Acute encephalitis syndrome and Japanese encephalitis in India: insights from a nationally representative laboratory...

Acute Encephalitis Syndrome (AES) is a critical public health issue, contributing significantly to morbidity and mortality in India, particularly among children. Despite ongoing vaccination efforts, Japanese Encephalitis (JE) remains a major cause of AES. This study analyzes the epidemiology of AES and JE in India from 2014 to 2023, using data from the Virus Research and Diagnostic Laboratory Network (VRDLN).

A cross-sectional analysis was conducted on AES cases reported by 159 VRDLN laboratories between 2014 and 2023. Standardized diagnostic tests such as polymerase chain reaction were used to identify causative pathogens, including JE virus. All the labs in the network followed BSL-2 standards. Descriptive analyses were performed on AES cases by year, etiology, and demographic factors. JE cases were further analyzed for geographic distribution, age, sex, and clinical characteristics.

Over the study period, 124,890 AES cases were reported, with 16.3% testing positive for at least one pathogen, including 10% confirmed as JE. The highest JE positivity was observed in the northeastern states. An increasing trend in the number of cases tested and JE detections was noted, alongside a shift in the age distribution towards younger populations. The median (IQR) annual test positivity for JEV among tested was 16.2% (14.5%, 18.4%).

The VRDLN has substantially enhanced India's capacity to diagnose and monitor AES and JE. Despite progress, JE transmission persists, particularly in endemic regions, posing significant public health challenges. Strengthened surveillance, improved diagnostic coverage, and integrated pathogen testing are essential for effective interventions. Targeted strategies and sustained public health efforts are critical to reducing the burden of AES and JE in India.