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Japanese Encephalitis

Ochlerotatus japonicus, formerly known as Aedes japonicus mosquitoJapanese encephalitis (JE) is a potentially severe disease caused by a virus spread by infected mosquitos in Asia and the western Pacific. JE virus is the leading cause of vaccine-preventable encephalitis (swelling of the brain) in Asia. For most travelers to Asia, the risk for JE is very low. It is higher for people living in areas where the disease is common, or for people traveling there for long periods of time.

The best way to prevent JE is to protect yourself from mosquito bites and get vaccinated before traveling to endemic areas if recommended by a healthcare professional.

Burden

JE occurs mainly in rural parts of Asia. Although most cases of JE are mild, the disease can be serious:

  • About 1 in 4 cases are fatal
  • Up to half of those who survive have permanent disability, including¬†neurologic, cognitive, or psychiatric symptoms

Symptoms

Most people infected with JE do not have symptoms or have only mild symptoms. It typically takes 5 to 15 days after the bite of an infected mosquito to develop symptoms which often include:

  • Fever
  • Chills
  • Headache
  • Nausea and vomiting
  • Fatigue

Initial symptoms may be followed by:

  • Mental status changes
  • Neurologic symptoms
  • Weakness
  • Movement disorders

A small percentage of infected people develop encephalitis (inflammation of the brain). Seizures are common, especially among children.

Prevention

JE can be prevented by avoiding mosquito bites:

  • Use insect repellent
  • Wear long-sleeved shirts and long pants
  • Use screens on windows and doors
  • Sleep under a mosquito bed net when outside or in a room that does not have screens

A JE vaccine is available in the US for people age 2 months and older. For most travelers, the risk of JE is very low. However, some travelers may be at greater risk for infection.

JE vaccine is recommended for people moving to a country where JE is common (endemic), long-term travelers (1 month or longer), and frequent travelers to JE-endemic areas. JE vaccine also should be considered for shorter-term travelers at increased risk of JE based on planned travel duration, season, location, activities, and accommodations.

If you are traveling to an area where JE is common, talk to a healthcare professional about whether JE vaccination is recommended for you.

JE vaccine is given as a 2-dose series. The last dose should be given at least 1 week before travel. A booster dose (third dose) may be needed for those who received the 2-dose primary vaccination series at least 1 year previously and continue to be at risk for JE virus infection or re-exposure.

Treatment

There are currently no specific drugs available to treat JE. Treatment focuses on relieving symptoms:

  • Rest
  • Drink plenty of fluids
  • Use pain relievers and medication to reduce fever

For some patients, hospitalization may be required for supportive care and close observation.

 

Reviewed March 2022

Source: Centers for Disease Control and Prevention