates of the susceptible population size and the current FOI were then used to estimate the JE burden from 2010 to 2019, as well as the impact of vaccination. Overall, 1,543.1 million (range: 1,292.6-2,019.9 million) people were estimated to live in areas suitable for endemic JEV transmission, which represents only 37.7% (range: 31.6-53.5%) of the over four billion people living in countries with endemic JEV transmission. Based on the baseline number of people at risk of infection, there were an estimated 56,847 (95% CI: 18,003-184,525) JE cases and 20,642 (95% CI: 2,252-77,204) deaths in 2019. Estimated incidence declined from 81,258 (95% CI: 25,437-273,640) cases and 29,520 (95% CI: 3,334-112,498) deaths in 2010, largely due to increases in vaccination coverage which have prevented an estimated 314,793 (95% CI: 94,566-1,049,645) cases and 114,946 (95% CI: 11,421-431,224) deaths over the past decade. India had the largest estimated JE burden in 2019, followed by Bangladesh and China. From 2010-2019, we estimate that vaccination had the largest absolute impact in China, with 204,734 (95% CI: 74,419-664,871) cases and 74,893 (95% CI: 8,989-286,239) deaths prevented, while Taiwan (91.2%) and Malaysia (80.1%) had the largest percent reductions in JE burden due to vaccination. Our estimates of the size of at-risk populations and current JE incidence highlight countries where increasing vaccination coverage could have the largest impact on reducing their JE burden.
    Matched MeSH terms: Encephalitis Virus, Japanese/genetics; Encephalitis Virus, Japanese/immunology*
  4. The appearance of a second genotype of Japanese encephalitis virus in the Australasian region
    Pyke AT, Williams DT, Nisbet DJ, van den Hurk AF, Taylor CT, Johansen CA, et al.
    Am J Trop Med Hyg, 2001 Dec;65(6):747-53.
    PMID: 11791969
    In mid-January 2000, the reappearance of Japanese encephalitis (JE) virus activity in the Australasian region was first demonstrated by the isolation of JE virus from 3 sentinel pigs on Badu Island in the Torres Strait. Further evidence of JE virus activity was revealed through the isolation of JE virus from Culex gelidus mosquitoes collected on Badu Island and the detection of specific JE virus neutralizing antibodies in 3 pigs from Saint Pauls community on Moa Island. Nucleotide sequencing and phylogenetic analyses of the premembrane and envelope genes were performed which showed that both the pig and mosquito JE virus isolates (TS00 and TS4152, respectively) clustered in genotype I, along with northern Thai, Cambodian, and Korean isolates. All previous Australasian JE virus isolates belong to genotype II, along with Malaysian and Indonesian isolates. Therefore, for the first time, the appearance and transmission of a second genotype of JE virus in the Australasian region has been demonstrated.
    Matched MeSH terms: Encephalitis Virus, Japanese/genetics*; Encephalitis Virus, Japanese/isolation & purification
  5. T cell-mediated cytotoxicity against dengue-infected target cells
    Pang T, Devi S, Blanden RV, Lam SK
    Microbiol. Immunol., 1988;32(5):511-8.
    PMID: 3262810 DOI: 10.1111/j.1348-0421.1988.tb01411.x
    A cytotoxic T lymphocyte (CTL) response to dengue virus-infected target cells is described. Effector cells were generated in an in vitro secondary culture and appeared to be T cells possessing both the Lyt 1.1 and Lyt 2.1 surface antigens. A stronger CTL response was noted with the H-2k haplotype compared to H-2d, and H-2 compatibility was required between CTL and target cells. CTL generated showed some cross-reactivity with target cells infected with Japanese encephalitis virus (JEV), another flavivirus, but not with target cells infected with an alphavirus, Sindbis. The significance and importance of these findings are discussed.
    Matched MeSH terms: Encephalitis Virus, Japanese/immunology
  6. Susceptibility of Culex sitiens to Japanese encephalitis virus in peninsular Malaysia
    Vythilingam I, Tan SB, Krishnasamy M
    Trop Med Int Health, 2002 Jun;7(6):539-40.
    PMID: 12031077
    The susceptibility of Culex sitiens to Japanese Encephalitis (JE) virus was examined in the laboratory. Cx. sitiens became infected with JE virus on day 8 and subsequently it is able to transmit the virus when it takes a blood meal. Both parts of the experiment were carried out using artificial membrane feeding technique.
    Matched MeSH terms: Encephalitis Virus, Japanese/isolation & purification*
  7. Fulltext Studies on adult mosquito vectors of Japanese encephalitis in a pig farm in Selangor, Malaysia
    Vythilingam I, Mahadevan S, Zaridah MZ, Ong KK, Abdullah G, Ong YF
    Southeast Asian J. Trop. Med. Public Health, 1994 Jun;25(2):383-6.
    PMID: 7855662
    Mosquito collections were carried out for a period of one year from January to December 1992 in a pig farm in Sungai Pelek, Selangor, Malaysia. A total of 41,022 mosquitos belonging to 52 species and 20 genera were collected. Culex tritaeniorhynchus and Cx. gelidus, the important vectors, comprised 63% of all mosquitos collected. Both these species were collected in large numbers during the wet months of May and December. The other predominant species in that area were Cx. fuscocephala, Cx. quinquefasciatus, Cx. sitiens, Aedes butleri, and Armigeres subalbatus.
    Matched MeSH terms: Encephalitis Virus, Japanese*
  8. Studies on Japanese encephalitis vector mosquitoes in Selangor, Malaysia
    Vythilingam I, Singh KI, Mahadevan S, Zaridah MS, Ong KK, Abidin MH
    J Am Mosq Control Assoc, 1993 Dec;9(4):467-9.
    PMID: 8126485
    Mosquito collections were carried out from May to June 1992 and from September to December 1992 in an area where a case of Japanese encephalitis was confirmed. A total of 40,072 mosquitoes belonging to 35 species and 8 genera were collected. The dominant species in that locality were Culex vishnui, Culex tritaeniorhynchus, Culex pseudovishnui, Culex gelidus, Aedes butleri, and Mansonia uniformis.
    Matched MeSH terms: Encephalitis Virus, Japanese/physiology
  9. Fulltext Southernmost Asia is the source of Japanese encephalitis virus (genotype 1) diversity from which the viruses disperse and evolve throughout Asia
    Gao X, Liu H, Wang H, Fu S, Guo Z, Liang G
    PLoS Negl Trop Dis, 2013;7(9):e2459.
    PMID: 24069502 DOI: 10.1371/journal.pntd.0002459
    Although a previous study predicted that Japanese encephalitis virus (JEV) originated in the Malaysia/Indonesia region, the virus is known to circulate mainly on the Asian continent. However, there are no reported systematic studies that adequately define how JEV then dispersed throughout Asia.
    Matched MeSH terms: Encephalitis Virus, Japanese/classification*; Encephalitis Virus, Japanese/genetics*; Encephalitis Virus, Japanese/isolation & purification
  10. Short report: a major genotype of Japanese encephalitis virus currently circulating in Japan
    Ma SP, Yoshida Y, Makino Y, Tadano M, Ono T, Ogawa M
    Am J Trop Med Hyg, 2003 Aug;69(2):151-4.
    PMID: 13677370
    A 240-nucleotide sequence of the capsid/premembrane gene region of 23 Japanese encephalitis virus (JEV) strains isolated in Tokyo and Oita, Japan was determined and phylogenetic analyses were performed. All the strains clustered into two distinct genotypes (III and I). All strains isolated before 1991 belonged to genotype III, while those isolated after 1994 belonged to genotype I. In addition, the strains of the genotype I isolated in Japan showed a close genetic relationship with those from Korea and Malaysia.
    Matched MeSH terms: Encephalitis Virus, Japanese/genetics*
  11. Fulltext Seroprevalence report on tick-borne encephalitis virus and Crimean-Congo hemorrhagic fever virus among Malaysian's farm workers
    Mohd Shukri M, Ling Kho K, Ghane Kisomi M, Lani R, Marlina S, Muhd Radzi SF, et al.
    BMC Public Health, 2015;15:704.
    PMID: 26205588 DOI: 10.1186/s12889-015-1901-4
    Tick-borne encephalitis virus (TBEV) and Crimean-Congo haemorrhagic fever virus (CCHFV) are important tick-borne viruses. Despite their wide geographical distribution and ease of acquisition, the prevalence of both viruses in Malaysia is still unknown. This study was conducted to determine the seroprevalence for TBEV and CCHFV among Malaysian farm workers as a high-risk group within the population.
    Matched MeSH terms: Encephalitis Virus, Japanese/immunology
  12. Serological evidence of the incidence of Japanese B encephalitis virus infection in Malaysia
    HALE JH, LEE LH
    Ann Trop Med Parasitol, 1955 Oct;49(3):293-8.
    PMID: 13259442
    Matched MeSH terms: Encephalitis Virus, Japanese*
  13. Serological evidence of DENV, JEV, and ZIKV among the indigenous people (Orang Asli) of Peninsular Malaysia
    Khor CS, Mohd-Rahim NF, Hassan H, Tan KK, Zainal N, Teoh BT, et al.
    J Med Virol, 2020 08;92(8):956-962.
    PMID: 31814135 DOI: 10.1002/jmv.25649
    Dengue virus (DENV), Japanese encephalitis virus (JEV), and Zika virus (ZIKV) are mosquito-borne flavivirus of medical importance in tropical countries such as Malaysia. However, much remains unknown regarding their prevalence among the underserved indigenous people (Orang Asli) living in communities in the forest fringe areas of Peninsular Malaysia. Information on the prevalence of diseases is necessary to elevate the effectiveness of disease control and preventive measures. This study aimed to determine the seroprevalence of the three major flaviviruses among the Orang Asli and investigate the association between demographic factors and seropositivities. Sampling activities were conducted in the Orang Asli villages to obtain serum samples and demographic data from consenting volunteers. The presence of DENV, JEV, and ZIKV immunoglobulin G (IgG) antibodies in the sera were examined using commercial enzyme-linked immunosorbent assay kits. A focus reduction neutralization assay was performed to measure virus-specific neutralizing antibodies. A total of 872 serum samples were obtained from the Orang Asli volunteers. Serological assay results revealed that DENV IgG, JEV IgG, and ZIKV IgG seropositivities among the Orang Asli were at 4.9%, 48.4%, and 13.2%, respectively. Neutralizing antibodies (FRNT50 ≥ 1:40) against JEV and ZIKV were found in 86.7% and 100.0%, respectively, out of the samples tested. Positive serology to all three viruses corresponded significantly to the age of the volunteers with increasing seropositivity in older volunteers. Findings from the study suggest that Orang Asli are at significant risk of contracting JEV and ZIKV infections despite the lack of active transmission of the viruses in the country.
    Matched MeSH terms: Encephalitis Virus, Japanese/immunology
  14. Fulltext Serological Evidence of Japanese Encephalitis Virus Circulation in Asian Children From Dengue-Endemic Countries
    Nealon J, Taurel AF, Yoksan S, Moureau A, Bonaparte M, Quang LC, et al.
    J Infect Dis, 2019 Jan 09;219(3):375-381.
    PMID: 30165664 DOI: 10.1093/infdis/jiy513
    Background: Japanese encephalitis virus (JEV) is a zoonotic, mosquito-borne flavivirus, distributed across Asia. Infections are mostly mild or asymptomatic, but symptoms include neurological disorders, sequelae, and fatalities. Data to inform control strategies are limited due to incomplete case reporting.

    Methods: We used JEV serological data from a multicountry Asian dengue vaccine study in children aged 2-14 years to describe JEV endemicity, measuring antibodies by plaque reduction neutralization test (PRNT50).

    Results: A total 1479 unvaccinated subjects were included. A minimal estimate of pediatric JEV seroprevalence in dengue-naive individuals was 8.1% in Indonesia, 5.8% in Malaysia, 10.8% in the Philippines, and 30.7% in Vietnam, translating to annual infection risks varying from 0.8% (in Malaysia) to 5.2% (in Vietnam). JEV seroprevalence and annual infection estimates were much higher in children with history of dengue infection, indicating cross-neutralization within the JEV PRNT50 assay.

    Conclusions: These data confirm JEV transmission across predominantly urban areas and support a greater emphasis on JEV case finding, diagnosis, and prevention.

    Matched MeSH terms: Encephalitis Virus, Japanese
  15. Fulltext Screening of pig sera for antibodies to Japanese encephalitis virus using a dot enzyme immunoassay and IgM capture ELISA: comparison with the hemagglutination inhibition and plaque reduction neutralization tests
    Cardosa MJ, Hah FL, Choo BH, Padmanathan S
    Southeast Asian J. Trop. Med. Public Health, 1993 Sep;24(3):472-6.
    PMID: 8160055
    A dot enzyme immunoassay for determination of antibodies to Japanese encephalitis virus was designed for use as a field technique for the surveillance of Japanese encephalitis virus activity among domestic pigs. The test was compared with the neutralization test and the hemagglutination inhibition test and found to be more sensitive than the hemagglutination inhibition test and comparable to the neutralization test in sensitivity but more simple to perform than either the neutralization or the hemagglutination inhibition tests. An IgM capture ELISA for the determination of JEV specific porcine IgM was also utilized to determine current infection rates in pigs. The tests which do not involve the determination of specific IgM are better used for testing sentinel animals for providing clues as to the rate of transmission of JEV among pigs. IgM tests determining acute infection are less likely to be useful unless animals are tested very frequently or if a great number of animals are tested at any one time.
    Matched MeSH terms: Encephalitis Virus, Japanese/immunology*
  16. Fulltext Prevalence and risk factors of Japanese encephalitis virus (JEV) in livestock and companion animal in high-risk areas in Malaysia
    Kumar K, Arshad SS, Selvarajah GT, Abu J, Toung OP, Abba Y, et al.
    Trop Anim Health Prod, 2018 Apr;50(4):741-752.
    PMID: 29243139 DOI: 10.1007/s11250-017-1490-6
    Japanese encephalitis (JE) is vector-borne zoonotic disease which causes encephalitis in humans and horses. Clinical signs for Japanese encephalitis virus (JEV) infection are not clearly evident in the majority of affected animals. In Malaysia, information on the prevalence of JEV infection has not been established. Thus, a cross-sectional study was conducted during two periods, December 2015 to January 2016 and March to August in 2016, to determine the prevalence and risk factors in JEV infections among animals and birds in Peninsular Malaysia. Serum samples were harvested from the 416 samples which were collected from the dogs, cats, water birds, village chicken, jungle fowls, long-tailed macaques, domestic pigs, and cattle in the states of Selangor, Perak, Perlis, Kelantan, and Pahang. The serum samples were screened for JEV antibodies by commercial IgG ELISA kits. A questionnaire was also distributed to obtain information on the animals, birds, and the environmental factors of sampling areas. The results showed that dogs had the highest seropositive rate of 80% (95% CI: ± 11.69) followed by pigs at 44.4% (95% CI: ± 1.715), cattle at 32.2% (95% CI: ± 1.058), birds at 28.9% (95% CI: ± 5.757), cats at 15.6% (95% CI: ± 7.38), and monkeys at 14.3% (95% CI: ± 1.882). The study also showed that JEV seropositivity was high in young animals and in areas where mosquito vectors and migrating birds were prevalent.
    Matched MeSH terms: Encephalitis Virus, Japanese/isolation & purification*
  17. Fulltext Pathological findings in a mouse model of Japanese encephalitis infected via the footpad
    Fu, Tzeh Long, Ong, Kien Chai, Wong, Kum Thong
    Neurology Asia, 2015;20(4):349-354.
    MyJurnal
    We have developed and characterised a mouse model of Japanese encephalitis virus (JEV) infection via
    footpad inoculation in order to better mimic viral transmission by mosquito bites. Two-week-old and
    5-week-old mice consistently developed signs of infection such as ruffled fur, weight loss, hunchback
    posture, tremors, mask-like facies and occasionally, hindlimb paralysis at 4 days post infection (dpi)
    and 11-13 dpi, respectively. Most of the animals died within 24 to 48 hours following the onset of signs
    of infection, with mortalities of 100% and 33.3% in 2-week-old and 5-week-old mice, respectively.
    Mild meningitis and variable parenchymal inflammation with formation of microglial nodules, focal
    necrosis and neuronophagia, and perivascular cuffing by inflammatory cells were observed in the
    caudate nucleus, putamen, thalamus, cerebral cortex, brainstem, and spinal cord. Viral antigens/RNA
    were demonstrated by immunohistochemisty and in situ hybridization, respectively, in most of these
    areas as well as in the hippocampus and cerebellum, albeit more focally. The pathological findings in
    this mouse model were generally similar to human Japanese encephalitis (JE) and other established JE
    models but perhaps, compared to other JEV mouse models, it demonstrates lethal encephalitic infection
    more consistently. We believe that our mouse model should be useful to study the pathogenesis of JE,
    and for testing anti-viral drugs and vaccines
    Matched MeSH terms: Encephalitis Virus, Japanese
  18. Fulltext Paddy, piggy and Japanese encephalitis in Kerian – a case series
    Rosilawati A. R., Mohd Zamri M. A.
    Malaysian Journal of Medicine and Health Sciences, 2019;15(106):40-40.
    MyJurnal
    Introduction: Japanese encephalitis (JE) is a vector-borne zoonotic disease caused by the Japanese encephalitis virus (JEV). Paddy fields are high risk area for JEV transmission due the presence of Culex tritaeniorhynchus as vector and wild boar as an amplifier host. Methods: We presented case reports for three patients infected with JEV residing in paddy field area from 2015 to 2018 in Kerian, Perak; illustrating the symptoms and epidemiology trend of the dis-ease. Results: All three cases live next to paddy field and were exposed during peak biting hours. They presented with fever and altered consciousness. IV Acylovir was started as one of the treatments and all had lumbar puncture for CSF testing. Two cases (adult) were confirmed JE after they had passed away. Two cases occurred during fasting month where food wastes were abundance. The source of infection was probably from wild boars that came out at night to hunt for food. Presence of C. tritaeniorhynchus was demonstrated as the main vector in these areas. Conclusion: JE has no cure and human vaccination is the main prevention method. At the moment, vector control, environmental management, chemical control and personal protection are the main mitigation strategies for this area. Further study on JEV and wild board in Kerian will be most beneficial.
    Matched MeSH terms: Encephalitis Virus, Japanese
  19. Fulltext Overview of Japanese encephalitis disease and its prevention. Focus on IC51 vaccine (IXIARO®)
    Amicizia D, Zangrillo F, Lai PL, Iovine M, Panatto D
    J Prev Med Hyg, 2018 Mar;59(1):E99-E107.
    PMID: 29938245 DOI: 10.15167/2421-4248/jpmh2018.59.1.962
    Japanese encephalitis (JE) is a vector-borne disease caused by the Japanese encephalitis virus (JEV). JEV is transmitted by mosquitoes to a wide range of vertebrate hosts, including birds and mammals. Domestic animals, especially pigs, are generally implicated as reservoirs of the virus, while humans are not part of the natural transmission cycle and cannot pass the virus to other hosts. Although JEV infection is very common in endemic areas (many countries in Asia), less than 1% of people affected develop clinical disease, and severe disease affects about 1 case per 250 JEV infections. Although rare, severe disease can be devastating; among the 30,000-50,000 global cases per year, approximately 20-30% of patients die and 30-50% of survivors develop significant neurological sequelae. JE is a significant public health problem for residents in endemic areas and may constitute a substantial risk for travelers to these areas. The epidemiology of JE and its risk to travelers have changed, and continue to evolve. The rapid economic growth of Asian countries has led to a surge in both inbound and outbound travel, making Asia the second most-visited region in the world after Europe, with 279 million international travelers in 2015. The top destination is China, followed by Thailand, Hong Kong, Malaysia and Japan, and the number of travelers is forecast to reach 535 million by 2030 (+ 4.9% per year). Because of the lack of treatment and the infeasibility of eliminating the vector, vaccination is recognized as the most efficacious means of preventing JE. The IC51 vaccine (IXIARO®) is a purified, inactivated, whole virus vaccine against JE. It is safe, well tolerated, efficacious and can be administered to children, adults and the elderly. The vaccination schedule involves administering 2 doses four weeks apart. For adults, a rapid schedule (0-7 days) is available, which could greatly enhance the feasibility of its use. Healthcare workers should inform both short- and long-term travelers of the risk of JE in each period of the year and recommend vaccination. Indeed, it has been shown that short-term travelers are also at risk, not only in rural environments, but also in cities and coastal towns, especially in tourist localities where excursions to country areas are organized.
    Matched MeSH terms: Encephalitis Virus, Japanese/drug effects*
  20. Origin and evolution of Japanese encephalitis virus in southeast Asia
    Solomon T, Ni H, Beasley DW, Ekkelenkamp M, Cardosa MJ, Barrett AD
    J Virol, 2003 Mar;77(5):3091-8.
    PMID: 12584335
    Since it emerged in Japan in the 1870s, Japanese encephalitis has spread across Asia and has become the most important cause of epidemic encephalitis worldwide. Four genotypes of Japanese encephalitis virus (JEV) are presently recognized (representatives of genotypes I to III have been fully sequenced), but its origin is not known. We have determined the complete nucleotide and amino acid sequence of a genotype IV Indonesian isolate (JKT6468) which represents the oldest lineage, compared it with other fully sequenced genomes, and examined the geographical distribution of all known isolates. JKT6468 was the least similar, with nucleotide divergence ranging from 17.4 to 19.6% and amino acid divergence ranging from 4.7 to 6.5%. It included an unusual series of amino acids at the carboxy terminus of the core protein unlike that seen in other JEV strains. Three signature amino acids in the envelope protein (including E327 Leu-->Thr/Ser on the exposed lateral surface of the putative receptor binding domain) distinguished genotype IV strains from more recent genotypes. Analysis of all 290 JEV isolates for which sequence data are available showed that the Indonesia-Malaysia region has all genotypes of JEV circulating, whereas only more recent genotypes circulate in other areas (P < 0.0001). These results suggest that JEV originated from its ancestral virus in the Indonesia-Malaysia region and evolved there into the different genotypes which then spread across Asia. Our data, together with recent evidence on the origins of other emerging viruses, including dengue virus and Nipah virus, imply that tropical southeast Asia may be an important zone for emerging pathogens.
    Matched MeSH terms: Encephalitis Virus, Japanese/classification; Encephalitis Virus, Japanese/genetics*; Encephalitis Virus, Japanese/pathogenicity
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