Japanese encephalitis virus

Background

Virology

• Single-stranded positive-sense enveloped virus in the family Flaviviridae and genus Flavivirus

Epidemiology

• Vector-borne, transmitted by Culex mosquitoes, mainly Culex tritaeniorhynchus
• Found in Asia and the western Pacific, including India, southeast Asia, and eastern Asia, and as far south as parts of northern Australia
• Enzoonotic transmission cycle includes mosquitoes, pigs, and water birds, primarily in rural and periurban areas
• Seasonal transmission
  • In temperate climates, transmission is more common in the warm season, which can include outbreaks and epidemics
  • In tropical and subtropical climates, transmission is year-round, but intensifies during the rainy season and in the pre-harvest season where rice is grown
• More common in children and non-immune adults
• Overall, extremely low risk for travellers with 66 cases in Western travellers since 1973 and estimated less than 1 case per 10 million trips

Clinical Manifestations

• Incubation period of 5 to 15 days
• 99% of infections are asymptomatic
• Mild infections can cause fever and headache, with or without other symptoms
• Severe illness has rapid onset high fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis, and death
  • May have parkinsonism

Prognosis and Complications

• 20-30% mortality among people who develop encephalitis
• 30-50% of survivors have permanent neuropsychiatric symptoms, including paralysis, seizures, and aphasia

Management

• Supportive

Prevention

• Vaccine is not routinely recommended due to the rarity of disease
• Vaccine may be considered if there will be rural exposure, repeated travel to risk areas, longer cumulative duration of travel (e.g., > 30 days), or travel in areas suffering an outbreak
  • However, disease is still rare