Japanese encephalitis

Japanese encephalitis is a type of viral brain infection spread through mosquito bites.

Introduction

Japanese encephalitis is a type of viral brain infection spread through mosquito bites. It’s common in rural areas throughout Southeast Asia, the Pacific islands and the Far East.

The virus is found in pigs and birds, and passed to mosquitoes that bite the infected animals. It’s more common in rural areas where there are pig farms and rice fields. It cannot be spread from human to human.

Read more about the causes of Japanese encephalitis.

Most people infected by the Japanese encephalitis virus do not develop any symptoms, or they get only mild, flu-like symptoms.

However, around one person in 250 infected by the virus has serious and severe symptoms, including:

  • being sick
  • seizures (fits)
  • headache
  • mental confusion

In serious cases, the virus can also cause swelling inside the brain (encephalitis), leading to increased pressure in the brain. This can cause permanent brain damage. Japanese encephalitis can be fatal in around one in three people who develop these serious symptoms.

Read more about the symptoms of Japanese encephalitis.

Treatment

There is currently no cure for Japanese encephalitis so treatment involves supporting the functions of the body as it tries to fight off the infection. This will usually involve admission to hospital.

A medication called mannitol can be used to reduce pressure inside the brain, which can sometimes prevent permanent brain damage.

Read more about the treatment of Japanese encephalitis.

Who is affected?

It’s rare for travellers from outside the region to be affected by Japanese encephalitis. It is estimated that only one in 1 million travellers will develop Japanese encephalitis in any year.

People who live and work in rural areas in parts of the world where the condition is widespread are most at risk. Around 9 out of 10 cases involve children under the age of 15 years.

There are an estimated 70,000 new cases every year, half of which occur in China.

Vaccination

Two vaccines are available for Japanese encephalitis. Vaccination is normally recommended if:

  • You are planning to spend a month or longer in a high-risk country during the rainy season.
  • You are planning to visit any rural areas in high-risk countries, even if only for a short time.
  • You will be taking part in any activities that may increase your risk of becoming infected, such as visiting rice fields or pig farms, cycling or camping.

Read more about vaccines for Japanese encephalitis.

Encephalitis is inflammation of the brain. This can develop as a result of infection (usually viral) or when the immune system attacks the tissue of the brain by mistake (post-infectious encephalitis).

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

The immune system is the body's defence system, which helps to protect it from disease, bacteria and viruses.

The electrical impulses in the brain are disrupted, causing both the brain and the body to behave strangely.

Symptoms

In most people, the Japanese encephalitis virus causes no symptoms or mild symptoms that are often mistaken for the flu.

Only around one person in 250 develops "fully blown" Japanese encephalitis after being infected. Symptoms usually develop six to eight days after infection (the incubation period).

Initial symptoms of infection include:

  • a high temperature (fever) of 38C (100.4F) or above
  • headache
  • feeling sick
  • being sick
  • diarrhoea
  • muscle pain

In more serious and rarer cases, these initial symptoms last for a few days before more wide-ranging and serious symptoms develop, such as:

  • seizures (fits)
  • changes in mental state, which can range from mild confusion to being very agitated or falling into a coma
  • uncontrollable shaking of body parts (tremor)
  • losing the ability to speak
  • muscle weakness
  • abnormally tense muscles (hypertonia)
  • movement problems, such as shaking, stiffness, slowness of movement or paralysis
  • difficulties in controlling the movements of the eyes
  • difficulties in controlling the muscles of the face
  • the back of the eyes can bulge outwards because of increased pressure inside the brain, though this is not noticable to the untrained observer

In people who survive the effects of infection, these symptoms should slowly improve. However, it can take several months to make a full recovery and this is not always possible in many cases.

Over half of people who survive a case of fully blown Japanese encephalitis are left with brain damage. This can lead to complications such as learning difficulties and paralysis (inability to move one or more parts of the body).

Read more about the complications of Japanese encephalitis.

Encephalitis is inflammation of the brain. This can develop as a result of infection (usually viral) or when the immune system attacks the tissue of the brain by mistake (post-infectious encephalitis).

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

The electrical impulses in the brain are disrupted, causing both the brain and the body to behave strangely.

Causes

Japanese encephalitis is caused by a flavivirus. This type of virus can affect both animals and humans. The virus is passed on to humans from animals through the bite of an infected mosquito.

Pigs and wading birds are the main carriers of the Japanese encephalitis virus. A mosquito becomes infected after sucking the blood from an infected animal or bird. If an infected mosquito bites you, it can pass the virus on to you. The virus cannot be passed from person to person.

Risk factors

Several factors can increase your risk of catching Japanese encephalitis, including:

  • the areas you visit
  • the time of year you visit
  • the activities you do

High-risk countries

Japanese encephalitis is found throughout Asia and beyond. The area in which it is found stretches from the Western Pacific islands in the east, such as Fiji, across to the borders of Pakistan in the west. It is found as far north as Korea and as far south as Papua New Guinea.

Most cases occur in

  • China
  • Myanmar (Burma)
  • Thailand
  • Vietnam
  • Cambodia
  • Laos
  • Nepal
  • India
  • Philippines
  • Sri Lanka
  • Malaysia
  • Indonesia

Despite its name, Japanese encephalitis is now relatively rare in Japan because of mass immunisation programmes.

Cases of Japanese encephalitis have also occurred on the Torres Strait Islands off the north coast of Australia. It is thought that migrating birds have introduced the disease to the area and it is now found in pigs there.

The mosquitoes that carry Japanese encephalitis usually breed in rural areas, particularly where there are flooded rice fields or marshes. The infected mosquitoes have also been found in urban areas. They usually feed between sunset and sunrise.

Rainy seasons

A sudden increase in the mosquito population, which can occur during the rainy season, could cause a sudden outbreak of Japanese encephalitis in humans:

  • May to September is the peak time for cases of Japanese encephalitis in Korea and Japan.
  • April to October is the peak time for cases of Japanese encephalitis in areas of Southeast Asia, such as Thailand, Cambodia and Vietnam.
  • September to December is the peak time for cases of Japanese encephalitis in Nepal and India.
  • Japanese encephalitis occurs all year round in Malaysia, Indonesia and the Philippines, where rain falls throughout the year.

This pattern can vary. For example, infected birds can change their migration patterns, so cases of Japanese encephalitis may be seen at other times of the year or in different places.

High-risk activities

If you are planning a short visit to Asia, the risk of contracting Japanese encephalitis is very low, particularly if you are going to be staying in urban areas. It is estimated that there is one case of Japanese encephalitis for every 1 million travellers.

Activities that may increase your risk of developing Japanese encephalitis include:

  • living or travelling in high-risk areas for a long time
  • visiting rural areas, particularly during the rainy season
  • fieldwork, camping or cycling in rural areas

Among travellers who visit rural areas and stay for long periods, the risk of catching Japanese encephalitis may increase. For example, one estimate has suggested that there could be up to two cases a week for every 100,000 travellers.

Diagnosis

If you have any of the symptoms of Japanese encephalitis and have recently visited or are still in a country where it is a risk, get medical help immediately.

For information about how to seek medical help abroad, read our travel health guide.

Your doctor or the healthcare professional treating you will ask about your symptoms, what you did on your trip and what vaccinations you have had.

Tests

Your doctor or healthcare professional will take a sample of blood from your arm and test it for antibodies. Antibodies are proteins that are produced by the body to neutralise or destroy disease-carrying organisms.

If you have been infected with the Japanese encephalitis virus, your body will start to produce a specific type of antibody to destroy the virus.

Around seven days after the start of your symptoms, the antibody should be noticeable in your blood.

The antibodies are also present in your cerebrospinal fluid (CSF), which surrounds your brain and spinal cord. In some cases, a sample of CSF may be taken and tested instead.

A sample of CSF is taken using a procedure called a lumbar puncture or spinal tap. A hollow needle is inserted between the vertebrae (back bones) in your lower spine and some of the fluid is drawn out.

Scans

If your doctor suspects that Japanese encephalitis may have spread to your brain, they may recommend a brain scan to check for any damage and to confirm the diagnosis. This could be:

Encephalitis is inflammation of the brain. This can develop as a result of infection (usually viral) or when the immune system attacks the tissue of the brain by mistake (post-infectious encephalitis).

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Meningitis is an infection of the meninges. These are protective membranes that surround the brain and spinal cord. Infection can cause the meninges to become inflamed and swell, which can damage the nerves and brain.

Vaccination or immunisation is usually given by an injection that makes the body's immune system produce antibodies that will fight off a virus.

Treatment

There is no specific treatment for Japanese encephalitis, although measures can be taken to control your symptoms and prevent complications from developing.

If your symptoms are severe, you may be admitted to hospital, often to an intensive care unit (ICU) or high dependency unit. The healthcare professionals treating you will try to reduce your high temperature and ease any pain.

You will be given an oxygen mask to help you breathe and a feeding tube to provide you with nutrition and keep you hydrated.

If you develop swelling inside your brain, you may be given other medicines to help control the symptoms.

Encephalitis is inflammation of the brain. This can develop as a result of infection (usually viral) or when the immune system attacks the tissue of the brain by mistake (post-infectious encephalitis).

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Complications

It can be hard to predict the long-term effects of having this type of brain infection. They can range from full recovery to being severely disabled.

One study from Malaysia, which looked at just over 100 people who were admitted to hospital for Japanese encephalitis, found that:

  • 41% of patients made a full recovery
  • 3% had mild disability
  • 26% had moderate disability
  • 31% had severe disability

Mild disability can take the form of:

  • uncontrollable shaking of the hands
  • changes to personality
  • muscle weakness and twitching in the arms and hands

Moderate disability can take the form of:

  • mild learning difficulties
  • paralysis of a single limb
  • weakness on one side of the body

Severe disability after Japanese encephalitis usually takes the form of a severe learning difficulty as well as muscle spasms and stiffness of the arms and legs.

Prevention

The vaccination against Japanese encephalitis is not completely effective, so you should also protect yourself against mosquito bites in high-risk areas.

Follow the advice below to prevent being bitten by infected mosquitoes:

  • If possible, sleep in rooms with close-fitting gauze over the windows and doors.
  • If this is not possible or you are sleeping outside, use mosquito nets that have been impregnated with an insecticide, such as permethrin.
  • Spray the room with insecticide in the early evening to kill any mosquitoes that have got in during the day.
  • Mosquitoes that carry the Japanese encephalitis virus are usually most active at dusk and enjoy warm, humid conditions. If you go outside after sunset, cover up with long-sleeved tops, trousers and socks.
  • Mosquitoes can bite through skin-tight clothing so, if possible, wear loose-fitting clothes.
  • Apply a good-quality insect repellent to any exposed areas of skin.

Insect repellent

Various types of insect repellent are available. Many contain diethyltoluamide (DEET). If you are allergic to DEET, other insect repellents are available, including dimethyl phthalate (contained in Shoo!) or eucalyptus oil (contained in Mosi-Guard).

When using insect repellent, follow the guidelines below:

  • Do not use the insect repellents on cuts, wounds or irritated skin.
  • Do not get insect repellent in your eyes, mouth and ears.
  • Do not spray the insect repellent directly onto your face. Spray it onto your hands and then apply it to your face.
  • Do not allow young children to apply insect repellent themselves. Put it on your hands and then apply it to your child.
  • Wash your hands thoroughly after applying insect repellent.
  • Wash off the repellent with soap and water when it is no longer needed.
  • Always follow the manufacturer's instructions.

If you or your children have an adverse reaction to insect repellent, such as redness, stop using it. Wash it off and contact your doctor or a local healthcare professional if you are abroad.

Prevention

Vaccination

A vaccine against Japanese encephalitis is available for people who are visiting a country where Japanese encephalitis is a risk. After a full course of the vaccine, you will have around 98% protection against Japanese encephalitis. This reduces to around 83% after 12 months.

If you are travelling to a country where the vaccination is recommended, visit your doctor or practice nurse at least six to eight weeks before you leave. They will discuss your trip with you and determine whether you should have the vaccination.

Recommendations

The Japanese encephalitis vaccine is recommended if:

  • you are planning to spend a month or longer in a high-risk country during the rainy season
  • you are planning to visit any rural areas in high-risk countries, even if only for a short period of time
  • you will be taking part in any activities that may increase your risk of becoming infected, such as visiting rice fields or pig farms, cycling, camping or fieldwork

The Japanese encephalitis vaccine is not suitable for children who are under one year of age.

If you have previously had a severe allergic reaction (anaphylaxis) to a Japanese encephalitis vaccine or are allergic to any of the ingredients in the vaccine, do not have it.

You may be more at risk of having an adverse reaction to the vaccine if:

  • you have other allergies, such as allergic rhinitis or asthma
  • you have a neurological condition, which is a condition that affects your nervous system (your brain, spinal cord and nerves) such as multiple sclerosis
  • you have had seizures (fits) in the previous year

In all cases, the risks of catching the Japanese encephalitis virus will be weighed up against the risks of having an adverse reaction to the vaccine.

There is no evidence that the Japanese encephalitis vaccine presents any risks for pregnant women or women who are breastfeeding.

The vaccine

Two vaccines for Japanese encephalitis may beavailable:

  • IXIARO®
  • Green Cross®

Both vaccines are given as a course of injections. Ideally, this should be completed at least one month before you travel. This gives enough time for your body to develop full immunity (resistance to the virus).

IXIARO® is given as two injections, with the second dose given 28 days after the first. A booster dose is required after 12 months. This vaccine is suitable for people who are 18 years of age and over.

Green Cross® is given as three injections. The second dose is given seven days after the first, and the third dose is given 28 days after the first. A booster dose is required after 12 months, and then annually (once a year) if you are still at risk of catching Japanese encephalitis. This vaccine is suitable for children who are over one year of age.

The Green Cross® vaccine must be completed at least 10 days before you travel because an allergic reaction to the vaccine can take this long to show up.

After each injection, you will be monitored for 30 minutes to check for any side effects (see below).

Rapid course

If there is not enough time before you travel to complete a full course as described above, you may be able to have a rapid course of the vaccination.

You can receive three doses of the Green Cross® vaccine with seven days between each dose, or you can receive two doses seven days apart with a booster dose three months later.

The two-dose rapid course of the Green Cross® vaccine will provide less protection than the three dose course. These will still need to be completed at least 10 days before you leave in case you have a reaction.

Side effects

Some people experience side effects after having the Japanese encephalitis vaccine.

Between 10% and 20% of people may experience:

  • soreness, redness or swelling at the site of the injection
  • a high temperature (fever) of 38°C (100.4°F) or over
  • dizziness
  • headache
  • feeling sick
  • being sick
  • abdominal pain
  • aching muscles

More serious side effects occur in around 1 in 200 people. These include:

  • urticaria or hives (a raised, itchy red rash)
  • swelling of the face
  • difficulty breathing

This type of reaction usually occurs within minutes of having the vaccine, although it could appear up to two weeks later.

If you have the vaccine while you are travelling abroad, stay in an area where you have access to a doctor or hospital for at least 10 days in case you have an adverse (bad) reaction.

Availability and cost

It is likely that you will need to pay for a course of vaccinations at a travel clinic (your doctor may also be able to provide vaccination for a fee).

Advice when travelling

If you choose not to be vaccinated you can still reduce your risk of catching Japanese encephalitis by taking some precautions to protect yourself against mosquito bites when travelling in high-risk areas.

These are:

  • If possible, sleep in rooms with close-fitting gauze over the windows and doors.
  • If this is not possible or you are sleeping outside, use mosquito nets that have been impregnated with an insecticide, such as permethrin.
  • Spray the room with insecticide in the early evening to kill any mosquitoes that have got in during the day.
  • Mosquitoes that carry the Japanese encephalitis virus are usually most active at dusk and enjoy warm, humid conditions. If you go outside after sunset, cover up with long-sleeved tops, trousers and socks.
  • Mosquitoes can bite through skin-tight clothing so, if possible, wear loose-fitting clothes.
  • Apply a good-quality insect repellent to any exposed areas of skin.

Insect repellent

Various types of insect repellent are available. Many contain diethyltoluamide (DEET). If you are allergic to DEET, other insect repellents are available, including Dimethyl Phthalate (contained in Shoo!) or Eucalyptus oil (contained in Mosi-Guard).

When using insect repellent, follow the guidelines below:

  • Do not use the insect repellents on cuts, wounds or irritated skin.
  • Do not get insect repellent in your eyes, mouth and ears.
  • Do not spray the insect repellent directly onto your face. Spray it onto your hands and then apply it to your face.
  • Do not allow young children to apply insect repellent themselves. Put it on your hands and then apply it to the child.
  • Wash your hands thoroughly after applying insect repellent.
  • Wash off the repellent with soap and water when it is no longer needed.
  • Always follow the manufacturer's instructions.

If you or your children have an adverse reaction to insect repellent, such as redness, stop using it.

Wash it off and contact your doctor or a local healthcare professional if you are abroad.

Vaccination

A vaccine against Japanese encephalitis is available for people visiting a country where there is an increased risk of catching the disease.

After a full course of the vaccine, you will have around 98% protection against Japanese encephalitis. This reduces to around 83% after 12 months.

High-risk areas for Japanese encephalitis include tropical northeast Australia and east Asia, including:

  • Cambodia
  • China
  • India
  • Indonesia
  • Korea
  • Laos
  • Malaysia
  • Myanmar (Burma)
  • Nepal
  • Philippines
  • Singapore
  • Sri Lanka
  • Thailand
  • Vietnam

If you are travelling to a country where vaccination is recommended, visit your doctor or practice nurse at least six to eight weeks before you leave to discuss whether you should have the vaccination.

When is the vaccine recommended?

The Japanese encephalitis vaccine is recommended if:

  • you are planning to spend a month or longer in a high-risk country during the rainy season
  • you are planning to visit any rural areas in high-risk countries, even if only for a short time
  • you will be taking part in any activities that may increase your risk of becoming infected, such as visiting rice fields or pig farms, cycling, camping or fieldwork

The vaccine

There are two vaccines available for Japanese encephalitis. Ideally, they need to be completed a month before you leave. The preferred vaccine requires two doses, with the second dose given 28 days after the first.

The other vaccine consists of three doses and is suitable for children over the age of one. The second dose is given seven days after the first, and the third dose is given 28 days after this. This vaccine needs to be completed at least 10 days before you leave in case you have an allergic reaction.

Both vaccines require a booster after one year. The Japanese encephalitis vaccine is not suitable for babies younger than one.

The course can sometimes be accelerated, but it will need to be completed at least 10 days before you travel. You will need to have a booster three months later.

Side effects

Some people get side effects after having the vaccine. Between 10-20% of people may experience:

  • soreness, redness or swelling at the site of the injection
  • a high temperature of 38ºC (100.4ºF) or over
  • dizziness
  • headache
  • feeling sick
  • vomiting
  • abdominal pain
  • aching muscles

More serious side effects occur in around 0.6% of people. These include:

  • a raised, itchy red rash (urticaria, or hives)
  • swelling of the face
  • difficulty breathing

If you have any of these symptoms, see your doctor immediately .

When is the vaccine not recommended?

The Japanese encephalitis vaccine is not suitable for children under the age of one.

If you previously had a severe allergic reaction (anaphylaxis) to a Japanese encephalitis vaccine, or are allergic to any of the ingredients in the vaccine, do not take it.

You may be more at risk of having an adverse reaction to the vaccine if:

  • you have other allergies, such as allergic rhinitis or asthma
  • you have a condition that affects your nervous system (your brain, spinal cord and nerves), such as multiple sclerosis
  • you have had convulsions (fits) in the previous year

In all cases, the risks of catching the Japanese encephalitis virus will be weighed up against the risks of having an adverse reaction to the vaccine.

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