What Is Japanese Encephalitis?
A serious mosquito-borne viral brain infection found across Asia and the Western Pacific, with a high fatality rate in symptomatic cases.
Pathogen: Japanese encephalitis virus (JEV, Flavivirus family)
Type: Virus
Transmission
Bite of infected Culex mosquitoes, which breed in rice paddies and other standing water. The virus cycles between mosquitoes and amplifying hosts (pigs and wading birds). Humans are dead-end hosts.
Vector: Culex mosquitoes (especially Culex tritaeniorhynchus), most active from dusk to dawn in rural agricultural areas
Symptoms
Most infections are asymptomatic. When encephalitis develops: sudden onset of high fever, headache, neck stiffness, disorientation, seizures, tremors, coma. Children are disproportionately affected. Paralysis and movement disorders may develop.
Incubation period: 5 – 15 days
Most commonly 5-15 days. The vast majority of infections (>99%) are asymptomatic or cause only mild febrile illness.
Timeline: Mild symptoms may appear 5-15 days after the infective bite. Encephalitis, when it develops, progresses rapidly over 1-6 days from fever to neurological deterioration.
Case fatality rate: 20-30% of those who develop encephalitis. Up to 50% of survivors have permanent neurological sequelae including intellectual impairment, paralysis, and seizure disorders.
Diagnosis & Treatment
Diagnosis: JE-specific IgM in cerebrospinal fluid (CSF) or serum (gold standard). PCR on CSF in early disease. Cross-reactivity with other flaviviruses (dengue, Zika) can complicate serological diagnosis.
Treatment: No specific antiviral treatment. Supportive care only, including intensive care for severe cases with airway management, seizure control, and management of raised intracranial pressure. Focus is on prevention through vaccination.
Prevention
- JE vaccination (Imojev or JEspect, available at Australian travel clinics)
- DEET-based insect repellent from dusk to dawn
- Insecticide-treated bed nets in rural areas
- Avoid outdoor exposure at dusk and dawn near rice paddies or pig farms
- Wear long sleeves and pants in the evening
- Use mosquito coils and plug-in repellents in accommodation
💉 Vaccine Available
A vaccine is available for Japanese Encephalitis. View the Japanese Encephalitis vaccine guide for details on schedule, cost, and availability in Australia.
Post-Exposure
There is no post-exposure prophylaxis. If you develop sudden high fever, severe headache, confusion, or seizures within 2 weeks of travel to an endemic area, seek emergency medical attention and inform the doctor of your travel history.
Long-Term Effects
Up to 50% of encephalitis survivors have permanent neurological damage including cognitive impairment, behavioural changes, motor deficits, epilepsy, and paralysis. Children are particularly vulnerable to long-term sequelae.
📋 Japanese encephalitis is a nationally notifiable disease in Australia. Local transmission was confirmed in south-eastern Australia in 2022 for the first time, linked to piggeries in Victoria, New South Wales, Queensland, and South Australia. The JE vaccine was added to the National Immunisation Program for eligible groups.
Frequently Asked Questions
Do I need the Japanese encephalitis vaccine for Bali?
JE risk in Bali is generally low for short-stay tourists in urban and resort areas. However, vaccination is recommended if you plan to spend time in rural areas, stay for a month or more, or travel during the wet season. The Australian Immunisation Handbook recommends discussing JE vaccination with a travel doctor for any travel to endemic areas in Asia.
Is the Japanese encephalitis vaccine covered by Medicare?
The JE vaccine is available free under the National Immunisation Program (NIP) for certain at-risk groups, including people living or working in areas where JE virus activity has been detected in Australia. For travellers, the vaccine is generally not covered by Medicare and costs approximately $250-350 per dose at travel clinics. Two doses are required for the JEspect vaccine (days 0 and 28).
How common is Japanese encephalitis in travellers?
JE is rare in travellers — the estimated risk for a short-term tourist is less than 1 in 1 million per week of travel. However, risk increases substantially with prolonged stays, rural exposure, and travel during the transmission season. Given the severity of the disease (20-30% fatality, 50% long-term disability in survivors), vaccination is recommended for at-risk travellers.
Can you get Japanese encephalitis in Australia?
Yes. JE virus was detected in south-eastern Australia for the first time in early 2022, associated with piggeries in Victoria, New South Wales, Queensland, and South Australia. Human cases were confirmed. The virus is now considered established in parts of northern Australia. The JE vaccine was added to the NIP for eligible groups following this outbreak.
How many doses of JE vaccine do I need before travelling?
For the JEspect (Vero cell) vaccine used in Australia for adults, two doses are given 28 days apart, with the second dose at least one week before travel. The Imojev (live attenuated) vaccine requires a single dose given at least 14 days before travel, with a booster after 1-2 years for ongoing risk. Your travel doctor will advise which vaccine is appropriate.
Is Japanese encephalitis found in Japan?
Yes, but the risk is very low for travellers to Japan. Japan has a successful national JE vaccination programme, and locally acquired cases are rare (fewer than 10 per year, mostly in elderly unvaccinated individuals). The JE vaccine is not routinely recommended for short-term travellers to Japan visiting urban areas only.
What time of year is Japanese encephalitis risk highest?
In tropical areas (Southeast Asia, southern India), transmission occurs year-round with peaks during the wet season. In temperate areas (northern India, China, Japan, Korea), transmission is seasonal, typically May to October. Monsoon and post-monsoon periods carry the highest risk due to increased mosquito breeding in rice paddies.
Who is most at risk of severe Japanese encephalitis?
Children under 10 and adults over 65 are at highest risk of severe disease. Travellers spending extended periods in rural agricultural areas (especially near rice paddies and pig farms) have greater exposure. Occupational exposure (farming, field research) also increases risk. Most infections in any age group are asymptomatic.
Sources & References
Last updated: April 2026