Differential Diagnosis of Japanese Encephalitis Virus Infections with the Inbios JE Detect™ and DEN Detect™ MAC-ELISA Kits

Japanese encephalitis genotype I virus-like particles stably expressed in BHK-21 cells serves as potential antigen in JE IgM ELISA

Abstract

Japanese encephalitis virus (JEV) is one of the leading causes of epidemic encephalitis in South Asian countries. Due to the short-term viremia, detecting IgM antibodies by ELISA is treated as the front-line diagnostic assay. Co-circulation and multiple exposures to antigenically cross-reactive flaviviruses in India pose a challenge in serodiagnosis. Replacing the whole virus antigen currently used in the JE IgM detection kits (ELISA) may improve the specificity and sensitivity of the existing JE MAC ELISA kits. For this purpose, we developed a stably transfected cell clone, BHK-IE6, which expresses a high amount of VLPs up to 37 µg/ml and is consistent in expression up to 40 passages. For the expression of VLPs in the secretory form, we cloned the JEV G-I prM-E coding gene along with the C-terminal signal sequence of capsid protein in the BHK-21 cells using the pcDNA3.1 + mammalian expression vector. The immune assays performed demonstrated its immune reactivity equivalent to the parental JEV strain. Simultaneously performed ELISAs using the whole virus antigen and newly developed antigen gave comparable results for JE positive and negative samples, which established the utility of developed JEV E-VLP as an antigen. Reduced cross-reactivity and increased specificity were observed when tested with dual positive sera for anti-JEV and DENV antibodies. These findings confirm the efficiency and reliability of newly developed recombinant E-VLP antigen expressed by the BHK-IE6 cell clone as an antigen in serodiagnostic assays. The implementation and progress in developing cross-reactivity-reduced antigens would improve serodiagnosis and disease burden estimates of flavivirus infection.

Key points

• pcDNA3.1/JE-Sig-prM-E plasmid transfected BHK-21 cells stably express VLPs.

• Sodium butyrate induction enhanced the extracellular expression of VLPs.

• Application of JEV-E VLPs increases the specificity of JE IgM ELISA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11825-1.

Aptamers isolated against mosquito-borne pathogens

Mosquito-borne diseases are a major threat to public health. The shortcomings of diagnostic tools, especially those that are antibody-based, have been blamed in part for the rising annual morbidity and mortality caused by these diseases. Antibodies harbor a number of disadvantages that can be clearly addressed by aptamers as the more promising molecular recognition elements. Aptamers are defined as single-stranded DNA or RNA oligonucleotides generated by SELEX that exhibit high binding affinity and specificity against a wide variety of target molecules based on their unique structural conformations. A number of aptamers were developed against mosquito-borne pathogens such as Dengue virus, Zika virus, Chikungunya virus, Plasmodium parasite, Francisella tularensis, Japanese encephalitis virus, Venezuelan equine encephalitis virus, Rift Valley fever virus and Yellow fever virus. Intrigued by these achievements, we carry out a comprehensive overview of the aptamers developed against these mosquito-borne infectious agents. Characteristics of the aptamers and their roles in diagnostic, therapeutic as well as other applications are emphasized.

Japanese Encephalitis Virus as Cause of Acute Encephalitis, Bhutan

In 2011, Bhutan's Royal Centre for Disease Control began Japanese encephalitis (JE) surveillance at 5 sentinel hospitals throughout Bhutan. During 2011-2018, a total of 20 JE cases were detected, indicating JE virus causes encephalitis in Bhutan. Maintaining JE surveillance will help improve understanding of JE epidemiology in this country.

The future of Japanese encephalitis vaccination: expert recommendations for achieving and maintaining optimal JE control

Vaccines against Japanese encephalitis (JE) have been available for decades. Currently, most JE-endemic countries have vaccination programs for their at-risk populations. Even so, JE remains the leading recognized cause of viral encephalitis in Asia. In 2018, the U.S. Centers for Disease Control and Prevention and PATH co-convened a group of independent experts to review JE prevention and control successes, identify remaining scientific and operational issues that need to be addressed, discuss opportunities to further strengthen JE vaccination programs, and identify strategies and solutions to ensure sustainability of JE control during the next decade. This paper summarizes the key discussion points and recommendations to sustain and expand JE control.

Rapid and simultaneous detection of Japanese encephalitis virus by real-time nucleic acid sequence-based amplification

Japaneses encephalitis (JE) is most common zoonoses caused by Japanese encephalitis virus (JEV) with a high mortality and disability rate. To take timely preventive and control measures, early and rapid detection of JE RNA is necessary. But due to characteristic brief and low viraemia, JE RNA detection remains challenging. In this study, a real-time nucleic acid sequence-based amplification (RT-NASBA) was developed for rapid and simultaneous detection of JEV. Four pairs of primer were designed using a multiple genome alignment of all JEV strains from GenBank. NASBA assay established and optimal reaction conditions were confirmed by using primers and probe on ns1 gene of JEV. The specificity and sensitivity of the assay were compared with RT-PCR by using serial RNA and virus cultivation dilutions. The results showed that JEV RT-NASBA assay was established, and robust signals could be observed in 10 min with high specificity. The limit of dectetion of RT-NASBA was 6 copies per reaction. The assay was thus 100 to 1, 000 times more sensitive than RT-PCR. The cross-reaction was performed with other porcine pathogens, and negative amplification results indicated the high specificity of this method. The novel JEV RT-NASBA assay could be used as an efficient molecular biology tool to diagnose JEV, which would facilitate the surveillance of reproductive failure disease in swine and would be beneficial for public health security.

Persistence of IgM Antibodies after Vaccination with Live Attenuated Japanese Encephalitis Vaccine

Japanese encephalitis (JE) is a vaccine-preventable, mosquito-borne disease. Substantial progress with JE control in Asia has been made during the past decade, with most endemic countries now having JE vaccination programs, commonly using live attenuated SA14-14-2 JE vaccine (trade name CD-JEV). If a child develops encephalitis during the weeks to months following CD-JEV vaccination and anti-JE virus IgM (JE IgM) antibody is detected in serum, the question arises if this is JE virus infection indicating vaccine failure, or persistent JE IgM antibody postvaccination. To better understand JE IgM seropositivity following vaccination, sera from 268 children from a previous CD-JEV study were tested by two different JE IgM assays to determine JE IgM antibody frequency on days 28, 180, and 365 postvaccination. With the CDC JE IgM antibody capture ELISA (MAC-ELISA), 110 children (41%) had JE IgM positive or equivocal results on their day 28 sample, and eight (3%) and two (1%) had positive or equivocal results on day 180 and day 365 samples, respectively. With the InBios JE Detect™ MAC-ELISA (Seattle, WA), 118 (44%) children had positive or equivocal results on day 28 sample, and three (1%) and one (0.4%) had positive or equivocal results on day 180 and day 365 samples, respectively. Our results indicate that more than 40% children vaccinated with CD-JEV can have JE IgM antibodies in their serum at 1 month postvaccination but JE IgM antibody is rare by 6 months. These data will help healthcare workers assess the likelihood that JE IgM antibodies in the serum of a child with encephalitis after vaccination are vaccine related.

A recombinant platform for flavivirus vaccines and diagnostics using chimeras of a new insect-specific virus

Flaviviruses such as dengue, yellow fever, Zika, West Nile, and Japanese encephalitis virus present substantial global health burdens. New vaccines are being sought to address safety and manufacturing issues associated with current live attenuated vaccines. Here, we describe a new insect-specific flavivirus, Binjari virus, which was found to be remarkably tolerant for exchange of its structural protein genes (prME) with those of the aforementioned pathogenic vertebrate-infecting flaviviruses (VIFs). Chimeric BinJ/VIF-prME viruses remained replication defective in vertebrate cells but replicated with high efficiency in mosquito cells. Cryo-electron microscopy and monoclonal antibody binding studies illustrated that the chimeric BinJ/VIF-prME virus particles were structurally and immunologically similar to their parental VIFs. Pilot manufacturing in C6/36 cells suggests that high yields can be reached up to 10^9.5 cell culture infectious dose/ml or ≈7 mg/liter. BinJ/VIF-prME viruses showed utility in diagnostic (microsphere immunoassays and ELISAs using panels of human and equine sera) and vaccine applications (illustrating protection against Zika virus challenge in murine IFNAR^-/- mouse models). BinJ/VIF-prME viruses thus represent a versatile, noninfectious (for vertebrate cells), high-yield technology for generating chimeric flavivirus particles with low biocontainment requirements.

Hospital-based surveillance for Japanese encephalitis in Bangladesh, 2007-2016: Implications for introduction of immunization

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Japanese encephalitis (JE) is largely preventable through vaccination.

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Several JE vaccines prequalified by World Health Organization are available.

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Hospital-based surveillance were conducted in Bangladesh to describe JE epidemiology.

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JE cases were identified each year, among all age groups, and from a widespread geographical area.

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Routine childhood immunization program or mass vaccination need to be examined.

Background

Japanese encephalitis (JE) virus is recognized as a major cause of encephalitis in Bangladesh. The World Health Organization (WHO) recommends human immunization as the most effective means to control JE. Several WHO-prequalified vaccines are available to prevent JE but no vaccination program has been implemented in Bangladesh.

Methods

We conducted hospital-based surveillance for acute meningitis-encephalitis syndrome (AMES) to describe JE epidemiology and help inform policy decisions about possible immunization strategies for Bangladesh.

Results

During 2007–2016, a total of 6543 AMES patients were identified at four tertiary hospitals. Of the 6525 patients tested, 548 (8%) were classified as JE cases. These 548 patients resided in 36 (56%) out of 64 districts of Bangladesh, with the highest proportion of JE cases among AMES patients (12% and 7%) presenting at two hospitals in the northwestern part of the country. The median age of JE cases was 30 years, and 193 (35%) were aged ≤15 years. The majority of JE cases (80%) were identified from July through November.

Conclusions

Surveillance results suggest that JE continues to be an important cause of meningo-encephalitis in Bangladesh. Immunization strategies including JE vaccine introduction into the routine childhood immunization program or mass vaccination in certain age groups or geographic areas need to be examined, taking into consideration the cost-effectiveness ratio of the approach and potential for decreasing disease burden.

Investigation of Japanese encephalitis virus as a cause of acute encephalitis in southern Pakistan, April 2015-January 2018

Background

Japanese encephalitis (JE) occurs in fewer than 1% of JE virus (JEV) infections, often with catastrophic sequelae including death and neuropsychiatric disability. JEV transmission in Pakistan was documented in 1980s and 1990s, but recent evidence is lacking. Our objective was to investigate JEV as a cause of acute encephalitis in Pakistan.

Methods

Persons aged ≥1 month with possible JE admitted to two acute care hospitals in Karachi, Pakistan from April 2015 to January 2018 were enrolled. Cerebrospinal fluid (CSF) or serum samples were tested for JEV immunoglobulin M (IgM) using the InBios JE Detect^TM assay. Positive or equivocal samples had confirmatory testing using plaque reduction neutralization tests.

Results

Among 227 patients, testing was performed on CSF in 174 (77%) and on serum in 53 (23%) patients. Six of eight patient samples positive or equivocal for JEV IgM had sufficient volume for confirmatory testing. One patient had evidence of recent West Nile virus (WNV) neurologic infection based on CSF testing. One patient each had recent dengue virus (DENV) infection and WNV infection based on serum results. Recent flavivirus infections were identified in two persons, one each based on CSF and serum results. Specific flaviviruses could not be identified due to serologic cross-reactivity. For the sixth person, JEV neutralizing antibodies were confirmed in CSF but there was insufficient volume for further testing.

Conclusions

Hospital-based JE surveillance in Karachi, Pakistan could not confirm or exclude local JEV transmission. Nonetheless, Pakistan remains at risk for JE due to presence of the mosquito vector, amplifying hosts, and rice irrigation. Laboratory surveillance for JE should continue among persons with acute encephalitis. However, in view of serological cross-reactivity, confirmatory testing of JE IgM positive samples at a reference laboratory is essential.

Serological Diagnosis of Flavivirus-Associated Human Infections

Arthropod-borne viruses (arboviruses) belonging to the Flavivirus genus of the Flaviviridae family, are a major public health threat in tropical and subtropical regions, and have recently become a medical concern in temperate zones. Most flaviviruses are classified as zoonotic viruses. Human flavivirus infections can be asymptomatic, responsible for unspecific symptoms in the first few days following infection, or responsible for severe complications potentially resulting in death. During the first days following symptom onset, laboratory diagnosis of acute human flavivirus infection is mainly based on molecular detection of the viral genome by RT-PCR methods, followed by the capture of specific antibodies using serological tests after the first week of infection. The detection of antibodies that have virus neutralizing activity can be used to confirm flavivirus infection. However, human flavivirus infections induce the production of cross-reactive antibodies, often making serology inconclusive. Indeed, serological diagnosis of flavivirus infection can be hampered by a patient's history of flavivirus exposure, particularly in regions where multiple antigenically related flaviviruses co-circulate. We focus our mini review on conventional immunoassays that allow the diagnosis of major flavivirus-associated human infections in basic, routine and high-profile central health centers; and the interpretation of diagnostic serology tests for patients living within different epidemiological situations.

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.

Multiepitope Subunit Vaccine to Evoke Immune Response against Acute Encephalitis

Acute encephalitis syndrome outbreak has emerged as a major health concern on both national and international scales. Brain inflammation/infections caused by Japanese encephalitis virus (JEV) can lead to death. The cases are growing in numbers globally, and this emergent health concern requires an effective and viable vaccine to strengthen the body's immune system against this deadly virus. Proteomic analyses of JEV revealed the envelope protein as a potential target for vaccine development by patient samples analysis. Hence, in this study, we aimed to design a multiepitope subunit vaccine for acute encephalitis using the advanced structural biology and immunoinformatics approaches. We report the multiepitope subunit vaccine consisted of the putative T-cell epitope (MHC-1 and MHC-2 restricted) and B-cell epitope and with high antigenicity and immunogenicity. The TAP affinity epitopes along with adjuvants were engineered to the vaccine, to ensure the ease transportation inside the host and elicitation of a strong immune response. The specificity of vaccine construct was evaluated by molecular docking with major histocompatibility complex (MHC) receptors and host membrane receptor TLR2. High docking scores and a close interaction to the binding groove of receptors confirmed the potency and specificity of the vaccine. Also, molecular dynamics simulation studies confirmed the stable interaction of vaccine with TLR2 for a long run (100 ns), which showed the prolonged elicitation of the strong immune response. Peptide dynamics studies showed the flexible, strong, and stable binding of vaccine with minimal deviation in root-mean-square deviation (RMSD), root-mean-square fluctuation (RMSF), and secondary structure estimation (SSE) plots till 100 ns simulation run. The in silico immune simulation approach based on the position-specific scoring matrix and machine learning methods resulted in the strong immune response reinforcement statistics of immune cells (T-cells, B-cells population, and memory cells) in response to vaccine candidate. The favorable results and well-correlated data of varied in silico techniques paved for a potent multiepitope vaccine and helped us to propose the mechanism of action of designed vaccine and generation of the immune response against acute encephalitis syndrome.

Rift Valley Fever Virus, Japanese Encephalitis Virus, and African Swine Fever Virus: Three Transboundary, Vector-Borne, Veterinary Biothreats With Diverse Surveillance, and Response Capacity Needs

Early detection of emerging foreign animal diseases is critical to pathogen surveillance and control programs. Rift valley fever virus (RVFV), Japanese encephalitis virus (JEV), and African swine fever virus (ASFV) represent three taxonomically and ecologically diverse vector-borne viruses with the potential to be introduced to the United States. To promote preparedness for such an event, we reviewed the current surveillance strategies and diagnostic tools in practice around the world for these emerging viruses, and summarized key points pertaining to the availability of existing guidelines and strategic approaches for early detection, surveillance, and disease management activities. We compare and contrast the surveillance and management approaches of these three diverse agents of disease as case studies to emphasize the importance of the ecological context and biology of vectors and vertebrate hosts. The information presented in this review will inform stakeholders of the current state of surveillance approaches against these transboundary foreign animal disease which threaten the United States.

Review of Emerging Japanese Encephalitis Virus: New Aspects and Concepts about Entry into the Brain and Inter-Cellular Spreading

Japanese encephalitis virus (JEV) is an emerging flavivirus of the Asia-Pacific region. More than two billion people live in endemic or epidemic areas and are at risk of infection. Recently, the first autochthonous human case was recorded in Africa, and infected birds have been found in Europe. JEV may spread even further to other continents. The first section of this review covers established and new information about the epidemiology of JEV. The subsequent sections focus on the impact of JEV on humans, including the natural course and immunity. Furthermore, new concepts are discussed about JEV’s entry into the brain. Finally, interactions of JEV and host cells are covered, as well as how JEV may spread in the body through latently infected immune cells and cell-to-cell transmission of virions or via other infectious material, including JEV genomic RNA.

Viral RNA Degradation Makes Urine a Challenging Specimen for Detection of Japanese Encephalitis Virus in Patients With Suspected CNS Infection

Background

Japanese encephalitis virus (JEV) is a leading cause of central nervous system (CNS) infections in Asia and results in significant morbidity and mortality. JEV RNA is rarely detected in serum or cerebrospinal fluid (CSF), and diagnosis of JEV infection is usually based on serological tests that are frequently difficult to interpret. Unlike serum or CSF, urine is relatively easy to obtain, but, to date, there has been minimal work on the feasibility of testing urine for JEV RNA.

Methods

We investigated the use of lysis buffer and a Microsep device to optimize urine storage for detection of JEV RNA by reverse transcription real-time polymerase chain reaction (RT-qPCR). The best of the studied methods was then evaluated in consecutive patients admitted to the hospital with suspected CNS infections in Laos.

Results

We demonstrated degradation of JEV RNA in urine after even short storage periods at 4°C or –80°C. Although there was no advantage in using a Microsep concentration device alone, immediate addition of lysis buffer to fresh urine improved the detection of JEV RNA at the limit of detection.

Conclusions

In 2 studies of 41 patients with acute encephalitis syndrome, 11 (27%) were positive for JEV IgM in CSF and/or serum, and 2 (4.9%) were JEV RT-qPCR positive from throat swabs. JEV RNA was not detected in any of these patients’ urine samples. However, lysis buffer was only used during a prospective study, that is, for only 17/41 (41%) patient urine samples. Our findings suggest a need for larger studies testing urine for JEV RNA, with urine collected at different times from symptom onset, and using lysis buffer, which stabilizes RNA, for storage.

Development of an improved RT-qPCR Assay for detection of Japanese encephalitis virus (JEV) RNA including a systematic review and comprehensive comparison with published methods

BACKGROUND

Japanese encephalitis virus (JEV) is a major cause of encephalitis in Asia, and the commonest cause of mosquito-borne encephalitis worldwide. Detection of JEV RNA remains challenging due to the characteristic brief and low viraemia, with 0-25% of patients positive, and the mainstay of diagnosis remains detection of anti-JEV IgM antibody.

METHODS

We performed a systematic review of published RT-PCR protocols, and evaluated them in silico and in vitro alongside new primers and probes designed using a multiple genome alignment of all JEV strains >9,000nt from GenBank, downloaded from the NCBI website (November 2016). The new assays included pan-genotype and genotype specific assays targeting genotypes 1 and 3.

RESULTS

Ten RT-qPCR assays were compared, a pre-existing in-house assay, three published assays and six newly designed assays, using serial RNA dilutions. We selected three assays, one published and two novel assays, with the lowest limit of detection (LOD) for further optimisation and validation. One of the novel assays, detecting NS2A, showed the best results, with LOD approximately 4 copies/ reaction, and no cross-reaction on testing closely related viruses in the JEV serocomplex, West Nile Virus and St. Louis Virus. The optimised assays were validated in consecutive patients with central nervous system infections admitted to hospitals in Laos, testing paired CSF and serum samples.

CONCLUSIONS

We succeeded in developing a JEV specific RT-qPCR assay with at least 1 log10 improved sensitivity as compared to existing assays. Further evaluation is required, field-testing the assay in a larger group of patients.

The aetiologies of central nervous system infections in hospitalised Cambodian children

BACKGROUND

Central nervous system (CNS) infections are an important cause of childhood morbidity and mortality. The aetiologies of these potentially vaccine-preventable infections have not been well established in Cambodia.

METHODS

We did a one year prospective study of children hospitalised with suspected CNS infection at Angkor Hospital for Children, Siem Reap. Cerebrospinal fluid specimens (CSF) samples underwent culture, multiplex PCR and serological analysis to identify a range of bacterial and viral pathogens. Viral metagenomics was performed on a subset of pathogen negative specimens.

RESULTS

Between 1st October 2014 and 30th September 2015, 284 analysable patients were enrolled. The median patient age was 2.6 years; 62.0% were aged <5 years. CSF white blood cell count was ≥10 cells/μL in 116/272 (42.6%) cases. CNS infection was microbiologically confirmed in 55 children (19.3%). Enteroviruses (21/55), Japanese encephalitis virus (17/55), and Streptococcus pneumoniae (7/55) accounted for 45 (81.8%) of all pathogens identified. Of the pathogens detected, 74.5% (41/55) were viruses and 23.6% (13/55) were bacteria. The majority of patients were treated with ceftriaxone empirically. The case fatality rate was 2.5%.

CONCLUSIONS

Enteroviruses, JEV and S. pneumoniae are the most frequently detected causes of CNS infection in hospitalised Cambodian children.

Towards Multiplex Molecular Diagnosis-A Review of Microfluidic Genomics Technologies

Highly sensitive and specific pathogen diagnosis is essential for correct and timely treatment of infectious diseases, especially virulent strains, in people. Point-of-care pathogen diagnosis can be a tremendous help in managing disease outbreaks as well as in routine healthcare settings. Infectious pathogens can be identified with high specificity using molecular methods. A plethora of microfluidic innovations in recent years have now made it increasingly feasible to develop portable, robust, accurate, and sensitive genomic diagnostic devices for deployment at the point of care. However, improving processing time, multiplexed detection, sensitivity and limit of detection, specificity, and ease of deployment in resource-limited settings are ongoing challenges. This review outlines recent techniques in microfluidic genomic diagnosis and devices with a focus on integrating them into a lab on a chip that will lead towards the development of multiplexed point-of-care devices of high sensitivity and specificity.

Epidemiological Features of Japanese Encephalitis in Taiwan from 2000 to 2014

The incidence of Japanese encephalitis (JE) decreased sharply after the national vaccination program was implemented in Taiwan in 1968. However, cases of JE still occur. The purpose of this study was to assess the epidemiology and vaccination policy for JE in Taiwan. We analyzed the data on JE cases reported to the Taiwan Centers for Disease Control (Taiwan CDC) between 2000 and 2014. During the 15-year study period, a total of 4,474 cases were reported to the Taiwan CDC. Of these, 379 (8.5%) were classified as confirmed cases, and 4,095 (91.5%) were classified as suspected cases. The incidence of JE ranged from 0.59 to 1.61 per 1,000,000 people and peaked in 2007. Men had a higher incidence of JE than women (1.37 versus 0.84 per 1,000,000; P = 0.03). Patients who were 40-59 years of age had a higher incidence than did patients younger than 20 years (1.82 versus 0.23; P < 0.001). Patients who lived in the eastern region of Taiwan had the highest incidence rate of JE (P < 0.001). Compared with those who were not vaccinated with the JE vaccine, patients who received four doses of JE vaccine had a lower risk of suffering from death and/or hospitalization (adjusted odds ratio: 0.26; 95% confidence interval: 0.08-0.90; P = 0.04). JE is still a public health problem in Taiwan, and monitoring JE via diagnostic testing to determine the best vaccination program along with enforcing JE vaccine boosters for adults is necessary to eliminate JE in Taiwan.