Japanese encephalitis
Japanese encephalitis is a mosquito-borne flavivirus infection and the leading vaccine-preventable cause of viral encephalitis in Asia, confirmed by cerebrospinal fluid IgM antibody testing and managed with supportive care plus empiric acyclovir until herpes simplex encephalitis is excluded.
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What this article covers
- Overview
The most prevalent vaccine-preventable cause of infectious encephalitis in Asia: Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is endemic throughout most of Asia and parts of the western Pacific.
- Epidemiology
Geographic distribution across Asia and the western Pacific: JEV is the leading cause of epidemic viral encephalitis in this region.
- Risk factors
Prolonged travel or residence in an endemic area, especially rural or agricultural regions: extended stays with outdoor evening exposure carry the highest risk.
- Pathophysiology
Mosquito-borne flaviviral inoculation followed by viremia: Culex mosquitoes transmit JEV via bite; most infections remain confined to peripheral replication and asymptomatic seroconversion.
- Clinical features
Nonspecific febrile prodrome with headache, followed rapidly by neurologic decline: the illness begins as an undifferentiated viral-like syndrome and progresses quickly to an encephalopathic state…
- Differential diagnosis
Herpes simplex virus (HSV) encephalitis: the most common cause of sporadic encephalitis in regions without endemic arboviral transmission, distinguished by unilateral temporal lobe edema or…
- Diagnosis
The diagnosis is confirmed by detection of virus-specific IgM antibodies in the cerebrospinal fluid, later also detectable in serum; there is no formal severity grading system for Japanese…
- Management
First, start empiric intravenous acyclovir while HSV encephalitis is being excluded: acyclovir 10 mg/kg IV every 8 hours for at least 14 to 21 days if HSV is confirmed, with prompt discontinuation…
- Complications
Permanent neurologic sequelae: survivors of severe encephalitis can be left with persistent motor deficits, cognitive impairment, or movement disorders from thalamic and basal ganglia injury.
- Prognosis
Mortality of 20% to 30% among those with symptomatic encephalitis: this reflects the subset who progress beyond asymptomatic or mild infection, not overall infected persons, since fewer than 1% of infections become clinically apparent.
- Prevention
Two-dose inactivated JEV vaccine for travelers with qualifying risk: in the United States, an inactivated vaccine is available and recommended for travelers to endemic areas based on individual risk…
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