Japanese Encephalitis

Overview

Japanese encephalitis is an infection caused by a virus that is spread by mosquito bites. The word encephalitis means inflammation of the brain. Most people who get infected have no symptoms or only a mild illness. In a small number of people, the virus can cause serious brain inflammation. Japanese encephalitis does not spread from person to person.

Japanese encephalitis is uncommon in most travelers, but it is a public health problem in some rural areas of Asia and the Western Pacific. Most people bitten by an infected mosquito do not become seriously ill.

It can affect anyone bitten by an infected mosquito. In areas where the virus is common, children are often most affected. Travelers, outdoor workers, and people staying for longer periods in rural risk areas may be at higher risk.

Symptoms

Common symptoms

• Many people have no symptoms at all.
• Mild fever and headache can occur.
• In serious cases: high fever, severe headache, stiff neck, vomiting, confusion, seizures, weakness, or unusual sleepiness.
• Symptoms usually appear about 5 to 15 days after an infected mosquito bite.

Symptoms in children

• Fever, irritability, and poor feeding.
• Vomiting and unusual sleepiness.
• Seizures or body movements that are not normal.
• A child who is hard to wake or seems floppy should be checked urgently.

Symptoms in older adults

• Fever with new confusion or reduced alertness.
• Weakness, falls, or trouble with walking.
• Seizures or unusual sleepiness.
• Symptoms may be mistaken for other age-related problems, so travel history matters.

Causes

Main causes

• Japanese encephalitis is caused by the Japanese encephalitis virus.
• The virus spreads through the bite of an infected mosquito, mainly in some rural areas of Asia and the Western Pacific.
• It does not spread from person to person through touch, coughing, or sneezing.

Risk factors

• Living in or traveling to rural areas where the virus is common.
• Staying for longer periods in risk areas, especially near rice fields, irrigation, or flooding.
• Spending time outdoors at dusk and dawn when mosquitoes are active.
• Not being vaccinated when vaccination is recommended for your situation.
• Being a child or an older adult may raise the chance of severe illness.

When to see a doctor

See a doctor urgently if:

• You have a fever, headache, or vomiting within a few weeks of travel to an area where Japanese encephalitis is found.
• You have a new seizure, confusion, weakness, or unusual sleepiness.
• A child is drowsy, irritable, feeding poorly, or has a seizure.
• You have any symptom that worries you after mosquito exposure in a risk area.

Book a routine appointment if:

• You are planning travel to Asia or the Western Pacific and want advice about vaccines and mosquito protection.
• You have questions about the Japanese encephalitis vaccine.
• You live in or work in a risk area and want to discuss prevention.

Diagnosis

Doctors ask about your symptoms, recent travel, and mosquito exposure. They examine you and may do tests to look for the virus or the body's immune response to it. Tests can also help rule out other causes of brain inflammation.

Tests that may be done

• Blood tests to look for signs of the virus or the body's response to it.
• Lumbar puncture (spinal tap): a small sample of fluid around the spinal cord is tested. Numbing medicine is used.
• MRI scan of the brain (a detailed magnetic scan).
• EEG (brain wave test) if there have been seizures.

What to expect at your appointment

You may be seen in hospital. Some tests take time, and you may be monitored while results come back. A lumbar puncture is usually done after an examination and sometimes after a scan. Your care team will explain each step.

Treatment

There is no specific medicine that cures Japanese encephalitis. Care focuses on supporting the body while it fights the virus and on preventing complications.

Self-care at home

• Rest and drink enough fluids if you are recovering at home, as advised by your care team.
• Keep using mosquito protection to avoid other mosquito-borne infections.
• Follow any rehabilitation exercises for movement, speech, or memory.
• Attend follow-up appointments.
• Return to work or school slowly.

Medical treatments

Hospital care may include close monitoring, oxygen, fluids, nutrition, help with breathing, seizure control, and treatment to reduce brain swelling. Rehabilitation may include physiotherapy, speech therapy, and occupational therapy. The care team will tailor treatment to the person's needs.

When is surgery considered?

Surgery is not used to treat the infection itself. In rare cases, specialists may consider surgery for a complication such as a build-up of fluid in the brain.

Living with this condition

Recovery is different for everyone. Some people feel tired or have memory, movement, or speech problems for weeks or months. A rehabilitation plan can help you rebuild skills and confidence.

Lifestyle tips

• Keep using mosquito protection if you are in a risk area.
• Get enough sleep and build activity slowly.
• Use reminders, notes, or lists if memory is affected.
• Ask family and friends for help with appointments and daily tasks.
• Go at a pace that suits your recovery.

Diet and exercise

Eat regular balanced meals and drink enough fluids. Gentle exercise and physiotherapy can help rebuild strength. Follow the advice of your care team before starting new exercise.

Mental health and emotional wellbeing

Changes in mood, anxiety, or memory can happen after a brain infection. This is not a sign of weakness. If you or someone you know is in crisis or having thoughts of self-harm, contact local emergency services or a local crisis line right away.

Prevention

Yes. You can lower your risk by getting vaccinated if it is recommended for you and by preventing mosquito bites. Japanese encephalitis does not spread from person to person.

Vaccines

A vaccine is available in some countries. It is recommended for some people living in or traveling to risk areas. Ask a travel health clinic or local health service whether it is right for you.

Screening programmes

There is no routine screening test for Japanese encephalitis. Before travel, a health professional can assess your risk and discuss prevention.

Complications

If left untreated

• Severe brain inflammation can lead to seizures, coma, weakness, speech or memory problems, and death.
• Without supportive hospital care, breathing problems, seizures, and brain swelling can become life-threatening.
• Some people have long-term movement, thinking, or behaviour changes.

Long-term outlook

Most people infected with the virus have no symptoms or only a mild illness. In severe cases, early hospital care and rehabilitation can make a real difference. Many people improve over time, though recovery may be slow. Seek care early if symptoms appear after travel to a risk area.

Find support

External links open third-party websites. Ruqelo Health is not responsible for external content. Listing an organisation does not imply endorsement.