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Clinical presentation

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team


Japanese Encephalitis (JE) is primarily a disease of children (although all age groups can be affected)

  • most adults in endemic countries have natural immunity after childhood infection (1)

The incubation period is from 5 to 15 days:

  • in survivors, the illness may range from asymptomatic infection to severe encephalitis with a high mortality and a high rate of permanent neurological sequelae (2)
    • most infections are asymptomatic (about one in 250 infections is estimated to become clinically apparent)
    • acute encephalitis is the most commonly recognized clinical manifestation of the disease (4)
    • in symptomatic cases the severity of the disease varies
      • mild disease is characterized by febrile headache or aseptic meningitis
      • illness usually begins with rapid onset and progression of fever, headache, and vomiting
      • over the next few days mental status of the patient changes and may develop focal neurologic deficits, generalized weakness, and movement disorders
      • Parkinson's-like syndrome with mask-like facies, tremor, cogwheel rigidity, and choreoathetoid movements are often seen
      • acute flaccid paralysis, with clinical and pathological features similar to those of poliomyelitis, has also been associated with JEV infection
      • seizures are common, especially among children.


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