Japanese encephalitis

Background

Japanese encephalitis geographic distribution

• Mosquito-borne flavivirus
• One of the most common causes of encephalitis globally
• Highly endemic in parts of Asia and the Western Pacific
• Up to 70,000 cases, 15,000 deaths annually
• Usually affects children in endemic areas, as most adults have been exposed and are immune
• Rare in tourists, as the vector Culex mosquito breeds primarily in rural rice paddies

Clinical Features

• 5-15 day incubation
• Sudden, high fever
• Headache
• Nuchal rigidity and other meningeal signs
• Seizure (especially in infants)
• Various pyramidal and extrapyramidal signs

Differential Diagnosis

• SAH
• Lyme disease
• Brain abscess
• Bacterial endocarditis
• Toxic / metabolic encephalopathy

Altered mental status and fever

• Infectious
  • Sepsis
  • Meningitis
  • Encephalitis
  • Cerebral malaria
  • Brain abscess
• Other
  • Neuroleptic malignant syndrome
  • Serotonin syndrome
  • Malignant hyperthermia
  • Sympathomimetic toxicity (cocaine, amphetamine, ketamine)
  • Anticholinergic toxicity
  • Heat stroke
  • Delirium tremens
  • Hypothalamic stroke
  • Pheochromocytoma
  • Thyroid storm

Evaluation

• Usually diagnosed by clinical suspicion
• Lumbar puncture if any concern for HSV, VZV, or bacterial meningitis
  • Can test CSF for Japanese encephalitis

Management

• Supportive
  • IVF, electrolyte repletion, antipyretics
  • Antiepileptics for seizures
  • Depressed mental status may require intubation for airway protection
• Consider empiric acyclovir and antibiotics if HSV or bacterial causes not ruled out

Disposition

• Admit all but very mild illness
• Recovery can take months, some deficits may be permanent

See Also

• Encephalitis
• Fever in traveler