Japanese Encephalitis among Adults: A Review

Novel envelope protein time-resolved fluoroimmunoassay as an alternative in vitro potency assay for quality control of inactivated Japanese encephalitis virus vaccine

Japanese encephalitis (JE) vaccination is the most effective way to prevent JE. Plaque reduction neutralization test (PRNT) as the standard method for potency testing for inactivated JE vaccine could not provide the exact potency value. Envelope (E) protein of JE virus induces the body to create neutralizing antibodies. There is a potential for using the determination of E protein to assess the immunogenicity and efficacy of JE vaccine. In this study, an automatic time-resolved fluoroimmunoassay for detection of E protein in JE vaccine was established as a simple and rapid in vitro potency assay to complement PRNT, including the expression and paired screening of monoclonal antibodies, the establishment of assay method and performance verification. A pair of anti-E protein neutralizing antibodies (L022 and L034) were screened to construct the sandwich detection pattern. After pre-treating the vaccine sample, the entire analysis was performed using a fully automated machine, which had a little detection time and eliminated manual error. The results of the validation experiment met the requirements for quality control. The linear range was from 0.78125 U/mL to 25 U/mL, the sensitivity was 0.01 U/mL, the intra-assay coefficient of variation was less than 5 %, and the inter-assay coefficient of variation was less than 10 %. The recovery from the dilution was between 90 % and 110 %. This present TRFIA shown good stability and effectiveness in quality control for samples related to JE vaccine production. The outcomes demonstrated that the present TRFIA could be an alternative in vitro potency assay in quality control for inactivated JE vaccine.

The seroprevalence of antibodies to Japanese encephalitis virus in five New South Wales towns at high risk of infection, 2022: a cross-sectional serosurvey

OBJECTIVES

To determine the proportion of people in New South Wales towns at high risk of Japanese encephalitis virus (JEV) infections during the 2022 outbreak; to identify risk factors for JEV infection.

STUDY DESIGN

Cross-sectional serosurvey study of the seroprevalence of JEV-specific antibodies in NSW.

SETTING, PARTICIPANTS

Convenience sample of people (all ages) from five regional NSW towns deemed to be at high risk of JEV infections after first outbreak of Japanese encephalitis in southeastern Australia in early 2022 (Balranald, Corowa, Dubbo, Griffith, Temora), 21 June - 22 July 2022.

MAIN OUTCOME MEASURES

Proportion of people seropositive for JEV total antibody, assayed by defined epitope-blocking enzyme-linked immunosorbent assay; prevalence odds ratios for exposure risk factors and protective behaviours.

RESULTS

Eighty of 917 eligible participants (559 girls or women, 61%; 42 Aboriginal and Torres Strait Islander people, 4.6%; median age, 52 years [IQR, 37-62 years]) were seropositive for JEV-specific total antibody (8.7%); the median age of seropositive people was 61 years (IQR, 48-70 years). The seropositivity proportion was largest for people aged 65 years or more (30 of 192; weighted proportion, 13.7%) and larger for male than female participants (30 of 358, 10.6% v 50 of 559, 7.5%). Five of 42 samples from Aboriginal and Torres Strait Islander participants were seropositive (12%). We found mixed associations with a range of potential risk factors.

CONCLUSION

We found evidence for a substantial number of JEV infections in five regional NSW towns during a single arbovirus season in 2022. Public health responses, including effective surveillance, vaccination against JEV, and mosquito management, are critical for controlling outbreaks. Promoting behaviours that reduce exposure to mosquitoes is a core component of prevention, particularly when the vaccine supply is limited.

Japanese Encephalitis Outbreak in Young Adults of Bastar District in Chhattisgarh: A Short Observational Study

Background Instant infections in children due to acute encephalitis syndrome (AES) were reported in a tribal district of Bastar in Chattisgarh, India, between August 2018 and August 2019. Objective The study was conducted to explore the possibility of a viral cause indicating an outbreak. Methods Clinical surveys and serological investigation tests were conducted to identify the viral etiology. The Bastar area in Chhattisgarh reported factors such as paddy fields near homes, a high pig-to-cattle ratio, a significant presence of Culex vishnui mosquitoes, low socioeconomic status, and a lack of health awareness among the tribal people. Result This study, conducted at the Late Baliram Kashyap Memorial Government Medical College in Jagdalpur, Bastar, Chhattisgarh, India, analyzed 128 samples from fever cases out of 213 patients visiting the Japanese encephalitis virus (JEV) testing center. Among these samples, 71 cases exhibited AES, and subsequent JEV IgM ELISA testing identified 18 cases as JEV-positive, signifying recent JEV infections. Notably, the overwhelming majority (94.44%) of JEV-positive patients were under 16 years old, highlighting the heightened vulnerability of children to JEV illness in the Bastar region. Although male patients accounted for 61.11% of the JEV-positive cases compared to 38.88% of female patients, statistical analysis revealed that this gender disparity was not statistically significant (p-value = 0.18). Conclusion The study emphasizes the significance of identifying the etiology and delivering evidence-based care to patients with AES. Improved diagnosis and management of AES may result from a greater comprehension of the advantages and disadvantages associated with the application and administration of common laboratory and diagnostic algorithms.

The spatiotemporal distribution and prognostic factors of Japanese encephalitis in Shanxi Province, China, 2005-2022

Japanese encephalitis (JE) is a naturally occurring localized disease caused by the Japanese encephalitis virus, which is spread by the Culex tritaeniorhynchus. China has a high rate of JE. Shanxi, located in North China, has a high prevalence of adult JE. Adult JE has more severe complications, mortality, and a higher disease burden, making it a public health issue. This retrospective study examined the dynamic epidemic changes, high-risk areas of JE, and clinical characteristics and prognostic factors of adult JE in Shanxi Province. The findings revealed that July to September was the primary epidemic season of JE and that JE cases were mainly in individuals over the age of 40. The incidence of JE from 2005 to 2022 demonstrated a positive spatial correlation with significant clustering characteristics, with high-incidence clusters in the south and southeast. Multivariate logistic regression analysis revealed that higher cerebrospinal fluid pressure, higher white blood cell counts, higher neutrophil percentage, deep coma, and lower albumin were independent factors for poor prognosis of adult JE. The developed risk prediction model holds great promise in early prognosis assessment of patients, providing a basis for clinical decision-making and early clinical intervention.

Ocular Manifestations of Flavivirus Infections

Flaviviruses are a group of positive-sense, single-stranded RNA viruses predominantly transmitted by arthropods (mainly mosquitoes) that cause severe endemic infections and epidemics on a global scale. They represent a major cause of systemic morbidity and death and are expanding worldwide. Among this group, dengue fever, the West Nile virus, yellow fever, Japanese Encephalitis, and, recently, the Zika virus have been linked to a spectrum of ocular manifestations. These manifestations encompass subconjunctival hemorrhages and conjunctivitis, anterior and posterior uveitis (inclusive of vitritis, chorioretinitis, and retinal vasculitis), maculopathy, retinal hemorrhages, and optic neuritis. Clinical diagnosis of these infectious diseases is primarily based on epidemiological data, history, systemic symptoms and signs, and the pattern of ocular involvement. Diagnosis confirmation relies on laboratory testing, including RT-PCR and serological testing. Ocular involvement typically follows a self-limited course but can result in irreversible visual impairment. Effective treatments of flavivirus infections are currently unavailable. Prevention remains the mainstay for arthropod vector and zoonotic disease control. Effective vaccines are available only for the yellow fever virus, dengue virus, and Japanese Encephalitis virus. This review comprehensively summarizes the current knowledge regarding the ophthalmic manifestations of the foremost flavivirus-associated human diseases.

A decision support tool for risk-benefit analysis of Japanese encephalitis vaccine in travellers

BACKGROUND

During pre-travel consultations, clinicians and travellers face the challenge of weighing the risks verus benefits of Japanese encephalitis (JE) vaccination due to the high cost of the vaccine, low incidence in travellers (~1 in 1 million), but potentially severe consequences (~30% case-fatality rate). Personalised JE risk assessment based on the travellers' demographics and travel itinerary is challenging using standard risk matrices. We developed an interactive digital tool to estimate risks of JE infection and severe health outcomes under different scenarios to facilitate shared decision-making between clinicians and travellers.

METHODS

A Bayesian network (conditional probability) model risk-benefit analysis of JE vaccine in travellers was developed. The model considers travellers' characteristics (age, sex, co-morbidities), itinerary (destination, departure date, duration, setting of planned activities) and vaccination status to estimate the risks of JE infection, the development of symptomatic disease (meningitis, encephalitis), clinical outcomes (hospital admission, chronic neurological complications, death) and adverse events following immunization.

RESULTS

In low-risk travellers (e.g. to urban areas for <1 month), the risk of developing JE and dying is low (<1 per million) irrespective of the destination; thus, the potential impact of JE vaccination in reducing the risk of clinical outcomes is limited. In high-risk travellers (e.g. to rural areas in high JE incidence destinations for >2 months), the risk of developing symptomatic disease and mortality is estimated at 9.5 and 1.4 per million, respectively. JE vaccination in this group would significantly reduce the risk of symptomatic disease and mortality (by ~80%) to 1.9 and 0.3 per million, respectively.

CONCLUSION

The JE tool may assist decision-making by travellers and clinicians and could increase JE vaccine uptake. The tool will be updated as additional evidence becomes available. Future work needs to evaluate the usability of the tool. The interactive, scenario-based, personalised JE vaccine risk-benefit tool is freely available on www.VaxiCal.com.

The reemerging and outbreak of genotypes 4 and 5 of Japanese encephalitis virus

The Japanese encephalitis virus (JEV) is classified into five distinct genotypes, with genotypes 1 and 3 historically showing higher activity. These genotypes are the primary agents of viral encephalitis in the Asian continent. Genotypes 4 and 5 have remained silent in low-latitude tropical regions since their discovery. From 2009, the hidden genotype 5 suddenly emerged simultaneously in mosquitoes from the Tibetan region of China and those from South Korea in East Asia. The detection of genotype 5 of JEV in these mosquitoes was associated with cases of viral encephalitis in the local population. Similarly, in 2022, the long-silent genotype 4 of JEV emerged in Australia, resulting in a local outbreak of viral encephalitis that primarily affected adults and caused fatalities. The emergence and outbreaks of genotypes 4 and 5 of JEV present new challenges for the prevention and control of Japanese encephalitis (JE). This study not only analyzes the recent emergence of these new genotypes but also discusses their implications in the development of JE vaccines and laboratory tests for newly emerging JEV infections.

A case of new onset refractory status epilepticus in a U.S. traveler with Japanese encephalitis

New onset refractory status epilepticus (NORSE) is a rare but critical condition characterized by refractory status epilepticus (RSE) in an individual without prior history of epilepsy or known structural, toxic, or metabolic cause. Postinfectious immune activation is an important cause of NORSE. Early testing for autoimmune antibodies is strongly recommended (Wickstrom et al., 2022). We report a case of NORSE triggered by Japanese encephalitis (JE) in an unvaccinated US adult traveler. Her CSF later revealed positive anti-N-methyl-d-aspartate (NMDA)-receptor antibody. The patient responded well to first line immunotherapy with favorable functional outcome. This case highlights the diagnostic and treatment challenges in this rare presentation.