For health professionals: Japanese encephalitis

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What health professionals need to know about Japanese encephalitis

Japanese encephalitis is caused by a Flavivirus. The virus is a prototype member of the Japanese encephalitis antigenic complex, which also includes the:

  • West Nile virus
  • St. Louis encephalitis virus
  • Murray Valley encephalitis virus

Japanese encephalitis is a disease spread to humans by the bite of an infected Culex or Aedes mosquito. The most important vectors are:

  • Culex annulus
  • Culex fuscocephalus
  • Culex vishnui complex
  • Culex gelidus (in the tropics)
  • Culex tritaeniorhynchus (major epidemic vector)

Clinical manifestations

Most human infections with Japanese encephalitis are asymptomatic. Less than 1% of people infected with Japanese encephalitis develop severe clinical illness.

Acute inflammatory viral disease of short duration involving parts of the:

  • brain
  • meninges
  • spinal cord

Syndromes range from febrile headache syndrome to acute encephalitis. Severe infections are marked by acute onset of:

  • chills
  • nausea
  • vomiting
  • headache
  • high fever

These symptoms are followed by:

  • stupor
  • photophobia
  • nuchal rigidity
  • disorientation
  • objective neurologic signs

Severe cases can also experience symptoms like:

  • coma
  • tremors
  • paralysis
  • mental retardation
  • convulsive disorder
  • convulsions in children
  • Parkinsonian syndrome
  • neuropsychiatric sequelae
  • paralysis of the upper extremities

The case-fatality rate among severe cases ranges from 20% to 30%. Among survivors, 30% to 50% have serious neurological, cognitive or psychiatric sequelae.


Monitor for:

  • symptoms
  • serological studies (detection of immunoglobulin [Ig] M and G antibodies)
  • isolation of virus from:
    • blood
    • cerebrospinal fluid
    • other body fluid


There is no specific treatment for Japanese encephalitis. However, medical care can help with recovery and the control of symptoms.

Medical care consists of supportive care, such as:

  • management of seizures
  • control of intracranial pressure
  • prevention of secondary complications

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