Reemergence of Japanese Encephalitis in South Korea, 2010-2015

Characterization of a Small Plaque Variant Derived from Genotype V Japanese Encephalitis Virus Clinical Isolate K15P38

Genotype V (GV) Japanese encephalitis virus (JEV) has been predominantly reported in the Republic of Korea (ROK) since 2010. GV JEV exhibits higher virulence and distinct antigenicity compared to other genotypes, which results in reduced efficacy of existing vaccines. Research on GV JEV is essential to minimize its clinical impact, but the only available clinical strain in the ROK is K15P38, isolated from the cerebrospinal fluid of a patient in 2015. We obtained this virus from National Culture Collection for Pathogens (NCCP) and isolated a variant forming small plaques during our research. We identified that this variant has one amino acid substitution each in the PrM and NS5 proteins compared to the reported K15P38. Additionally, we confirmed that this virus exhibits delayed propagation in vitro and an attenuated phenotype in mice. The isolation of this variant is a critical reference for researchers intending to study K15P38 obtained from NCCP, and the mutations in the small plaque-forming virus are expected to be useful for studying the pathology of GV JEV.

Shift in dominant genotypes of Japanese encephalitis virus and its impact on current vaccination strategies

Japanese encephalitis (JE) is a zoonotic ailment from the Japanese encephalitis virus (JEV). JEV belongs to the flavivirus genus and is categorized into a solitary serotype consisting of five genetically diverse genotypes (I, II, III, IV, and V). The JEV genotype III (GIII) was the prevailing strain responsible for multiple outbreaks in countries endemic to JEV until 1990. In recent years, significant improvements have occurred in the epidemiology of JE, encompassing the geographical expansion of the epidemic zone and the displacement of prevailing genotypes. The dominant genotype of the JEV has undergone a progressive shift from GIII to GI due to variations in its adaptability within avian populations. From 2021 to 2022, Australia encountered an epidemic of viral encephalitis resulting from infection with the GIV JEV pathogen. The current human viral encephalitis caused by GIV JEV is the initial outbreak since its initial discovery in Indonesia during the late 1970s. Furthermore, following a time frame of 50 years, the detection and isolation of GV JEV have been reported in Culex mosquitoes across China and South Korea. Evidence suggests that the prevalence of GIV and GV JEV epidemic regions may be on the rise, posing a significant threat to public safety and the sustainable growth of animal husbandry. The global approach to preventing and managing JE predominantly revolves around utilizing the GIII strain vaccine for vaccination purposes. Nevertheless, research has demonstrated that the antibodies generated by the GIII strain vaccine exhibit limited capacity to neutralize the GI and GV strains. Consequently, these antibodies cannot protect against JEV challenge caused by animal GI and GV strains. The limited cross-protective and neutralizing effects observed between various genotypes may be attributed to the low homology of the E protein with other genotypes. In addition, due to the GIV JEV outbreak in Australia, further experiments are needed to evaluate the protective efficiency of the current GIII based JE vaccine against GIV JEV. The alteration of the prevailing genotype of JEV and the subsequent enlargement of the geographical extent of the epidemic have presented novel obstacles in JE prevention and control. This paper examines the emerging features of the JE epidemic in recent years and the associated problems concerning prevention and control.

Japanese Encephalitis among Adults: A Review

Japanese encephalitis (JE) is becoming an increasingly important issue among adults. The reasons for this are multifactorial. During the past decades, new areas of Japanese encephalitis virus (JEV) transmission have occurred in several locations, most notably in a markedly expanded area of Australia during 2021-2022. When JEV enters new areas, cases in adults frequently occur. This is unlike the typical pattern in endemic areas where the burden of disease is in children because most adults are protected through natural immunity following earlier exposure to the virus. Even in endemic areas, JEV has become relatively more important in adults because improved JE control through childhood immunization programs has resulted in a substantial decrease in pediatric JE cases and thus more prominence of adult JE cases. Finally, increases in tourism to JE risk areas have resulted in more exposure of adult travelers, who are usually non-immune, to infection in JE risk areas. In this review we describe the increasing importance of JE in adults in some areas and then consider the comparative clinical presentation and severity of illness among children and adults.

Japanese encephalitis virus induces vasodilation and severe lethality in adult and aged AG129 mice lacking alpha, beta and gamma interferon receptors

Japanese encephalitis virus (JEV) is a single-stranded positive-sense RNA virus belonging to the Flaviviridae family. The JEV is the leading cause of viral encephalitis in children and the elderly which is spread by mosquitoes. JEV infection has been established in different animal models such as mouse, hamster, guinea pig, swine, rat, monkey, rabbit by using the different routes of inoculations. Here, we have shown that the alpha/beta and gamma -receptor deficient AG129 mouse induces fatal encephalitis in both young and aged old mice, when challenged with high titer JEV Indian clinical isolate by both intraperitoneal and intradermal route. The JEV infected AG129 mouse have shown neurological symptoms, JEV-induced pathological features and supported high level viral replication. Additionally, administration of JEV in AG129 mice resulted in the induction of severe peripheral vascular permeability, which is a major hall mark of Dengue infection but not shown in JEV. Taken together, our results demonstrate interferon α/β and γ receptors knock out AG129 mouse does not need adaptation of JEV clinical isolates and could be is a promising JEV challenge mouse model by mimicking the natural intradermal route of administration for rapid screening of novel antivirals and vaccines.

A comparison of clinical manifestations of Japanese encephalitis between children and adults in Gansu Province, Northwest China (2005-2020)

Japanese encephalitis (JE), a mosquito-borne zoonotic disease, has emerged as a major public health concern around the world. Previous research has shown that JE has serious sequelae, and the recent shift in the population from children to adults presents a significant challenge for JE treatment and prevention. Therefore, we examined the differences in clinical manifestations (clinical symptoms, clinical signs, complications, and clinical typing) of JE between children and adults over the 15 years in Gansu Province to provide a theoretical basis for better response to JE treatment. Clinical typing was found to be statistically significant in the child versus adult groups and the groups with or without vaccination. Only the dysfunction of consciousness differed statistically between children with and without vaccination, whereas neurological symptoms such as vomiting (jet vomiting), irritability, drowsiness, convulsions, and hyperspasmia differed statistically between children and adults, and the rest of the symptoms did not differ statistically. Only pupil size changes were statistically different in clinical signs between the children with and without vaccination, while blood pressure changes, change in pupil size, positive meningeal stimulation signs, and positive pathological reflexes (increased muscle tone and Babinski's sign) were statistically different between adults and children. Bronchopneumonia was the most common complication, especially in adults. Therefore, the authors believe that children and adults differ in some clinical manifestations and propose that efforts should be directed toward developing individualized treatment plans for different age groups and employing more effective supportive treatment for various populations. In addition, we suggest expanding the coverage of the JE vaccine and increasing overall vaccination rates and adopting multiple measures in conjunction with JE prevention and control.

Changes in age-specific seroprevalence of Japanese encephalitis virus and impact of Japanese encephalitis vaccine in Korea

The Japanese encephalitis (JE) virus is the leading cause of vaccine-preventable encephalitis in Asia. Since the introduction of a universal JE vaccination program and urbanization of Korea, the incidence of JE has dramatically decreased in Korea. However, recent JE cases have occurred, predominantly among unvaccinated adults and with a shift in age distribution. Here we aimed to review the changes in age-specific JE seroprevalence over time and discuss the implications of JE vaccination programs in Korea. Following the last epidemic in 1982-1983, mandatory vaccination for all children aged 3-15 years was conducted annually until 1994. However, JE has reemerged, predominantly affecting unvaccinated adults aged 40 years or older and demonstrating a shift in age distribution toward older populations. The age-specific seroprevalence of the JE virus in Korea has changed noticeably over time. Seropositivity in children and adolescents increased from 10%-59% in the 1970s to 90%-92% in the 1980s after the implementation of the JE vaccination program and increased further to 98% in 2012. No age-specific difference in the seroprevalence of JE was found, and appropriate levels of immunity to JE were maintained for all age groups. Continuous surveillance of the seroprevalence of JE is essential to establish a proper immunization policy in Korea.

Environmental factors and spatiotemporal distribution of Japanese encephalitis after vaccination campaign in Guizhou Province, China (2004-2016)

Background

Although a vaccination campaign has been conducted since 2004, Japanese encephalitis (JE) is still a public health problem in Guizhou, one of the provinces with the highest incidence of JE in China. The aim of this study was to understand the spatiotemporal distribution of JE and its relationship with environmental factors in Guizhou Province in the post-vaccination era, 2004–2016.

Methods

We collected data on human JE cases in Guizhou Province from 2004 to 2016 from the national infectious disease reporting system. A Poisson regression model was used to analyze the relationship between JE occurrence and environmental factors amongst counties.

Results

Our results showed that the incidence and mortality of JE decreased after the initiation of vaccination. JE cases were mainly concentrated in preschool and school-age children and the number of cases in children over age 15 years was significantly decreased compared with the previous 10 years; the seasonality of JE before and after the use of vaccines was unchanged. JE incidence was positively associated with cultivated land and negatively associated with gross domestic product (GDP) per capita, vegetation coverage, and developed land. In areas with cultivated land coverage < 25%, vegetation coverage > 55%, and urban area coverage > 25%, the JE risk was lower. The highest JE incidence was among mid-level GDP areas and in moderately urbanized areas.

Conclusions

This study assessed the relationship between incidence of JE and environmental factors in Guizhou Province. Our results highlight that the highest risk of JE transmission in the post-vaccination era is in mid-level developed areas.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06857-3.

Long-term neurological and healthcare burden of adults with Japanese encephalitis: A nationwide study 2000-2015

Objective

To assess the healthcare utilization, economic burden, and long-term neurological complications and mortality of an adult population with Japanese encephalitis (JE).

Methods

This study utilized two nationwide datasets in Taiwan: the Notifiable Disease Dataset of confirmed cases from the Centers for Disease Control to identify JE patients, and the National Health Insurance Research Database to obtain patients’ healthcare utilization. Survival analyses were performed to identify prognostic factors associated with the all-cause mortality of patients.

Results

This study included 352 adult cases with JE (aged≥20 years). The mean age of JE patients was 45 years. Stroke (event rate: 3.49/100 person-years) was the most common neurological complication, followed by epilepsy/convulsions (3.13/100 person-years), encephalopathy/delirium (2.20/100 person-years), and parkinsonism (1.97/100 person-years). Among the 336 hospitalized patients at JE diagnosis, 58.33% required intensive care. Among 79 patients who died following JE diagnosis, 48.84% of death events occurred within the year of diagnosis. The medical costs increased considerably at JE diagnosis and subsequent-year costs remained significantly higher than the costs before diagnosis (p<0.05). Having a four-dose JE vaccination (i.e., born after 1976) versus no JE vaccination history (i.e., born before 1963) was significantly associated with lower all-cause mortality (hazard ratio: 0.221 [95% confidence interval: 0.067, 0.725]). Comorbid diabetes and incident epilepsy/convulsion events significantly increased the mortality risk by 2.47- and 1.85-fold, respectively (p<0.05).

Conclusion

A considerable medical burden associated with JE was observed in affected adults, even in the years following JE diagnosis. Vaccination should be considered to prevent this sporadic, but lethal, viral infection.

The epidemiology of adulthood Japanese encephalitis (JE) remains limited, and data on the economic burden associated with JE is lacking. This study is the first to comprehensively examine the healthcare burden (i.e., healthcare utilization and costs, neurological complications, all-cause mortality) of an adult population with JE, utilizing a nationwide cohort of JE-infected adults with up to 16 years of follow-up. In the first 6 months following JE diagnosis, a higher rate of neurological disorders was found, compared to the years after the diagnosis, with stroke being the most common neurological complication, followed by epilepsy/convulsions. The healthcare utilization of JE patients was higher in the first 6 months after the diagnosis compared to the years following the diagnosis. Medical costs increased considerably at JE diagnosis and subsequent-year costs after diagnosis remained higher than the cost before diagnosis. Having comorbid diabetes or incident epilepsy/convulsion events was a significant risk factor for mortality of adults with JE. Being born after 1976 in Taiwan, and thus likely receiving a four-dose schedule of vaccination, was associated with reduced mortality. Therefore, special attention is required for JE patients with comorbid diabetes or incident epilepsy/convulsion events, and JE vaccination should be considered to prevent this sporadic but lethal viral infection.

Metagenomic analysis reveals Culex mosquito virome diversity and Japanese encephalitis genotype V in the Republic of Korea

Recent outbreaks of emerging and re-emerging viruses have shown that timely detection of novel arboviruses with epidemic potential is essential to mitigate human health risks. There are rising concerns that emergent JEV genotype V (GV) is circulating in Asia, against which current vaccines may not be efficacious. To ascertain if JEV GV and other arboviruses are circulating in East Asia, we conducted next-generation sequencing on 260 pools of Culex tritaeniorhynchus and Culex bitaeniorhynchus mosquitoes (6540 specimens) collected at Camp Humphreys, Republic of Korea (ROK) in 2018. Interrogation of our data revealed a highly abundant and diverse virosphere that contained sequences from 122 distinct virus species. Our statistical and hierarchical analysis uncovered correlates of potential health, virological, and ecological relevance. Furthermore, we obtained evidence that JEV GV was circulating in Pyeongtaek and, retrospectively, in Seoul in 2016 and placed these findings within the context of human and fowl reservoir activity. Sequence-based analysis of JEV GV showed a divergent genotype that is the most distant from the GIII-derived live attenuated SA14-14-2 vaccine strain and indicated regions probably responsible for reduced antibody affinity. These results emphasize recent concerns of shifting JEV genotype in East Asia and highlight the critical need for a vaccine proven efficacious against this re-emergent virus. Together, our one-health approach to Culex viral metagenomics uncovered novel insights into virus ecology and human health.

First detection of a novel 'unknown host' flavivirus in a Malaysian rodent

Current phylogenetic analysis of the flavivirus genus has identified a group of mosquito-borne viruses for which the vertebrate hosts are currently unknown. Here we report the identification of a novel member of this group from a peridomestic rodent species (Sundamys muelleri) collected in Sarawak, Malaysia in 2016. We propose to name this novel flavivirus Batu Kawa virus after the location in which it was identified, with the abbreviation BKWV. Characterization of the BKWV genome allowed identification of putative mature peptides, potential enzyme motifs and conserved structural elements. Phylogenetic analysis found BKWV to be most closely related to Nhumirim virus (from Brazil) and Barkedji virus (from Senegal and Israel). Both of these viruses have been identified in Culex mosquitoes and belong to a group of viruses with unknown vertebrate hosts. This is the first known report of a member of this group of viruses from a potential mammalian host.

Clinical Outcomes of Japanese Encephalitis after Combination Treatment of Immunoglobulin, Ribavirin, and Interferon-α2b

Background and Purpose

Japanese encephalitis (JE) is caused by the JE virus of the Flaviviridae family and is spread by mosquito bites, and no specific antiviral treatment for it exists. Here we describe the clinical presentations, laboratory findings, clinical outcomes, and adverse events after combination treatment of immunoglobulin, ribavirin, and interferon-α2b administered to patients with JE.

Methods

Data were collected and reviewed from a prospective cohort of encephalitis patients admitted to Seoul National University Hospital between August 1, 2010 and October 31, 2019. We reviewed the medical records of the patients diagnosed with JE and treated either with supportive care only or with combination treatment of intravenous immunoglobulin, oral ribavirin, and subcutaneous interferon-α2b.

Results

Eleven patients were diagnosed with laboratory-confirmed JE based on the diagnosis criteria of JE. The median age was 61 years, and five patients were male. Eight patients were treated with the combination therapy, while three patients received supportive management only. Four of the eight patients (50%) treated with the combination therapy showed partial recovery, while one patient (12.5%) showed complete recovery. Two patients experienced hemolytic anemia related to ribavirin and febrile reaction to immunoglobulin, respectively. Among the three patients who received supportive management only, one (33.3%) showed partial recovery and the other two (67.7%) did not show improvement.

Conclusions

Combination treatment of immunoglobulin, ribavirin, and interferon-α2b was found to be tolerable in JE in this study. Further studies of appropriate designs and involving larger numbers of patients are warranted to explore the efficacy of this combination therapy.

Emergence of Japanese encephalitis among adults 40 years of age or older in northern China: Epidemiological and clinical characteristics

Japanese encephalitis (JE) is a vector-borne vaccine preventable infectious disease for which vaccine provides direct protection. China introduced nationwide JE vaccination of young children in 2007, rapidly achieving high coverage. In 2018, 1,800 JE cases were reported in China, with morbidity and mortality rates of 0.13/100,000 and 0.0097/100,000. Nationally, 64% of cases were among adults aged 40 years or older, and in northern China, 82% were among adults, mainly in outbreaks. Severity varied little by age grouping. Compared with the previous 10 years, the proportion and absolute number of cases among adults increased, indicating possible emergence of adult JE in China as childhood JE decreased. We describe JE epidemiology and clinical features nationally and in areas with low endemicity after more than 10 years of routine childhood JE vaccination. Determining population JE seroprevalence should be a priority; vaccination campaigns among adults in high risk areas should be considered.

Post-Marketing Surveillance of Adverse Events Following Vaccination with the Live-Attenuated Japanese Encephalitis Chimeric Virus Vaccine (Imojev®) in South Korea, 2015-2019

INTRODUCTION

The live attenuated Japanese encephalitis chimeric virus vaccine (JE-CV; Imojev®) has been approved in South Korea for use in subjects aged ≥ 12 months since 2015. As part of the license agreement, a post-marketing surveillance study was undertaken to actively monitor the safety profile of JE-CV in the Korean population.

METHODS

An observational, active safety surveillance study was conducted from 3 April 2015 through to 2 April 2019 at 12 centers in South Korea. Subjects aged ≥ 12 months who received a single dose of JE-CV (primary or booster) during a routine healthcare visit were recruited and followed up for solicited reactions (7 and 14 days for injection site and systemic reactions, respectively), non-serious unsolicited adverse events and serious adverse events within 42 days after vaccination.

RESULTS

Overall, 810 subjects who received JE-CV were included in our analysis, the majority received the vaccine as a primary vaccination (94.9%; 769/810). There were 179 solicited reactions reported by 111 subjects; the majority of solicited reactions occurred within 0-3 days (80.4%; 144/179), were of 1-3 days' duration (79.3%; 142/179) and of grade 1 intensity (70.9%; 127/179). There were three grade 3 adverse reactions (irritability, pyrexia and malaise); all resolved within a few days. The incidence of solicited reactions were highest in those aged 12 to < 24 months (34.7% [52/150] subjects; 107 events) and 2 to < 10 years (17.8% [8/45] subjects; 14 events). All unsolicited adverse events (serious and non-serious) were unrelated to vaccination. There were no discontinuations due to adverse reactions/events.

CONCLUSION

JE-CV has a good safety profile under practice conditions in South Korea. No new safety issues were identified.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT02933710.

Genotype-specific neutralizing antibody titers against Japanese encephalitis virus genotypes 1 and 3 in horses immunized with a genotype 3 vaccine

Purpose

Japanese encephalitis is one of the most important mosquito-borne and zoonotic diseases in Asia and the Pacific region. Although the dominant Japanese encephalitis virus (JEV) genotype has shifted from G3 to G1 in Korea since 1990, a G3 strain (Anyang 300) has been used in vaccines for horses for almost 40 years. This study aimed to investigate the seroconversion rates and geometric mean titers (GMTs) of virus-neutralizing antibodies (VNAs) against JEV G1 and G3 in horses immunized with the G3 vaccine.

Materials and Methods

Serum samples of 1,231 horses immunized with the Anyang 300 vaccine were collected in 2018. VNA titers against JEV KV1899 (G1) and Anyang 300 (G3) were measured in all serum samples using the virus neutralization test. Titers were analyzed according to blood sampling time (prior to and following annual revaccination), age, and region.

Results

Rates of VNA titer >10 were 45.1% and 77.8% for G1, and 49.1% and 82.9% for G3 in samples taken before and after revaccination, respectively. GMTs of genotype-specific VNAs against JEV G1 and G3 were 8.3 and 11.6 before revaccination and rose to 27.2 and 65.4 following revaccination. Overall sero-positivity did not significantly differ between genotypes, but GMTs significantly differed among genotypes and sampling times. No significant difference was found in GMTs among age groups or regions.

Conclusion

Genotype-specific neutralizing antibody titers against JEV G1 and G3 differed significantly in horses immunized with the G3 vaccine. Antigenic differences between genotypes could reduce the vaccine's efficacy, requiring the development of a new vaccine.

Serological and molecular epidemiology of Japanese Encephalitis in Zhejiang, China, 2015-2018

Background

Shifts have occurred in the epidemiological characteristics of Japanese encephalitis (JE), extending from the molecular level to the population level. The aim of this study was to investigate the seroprevalence of JE neutralizing antibodies in healthy populations from different age groups in Zhejiang Province, and to conduct mosquito monitoring to evaluate the infection rate of Japanese encephalitis virus (JEV) among vectors, as well as the molecular characteristics of the E gene of isolated JEV strains.

Methodology/Principal findings

A total of 1190 sera samples were screened by a microseroneutralization test, including 429 infants (28d-11m) and 761 participants (2y-82y). For those under 1 year old, the geometric mean titers (GMTs) of the JE neutralizing antibody was 9.49 at birth and significantly declined as the age of month increased (r = -0.225, P<0.001). For those above 1-year old, seropositive proportions were higher in subjects aged 1–3 years old as well as ≥25 years old (65%-75%), and relatively lower in subjects aged between 4–25 years old (22%-55%). Four or more years after the 2^nd dose of JEV-L (first dose administered at 8 months and the second at 2 years of age), the seropositive proportion decreased to 32.5%, and GMTs decreased to 8.08. A total of 87,201 mosquitoes were collected from livestock sheds in 6 surveillance sites during 2015–2018, from which 139 E gene sequences were successfully amplified. The annual infection rate according to bias-corrected maximum likelihood estimation of JEV in Culex tritaeniorhynchus was 1.56, 2.36, 5.65 and 1.77 per 1000, respectively. JEV strains isolated during 2015–2018 all belonged to Genotype I. The E gene of amplified 139 samples differed from the JEV-L vaccine strain at fourteen amino acid residues, including the eight key residues related to virulence and virus attenuation. No divergence was observed at the sites related to antigenicity.

Conclusions/Significance

Zhejiang Province was at a high risk of JE exposure due to relatively lower neutralizing antibody levels among the younger-aged population and higher infection rates of JEV in mosquitoes. Continuous, timely and full coverage of JE vaccination are essential, as well as the separation of human living areas and livestock shed areas. In addition, annual mosquito surveillance and periodic antibody level monitoring are important for providing evidence for improvement in JE vaccines and immunization schedules.

Although Japanese encephalitis (JE) has been well-controlled in Zhejiang Province, it remains a hot public health issue due to heavy disease burden. The epidemiological characteristics of JE have changed recently in Zhejiang Province. Increasing proportion of adult cases (>40 years old) have been reported. Genotype I (GI) of JEV has displaced genotype III (GIII) as the dominant genotype. The population immunity against JE was notably low among participants aged 4–25 years old, with the lowest GMT being in the 7-14-year-old group. Two doses of JEV-L did not provide effective protection after 4 or more years past the 2^nd dose. Therefore, issues about duration of protection and necessity of a booster dose at 6 years of age need further research. JEV strains isolated from mosquitoes during 2015–2018 in Zhejiang Province all belonged to GI. Compared with the JE vaccine strain, mutations at the eight amino acid residues on E gene related to virulence in Zhejiang strains were detected, while the antigenic sites remained the same. JE serological survey in healthy populations with different sequential immunization schedule should be conducted to provide evidence for reformation on JE immunization strategy, including type, dose and interval.

Neutralizing antibody rather than cellular immune response is maintained for nearly 20 years among Japanese encephalitis SA14-14-2 vaccinees in an endemic setting

Japanese encephalitis (JE), caused by infection with Japanese encephalitis virus (JEV), is the most important viral encephalitis in Asia. JE incidence has significantly decreased by immunization with live-attenuated vaccine SA14-14-2. However, the duration of immune response overtime after vaccination is inconclusive and may be associated with the risk of JE occurrence in adults. A cross-sectional study was conducted in 961 JE-vaccinated local residents aged 19-20 years in Beijing, China. 620 (65%) and 513 (53%) individuals were anti-JEV IgG antibody and neutralizing antibody (nAb) positive, respectively. The geometric mean titer (GMT) of nAb was 1:11, suggesting a seroprotection among the study population. As for IFN-γ production, peripheral blood mononuclear cell (PBMC) samples isolated from 60 subjects showed negative response following the stimulation with concentrated JEV particles. Overall, longer persistence of nAb response among vaccinees is observed than that of cellular immune response after 17-18 years of vaccination. Taken together, our results not only provide the data for evaluating herd immunity against JEV among vaccinated adults in Beijing but also offer useful information for JE prevention and control in endemic areas.

Seroprevalence of Neutralizing Antibodies against Japanese Encephalitis Virus among Adolescents and Adults in Korea: A Prospective Multicenter Study

The immunization schedule for the Japanese encephalitis (JE) vaccine in Korea is a two-dose primary series at 12-24 months of age, followed by booster doses 12 months after the second dose and at the ages of 6 and 12 years. Although the number of JE cases has markedly decreased after the universal vaccination program, JE predominantly occurs in adults. The aim of this study was to assess the age-specific prevalence of the JE-neutralizing antibody (NTAb) among adolescents and adults in Korea. A total of 1603 specimens were collected from a healthy Korean population above 15 years old in five provinces. The JE-NTAb titers were measured with the pseudotyped virus assay and considered to be positive at ≥ 1:50. The seropositivity of JE-NTAb was the highest in the 15-29 years category (>95%) and gradually began to decrease in the age group of 30-44 years (89.42%). The lowest and second lowest JE-NTAb seropositive rates were observed among those aged 70 years or older (59.77%) and those aged 55-59 years (75.24%), respectively. Subjects from Seoul exhibited the highest JE-NTAb titer in all age groups compared to other provinces. In conclusion, the JE-NTAb seropositive rates and titers have maintained appropriate levels in the general Korean population. We propose that adult immunization and boosters at 12 years of age against JE are not strongly recommended in Korea.

A need to raise the bar - A systematic review of temporal trends in diagnostics for Japanese encephalitis virus infection, and perspectives for future research

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Japanese encephalitis virus (JEV) remains a leading cause of neurological infection in Asia.

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A systematic review identified 20,212 published human cases of laboratory-confirmed JEV infections from 205 studies.

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15,167 (75%) of cases were confirmed with the lowest confidence diagnostic test, i.e., level 3 or 4, or level 4.

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Only 109 (53%) of the studies reported contemporaneous testing for dengue-specific antibodies.

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A fundamental pre-requisite for the control of JE is lacking — that of a simple and specific diagnostic procedure that can be adapted for point-of-care tests and readily used throughout JE endemic regions of the world.

Objective

Japanese encephalitis virus infection (JE) remains a leading cause of neurological disease in Asia, mainly involving individuals living in remote areas with limited access to treatment centers and diagnostic facilities. Laboratory confirmation is fundamental for the justification and implementation of vaccination programs. We reviewed the literature on historical developments and current diagnostic capability worldwide, to identify knowledge gaps and instill urgency to address them.

Methods

Searches were performed in Web of Science and PubMed using the term 'Japanese encephalitis' up to 13th October 2019. Studies reporting laboratory-confirmed symptomatic JE cases in humans were included, and data on details of diagnostic tests were extracted. A JE case was classified according to confirmatory levels (Fischer et al., 2008; Campbell et al., 2011; Pearce et al., 2018; Heffelfinger et al., 2017), where level 1 represented the highest level of confidence.

Findings

20,212 published JE cases were identified from 205 studies. 15,167 (75%) of these positive cases were confirmed with the lowest-confidence diagnostic tests (level 3 or 4, or level 4). Only 109 (53%) of the studies reported contemporaneous testing for dengue-specific antibodies.

Conclusion

A fundamental pre-requisite for the control of JEV is lacking — that of a simple and specific diagnostic procedure that can be adapted for point-of-care tests and readily used throughout JE-endemic regions of the world.

Perspectives Regarding the Risk of Introduction of the Japanese Encephalitis Virus (JEV) in the United States

Japanese encephalitis (JE) is a zoonotic, emerging disease transmitted by mosquito vectors infected with the Japanese encephalitis virus (JEV). Its potential for emergence into susceptible regions is high, including in the United States (US), and is a reason of economic concern among the agricultural community, and to public health due to high morbidity and mortality rates in humans. While exploring the complexities of interactions involved with viral transmission, we proposed a new outlook on the role of vectors, hosts and the environment under changing conditions. For instance, the role of feral pigs may have been underappreciated in our previous work, given research keeps pointing to the importance of susceptible populations of wild swine in naïve regions as key elements for the introduction of emergent vector-borne diseases. High risk of JEV introduction has been associated with the transportation of infected mosquitoes via aircraft. Nonetheless, no JEV outbreaks have been reported in the US to date and results from a qualitative risk assessment considered the risk of establishment to be negligible under the current conditions (environmental, vector, pathogen, and host). In this work, we discuss virus-vector-host interactions and ecological factors important for virus transmission and spread, review research on the risk of JEV introduction to the US considering the implications of risk dismissal as it relates to past experiences with similar arboviruses, and reflect on future directions, challenges, and implications of a JEV incursion.

How Central Is the Domestic Pig in the Epidemiological Cycle of Japanese Encephalitis Virus? A Review of Scientific Evidence and Implications for Disease Control

Despite the existence of human vaccines, Japanese encephalitis (JE) remains the leading cause of human encephalitis in Asia. Pigs are described as the main amplifying host, but their role in JE epidemiology needs to be reassessed in order to identify and implement efficient control strategies, for both human and animal health. We aimed to provide a systematic review of publications linked to JE in swine, in terms of both individual and population characteristics of JE virus (JEV) infection and circulation, as well as observed epidemiological patterns. We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement to select and analyze relevant articles from the Scopus database, 127 of which were included in the review. Pigs are central, but the implication of secondary hosts cannot be ruled out and should be further investigated. Although human vaccination cannot eradicate the virus, it is clearly the most important means of preventing human disease. However, a better understanding of the actual involvement of domestic pigs as well as other potential JEV hosts in different JEV epidemiological cycles and patterns could help to identify additional/complementary control measures, either by targeting pigs or not, and in some specific epidemiological contexts, contribute to reduce virus circulation and protect humans from JEV infection.

Mortality and Disability Due to Japanese Encephalitis in Elderly Adults: Evidence From an Adult Tertiary Care Center in West China

Japanese encephalitis (JE) is the most important cause of viral encephalitis in Asia, with most cases seen in children <15 years. Recently, cases of JE in people aged >50 years have been increasingly reported, but the clinical presentation in these cases is largely unknown. We report here the first case series of elderly JE patients from an adult tertiary hospital in West China. Medical records of laboratory-confirmed JE patients diagnosed from January 2011 to September 2018 were reviewed retrospectively. Patients were grouped into the elderly (patients > 50 years old) and control groups (patients aged 14-50 years). Data regarding demographics, clinical features, and outcome at discharge were collected. Telephonic follow-up was performed with the survivors in November 2018. Of the 50 patients with laboratory-confirmed JE, 11 were aged >50 years. In the elderly group, all patients had high fever and altered sensorium, and six had symptomatic seizures. Though the key symptoms as well as the cerebrospinal fluid and neuroimaging findings were similar in both groups, the worst Glasgow coma scale score was lower in the elderly group (6.14 ± 2.27 vs. 10.54 ± 3.37, p = 0.001). Compared to the control group, the incidence of acute secondary complications, including respiratory failure requiring mechanical ventilation or tracheotomy (81.82%), hypoalbuminemia (100%), thrombocytopenia (100%), deep venous thrombosis (63.64%), septicemia (36.36%), and upper gastrointestinal bleeding (27.27%) was higher in the elderly. The median modified Rankin scale (mRS) score at discharge was lower in the elderly group than in the control group (5 vs. 3, p = 0.017), with four and two cases of death, respectively. During the average 18-month follow-up, the median mRS score was 5 in the elderly and 2 in the control group (p = 0.001). Patients >50 years old accounted for 22% of JE cases diagnosed in a tertiary adult center, with high mortality rate and long-term disability compared to younger patients. Though no particular findings were found regarding clinical features and investigations in patients >50 years, most needed intensive care. In the future, it is imperative to recognize the importance of JE in adults and to reconsider the vaccination strategy in adult residents of endemic areas, especially for those over 50 years.

Japanese Encephalitis Vaccine: Recommendations of the Advisory Committee on Immunization Practices

This report updates the 2010 recommendations from the CDC Advisory Committee on Immunization Practices (ACIP) regarding prevention of Japanese encephalitis (JE) among U.S. travelers and laboratory workers (Fischer M, Lindsey N, Staples JE, Hills S. Japanese encephalitis vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep 2010;59[No. RR-1]). The report summarizes the epidemiology of JE, describes the JE vaccine that is licensed and available in the United States, and provides recommendations for its use among travelers and laboratory workers.JE virus, a mosquitoborne flavivirus, is the most common vaccine-preventable cause of encephalitis in Asia. JE occurs throughout most of Asia and parts of the western Pacific. Approximately 20%-30% of patients die, and 30%-50% of survivors have neurologic, cognitive, or behavioral sequelae. No antiviral treatment is available.Inactivated Vero cell culture-derived JE vaccine (Ixiaro [JE-VC]) is the only JE vaccine that is licensed and available in the United States. In 2009, the U.S. Food and Drug Administration (FDA) licensed JE-VC for use in persons aged ≥17 years; in 2013, licensure was extended to include children aged ≥2 months.Most travelers to countries where the disease is endemic are at very low risk for JE. However, some travelers are at increased risk for infection on the basis of their travel plans. Factors that increase the risk for JE virus exposure include 1) traveling for a longer period; 2) travel during the JE virus transmission season; 3) spending time in rural areas; 4) participating in extensive outdoor activities; and 5) staying in accommodations without air conditioning, screens, or bed nets. All travelers to countries where JE is endemic should be advised to take precautions to avoid mosquito bites to reduce the risk for JE and other vectorborne diseases. For some persons who might be at increased risk for JE, the vaccine can further reduce the risk for infection. The decision about whether to vaccinate should be individualized and consider the 1) risks related to the specific travel itinerary, 2) likelihood of future travel to countries where JE is endemic, 3) high morbidity and mortality of JE, 4) availability of an effective vaccine, 5) possibility (but low probability) of serious adverse events after vaccination, and 6) the traveler's personal perception and tolerance of risk.JE vaccine is recommended for persons moving to a JE-endemic country to take up residence, longer-term (e.g., ≥1 month) travelers to JE-endemic areas, and frequent travelers to JE-endemic areas. JE vaccine also should be considered for shorter-term (e.g., <1 month) travelers with an increased risk for JE on the basis of planned travel duration, season, location, activities, and accommodations and for travelers to JE-endemic areas who are uncertain about their specific travel duration, destinations, or activities. JE vaccine is not recommended for travelers with very low-risk itineraries, such as shorter-term travel limited to urban areas or outside of a well-defined JE virus transmission season.

Changing Geographic Distribution of Japanese Encephalitis Virus Genotypes, 1935-2017

Japanese encephalitis virus (JEV) is a representative virus of the JEV serogroup in genus Flavivirus, family Flaviviridae. JEV is a mosquito-borne virus that causes Japanese encephalitis (JE), one of the most severe viral encephalitis diseases in the world. JEV is divided into five genotypes (G1-G5), and each genotype has its own distribution pattern. However, the distribution of different JEV genotypes has changed markedly in recent years. JEV G1 has replaced G3 as the dominant genotype in the traditional epidemic areas in Asia, while G3 has spread from Asia to Europe and Africa and caused domestic JE cases in Africa. G2 and G5, which were endemic in Malaysia, exhibited great geographical changes as well. G2 migrated southward and led to prevalence of JE in Australia, while G5 emerged in China and South Korea after decades of silence. Along with these changes, JE occurred in some non-traditional epidemic regions as an emerging infectious disease. The regional changes in JEV pose a great threat to human health, leading to huge disease burdens. Therefore, it is of great importance to strengthen the monitoring of JEV as well as virus genotypes, especially in non-traditional epidemic areas.

Review of the Incidence of Japanese Encephalitis in Foreign-Born and Korean Nationals Living in the Republic of Korea, 2007-2016

The Japanese encephalitis (JE) vaccine was introduced to the national immunization program in 1985, which has led to a dramatic decrease in the number of reported cases, but JE continues to occur in foreign nationals residing in or traveling to Korea. Although the incidence is low, this study demonstrated that more Koreans were infected with JE than foreign-born expatriates. The incidence rates of Korean-born nationals were between 0.01 and 0.08 cases per 100,000. In contrast, the incidence rates of foreign-born nationals ranged between 0 and 0.26 cases per 100,000. The incidence rates clearly showed that foreign-born expatriates were more at risk, which underscores the importance of vaccination. We recommend heightened surveillance among JE-susceptible individuals and promote vaccination among foreign-born nationals living in Korea.

Evolving Epidemiology of Japanese Encephalitis: Implications for Vaccination

PURPOSE OF REVIEW

We examine the present global burden of Japanese encephalitis (JE) in endemic populations, summarize published cases in travelers since 2009, examine current guidelines for vaccination for international travelers, and consider challenges in prevention of this vector-borne disease.

RECENT FINDINGS

We identified 11 JE cases in travelers that were published in peer-reviewed literature since 2009. JE incidence in endemic countries appears to be declining but the number of JE cases reported to the World Health Organization (WHO) varied from estimates derived from other published reports based on serosurveys or sentinel surveillance. Current JE vaccines appear to be safe and are not associated with delayed hypersensitivity in contrast to the older mouse brain vaccine. Given differences between WHO-reported cases and local surveillance data, future research on true incidence is needed. Regular assessment will inform JE risk in travelers. National and international guidelines on JE vaccination varied; we suggest areas for improvement.

Modelling the skip-and-resurgence of Japanese encephalitis epidemics in Hong Kong

Japanese encephalitis virus (JEV) is a zoonotic mosquito-borne virus, persisting in pigs, Ardeid birds and Culex mosquitoes. It is endemic to China and Southeastern Asia. The case-fatality ratio (CFR) or the rate of permanent psychiatric sequelae is 30% among symptomatic patients. There were no reported local JEV human cases between 2006 and 2010 in Hong Kong, but it was followed by a resurgence of cases from 2011 to 2017. The mechanism behind this "skip-and-resurgence" patterns is unclear. This work aims to reveal the mechanism behind the "skip-and-resurgence" patterns using mathematical modelling and likelihood-based inference techniques. We found that pig-to-pig transmission increases the size of JEV epidemics but is unlikely to maintain the same level of transmission among pigs. The disappearance of JEV human cases in 2006-2010 could be explained by a sudden reduction of the population of farm pigs as a result of the implementation of the voluntary "pig-rearing licence surrendering" policy. The resurgence could be explained by of a new strain in 2011, which increased the transmissibility of the virus or the spill-over ratio from reservoir to host or both.

An Outbreak of Japanese Encephalitis in Adults in Northern China, 2013: A Population-Based Study

BACKGROUND

A Japanese encephalitis (JE) epidemic occurred in 2013 in China. The aim of this study was to determine the spatial-temporal pattern of JE cases in adults occurring in 2013, as well as identify potential hotspots of incidences in the afflicted regions in China.

METHODS/PRINCIPAL FINDINGS

To generate a spatial-temporal pattern of JE cases in China, epidemiological and demographic data between 2011 and 2013 were collected. Our results indicate that the total number of JE cases in 2013 was significantly higher compared with those in 2011 and 2012. While the incidence of JE in individuals aged less than 15 years decreased in 2013, the incidence rate increased substantially in those aged 15 years and older. The population aged over 40 years was associated with the greatest increase of JE. Demographic analysis revealed a consistent increase in the proportion of JE cases aged 15 years and older in 2013 (42%) compared with that in 2012 (15%). In addition, JE cases from areas located between 35°N, 114°E and 40°N, 120°E in northern China were found to account for 27.17% of total JE cases nationwide in 2013, compared with 2.21% and 3.13% in 2011 and 2012, respectively. In these northern regions, the group aged 15 years and older represents the predominant population with JE, accounting for 73% of total cases. Further cluster analysis identified a large number of hotspots of JE in adults (>15 years of age) in northern China.

CONCLUSIONS/SIGNIFICANCE

Unlike the JE epidemics primarily in children below 15 years old in southern China, a significant outbreak of JE occurred in northern China in 2013, with the older age groups being the primary population affected. The increasing incidence of JE in adults has become an important public health issue and poses a new challenge to the successful prevention and control of JE in China, as well as other countries in East Asia.

Clinical Characteristics of Severe Japanese Encephalitis: A Case Series from South Korea

Japanese encephalitis (JE) virus is a major cause of devastating viral encephalitis, especially in Asia. Although a successful vaccination program led to its near-elimination over three decades in South Korea, the incidence of JE has increased since 2010. The present study investigated the clinical manifestations, laboratory findings, and factors affecting neurological outcomes of reemerging JE. We retrospectively reviewed medical records of laboratory-confirmed JE patients who presented with acute encephalitis syndrome at three tertiary hospitals between 2010 and 2015. A total of 17 patients with JE were identified. Their median age was 51 years, and 10 (58.5%) were men. The most common symptoms and signs were fever (94.1%), altered consciousness (94.1%), and headache (80.2%). Hyporeflexia (47.1%), seizures (35.2%), abnormal brainstem reflex (23.5%), and flaccid weakness (17.6%) were also noted. Brain imaging revealed thalamic lesions in all patients, with the hippocampus, midbrain, basal ganglia, and cerebral cortex affected to varying degrees. Sixteen patients (94.1%) required management in the intensive care unit with mechanical ventilation due to neurological deterioration. At the time of discharge, 11 (64.7%) had poor recovery, defined as Glasgow coma scale scores of less than 8, and remained ventilator dependent. Comparison between the two outcome groups indicated that midbrain involvement (P = 0.028) and rapid deterioration (P = 0.005) were associated with severe neurological sequelae. Given that JE is a vaccine-preventable disease, vaccination for adults should be considered in response to the reemergence of JE.