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Japanese Encephalitis


Japanese encephalitis is an arthropod-borne viral encephalitis (an inflammation of the brain caused by a virus spread by mosquitoes). 

It is not found in North America, but is considered the leading cause of viral encephalitis in Asia.

It is vaccine-preventable, and travelers should consult a travel clinic about their destinations to see if this is one disease to be concerned about.

Information for Health Professionals

Japanese B encephalitis (or, Japanese encephalitis) is a viral disease spread by infected mosquitoes. The risk of disease is greatest in parts of Southern and Eastern Asia, the Indian subcontinent, Micronesia and Melanesia. The risk of disease is greatest in rural areas, changes with the season and varies by region. It is not spread by mosquitoes in North America. 

In its early stages, Japanese encephalitis is similar to a flu-like illness.


Symptoms appear five to 15 days after infection and may include:

  • headache
  • fever
  • nausea
  • vomiting
  • diarrhea
  • confusion, and other changes in behaviour.

Anywhere from 50 to 300 cases occur for every clinical case identified. 


The causative agent is a virus belonging to the family Faviviridae. It is spread by the bite of mosquitoes belonging to the Culex genus. 

The disease is not spread from person to person.


Travelers of all ages are at risk of getting the disease if bitten by mosquitoes. Older travelers who get infected often develop symptoms of confusion or changes in behavior. In about one out of every 200 cases, the illness progresses to swelling of the brain. More than half of these cases end in permanent disability or death. 

Infection during the first six months of pregnancy may result in infection of the baby and miscarriage. 

There is currently no drug treatment for the disease - it can only run its course.


Detection of antibodies in the blood serum is the most common means of diagnosing Japanese encephalitis.


You can be immunized against Japanese encephalitis, although the risk for travelers who are staying less than 30 days in the regions listed above is low. The vaccine is recommended for travelers staying longer than one month, particularly if they are staying in rural areas. 

Use of the vaccine depends on:

  • the season when travelling
  • the destination
  • length of travel and
  • what you will be doing when you get there.

You should consult a travel clinic or your family doctor before you go. The vaccine is used for children over one year of age, and for adults. It is not generally recommended for pregnant travelers unless the risk of the infection outweighs the risk of the immunization. 

The vaccine is given in three doses in the arm over a period of 30 days. A booster dose may be considered at intervals of one to three years. You should allow 10 days between the time of your last shot and the time you leave for your trip to allow your body to develop immunity. The three dose series of this vaccine prevents Japanese encephalitis in about 9 out of 10 people. 

Possible side effects of the vaccine may include: 

  • tenderness, redness, swelling 
  • fever
  • headache
  • feeling unwell 
  • rash
  • chills
  • dizziness 
  • nausea
  • vomiting
  • abdominal pain

Many of these last only a short time and can be relieved by using acetaminophen. However, you should report any of these side effects if they last for longer than a few days and do not seem to be getting better. With any vaccine there is a possibility that an allergic reaction may occur. It can occur within minutes, or up to as many as nine days after the shot. 

Early reactions (within minutes or a few hours) may include:

  • hives
  • wheezy breathing, or
  • swelling of some part of the body.

If this happens, particularly swelling around the throat, immediately get to your family doctor or hospital emergency. It is suggested that persons stay in the clinic for at least 30 minutes after receiving an immunization shot for Japanese encephalitis. Also, you should not go on international travel within 10 days of immunization because of the possibility of delayed allergic reactions. You should remain in an area with easy access to medical care for the 10 days following your immunization with this particular vaccine. Report serious reactions to your local public health nurse or family doctor. 

Note: Acetaminophen is recommended if there is fever or pain following immunization. Acetylsalicylic acid (ASA or aspirin) must NOT be given to children. The vaccine will not be given if you have:

  • a moderate or severe illness
  • allergy to any part of the vaccine, including formalin, protamine sulfate, thimerosal, proteins of rodent or neural origin or a history of anaphylaxis following a previous dose of Japanese encephalitis vaccine.

Mature minor consent 

While every effort is made to seek parental or guardian consent prior to immunizations, children under the age of 19 who are able to fully understand the risks and benefits of specific immunizations may consent to or refuse such immunizations regardless of parental/guardian wishes. Appropriate steps are taken to avoid peer influence in these decisions. Parents/guardians and their minor children are advised to discuss consent issues. For further information, please contact your local health unit or department.


The best way to prevent this disease is to avoid being bitten by mosquitoes in the first place!

  • If you are taking part in outdoor activities between dusk and dawn, use insect repellent on all exposed skin (one containing at least 30% concentration of DEET). Follow application instructions carefully.
  • Wear light-coloured clothing with long sleeves, trousers and socks.
  • Sleep in places with screened windows and doors, or places which have air conditioning (so you can close the windows and doors without being too hot and uncomfortable).
  • Sleep under an intact, small-mesh mosquito net which has been sprayed with a permethrin (insecticide) preparation. Tuck mosquito net under mattress before nightfall. The mosquito net is particularly important if it is not possible to stop mosquitoes from entering your room.
  • Use insecticidal spray indoors in the evening.
  • Use non-perfumed cosmetics and toiletries. Mosquitoes are attracted to scented products.  

Control of Communicable Diseases Manual, Heymann, 2008.
Public Health Agency of Canada website.

Last Updated: March 13, 2012

SOURCE: Japanese Encephalitis ( )
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