Japanese Encephalitis

Definition

Japanese encephalitis (JE) is a mosquito-borne viral infection caused by the Japanese encephalitis virus (JEV), leading to inflammation of the brain. It predominantly affects children in endemic regions of Asia and can result in neurological complications or death.

Epidemiology

• Endemic in rural and suburban areas of Asia and the Western Pacific
• Incidence highest in children aged 1–15 years
• Seasonal outbreaks often coincide with rainy seasons due to increased mosquito breeding
• Estimated 68,000 clinical cases annually worldwide
• Case-fatality rate approximately 20–30% in symptomatic cases

Etiology

• Japanese encephalitis virus (JEV), a flavivirus
• Transmitted by Culex mosquitoes, primarily Culex tritaeniorhynchus
• Amplified in pigs and wading birds acting as reservoirs
• Humans are incidental hosts; human-to-human transmission is rare
• Children and non-immune individuals are at higher risk
• Travel to endemic areas increases exposure risk

Pathophysiology

• Virus enters through mosquito bite and replicates in local tissues
• Viremia allows virus to cross the blood-brain barrier
• Infection of neurons leads to inflammation, neuronal death, and cerebral edema
• Cytokine release and immune-mediated damage contribute to neurological symptoms
• Severe cases involve widespread neuronal damage, brainstem involvement, and raised intracranial pressure
• Long-term neurological sequelae result from irreversible neuronal injury