Areas of heightened disease reporting: LO HI

Japanese Encephalitis

Spread By Mosquitos

Data Source For Areas Affected

The maps designate countries considered to be affected by a disease. Areas within countries may or may not be affected by a specific disease. Consult with a Travel Healthcare Provider or about your specific itinerary prior to travel.

Reporting activity data are provided by Sitata and derived from numerous sources, including official surveillance data and news reports. Reporting activity does not reflect current risk of infection with a disease. Not all areas report cases of disease; therefore, the absence of activity on the map does not indicate that a disease is not present. The relationship between the intensity of reporting activity and actual disease transmission is unknown and does not indicate a difference in risk. Maps do not reflect differential distribution of diseases within a country.

What Is It?

Japanese encephalitis is caused by a virus that is spread by mosquitos.

The Japanese encephalitis virus may be found in areas of Southeast Asia and the Western Pacific region. Although most Japanese encephalitis infections are mild (fever and headache) or have no symptoms, a small proportion develop clinical disease. Symptoms such as rapid onset of high fever, headache, neck stiffness, confusion, coma, seizures, and spastic paralysis may develop. While symptomatic Japanese encephalitis is rare, a proportion of individuals with symptoms such as encephalitis (swelling of the brain) die or suffer permanent neurologic or psychiatric consequences.

How is it Acquired?

Japanese encephalitis is spread by mosquitos.

The mosquitos that spread Japanese encephalitis are found in rural and suburban settings, are active at night, and bite people both indoors and outdoors.

In areas of Asia with milder temperatures, Japanese encephalitis virus is usually spread during the warm season; in more tropical or subtropical areas, the virus can be spread year round, but is more common during the rainy season.

For most travelers, the likelihood of acquiring Japanese encephalitis is extremely low.

The chance of getting infected by the Japanese encephalitis virus is higher for people traveling to rural areas, those who will be outside often, or those who will be in Asia for a long period of time. In milder climates of northern Asia, the chance of acquiring Japanese encephalitis is higher during summer and fall; in tropical and subtropical areas, it is year-round.

Signs and Symptoms

Most Japanese encephalitis infections are mild (fever and headache) or cause no symptoms.

A small proportion of people progress to severe Japanese encephalitis, which can include:

  • Rapid onset of high fever
  • Headache
  • Neck stiffness
  • Confusion
  • Coma
  • Seizures
  • Spastic paralysis

Among those who survive severe Japanese encephalitis, some suffer permanent problems such as paralysis, seizures, or the inability to speak.

Precautions to Take

Try to reduce the likelihood of mosquito bites. Some precautions include:

  • Sleeping in a room with window/door screens
  • Using air conditioning
  • Using mosquito repellent on bare skin
  • Treating clothes and shoes with mosquito repellent
  • Using a mosquito net treated with mosquito repellent over the bed
  • Wearing long pants and long-sleeved shirts, socks, and shoes

Discuss with your healthcare provider if you should be vaccinated for Japanese encephalitis.

Check out the Mosquito Protection Guidelines from the Centers for Disease Control and Prevention or the American Mosquito Control Association for more information.

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