ConditionInfections
Japanese Encephalitis
Japanese encephalitis (JE) is a viral infection spread by mosquitoes in rural parts of Asia and the western Pacific. Most infected people have no symptoms or a mild fever, but about 1 in 250 develops encephalitis, a dangerous inflammation of the brain, with high fever, headache, confusion, seizures and paralysis. Of those, up to 1 in 3 die and many survivors have lasting brain damage. There is no antiviral cure, but a safe vaccine and mosquito bite prevention protect travelers and residents.
Also called: JE, Japanese B encephalitis, JE virus infection
At a glance
- Cause
- Japanese encephalitis virus, a flavivirus spread by Culex mosquitoes.
- Where
- Rural and farming areas of South, Southeast and East Asia and parts of the western Pacific, especially near rice fields and pig farms.
- Symptoms
- Most infections are silent; severe cases cause fever, headache, vomiting, confusion, seizures, paralysis.
- Severity
- Severe disease is fatal in roughly 20 to 30% of cases; 30 to 50% of survivors have lasting effects.
- Prevention
- Vaccination for at-risk travelers and residents; avoiding mosquito bites.
When to get help
Call 911 or go to the ER
- Fever with confusion, unusual drowsiness, a seizure, weakness, stiff neck or abnormal movements during or after travel to Asia: call 911 or your local emergency number
See a doctor within a day or two
- Fever and severe headache within about 2 weeks of returning from rural Asia
- A child with fever and vomiting after travel to an endemic area
Book a routine appointment
- Planning travel to rural Asia, long stays, or outdoor activities near rice fields or farms: see a travel clinic at least a month before departure
How it spreads
The virus circulates between Culex mosquitoes, pigs and wading birds. Mosquitoes that bite infected animals then bite humans. Humans are "dead-end" hosts and do not spread the virus to others. It is not passed from person to person.
Transmission is highest in rural farming areas, during and after the rainy season in temperate areas, and year-round in tropical regions. Mosquitoes bite mostly from dusk to dawn.
Who is at risk
- children in endemic countries without vaccination
- travelers spending a month or more in endemic areas
- shorter-term travelers to rural areas, especially with outdoor activities such as camping, cycling or fieldwork
- laboratory workers handling the virus
The risk for most short-term travelers to cities is very low.
Symptoms
The incubation period is 5 to 15 days. Most people have no symptoms or a mild, flu-like illness. Severe disease begins with:
- sudden fever, headache, vomiting and tiredness
Over hours to days, encephalitis may develop:
- confusion, disorientation and behavior changes
- seizures, especially in children
- neck stiffness
- weakness or paralysis
- abnormal movements, tremor and Parkinson-like stiffness
- coma
Diagnosis
Diagnosis requires a high level of suspicion in anyone with encephalitis after travel to an endemic area. Tests include:
- blood and spinal fluid tests for JE virus-specific IgM antibodies
- lumbar puncture showing inflammation
- MRI of the brain, which may show changes in the thalamus and basal ganglia
- tests for other causes of encephalitis and meningitis, including herpes, other flaviviruses and bacterial infections
Treatment
There is no specific antiviral treatment. Hospital care focuses on:
- managing brain swelling and seizures
- support for breathing, fluids and nutrition
- intensive care for severe cases
- rehabilitation for survivors, including physical, occupational and speech therapy
Complications and outlook
Among people who develop encephalitis, about 20 to 30% die. Of survivors, 30 to 50% have lasting problems such as paralysis, seizures, movement disorders, learning difficulties, memory and behavior problems, or speech difficulties. Children are particularly vulnerable.
Prevention
Vaccination
An inactivated JE vaccine (Ixiaro in the US) is recommended for:
- travelers spending a month or longer in endemic areas during transmission season
- shorter-term travelers at increased risk based on itinerary, season and activities
The usual schedule is 2 doses given 28 days apart, completed at least 1 week before travel. Adults 18 to 65 can receive an accelerated schedule with doses 7 days apart. A booster may be recommended if continued risk exists. Many endemic countries vaccinate children routinely.
Mosquito bite prevention
- use EPA-registered repellents such as DEET, picaridin or oil of lemon eucalyptus, following label instructions
- wear long sleeves and long pants, especially from dusk to dawn
- treat clothing with permethrin
- sleep in air-conditioned or screened rooms, or under bed nets
These measures also protect against dengue, malaria and other mosquito-borne infections.
Frequently asked questions
What are the symptoms of Japanese encephalitis?
Most infected people have no symptoms. Severe cases start with fever, headache and vomiting, followed by confusion, seizures, neck stiffness, weakness or paralysis, and abnormal movements. Severe disease needs emergency hospital care.
Do I need the Japanese encephalitis vaccine for travel?
It is recommended for travelers spending a month or more in endemic areas, and for shorter trips with rural or outdoor exposure during transmission season. A travel clinic can assess your itinerary.
Is Japanese encephalitis contagious between people?
No. It spreads only through the bite of an infected mosquito. People with the infection cannot pass it to others.
Is there a cure for Japanese encephalitis?
There is no antiviral cure. Treatment is supportive care in hospital. Prevention through vaccination and avoiding mosquito bites is the best protection. See also viral encephalitis.
Sources
This guide was written from current patient and clinical guidance, including:
- CDC: Japanese encephalitis: clinical overview; Yellow Book: Japanese encephalitis
- World Health Organization: Japanese encephalitis fact sheet
- Advisory Committee on Immunization Practices (ACIP): Japanese encephalitis vaccine recommendations
- NHS: Japanese encephalitis
- MedlinePlus: Japanese encephalitis