Japanese encephalitis virus

Background

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

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

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

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

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