Recent advances in Japanese encephalitis

Generation of rescued Japanese encephalitis virus genotype 1 from infectious full-size clone using reverse genetics

Japanese encephalitis virus (JEV) is a pathogen responsible for high mortality and morbidity rates among children with encephalitis. Since JEV genotype 1 (GI) is the most prevalent strain in South Korea these days, corresponding research and vaccine development is urgently required. Molecular genetic studies on JEV vaccines can be boosted by obtaining genetically stable full-length infectious JEV complementary DNA (cDNA) clones. Furthermore, the significance of the reverse genetics system in facilitating molecular biological analyses of JEV properties has been demonstrated. This study constructed a recombinant JEV-GI strain using a reverse genetics system based on a Korean wild-type GI isolate (K05GS). RNA extracted from JEV-GI was used to synthesize cDNA, a recombinant full-length JEV clone, pTRE-JEVGI, was generated from the DNA fragment, and the virus was rescued. We performed in vitro and in vivo experiments to analyze the rescued JEV-GI virus. The rescued JEV-GI exhibited similar characteristics to wild-type JEV. These results suggest that our reverse genetics system can generate full-length infectious clones that can be used to analyze molecular biological factors that influence viral properties and immunogenicity. Additionally, it may be useful as a heterologous gene expression vector and help develop new strains for JEV vaccines.

Japanese Encephalitis Virus-Infected Cells

RNA virus infections have been a leading cause of pandemics. Aided by global warming and increased connectivity, their threat is likely to increase over time. The flaviviruses are one such RNA virus family, and its prototypes such as the Japanese encephalitis virus (JEV), Dengue virus, Zika virus, West Nile virus, etc., pose a significant health burden on several endemic countries. All viruses start off their life cycle with an infected cell, wherein a series of events are set in motion as the virus and host battle for autonomy. With their remarkable capacity to hijack cellular systems and, subvert/escape defence pathways, viruses are able to establish infection and disseminate in the body, causing disease. Using this strategy, JEV replicates and spreads through several cell types such as epithelial cells, fibroblasts, monocytes and macrophages, and ultimately breaches the blood-brain barrier to infect neurons and microglia. The neurotropic nature of JEV, its high burden on the paediatric population, and its lack of any specific antivirals/treatment strategies emphasise the need for biomedical research-driven solutions. Here, we highlight the latest research developments on Japanese encephalitis virus-infected cells and discuss how these can aid in the development of future therapies.

Zinc finger protein ZFP36L1 inhibits flavivirus infection by both 5'-3' XRN1 and 3'-5' RNA-exosome RNA decay pathways

Zinc-finger protein 36, CCCH type-like 1 (ZFP36L1), containing tandem CCCH-type zinc-finger motifs with an RNA-binding property, plays an important role in cellular RNA metabolism mainly via RNA decay pathways. Recently, we demonstrated that human ZFP36L1 has potent antiviral activity against influenza A virus infection. However, its role in the host defense response against flaviviruses has not been addressed. Here, we demonstrate that ZFP36L1 functions as a host innate defender against flaviviruses, including Japanese encephalitis virus (JEV) and dengue virus (DENV). Overexpression of ZFP36L1 reduced JEV and DENV infection, and ZFP36L1 knockdown enhanced viral replication. ZFP36L1 destabilized the JEV genome by targeting and degrading viral RNA mediated by both 5'-3' XRN1 and 3'-5' RNA-exosome RNA decay pathways. Mutation in both zinc-finger motifs of ZFP36L1 disrupted RNA-binding and antiviral activity. Furthermore, the viral RNA sequences specifically recognized by ZFP36L1 were mapped to the 3'-untranslated region of the JEV genome with the AU-rich element (AUUUA) motif. We extend the function of ZFP36L1 to host antiviral defense by directly binding and destabilizing the viral genome via recruiting cellular mRNA decay machineries. Importance Cellular RNA-binding proteins are among the first lines of defense against various viruses, particularly RNA viruses. ZFP36L1 belongs to the CCCH-type zinc-finger protein family and has RNA-binding activity; it has been reported to directly bind to the AU-rich elements (AREs) of a subset of cellular mRNAs and then lead to mRNA decay by recruiting mRNA degrading enzymes. However, the antiviral potential of ZFP36L1 against flaviviruses has not yet been fully demonstrated. Here, we reveal the antiviral potential of human ZFP36L1 against Japanese encephalitis virus (JEV) and dengue virus (DENV). ZFP36L1 specifically targeted the ARE motif within viral RNA and triggered the degradation of viral RNA transcripts via cellular degrading enzymes, 5'-3' XRN1 and 3'-5' RNA exosome. These findings provide mechanistic insights into how human ZFP36L1 serves as a host antiviral factor to restrict flavivirus replication.

The spatiotemporal distribution of Japanese Encephalitis cases in Yunnan Province, China, from 2007 to 2017

BACKGROUND

Japanese encephalitis (JE) is a vector-borne disease with a high prevalence in Yunnan Province, China. However, there has been a lack of a JE epidemic systematic analysis, which is urgently needed to guide control and prevention efforts.

METHODS

This study explored and described the spatiotemporal distribution of JE cases observed among two different age groups in Yunnan Province from 2007 to 2017. The epidemiological features and spatial features were analyzed according to basic statistics, ArcGIS software (version 9.3; ESRI, Redlands, CA) and SPSS software (version 20; IBM Corp., Armonk, New York).

RESULTS

Overall, the whole province had a high incidence of JE. The annual incidence rates in 2007 and 2017 were 1.668/100,000 and 0.158/100,000, respectively. The annual mortality was under 0.095/100,000 for these years. Although the whole province was in danger of JE, the Diqing autonomous prefecture and the Lijiang autonomous prefecture had no JE cases recorded for over 10 years. The JE cases were reported by hospitals located in 60 counties of 14 municipalities. The top ten areas with the most JE cases were Kunming City, Zhaotong City, Jinghong City, Wenshan City, Mangshi City, Pu'er City, Baoshan City, Dali City, Chuxiong City, and Gejiu City. The incidence declined smoothly, with a peak occurring from June to September, which accounted for 96.1% of the total cases. Children whose age was equal or less than 10 years old (LEQ10) still maintained a high frequency of JEV infection, and a large number of cases were reported in August, despite the Expanded Program on Immunization (EPI), which was established in April 2008. There was no difference in the quantity of cases between the two groups (t = -0.411, P>0.05); additionally, the number of JE cases among patients LEQ10 were significantly greater than those among patients older than 10 years (GTR10). Further analysis using local indicators of spatial association (LISA) revealed that the distribution of JE exhibited a high-high cluster characteristic (Z = 2.06, P<0.05), which showed that Jinghong City, Guangnan County, Yanshan County, Funing County, and Mengzi City were hot spots for the JE epidemic.

CONCLUSIONS

Although the EPI was established in 2008 and the incidence of JE declined smoothly in Yunnan Province, there was no difference in the number of cases between the two age groups, which reveals that the EPI has been conducted with a low level success. In the context of limited vaccine supply capacity, we should strengthen the implementation of the children's immunization program before strengthening other immunization programs.

Zika Virus and Other Emerging Arboviral Central Nervous System Infections

PURPOSE OF REVIEW

In recent years, we have observed the emergence and reemergence of a number of arthropod-borne viruses (arboviruses). Zika virus is the most recent addition to this group, first causing sporadic cases of uncomplicated febrile illness followed by sizeable outbreaks in the Pacific. However, the epidemiology and clinical features of Zika virus infection have changed rapidly and dramatically; it is now recognized as causing Guillain-Barré syndrome (GBS) in children and adults and congenital abnormalities in infected fetuses. This article reviews the epidemiology, clinical features, and diagnosis of Zika virus-associated neurologic illness and briefly reviews features of West Nile virus and Japanese encephalitis virus.

RECENT FINDINGS

Zika virus has emerged as a significant human pathogen in recent years. In 2015, it began to cause large outbreaks of febrile rash illness in South America and the Caribbean. During these large Zika virus outbreaks, a significant increase in the incidence of GBS was also observed in multiple countries/territories. Zika virus-associated GBS has several unique features, including a relatively short interval between febrile illness and GBS onset, an unusually high incidence among older people, and prominent cranial nerve abnormalities. Congenital Zika syndrome includes a myriad of abnormalities, including microcephaly, lissencephaly, hydrocephalus, arthrogryposis, and parenchymal calcifications. Currently, no treatment has been identified for Zika virus, although work on vaccines is under way.

SUMMARY

Arboviruses continue to surprise us with unexpected emergence in various locations, the nature of clinical illness, and outcomes. Zika virus presents a classic example of this type of emergence. Ongoing surveillance will be needed to evaluate the long-term pattern of Zika virus and related arboviruses.

Neutralization Potency of Sera from Vietnamese Patients with Japanese Encephalitis (JE) against Genotypes I and V JE Viruses

Japanese encephalitis virus (JEV) is classified into 5 genotypes (GI, GII, GIII, GIV, and GV), and the GI and GIII strains are the most widely distributed in JE endemic areas. In recent years, GV JEV has been detected in China and Korea, suggesting that GV JEV may invade other JE endemic areas, including Vietnam, and that more attention should be paid to the JEV strains circulating in these areas. In this study, we investigated the neutralization ability of the sera collected from 22 Vietnamese patients with JE who lived in northern Vietnam against the GI and GV JEV strains. In most cases, the ratios of the titer against GV to that against GI (GV:GI) were equal to or less than 1:4. However, the titer against GV JEV was equivalent (1:1) to that against GI JEV in only a few cases, and no serum had a ratio higher than 1:1. Thus, our results did not show convincing evidence that GV JEV was emerging in northern Vietnam in 2014.

Zika virus tropism and interactions in myelinating neural cell cultures: CNS cells and myelin are preferentially affected

The recent global outbreak of Zika virus (ZIKV) infection has been linked to severe neurological disorders affecting the peripheral and central nervous systems (PNS and CNS, respectively). The pathobiology underlying these diverse clinical phenotypes are the subject of intense research; however, even the principal neural cell types vulnerable to productive Zika infection remain poorly characterised. Here we used CNS and PNS myelinating cultures from wild type and Ifnar1 knockout mice to examine neuronal and glial tropism and short-term consequences of direct infection with a Brazilian variant of ZIKV. Cell cultures were infected pre- or post-myelination for various intervals, then stained with cell-type and ZIKV-specific antibodies. In bypassing systemic immunity using ex vivo culture, and the type I interferon response in Ifnar1 deficient cells, we were able to evaluate the intrinsic infectivity of neural cells. Through systematic quantification of ZIKV infected cells in myelinating cultures, we found that ZIKV infection is enhanced in the absence of the type I interferon responses and that CNS cells are considerably more susceptible to infection than PNS cells. In particular, we demonstrate that CNS axons and myelinating oligodendrocytes are especially vulnerable to injury. These results have implications for understanding the pathobiology of neurological symptoms associated with ZIKV infection. Furthermore, we provide a quantifiable ex vivo infection model that can be used for fundamental and therapeutic studies on viral neuroinvasion and its consequences.

Seasonality of Viral Encephalitis and Associated Environmental Risk Factors in Son La and Thai Binh Provinces in Vietnam from 2004 to 2013

In Vietnam, Japanese encephalitis virus accounts for 12-71% of viral encephalitis (VE) cases followed by enteroviruses and dengue virus among identified pathogens. This study is the first attempt to evaluate the seasonality of VE and associated environmental risk factors in two provinces from 2004 to 2013 using a seasonal trend-decomposition procedure based on loess regression and negative binomial regression models. We found seasonality with a peak of VE in August and June in Son La and Thai Binh, respectively. In Son La, the model showed that for every 1°C increase in average monthly temperature, there was a 4.0% increase in monthly VE incidence. There was a gradual decline in incidence rates as the relative humidity rose to its mean value (80%) and a dramatic rise in incidence rate as the relative humidity rose past 80%. Another model found that a 100 mm rise in precipitation in the preceding and same months corresponded to an increase in VE incidence of 23% and 21%, respectively. In Thai Binh, our model showed that a 1°C increase in temperature corresponded with a 9% increase in VE incidence. Another model found that VE incidence increased as monthly precipitation rose to its mean value of 130 mm but declined gradually as precipitation levels rose beyond that. The last model showed that a monthly increase in duration of sunshine of 1 hour corresponded to a 0.6% increase in VE incidence. The findings may assist clinicians by improving the evidence for diagnosis.

Enteroviral encephalitis in children: clinical features, pathophysiology, and treatment advances

Enteroviruses (EVs) have emerged as one of the important etiological agents as a causative organism for encephalitis, especially in children and adults. After the first report of EV encephalitis cases in 1950s, there have been increasing reports of regular outbreaks of EV encephalitis worldwide. Enteroviruses are RNA viruses of the family Picornaviridae that consists of more than 100 serotypes, which are characterized by a single positive-strand genomic RNA. The clinical features are pleomorphic and can be accompanied by mucocutaneous manifestations or isolated encephalitis only. The incidence of encephalitis in EV infection is reported to be about 3% and is associated with high mortality and morbidity. A number of newer therapeutic agents have been used in EV encephalitis with variable results. This review will focus on clinical features, pathophysiology, and newer treatment modality in EV encephalitis.

Acute encephalitis in children: Progress and priorities from an Australasian perspective

Encephalitis is a complex neurological syndrome caused by inflammation of the brain that occurs with highest incidence in children. It is challenging to diagnose and manage due to the variety of aetiologies and non-specific clinical presentations. We discuss the recent progress in clinical case definitions; review recent, large, prospective epidemiological studies; and describe aetiologies. We emphasise infectious causes relevant to children in Australasia but also consider emerging immune-mediated syndromes responsive to immune therapies. We identify priorities for future research in children, given the potential for climate change and international travel to influence the emergence of infectious agents in our region.

A Japanese Encephalitis Vaccine From India Induces Durable and Cross-protective Immunity Against Temporally and Spatially Wide-ranging Global Field Strains

BACKGROUND

Japanese encephalitis (JE) is a vaccine-preventable acute disease. We report the results of a phase 2/3 trial of JENVAC, a Vero cell-derived vaccine developed using an Indian strain of JE virus (JEV).

METHODS

JENVAC was administered in 2 doses 28 days apart, and immunogenicity was compared to that from a single dose of SA-14-14-2, the only approved JE vaccine and regimen at the time in India.

RESULTS

After both the doses, seroconversion and seroprotection were >90% for JENVAC. For SA-14-14-2, seroconversion and seroprotection were 57.69% and 77.56%, respectively, on day 28 and 39.74% and 60.26%, respectively, on day 56. The geometric mean titers at day 28 and day 56 were 145.04 and 460.53, respectively, for JENVAC and 38.56 and 25.29, respectively, for SA-14-14-2. With a single dose of JENVAC, seroprotection titers lasted at least 12 months in >80% of the subjects. Following receipt of 2 doses, 61.17% of subjects retained seroprotection titers at 24 months, and immunogenicity criteria were higher than that for SA-14-14-2 at 12, 18, and 24 months each. Sera from JENVAC subjects neutralized JEV genotypes I, II, III, and IV equally well. Adverse events were not significantly different between the 2 vaccines.

CONCLUSIONS

JENVAC elicits long-lasting, broadly protective immunity.

CLINICAL TRIALS REGISTRATION

CTRI/2011/07/001855.

Novel transgenic rice-based vaccines

Oral vaccination can induce both systemic and mucosal antigen-specific immune responses. To control rampant mucosal infectious diseases, the development of new effective oral vaccines is needed. Plant-based vaccines are new candidates for oral vaccines, and have some advantages over the traditional vaccines in cost, safety, and scalability. Rice seeds are attractive for vaccine production because of their stability and resistance to digestion in the stomach. The efficacy of some rice-based vaccines for infectious, autoimmune, and other diseases has been already demonstrated in animal models. We reported the efficacy in mice, safety, and stability of a rice-based cholera toxin B subunit vaccine called MucoRice-CTB. To advance MucoRice-CTB for use in humans, we also examined its efficacy and safety in primates. The potential of transgenic rice production as a new mucosal vaccine delivery system is reviewed from the perspective of future development of effective oral vaccines.

Comparison of JEV neutralization assay using pseudotyped JEV with the conventional plaque-reduction neutralization test

We previously reported the development of a neutralization assay system for evaluating Japanese Encephalitis Virus (JEV) neutralizing antibody (NAb) using pseudotyped-JEV (JEV-PV). JEV-PV-based neutralization assay offers several advantages compared with the current standard plaque-reduction neutralization test (PRNT), including simplicity, safety, and speed. To evaluate the suitability of the JEV-PV assay as new replacement neutralization assay, we compared its repeatability, reproducibility, specificity, and correlated its results with those obtained using the PRNT. These analyses showed a close correlation between the results obtained with the JEV-PV assay and the PRNT, using the 50% plaque reduction method as a standard for measuring NAb titers to JEV. The validation results met all analytical acceptance criteria. These results suggest that the JEV-PV assay could serve as a safe and simple method for measuring NAb titer against JEV and could be used as an alternative approach for assaying the potency of JEV neutralization.

Cellular DDX3 regulates Japanese encephalitis virus replication by interacting with viral un-translated regions

Japanese encephalitis virus is one of the most common causes for epidemic viral encephalitis in humans and animals. Herein we demonstrated that cellular helicase DDX3 is involved in JEV replication. DDX3 knockdown inhibits JEV replication. The helicase activity of DDX3 is crucial for JEV replication. GST-pulldown and co-immunoprecipitation experiments demonstrated that DDX3 could interact with JEV non-structural proteins 3 and 5. Co-immunoprecipitation and confocal microscopy analysis confirmed that DDX3 interacts and colocalizes with these viral proteins and viral RNA during the infection. We determined that DDX3 binds to JEV 5′ and 3′ un-translated regions. We used a JEV-replicon system to demonstrate that DDX3 positively regulates viral RNA translation, which might affect viral RNA replication at the late stage of virus infection. Collectively, we identified that DDX3 is necessary for JEV infection, suggesting that DDX3 might be a novel target to design new antiviral agents against JEV or other flavivirus infections.

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DDX3 is necessary for JEV replication.

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DDX3 interacts with JEV NS3, NS5 proteins.

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DDX3 can bind to the JEV 5′ and 3′ UTR.

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DDX3 plays important roles in viral protein translation and viral RNA replication.

The DEAD-box RNA helicase DDX5 acts as a positive regulator of Japanese encephalitis virus replication by binding to viral 3' UTR

Japanese encephalitis virus (JEV), one of the causes for epidemic encephalitis, belongs to the family of Flaviviridae. In this study, we demonstrated that cellular DEAD-box RNA helicase DDX5 plays an important role in JEV replication. The knockdown of DDX5 was able to decrease JEV replication, and overexpression of DDX5 mutants lacking the helicase activity also reduced JEV replication, suggesting the helicase activity is essential for JEV replication. DDX5 knockdown did not affect virus assembly and release. GST-pulldown and co-immunoprecipitation experiments demonstrated that DDX5 could interact with JEV core protein, non-structural protein 3 (NS3) and 5 (NS5-MTase and NS5-RdRp domains). Meanwhile, we also confirmed that DDX5 interacts with these viral proteins during JEV infection. Confocal microscopy analysis showed that endogenous DDX5 is recruited to the cytoplasm and colocalizes with these viral proteins and viral RNA. RNA-pulldown experiment showed that DDX5 only binds to the JEV 3' untranslated region (UTR). Finally, we confirmed the role of DDX5 in JEV RNA replication using JEV-replicon system. In conclusion, we identified DDX5 as a positive regulator for JEV replication.

Review of climate, landscape, and viral genetics as drivers of the Japanese encephalitis virus ecology

The Japanese encephalitis virus (JEV), an arthropod-born Flavivirus, is the major cause of viral encephalitis, responsible for 10,000–15,000 deaths each year, yet is a neglected tropical disease. Since the JEV distribution area has been large and continuously extending toward new Asian and Australasian regions, it is considered an emerging and reemerging pathogen. Despite large effective immunization campaigns, Japanese encephalitis remains a disease of global health concern. JEV zoonotic transmission cycles may be either wild or domestic: the first involves wading birds as wild amplifying hosts; the second involves pigs as the main domestic amplifying hosts. Culex mosquito species, especially Cx. tritaeniorhynchus, are the main competent vectors. Although five JEV genotypes circulate, neither clear-cut genotype-phenotype relationship nor clear variations in genotype fitness to hosts or vectors have been identified. Instead, the molecular epidemiology appears highly dependent on vectors, hosts' biology, and on a set of environmental factors. At global scale, climate, land cover, and land use, otherwise strongly dependent on human activities, affect the abundance of JEV vectors, and of wild and domestic hosts. Chiefly, the increase of rice-cultivated surface, intensively used by wading birds, and of pig production in Asia has provided a high availability of resources to mosquito vectors, enhancing the JEV maintenance, amplification, and transmission. At fine scale, the characteristics (density, size, spatial arrangement) of three landscape elements (paddy fields, pig farms, human habitations) facilitate or impede movement of vectors, then determine how the JEV interacts with hosts and vectors and ultimately the infection risk to humans. If the JEV is introduced in a favorable landscape, either by live infected animals or by vectors, then the virus can emerge and become a major threat for human health. Multidisciplinary research is essential to shed light on the biological mechanisms involved in the emergence, spread, reemergence, and genotypic changes of JEV.

MCPIP1 ribonuclease exhibits broad-spectrum antiviral effects through viral RNA binding and degradation

Monocyte chemoattractant protein 1-induced protein 1 (MCPIP1), belonging to the MCPIP family with highly conserved CCCH-type zinc finger and Nedd4-BP1, YacP Nuclease domains, has been implicated in negative regulation of the cellular inflammatory responses. In this report, we demonstrate for the first time that this RNA-binding nuclease also targets viral RNA and possesses potent antiviral activities. Overexpression of the human MCPIP1, but not MCPIP2, MCPIP3 or MCPIP4, inhibited Japanese encephalitis virus (JEV) and dengue virus (DEN) replication. The functional analysis of MCPIP1 revealed that the activities of RNase, RNA binding and oligomerization, but not deubiqutinase, are required for its antiviral potential. Furthermore, infection of other positive-sense RNA viruses, such as sindbis virus and encephalomyocarditis virus, and negative-sense RNA virus, such as influenza virus, as well as DNA virus, such as adenovirus, can also be blocked by MCPIP1. Moreover, the endogenous MCPIP1 gene expression was induced by JEV and DEN infection, and knockdown of MCPIP1 expression enhanced the replication of JEV and DEN in human cells. Thus, MCPIP1 can act as a host innate defense via RNase activity for targeting and degrading viral RNA.

Japanese encephalitis: a review of the Indian perspective

Japanese encephalitis virus (JEV) causes Japanese encephalitis, which is a leading form of viral encephalitis in Asia, with around 50,000 cases and 10,000 deaths per year in children below 15 years of age. The JEV has shown a tendency to extend to other geographic regions. Case fatality averages 30% and a high percentage of the survivors are left with permanent neuropsychiatric sequelae. Currently, there is no cure for JEV, and treatment is mainly supportive. Patients are not infectious, but should avoid further mosquito bites. A number of antiviral agents have been investigated; however, none of these have convincingly been shown to improve the outcome of JEV. In this review, the current knowledge of the epidemiology and the pathogenesis of this deadly disease have been summarized.

A single nucleotide mutation in NS2A of Japanese encephalitis-live vaccine virus (SA14-14-2) ablates NS1' formation and contributes to attenuation

Japanese encephalitis (JE) remains the leading cause of viral encephalitis in the Asia-Pacific region, and the live vaccine SA14-14-2 is currently recommended by WHO and widely used in Asian countries with a good safety and efficacy profile. In this study, we demonstrated that SA14-14-2 failed to produce NS1', the larger NS1-related protein, compared with its parental strain SA14 in various cells. Sequence analysis and secondary structure prediction identified a single silent mutation G66A in the NS2A-coding region of SA14-14-2 destabilized the conserved pseudoknot structure, which was associated with a -1 ribosomal frame shift event. Using reverse genetic technology and animal study, we provided solid evidence that this single silent mutation G66A in the NS2A gene abolished the production of NS1' in vitro and reduced neurovirulence and neuroinvasiveness in mice. These findings provide critical information in understanding the molecular mechanism of JE vaccine attenuation and is critical for JE vaccine quality control.

Enzymatic analysis of recombinant Japanese encephalitis virus NS2B(H)-NS3pro protease with fluorogenic model peptide substrates

Background

Japanese encephalitis virus (JEV), a member of the Flaviviridae family, causes around 68,000 encephalitis cases annually, of which 20–30% are fatal, while 30–50% of the recovered cases develop severe neurological sequelae. Specific antivirals for JEV would be of great importance, particularly in those cases where the infection has become persistent. Being indispensable for flaviviral replication, the NS2B-NS3 protease is a promising target for design of anti-flaviviral inhibitors. Contrary to related flaviviral proteases, the JEV NS2B-NS3 protease is structurally and mechanistically much less characterized. Here we aimed at establishing a straightforward procedure for cloning, expression, purification and biochemical characterization of JEV NS2B(H)-NS3pro protease.

Methodology/Principal Findings

The full-length sequence of JEV NS2B-NS3 genotype III strain JaOArS 982 was obtained as a synthetic gene. The sequence of NS2B(H)-NS3pro was generated by splicing by overlap extension PCR (SOE-PCR) and cloned into the pTrcHisA vector. Hexahistidine-tagged NS2B(H)-NS3pro, expressed in E. coli as soluble protein, was purified to >95% purity by a single-step immobilized metal affinity chromatography. SDS-PAGE and immunoblotting of the purified enzyme demonstrated NS2B(H)-NS3pro precursor and its autocleavage products, NS3pro and NS2B(H), as 36, 21, and 10 kDa bands, respectively. Kinetic parameters, K_m and k_cat, for fluorogenic protease model substrates, Boc-GRR-amc, Boc-LRR-amc, Ac-nKRR-amc, Bz-nKRR-amc, Pyr-RTKR-amc and Abz-(R)₄SAG-nY-amide, were obtained using inner filter effect correction. The highest catalytic efficiency k_cat/K_m was found for Pyr-RTKR-amc (k_cat/K_m: 1962.96±85.0 M⁻¹ s⁻¹) and the lowest for Boc-LRR-amc (k_cat/K_m: 3.74±0.3 M⁻¹ s⁻¹). JEV NS3pro is inhibited by aprotinin but to a lesser extent than DEN and WNV NS3pro.

Conclusions/Significance

A simplified procedure for the cloning, overexpression and purification of the NS2B(H)-NS3pro was established which is generally applicable to other flaviviral proteases. Kinetic parameters obtained for a number of model substrates and inhibitors, are useful for the characterization of substrate specificity and eventually for the design of high-throughput assays aimed at antiviral inhibitor discovery.

TNF-α promoter polymorphism: a factor contributing to the different immunological and clinical phenotypes in Japanese encephalitis

Background

More than three billion populations are living under the threat of Japanese encephalitis in South East Asian (SEA) countries including India. The pathogenesis of this disease is not clearly understood and is probably attributed to genomic variations in viral strains as well as the host genetic makeup. The present study is to determine the role of polymorphism of TNF-alpha promoter regions at positions -238G/A, -308G/A, -857C/T and -863C/A in the severity of Japanese encephalitis patients.

Methods

Total of 142 patients including 66 encephalitis case (IgM/RT-PCR positive), 16 fever cases (IgM positive) without encephalitis and 60 apparently healthy individuals (IgG positive) were included in the study. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) using site specific restriction enzymes were implemented for polymorphism study of TNF alpha promoter.

Results

Following the analysis of the digestion patterns of four polymorphic sites of the TNF- alpha promoter region, a significant association was observed between the allele -308A and -863C with the patients of Japanese encephalitis.

Conclusions

TNF- alpha 308 G/A has been shown to be associated with elevated TNF- alpha transcriptional activity. On the other hand, polymorphism at position -863C/A in the promoter region has been reported to be associated with reduced TNF- alpha promoter activity and lower plasma TNF levels. As per the literature search, this is the first study to identify the role of TNF- alpha promoter in JE infection. Our results show that subjects with - 308A and -863C alleles are more vulnerable to the severe form of JE infection.

Antiviral and neuroprotective role of octaguanidinium dendrimer-conjugated morpholino oligomers in Japanese encephalitis

Background

Japanese encephalitis (JE), caused by a mosquito-borne flavivirus, is endemic to the entire south-east Asian and adjoining regions. Currently no therapeutic interventions are available for JE, thereby making it one of the most dreaded encephalitides in the world. An effective way to counter the virus would be to inhibit viral replication by using anti-sense molecules directed against the viral genome. Octaguanidinium dendrimer-conjugated Morpholino (or Vivo-Morpholino) are uncharged anti-sense oligomers that can enter cells of living organisms by endocytosis and subsequently escape from endosomes into the cytosol/nuclear compartment of cells. We hypothesize that Vivo-Morpholinos generated against specific regions of 3′ or 5′ untranslated regions of JEV genome, when administered in an experimental model of JE, will have significant antiviral and neuroprotective effect.

Methodology/Principal Findings

Mice were infected with JEV (GP78 strain) followed by intraperitoneal administration of Morpholinos (5 mg/kg body weight) daily for up to five treatments. Survivability of the animals was monitored for 15 days (or until death) following which they were sacrificed and their brains were processed either for immunohistochemical staining or protein extraction. Plaque assay and immunoblot analysis performed from brain homogenates showed reduced viral load and viral protein expression, resulting in greater survival of infected animals. Neuroprotective effect was observed by thionin staining of brain sections. Cytokine bead array showed reduction in the levels of proinflammatory cytokines in brain following Morpholino treatment, which were elevated after infection. This corresponded to reduced microglial activation in brain. Oxidative stress was reduced and certain stress-related signaling molecules were found to be positively modulated following Morpholino treatment. In vitro studies also showed that there was decrease in infective viral particle production following Morpholino treatment.

Conclusions/Significance

Administration of Vivo-Morpholino effectively resulted in increased survival of animals and neuroprotection in a murine model of JE. Hence, these oligomers represent a potential antiviral agent that merits further evaluation.

Japanese encephalitis (JE) is caused by a flavivirus that is transmitted to humans by mosquitoes belonging to the Culex sp. The threat of JE looms over a vast geographical realm, encompassing approximately 10 billion people. The disease is feared because currently there are no specific antiviral drugs available. There have been reports where other investigators have shown that agents that block viral replication can be used as effective therapeutic countermeasures. Vivo-Morpholinos (MOs) are synthetically produced analogs of DNA or RNA that can be modified to bind with specific targeted regions in a genome. In this study the authors propose that in an animal model of JE, MOs specifically designed to bind with specific region of JE virus (JEV) genome, blocks virus production in cells of living organisms. This results in reduced mortality of infected animals. As the major target of JEV is the nerve cells, analysis of brain of experimental animals, post treatment with MOs, showed neuroprotection. Studies in cultured cells were also supportive of the antiviral role of the MOs. The potent anti-sense effect in animals and lack of obvious toxicity at the effective dosage make these MOs good research reagents with future therapeutic applications in JE.

The blood-brain barrier in the cerebrum is the initial site for the Japanese encephalitis virus entering the central nervous system

Japanese encephalitis (JE) virus is a member of the encephalitic flaviviruses and frequently causes neurological sequelae in a proportion of patients who survive the acute phase of the infection. In the present study, we molecularly identified viral infection in the brain of mice with rigidity of hindlimbs and/or abnormal gait, in which JE virus particles appeared within membrane-bound vacuoles of neurons throughout the central nervous system. Deformation of tight junctions (TJs) shown as dissociation of endothelial cells in capillaries, implying that the integrity of the blood-brain barrier (BBB) has been compromised by JE virus infection. BBB permeability evidently increased in the cerebrum, but not in the cerebellum, of JE virus-infected mice intravenously injected with the tracer of Evans blue dye. This suggests that the permeability of the BBB differentially changed in response to viral infection, leading to the entry of JE virions and/or putatively infected leukocytes from the periphery to the cerebrum as the initial site of infection in the central nervous system (CNS). Theoretically, the virus spread to the cerebellum soon after the cerebrum became infected.

Japanese encephalitis virus utilizes the canonical pathway to activate NF-kappaB but it utilizes the type I interferon pathway to induce major histocompatibility complex class I expression in mouse embryonic fibroblasts

Flaviviruses have been shown to induce cell surface expression of major histocompatibility complex class I (MHC-I) through the activation of NF-kappaB. Using IKK1(-/-), IKK2(-/-), NEMO(-/-), and IKK1(-/-) IKK2(-/-) double mutant as well as p50(-/-) RelA(-/-) cRel(-/-) triple mutant mouse embryonic fibroblasts infected with Japanese encephalitis virus (JEV), we show that this flavivirus utilizes the canonical pathway to activate NF-kappaB in an IKK2- and NEMO-, but not IKK1-, dependent manner. NF-kappaB DNA binding activity induced upon virus infection was shown to be composed of RelA:p50 dimers in these fibroblasts. Type I interferon (IFN) production was significantly decreased but not completely abolished upon virus infection in cells defective in NF-kappaB activation. In contrast, induction of classical MHC-I (class 1a) genes and their cell surface expression remained unaffected in these NF-kappaB-defective cells. However, MHC-I induction was impaired in IFNAR(-/-) cells that lack the alpha/beta IFN receptor, indicating a dominant role of type I IFNs but not NF-kappaB for the induction of MHC-I molecules by Japanese encephalitis virus. Our further analysis revealed that the residual type I IFN signaling in NF-kappaB-deficient cells is sufficient to drive MHC-I gene expression upon virus infection in mouse embryonic fibroblasts. However, NF-kappaB could indirectly regulate MHC-I expression, since JEV-induced type I IFN expression was found to be critically dependent on it.

Development of a vaccine to prevent Japanese encephalitis: a brief review

Japanese encephalitis (ICD 10: A83.0) is an important specific viral encephalitis caused by the Japanese encephalitis virus, a virus of the Flavivirus group. Millions of people, especially those in endemic areas of developing countries in Asia, are at high risk from this infection. Therefore proper management to deal with this virus is essential. There is no specific treatment for Japanese encephalitis virus. Supportive and symptomatic treatments are usually used, which emphasize the importance of prevention in this specific neurological disorder. Vector control or vaccination can be used to prevent the disease. Because the existing Japanese encephalitis vaccine poses some undesirable problems, a new vaccine is needed. The process of developing a new vaccine is briefly discussed.

3' cis-acting elements that contribute to the competence and efficiency of Japanese encephalitis virus genome replication: functional importance of sequence duplications, deletions, and substitutions

The positive-strand RNA genome of Japanese encephalitis virus (JEV) terminates in a highly conserved 3'-noncoding region (3'NCR) of six domains (V, X, I, II-1, II-2, and III in the 5'-to-3' direction). By manipulating the JEV genomic RNA, we have identified important roles for RNA elements present within the 574-nucleotide 3'NCR in viral replication. The two 3'-proximal domains (II-2 and III) were sufficient for RNA replication and virus production, whereas the remaining four (V, X, I, and II-1) were dispensable for RNA replication competence but required for maximal replication efficiency. Surprisingly, a lethal mutant lacking all of the 3'NCR except domain III regained viability through pseudoreversion by duplicating an 83-nucleotide sequence from the 3'-terminal region of the viral open reading frame. Also, two viable mutants displayed severe genetic instability; these two mutants rapidly developed 12 point mutations in domain II-2 in the mutant lacking domains V, X, I, and II-1 and showed the duplication of seven upstream sequences of various sizes at the junction between domains II-1 and II-2 in the mutant lacking domains V, X, and I. In all cases, the introduction of these spontaneous mutations led to an increase in RNA production that paralleled the level of protein accumulation and virus yield. Interestingly, the mutant lacking domains V, X, I, and II-1 was able to replicate in hamster BHK-21 and human neuroblastoma SH-SY5Y cells but not in mosquito C6/36 cells, indicating a cell type-specific restriction of its viral replication. Thus, our findings provide the basis for a detailed map of the 3' cis-acting elements in JEV genomic RNA, which play an essential role in viral replication. They also provide experimental evidence for the function of 3' direct repeat sequences and suggest possible mechanisms for the emergence of these sequences in the 3'NCR of JEV and perhaps in other flaviviruses.

A Japanese encephalitis virus vaccine candidate strain is attenuated by decreasing its interferon antagonistic ability

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes acute encephalitis with high mortality in humans. To understand the virus-host interactions that influence JEV virulence, we determined the lethality of a neurovirulent (RP-9) and an attenuated (RP-2ms) variant of JEV in several immunodeficient mice strains. The attenuated phenotype of RP-2ms was completely lost in Stat-1-deficient mice, but its virulence was only slightly increased in mice lacking the components of adaptive immunity, suggesting an important role of the interferon (IFN) system in controlling JEV infection. Cell-based assays demonstrated that RP-2ms is more sensitive to IFN-alpha treatment; however, the NS5 protein of RP-2ms was still a potent antagonist of IFN, like RP-9 NS5. Using a recombinant infectious clone of RP-9, we found that a single Glu-->Lys mutation at residue 138 of the envelope protein (E-E138K) rendered the mutated RP-9 sensitive to the antiviral effect of IFN-alpha. Furthermore, IFN signaling was blocked earlier in the RP-9-infected cells relative to that in cells infected with RP-2ms or recombinant RP-9 bearing the E-E138K mutation. Thus, the E-E138K mutation of JEV appears to affect the viral growth properties, leading to a reduced efficiency in blocking IFN signaling, which then results in an attenuated phenotype in inoculated animals.

Inhibition of Japanese encephalitis virus replication by peptide nucleic acids targeting cis-acting elements on the plus- and minus-strands of viral RNA

Japanese encephalitis virus (JEV) is a major cause of acute viral encephalitis in humans. The single-stranded, plus-sense viral genome, which is used for translation and minus-strand RNA synthesis, and its complementary minus-strand viral RNA contain various sequences and RNA secondary structures conserved in flaviviruses, providing potential targets for antisense agents. Here, we investigated the antiviral effects of peptide nucleic acids (PNAs) targeting cis-acting signals at the 5'-untranslated region (UTR), 3'-UTR, and genome cyclization motifs on the plus-strand RNA, as well as the 95-nucleotide 3'-end of the minus-strand RNA, which serves as a template for plus-strand RNA synthesis by the viral RNA-dependent RNA polymerase (RdRp). Among the tested cell-penetrating peptide (CPP)-PNA conjugates, a 17-mer PNA conjugate targeting the top of the 3'-UTR loop structure was most effective in suppressing virus proliferation. In vitro RdRp assays and electrophoretic mobility shift assays using a functional recombinant JEV RdRp showed that the 3'-terminal region-targeting PNAs could inhibit RNA synthesis by competing with viral RdRp for binding to a selected cis-acting element at the 3'-end of plus- and minus-strand viral RNAs. Collectively, our results suggest that CPP-PNA conjugates can suppress JEV proliferation by blocking RNA-protein or RNA-RNA interactions essential for productive viral infection.

Ecology and geographical expansion of Japanese encephalitis virus

Japanese encephalitis virus (JEV) (Flavivirus: Flaviviridae) is a leading cause of encephalitis in eastern and southern Asia. The virus is maintained in a zoonotic cycle between ardeid wading birds and/or pigs and Culex mosquitoes. The primary mosquito vector of JEV is Culex tritaeniorhynchus, although species such as Cx. gelidus, Cx. fuscocephala, and Cx. annulirostris are important secondary or regional vectors. Control of JEV is achieved through human and/or swine vaccination, changes in animal husbandry, mosquito control, or a combination of these strategies. This review outlines the ecology of JEV and examines the recent expansion of its geographical range, before assessing its ability to emerge in new regions, using the hypothetical establishment in the United States as a case study.

A complex RNA motif defined by three discontinuous 5-nucleotide-long strands is essential for Flavivirus RNA replication

Tertiary or higher-order RNA motifs that regulate replication of positive-strand RNA viruses are as yet poorly understood. Using Japanese encephalitis virus (JEV), we now show that a key element in JEV RNA replication is a complex RNA motif that includes a string of three discontinuous complementary sequences (TDCS). The TDCS consists of three 5-nt-long strands, the left (L) strand upstream of the translation initiator AUG adjacent to the 5'-end of the genome, and the middle (M) and right (R) strands corresponding to the base of the Flavivirus-conserved 3' stem-loop structure near the 3'-end of the RNA. The three strands are arranged in an antiparallel configuration, with two sets of base-pairing interactions creating L-M and M-R duplexes. Disrupting either or both of these duplex regions of TDCS completely abolished RNA replication, whereas reconstructing both duplex regions, albeit with mutated sequences, fully restored RNA replication. Modeling of replication-competent genomes recovered from a large pool of pseudorevertants originating from six replication-incompetent TDCS mutants suggests that both duplex base-pairing potentials of TDCS are required for RNA replication. In all cases, acquisition of novel sequences within the 3'M-R duplex facilitated a long-range RNA-RNA interaction of its 3'M strand with either the authentic 5'L strand or its alternative (invariably located upstream of the 5' initiator), thereby restoring replicability. We also found that a TDCS homolog is conserved in other flaviviruses. These data suggest that two duplex base-pairings defined by the TDCS play an essential regulatory role in a key step(s) of Flavivirus RNA replication.

Engineering the Japanese encephalitis virus RNA genome for the expression of foreign genes of various sizes: implications for packaging capacity and RNA replication efficiency

Using the RNA replication machinery of Japanese encephalitis virus (JEV), the authors have established and characterized three strategies for the expression of foreign genes. Initially, approximately 11 kb genomic RNA was engineered to express heterologous genes of various sizes by preferentially inserting a new cistron at the beginning of the 3' nontranslated variable region. RNA transfection yielded recombinant viruses that initiated foreign gene expression after infecting permissive cells. JEV was capable of packaging recombinant genomes as large as approximately 15 kb. However, larger genome size was inversely correlated with RNA replication efficiency and cytopathogenicity, with no significant change in infectivity. Second, a variety of self-replicating propagation-deficient viral replicons were constructed by introducing one to three in-frame deletions into the ectodomains of all the structural proteins of JEV. These replicons displayed a spectrum of RNA replication efficiency upon transfection, suggesting that remnant transmembrane domains play a suppressive role in this process. Third, the authors generated a panel of stable packaging cell lines (PCLs) providing all three JEV structural proteins in trans. These PCLs efficiently packaged viral replicon RNAs into single-round infectious viral replicon particles. These JEV-based virus/vector systems may provide useful tools for a variety of biological applications, including foreign gene expression, antiviral compound screening, and genetic immunization.

Immunization with West Nile virus envelope domain III protects mice against lethal infection with homologous and heterologous virus

The Japanese encephalitis virus (JEV) serocomplex-group consists of mosquito-borne flaviviruses, which include West Nile virus (WNV) and JEV, and both may cause severe encephalitis in humans. WNV has spread rapidly across the United States since its introduction in 1999 and its geographical distribution within the western hemisphere is expected to further expand, whereas, JEV is the most common cause of viral encephalitis in Southeast Asia, China and India. Currently, there is no registered human vaccine or specific therapy to prevent or treat WNV infection. Here we describe the efficacy of recombinant domain III (DIII) of WNV glycoprotein E in a mouse model. It induces high neutralizing antibody titers, as well as, protection against lethal WNV infection in C57BL/6 mice. This vaccine preparation also afforded partial protection against lethal JEV infection.

Cytomegalovirus induces interferon-stimulated gene expression and is attenuated by interferon in the developing brain

Cytomegalovirus (CMV) is considered the most common infectious agent causing permanent neurological dysfunction in the developing brain. We have previously shown that CMV infects developing brain cells more easily than it infects mature brain cells and that this preference is independent of the host B- and T-cell responses. In the present study, we examined the innate antiviral defenses against mouse (m) and human (h) CMVs in developing and mature brain and brain cells. mCMV infection induced interferon (IFN)-stimulated gene expression by 10- to 100-fold in both glia- and neuron-enriched cultures. Treatment of primary brain cultures with IFN-alpha, -beta, and -gamma or a synthetic RNA, poly(I:C), reduced the number of mCMV-infected cells, both in older cells and in fresh cultures from embryonic mouse brains. When a viral dose that killed almost all unprotected cells was used, IFN-protected cells had a natural appearance, and when they were tested with whole-cell patch clamp recording, they appeared physiologically normal with typical resting membrane potentials and action potentials. mCMV infection increased expression of representative IFN-stimulated genes (IFIT3, OAS, LMP2, TGTP, and USP18) in both neonatal and adult brains to similarly large degrees. The robust upregulation of gene expression in the neonatal brain was associated with a much higher degree of viral replication at this stage of development. In contrast to the case for downstream gene induction, CMV upregulated IFN-alpha/beta expression to a greater degree in the adult brain than in the neonatal brain. Similar to the case with cultured brain cells, IFN treatment of the developing brain in vivo depressed mCMV replication. In parallel work with cultured primary human brain cells, IFN and poly(I:C) treatment reduced hCMV infection and prevented virus-mediated cell death. These results suggest that coupling IFN administration with current treatments may reduce CMV infections in the developing brain.

Blocking of interferon-induced Jak-Stat signaling by Japanese encephalitis virus NS5 through a protein tyrosine phosphatase-mediated mechanism

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus that causes severe human disease, has been shown to block the interferon (IFN)-induced Janus kinase signal transducer and activation of transcription (Jak-Stat) signaling cascade by preventing Tyk2 tyrosine phosphorylation and Stat activation. In this study, we demonstrate that expression of the JEV nonstructural protein NS5 readily blocked IFN-stimulated Jak-Stat signaling events such as Stat1 nuclear translocation and tyrosine phosphorylation of Tyk2 and Stat1. The region of JEV NS5 responsible for Stat1 suppression was identified using various deletion clones. Deletion of 83 N-terminal residues of JEV NS5, but not the 143 C-terminal residues, abolished its ability to block IFN-stimulated Stat1 activation. The role of JEV NS5 as an IFN antagonist was further demonstrated by its ability to block the induction of interferon-stimulated genes and the antiviral effect of IFN-alpha against the IFN-sensitive encephalomyocarditis virus, which appears to replicate and kill cells that express NS5 even with alpha IFN treatment. Furthermore, the molecular mechanism responsible for IFN antagonism by NS5 probably involves protein tyrosine phosphatases (PTPs), as the IFN-blocking events in both JEV-infected and NS5-expressing cells were reversed by sodium orthovanadate, a broad-spectrum inhibitor of PTPs. We suggest that JEV NS5 is an IFN antagonist and that it may play a role in blocking IFN-stimulated Jak-Stat signaling via activation of PTPs during JEV infection.

NEUROLOGICAL INFECTIONS IN THE RETURNING INTERNATIONAL TRAVELER

Clinicians may encounter international travelers returning with exotic infections, emerging infectious diseases, or resurgent old-world infections. Many of these infectious diseases can affect the nervous system directly or indirectly. The contemporary neurologist should therefore be cognizant of the clinical manifestations, potential complications, and appropriate management of common travel-related infections. This chapter focuses on five important infections that affect the central nervous system and that may be encountered in returning travelers: Japanese encephalitis, malaria, rabies, dengue, and neurocysticercosis. The clinical manifestations, suggested evaluation, and treatment are discussed for each infection.

The ecology of emerging neurotropic viruses

The authors review common themes in the ecology of emerging viruses that cause neurological disease. Three issues emerge. First, 49% of emerging viruses are characterized by encephalitis or serious neurological clinical symptoms. Second, all of these viruses are driven to emerge by ecological, environmental, or human demographic changes, some of which are poorly understood. Finally, the control of these viruses would be enhanced by collaborative multidisciplinary research into these drivers of emergence. The authors highlight this review with a case study of Nipah virus, which emerged in Malaysia due largely to shifts in livestock production and alterations to reservoir host habitat. Collaboration between virologists, ecologists, disease modelers and wildlife biologists has been instrumental in retracing the factors involved in this virus's emergence.

Emerging zoonotic encephalitis viruses: lessons from Southeast Asia and Oceania

The last decade of the 20th Century saw the introduction of an unprecedented number of encephalitic viruses emerge or spread in the Southeast Asian and Western Pacific regions (Mackenzie et al, 2001; Solomon, 2003a). Most of these viruses are zoonotic, either being arthropod-borne viruses or bat-borne viruses. Thus Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, has spread through the Indonesian archipelago to Papua New Guinea (PNG) and to the islands of the Torres Strait of northern Australia, to Pakistan, and to new areas in the Indian subcontinent; a strain of tick-borne encephalitis virus (TBEV) was described for the first time in Hokkaido, Japan; and a novel mosquito-borne alphavirus, Me Tri virus, was described from Vietnam. Three novel bat-borne viruses emerged in Australia and Malaysia; two, Hendra and Nipah viruses, represent the first examples of a new genus in the family Paramyxoviridae, the genus Henipaviruses, and the third, Australian bat lyssavirus (ABLV) is new lyssavirus closely related to classical rabies virus. These viruses will form the body of this brief review.

[West Nile fever/encephalitis as one of the arboviral infections]

West Nile virus maintains natural infection cycle between birds and mosquitoes. It has been known that about 200 species of birds are infected with West Nile virus and the virus is isolated from more than 40 species of mosquitoes. This suggests that West Nile virus has an ability to be transmitted by many species of mosquitoes and infect many kinds of animals. Approximately 20% of infected humans develop symptoms. West Nile fever, an acute febrile illness, is the main disease, and meningitis and encephalitis (meningoencephalitis) occasionally occur. Cases with flaccid paralysis or polyneuritis have been recently reported. Thus, West Nile virus causes multiple types of symptoms in humans. The endemic area has expanded in North America and Siberia. West Nile virus may enter Japan in the near future; therefore, we should keep paying attention to the endemic and epidemic situations in the world.

Viral encephalitis

Acute viral encephalitis may be caused by a wide range of viruses but the most important is herpes simplex encephalitis (HSE) because of its severity, especially if untreated, and its good response to specific treatment with acyclovir. The outcome of any CNS viral infection is dependent on both the immune status of the host and the virulence of the infecting virus. In evaluating a patient with suspected viral encephalitis there are 3 essential steps, namely the identification of a true parenchymal virus infection of the brain rather than a non-infective encephalopathy, the distinction of an infectious viral encephalitis from an acute disseminated encephalomyelitis (ADEM), and then the determination, where possible, of the specific virus involved. In practice, the precise viral cause of the encephalitis may never be established. Analysis of the CSF for herpes simplex virus (HSV) DNA using the Polymerase Chain Reaction (PCR) has been a significant advance in the diagnosis of HSE as this test has a very high sensitivity and specificity especially with appropriate sample timing. It is essential to commence early treatment with intravenous acyclovir in patients suspected of having HSE because of the remarkable safety and efficacy of this drug and the dangers of delaying potentially effective treatment of life threatening disease. This review outlines the general management approach in patients suspected of having viral encephalitis.

Neurovirulence and host factors in flavivirus encephalitis--evidence from clinical epidemiology

Japanese encephalitis virus (JEV) and West Nile virus (WNV) provide some of the most important examples of emerging zoonotic viral encephalitides. For these flaviviruses, only a small proportion of those infected develop clinical features, and these may range from a non-specific flu-like illness to a severe fatal meningoencephalitis, often with Parkinsonian features, or a poliomyelitis-like flaccid paralysis. The factors governing the clinical presentations, and outcome of flavivirus infections are poorly understood, but studies have looked at viral virulence determinants and the host immune response. Previous studies on JEV have suggested that the distribution of the four genotypes across Asia may relate to the differing clinical epidemiology (epidemic disease in the north, endemic disease in the south). However, new data based on the complete nucleotide sequence of a virus representing one of the oldest lineages, and phylogenetic analyses of all JEV strains for which genetic data are available, suggest that the distribution is best explained in terms of the virus' origin in the Indonesia-Malaysia region (where all genotypes have been found), and the spread of the more recent genotypes to new geographical areas. Clinical studies have shown that innate immunity, as manifested by interferon alpha levels, is important in JEV and other flaviviruses, but treatment with interferon alpha did not improve the outcome. A failure of the humoral immune response, is associated with death from encephalitis caused by JEV and WNV. Cellular immunity has been less well characterized, but CD8+ and CD4+ T cells are thought to be important.

Natural and nosocomial infection in a patient with West Nile encephalitis and extrapyramidal movement disorders

Since its first recognition in North America in 1999, West Nile virus (WNV) has spread rapidly across the continent, but in many communities, rapid diagnostic tests for detection of WNV infection are not fully available. We describe a patient with extrapyramidal movement disorders and changes in the basal ganglia noted on magnetic resonance images that are characteristic of other flavivirus encephalitides and may help in the recognition of patients with West Nile encephalitis. Detailed molecular analysis suggested that, although our patient received a blood transfusion infected with WNV, the virus that caused his initial infection and encephalitis was probably acquired naturally from a mosquito.