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Japanese Encephalitis

Japanese encephalitis (JE) is a viral disease caused by a type of virus called a flavivirus. It is spread through the bite of an infected mosquito. In most cases, the illness is mild, with symptoms including headaches and a high temperature (fever).

Serious symptoms

JE can cause more serious symptoms, such as vomiting or seizures (convulsions). Encephalitis (inflammation of the brain) can develop in around 1 in 300 cases. Among those who develop more serious symptoms, there is around a 30% chance that JE can be fatal.

JE occurs throughout Southeast Asia, the Far East and the Pacific islands. The virus is found in pigs and birds, and is passed to mosquitoes that bite the infected animals. JE is more common in areas where there are pig farms and rice fields, both of which are ideal breeding grounds for mosquitoes.

JE is usually seasonal, occurring during the rainy season, and varies from country to country.

How common is Japanese encephalitis?

According to the World Health Organization (WHO), at least 50,000 people in Asia develop visible symptoms of Japanese encephalitis each year. Around 1 in 200 people develop more serious symptoms, which can lead to permanent brain damage or death.

Travellers are very rarely affected by JE. The American Center for Disease Control estimates that there is less than one case of JE for every million travellers. There have also only been two documented cases of UK travellers contracting JE, one in 1982 and one in 1994.

Outlook

Anyone who catches JE and recovers will develop immunity (resistance) to the virus. This means that if they become infected again, they should not experience any severe symptoms.

In areas where JE is common, older children and adults are often immune to JE. The more serious complications usually occur in young children who have caught JE for the first time. 

WHO estimates that there are around 10,000 deaths from JE every year, mainly in children.

There is currently no specific treatment for the virus that causes JE. However, a vaccination is available for travellers who may be at risk of catching the disease.

Symptoms

In most cases, the symptoms of Japanese encephalitis (JE) are mild. There may be no symptoms at all. However, in about 1 in 200 cases, the symptoms of JE are severe.

The virus affects the membranes around the brain. After a bite from an infected mosquito, it will take between 5 and 16 days for symptoms to appear.

Mild symptoms

For most people, JE has no symptoms or only mild, flu-like symptoms, such as headache or slightly high temperature.

Severe symptoms

More serious symptoms of JE include:

• high temperature (fever) of 38°C (100.4°F) or over,
• headache,
• vomiting,
• neck stiffness,
• confusion,
• feeling weak,
• coma (a sleep-like state when someone is unconscious for a long time),
• seizures (fits or convulsions),
• focal neurological deficits (a problem with a nerve in a specific location, such as the tongue),
• movement problems, such as shaking, stiffness, slowness of movement or paralysis, and
• meningitis (an infection of the meninges, which are the protective membranes that surround the brain and spinal cord).

These symptoms can appear suddenly and get rapidly worse. In around 1 in 300 cases of JE, the symptoms develop into encephalitis (inflammation of the brain). The rate of death among people who develop severe symptoms is around 30%.

As JE is caused by bites from infected mosquitoes, outbreaks of JE are usually linked to the mosquito population. A sudden increase in the mosquito population could cause a sudden outbreak of JE in humans. In some cases, the fatality rate during such an outbreak could be as high as 60%, particularly if many young children are affected.

Around 30% of those who survive a severe case of JE may be left with permanent damage to their central nervous system (the brain, nerves and spinal cord), such as:

• paralysis (loss of strength in a muscle so that you are unable to move it),
• ataxia (loss of physical coordination), or
• speech difficulties.

Causes

Japanese encephalitis (JE) is caused by a flavivirus. This is a type of virus that 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 JE 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

There are a number of factors that can increase your risk of catching JE. These include:

• the areas you visit,
• the time of year you visit them, and
• the activities you do.

Risk areas

JE 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, Korea, Malaysia, Indonesia and Singapore.

Cases of JE 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 JE 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.

The spread of JE is closely linked to areas of irrigated rice production and pig farming. The disease is less common in Muslim countries where pigs are not eaten and, therefore, not farmed.

Risk seasons

The occurrence of JE in humans usually coincides with the rainy seasons.

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

This pattern can vary. For example, farming communities who use irrigation to help their crops grow can flood their rice fields outside the rainy season. The water will attract infected mosquitoes at other times of the year.

Infected birds can change their migration patterns, so cases of JE may be seen at other times of the year or in different places. 

Risk activities

If you are planning a short visit to Asia, the risk of contracting JE is very low, particularly if you are going to be staying in urban areas. It is estimated that there is one case of JE for every million travellers. Activities that may increase your risk of developing JE include:

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

Among travellers who visit rural areas and stay for long periods, the risk of catching JE 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 experience any of the symptoms of Japanese encephalitis (JE) 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 or the advice on the Foreign and Commonwealth Office website. If you are back in the UK, visit your GP.

Your GP or the healthcare professional treating you will ask about your symptoms, what you have done on your trip and what vaccinations (if any) you have had.

Tests

Your GP 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 JE 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. This may be used because it can quickly diagnose meningitis and encephalitis, which are both serious symptoms of JE.

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 GP suspects that JE 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:

• a computerised tomography (CT) scan, which takes a series of X-rays of your body at slightly different angles to produce a clear image of the inside of your body, or
• a magnetic resonance imaging (MRI) scan, which uses a strong magnetic field and radio waves to produce detailed images of the inside of your body. 

Treatment

At the moment, there is no specific treatment for Japanese encephalitis (JE), 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). The healthcare professionals treating you will try to reduce your high temperature (fever) 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 have particular complications, such as encephalitis (inflammation in the brain), further treatment, such as medication, may be used.

Medical treatment abroad

Before leaving the UK, make sure you know how to access medical treatment in the country you are visiting. See Getting help abroad for advice.

The Foreign & Commonwealth Office website provides comprehensive travel advice by country, including information about UK embassies and consular offices. It also has a travel checklist that you should use before you leave.

Alternatively, talk to your travel agent, if you have one. You can also get information from the tourist office, embassy or high commission of the country you are visiting while you are there.

When getting medical treatment abroad, you may find the following advice useful.

• Make sure that you have all the documents you need, such as your passport, travel insurance details and European Health Insurance Card (EHIC) if travelling in Europe, proof of UK residence (for example, your driving licence or NHS card) and vaccination certificates.
• Contact your travel company representative, if you have one.
• Give the healthcare professional treating you the name of any medication (the generic name as well as the brand name) that you are taking.
• Tell them if you have been to any other countries during your trip.
• Keep the names and addresses of a few friends and relatives with your passport so that they can be contacted if necessary.
• Contact British Consular officials if you need to get back to the UK quickly. They may be able to arrange this for you, but you will have to pay.
• Keep all receipts, proof of purchase, price tags and labels of treatment or medication that you pay for and plan to claim on your insurance or get a refund for.

Vaccination

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

For up-to-date information about which countries are considered high risk for JE, check the NHS Fit for Travel website or the National Travel Health Network and Centre (NaTHNaC) website.

If you are travelling to a country where the vaccination is recommended, visit your GP 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.

When is the JE vaccine recommended?

The JE 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, or
• 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

Two vaccines for JE are currently available in the UK:

• IXIARO®, and
• 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 JE. 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 JE 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,
• nausea (feeling sick),
• vomiting,
• abdominal pain, or
• aching muscles.

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

• urticaria or hives (a raised, itchy red rash),
• swelling of the face, or
• 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 experience any of these symptoms, visit your GP immediately or call NHS Direct on 0845 4647.

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.

When is the JE vaccine not recommended?

The JE 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 JE 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, or
• you have had convulsions (fits) in the previous year.

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

Prevention

As the vaccination against Japanese encephalitis (JE) is not completely effective, 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 JE 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 GP or a local healthcare professional if you are abroad.