DEMELE-JEV (ANRS 0629s): Prospective Cohort Study Protocol to Assess Japanese Encephalitis Burden, Virological Diagnosis, and Clinical Outcomes in Cambodian Children (Preprint)

BACKGROUND Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in Asia and remains a major pediatric threat in Cambodia despite vaccine introduction. However, diagnosis and surveillance are still constrained in routine care. Integrating modern multiplex diagnostics and longitudinal cohorts could clarify the true burden, drivers of transmission, and predictors of severe outcomes to inform prevention and care. OBJECTIVE Primary objectives are (1) to quantify asymptomatic JEV circulation among community children and (2) to describe the clinical burden and outcomes of JEV in children hospitalized with febrile neurological syndrome (FNS). Secondary aims include estimating age-specific anti-JEV seropositivity, identifying individual, environmental, and immunological risk factors for infection and severity, characterizing interactions between pre-existing dengue immunity and JEV, evaluating novel diagnostic tools, and strengthening national surveillance METHODS DEMELE-JEV is a prospective, observational cohort study conducted at Kantha Bopha Children’s Hospital (Phnom Penh) and Jayavarman VII Children’s Hospital (Siem Reap). We recruit two groups of children aged 2–14 years: (i) 2000 non-febrile attendees (Cohort 1) followed at 12 and 24 months to estimate JEV incidence via clinical episode or seroconversion; and (ii) 2000 FNS inpatients of whom ~600 with confirmed JEV are included in Cohort 2 and are followed at 1, 3, 6, and 12 months to assess sequelae and severity (death or severe neurological impairment). Diagnostic work-up includes QIAstat-Dx meningitis/encephalitis panel on CSF, targeted RT-PCRs for regional pathogens, and JEV/DENV ELISA with confirmatory microneutralization. We will pilot Luminex-based serologic assays and host protein signatures for JE, and perform human genetic (WES/WGS) and anti–type I IFN auto-antibody analyses to investigate determinants of severe disease. Geo-epidemiological tasks link infections to landscapes, climate, vectors, and living conditions; a dashboard integrates findings with national surveillance. The protocol (ANRS 0629s; version 2, January 14, 2025) is registered at ClinicalTrials.gov (NCT0667483) and sponsored by Inserm-ANRS and French Foreign office. RESULTS The study will generate (1) estimates of pediatric JEV seroprevalence; (2) clinical, laboratory, and environmental predictors of severity and treatable etiologies in FNS; (3) validated diagnostic algorithms suitable for Cambodian hospitals; and (4) capacity-building outcomes including biobanking, advanced serology, and a functioning JE surveillance dashboard aligned with the national system. CONCLUSIONS By combining prospective cohorts, enhanced diagnostics, host-factor investigations, and real-time surveillance, DEMELE-JEV will deliver actionable evidence to optimize JE prevention (including vaccine policy), diagnosis, and post-acute care pathways targetting strategies to population, behaviors and environments, in Cambodia and similar settings. CLINICALTRIAL ClinicalTrials.gov NCT0667483.