Japanese encephalitis (JE) virus is the leading cause of vaccine-preventable encephalitis in Asia and the western Pacific. For most travelers to Asia, the risk for JE is very low but varies based on destination, length of travel, season, and activities. Most people infected with JE do not have symptoms or have only mild symptoms. However, a small percentage of infected people develop inflammation of the brain (encephalitis), with symptoms including sudden onset of headache, high fever, disorientation, coma, tremors and convulsions. About 1 in 4 cases are fatal. To prevent getting sick from JE, use an EPA-registered insect repellent, wear long-sleeved shirts and long pants, and get vaccinated.

What is Japanese encephalitis?

Japanese encephalitis (JE) is a potentially severe disease. JE is caused by a virus spread by infected mosquitoes in Asia and the western Pacific. JE virus is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis).

Where does Japanese encephalitis occur?

JE occurs in Asia and parts of the western Pacific. It usually occurs in rural or agricultural areas, often associated with rice farming. In temperate areas of Asia, transmission is seasonal, and human disease usually peaks in the summer and fall. In the subtropics and tropics, transmission can occur year-round, often with a peak during the rainy season.

How soon do people get sick after being bitten by an infected mosquito?

It takes 5 to 15 days after the bite of an infected mosquito to develop symptoms.

What are the symptoms of Japanese encephalitis?

Most people who are infected develop mild symptoms or no symptoms at all. In people who develop severe disease, initial symptoms include fever, chills, headache, fatigue, nausea and vomiting. The disease can progress to inflammation of the brain (encephalitis) and is often accompanied by seizures. Coma and paralysis occur in some cases.

How is Japanese encephalitis diagnosed?

Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid. These tests typically detect antibodies that the immune system makes against the viral infection.

What is the treatment for Japanese encephalitis?

There is no specific treatment. Severe illnesses are treated by supportive therapy which may include hospitalization, respiratory support, and intravenous fluids.

What should I do if I think a family member might have Japanese encephalitis?

Consult a healthcare provider for evaluation and diagnosis.

How can people reduce the chance of getting infected?

• Use insect repellent and wear long pants and sleeves
• Sleep in air-conditioned or well-screened rooms or use bed nets
• A vaccine against JE virus is available. Talk to your healthcare provider about whether this vaccine is right for you.

Who should get Japanese encephalitis vaccine?

JE vaccine is recommended for persons moving to a JE-endemic country to live, longer-term (e.g., 1 month or longer) travelers, and frequent travelers to JE-endemic areas. JE vaccine also should be considered for shorter-term (e.g., less than 1 month) travelers with an increased risk of JE based on planned travel duration, season, location, activities, and accommodations. Vaccination also should be considered for travelers to endemic areas who are uncertain of specific duration of travel, destinations, or activities.

JE vaccine is not recommended for travelers with very low risk itineraries, such as shorter-term travel limited to urban areas or travel that occurs outside of a well-defined JE virus transmission season.

How long does the Japanese encephalitis vaccination last?

The duration of protection is unknown. A booster dose may be given if the primary two-dose vaccination series was given one year or more previously and there is continued risk of exposure.

What are the side effects of Japanese encephalitis vaccination?

Pain and tenderness are the most commonly reported symptoms. Headache, muscle pain and fatigue can also occur.

I think I got sick from the vaccine, what should I do?

Consult with your healthcare provider. Ask your healthcare provider to report your case to the Vaccine Adverse Events Reporting System (VAERS) if he or she thinks the vaccine has made you sick.

Japanese encephalitis (JE) virus, a flavivirus, is closely related to West Nile and St. Louis encephalitis viruses. JE virus is transmitted to humans through the bite of infected Culex species mosquitoes, particularly Culex tritaeniorhynchus.

The virus is maintained in a cycle between mosquitoes and vertebrate hosts, primarily pigs and wading birds. Humans are incidental or dead-end hosts, because they usually do not develop high enough concentrations of JE virus in their bloodstreams to infect feeding mosquitoes.

JE virus transmission occurs primarily in rural agricultural areas, often associated with rice production and flooding irrigation. In some areas of Asia, these conditions can occur near urban centers.

In temperate areas of Asia, JE virus transmission is seasonal. Human disease usually peaks in the summer and fall. In the subtropics and tropics, transmission can occur year-round, often with a peak during the rainy season.

Countries in which Japanese encephalitis virus has been identified

• Australia
• Bangladesh
• Brunei*
• Burma
• Cambodia
• China
• Guam
• India
• Indonesia
• Japan
• Laos
• Malaysia
• Nepal
• North Korea
• Pakistan
• Papua New Guinea
• Phillipines
• Russia
• Saipan
• Singapore
• South Korea
• Sri Lanka
• Taiwan
• Thailand
• Timor-Leste
• Vietnam

• Less than 1% of people infected with Japanese encephalitis (JE) virus develop clinical illness.
• In persons who develop symptoms, the incubation period (time from infection until illness) is typically 5-15 days.
• Initial symptoms often include fever, headache, and vomiting.
• Mental status changes, neurologic symptoms, weakness, and movement disorders might develop over the next few days.
• Seizures are common, especially among children.

Japanese encephalitis (JE) should be considered in a patient with evidence of a neurologic infection (e.g., meningitis, encephalitis, or acute flaccid paralysis) who has recently traveled to or resided in an endemic country in Asia or the western Pacific.

Laboratory diagnosis of JE is generally accomplished by testing of serum or cerebrospinal fluid (CSF) to detect virus-specific IgM antibodies. JE virus IgM antibodies are usually detectable 3 to 8 days after onset of illness and persist for 30 to 90 days, but longer persistence has been documented. Therefore, positive IgM antibodies occasionally may reflect a past infection or vaccination. Serum collected within 10 days of illness onset may not have detectable IgM, and the test should be repeated on a convalescent sample. For patients with JE virus IgM antibodies, confirmatory neutralizing antibody testing should be performed. In fatal cases, nucleic acid amplification, histopathology with immunohistochemistry, and virus culture of autopsy tissues can also be useful.

Treatment

• No specific treatments have been found to benefit patients with JE, but hospitalization for supportive care and close observation is generally required.
• Treatment is symptomatic. Rest, fluids, and use of pain relievers and medication to reduce fever may relieve some symptoms.

Outcome

• Among patients who develop encephalitis, 20% – 30% die.
• Although some symptoms improve after the acute illness, 30%-50% of survivors continue to have neurologic, cognitive, or psychiatric symptoms.

The most effective way to prevent infection from Japanese Encephalitis virus is to prevent mosquito bites. Mosquitoes bite during the day and night. Use insect repellent, wear long-sleeved shirts and pants, treat clothing and gear, and get vaccinated before traveling, if vaccination is recommended for you.

Protect yourself and your family from mosquito bites

Use Insect Repellent

Use Environmental Protection Agency (EPA)-registered insect repellents with one of the active ingredients below. When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breastfeeding women.

• DEET
• Picaridin (known as KBR 3023 and icaridin outside the US)
• IR3535
• Oil of lemon eucalyptus (OLE)
• Para-menthane-diol (PMD)
• 2-undecanone

Tips for babies and children

• Always follow instructions when applying insect repellent to children.
• Do not use insect repellent on babies younger than 2 months old.
  • Instead, dress your child in clothing that covers arms and legs.
  • Cover strollers and baby carriers with mosquito netting.
• Do not use products containing oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD) on children under 3 years old.
• Do not apply insect repellent to a child’s hands, eyes, mouth, cuts, or irritated skin.
  • Adults: Spray insect repellent onto your hands and then apply to a child’s face.

Tips for Everyone

• Always follow the product label instructions.
• Reapply insect repellent as directed.
  • Do not spray repellent on the skin under clothing.
  • If you are also using sunscreen, apply sunscreen first and insect repellent second.

Natural insect repellents (repellents not registered with EPA)

• We do not know the effectiveness of non-EPA registered insect repellents, including some natural repellents.
• To protect yourself against diseases spread by mosquitoes, CDC and EPA recommend using an EPA-registered insect repellent.
• Choosing an EPA-registered repellent ensures the EPA has evaluated the product for effectiveness.

Wear long-sleeved shirts and long pants

Treat clothing and gear

• Use permethrin to treat clothing and gear (such as boots, pants, socks, and tents) or buy permethrin-treated clothing and gear.
  • Permethrin is an insecticide that kills or repels mosquitoes.
  • Permethrin-treated clothing provides protection after multiple washings.
  • Read product information to find out how long the protection will last.

  If treating items yourself, follow the product instructions.

• Do not use permethrin products directly on skin.

Take steps to control mosquitoes indoors and outdoors

• Use screens on windows and doors. Repair holes in screens to keep mosquitoes outdoors.
• Use air conditioning, if available.
• Stop mosquitoes from laying eggs in or near water.
  • Once a week, empty and scrub, turn over, cover, or throw out items that hold water, such as tires, buckets, planters, toys, pools, birdbaths, flowerpots, or trash containers.
  • Check indoors and outdoors.

Prevent mosquito bites when traveling overseas

• Choose a hotel or lodging with air conditioning or screens on windows and doors.
• Sleep under a mosquito bed net if you are outside or in a room that does not have screens.
  • Buy a bed net at your local outdoor store or online before traveling overseas.
  • Choose a WHOPES-approved bed net: compact, white, rectangular, with 156 holes per square inch, and long enough to tuck under the mattress.
  • Permethrin-treated bed nets provide more protection than untreated nets.
    • Do not wash bed nets or expose them to sunlight. This will break down the insecticide more quickly.

Inactivated Vero cell culture-derived Japanese encephalitis (JE) vaccine (manufactured as IXIARO) is the only JE vaccine licensed and available in the United States. This vaccine was approved in March 2009 for use in people aged 17 years and older and in May 2013 for use in children 2 months through 16 years of age. Other JE vaccines are manufactured and used in other countries but are not licensed for use in the United States.

IXIARO is given as a two-dose series, with the doses spaced 28 days apart. Adults aged 18–65 years can get the second dose as early as 7 days after the first dose. The last dose should be given at least 1 week before travel. A booster dose (third dose) should be given if a person has received the two-dose primary vaccination series one year or more previously and there is a continued risk for JE virus infection or potential for reexposure.

For adults and children aged 3 years or older, each dose of IXIARO is 0.5 mL. For children aged 2 months through 2 years, each dose is 0.25 mL.

JE Vaccine for Travelers

JE is a very low risk disease for most travelers to JE-endemic countries. However, some travelers will be at increased risk of infection based on factors including longer periods of travel, travel during the JE virus transmission season, spending time in rural areas, participating in a lot of outdoor activities, and staying in accommodations without air conditioning, screens, or bed nets.

All travelers to JE-endemic countries should take steps to avoid mosquito bites, and discuss the need for vaccination with their healthcare provider. The discussion should include the risks related to the specific travel itinerary, the likelihood of future travel to countries where JE occurs, the possible severe outcomes of JE disease, and information about the vaccine including cost and possible side effects.

JE Vaccine Recommendations

JE vaccine is recommended for persons moving to a JE-endemic country to live, longer-term (e.g., 1 month or longer) travelers, and frequent travelers to JE-endemic areas. JE vaccine also should be considered for shorter-term (e.g., less than 1 month) travelers with an increased risk of JE based on planned travel duration, season, location, activities, and accommodations. Vaccination also should be considered for travelers to endemic areas who are uncertain of specific duration of travel, destinations, or activities.

JE vaccine is not recommended for travelers with very low risk itineraries, such as shorter-term travel limited to urban areas or travel that occurs outside of a well-defined JE virus transmission season.

Precautions and Contraindications

• A serious allergic reaction after a previous dose of IXIARO, after any other JE vaccine, or after any component of IXIARO is a contraindication to further doses. The vaccine contains protamine sulfate, a compound known to cause allergic reactions in some people.
• No studies of IXIARO in pregnant women have been conducted. Therefore, administration of IXIARO to pregnant women usually should be deferred. However, pregnant women who must travel to an area where risk for infection is high should be vaccinated when the theoretical risk of immunization is outweighed by the risk of infection.

Reactions to JE Vaccine

Reactions to IXIARO are generally mild and include pain and tenderness, mild headaches, myalgia (muscle aches), and low-grade fevers.

What is Japanese encephalitis?

Japanese encephalitis virus is spread to people through the bite of an infected mosquito.

Most people who get infected experience mild or no symptoms. In people who develop severe disease, early symptoms include fever, headache, and vomiting. These symptoms may be followed by disorientation, coma, and seizures. Seizures are more common in children.

Who is at risk?

Travelers to some parts of Asia and the Western Pacific can get infected if bitten by an infected mosquito. However, for most travelers the chance of getting infected with Japanese encephalitis is low.

Activities that can increase a traveler’s chance of getting Japanese encephalitis include:

• Spending a lot of time outdoors
• Traveling during times of the year when mosquitoes are more common, such as during the summer
• Traveling for long periods of time in a place that has Japanese encephalitis

In places with four seasons, your chances of getting Japanese encephalitis are greatest in the summer and fall. In tropical and subtropical areas, mosquitoes spread the virus all year long.

What can travelers do to prevent Japanese encephalitis?

Travelers can protect themselves against Japanese encephalitis by taking the following steps.

Get vaccinated if recommended:

Japanese encephalitis vaccine is recommended for travelers who

• Are moving to an area with Japanese encephalitis to live
• Spend long periods of time, such as a month or more, in areas with Japanese encephalitis
• Frequently travel to areas with Japanese encephalitis

Consider vaccination for travelers

• Spending less than a month in areas with Japanese encephalitis but will be doing activities that increase risk of infection, such as visiting rural areas, hiking or camping, or staying in places without air conditioning, screens, or bed nets
• Going to areas with Japanese encephalitis who are uncertain of their activities or how long they will be there

Not recommended for travelers planning short-term travel to urban areas or travel to areas with no clear Japanese encephalitis season.

Use an EPA-registered insect repellent

• Use Environmental Protection Agency (EPA)-registered insect repellents with one of the active ingredients below. When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breastfeeding women. If also using sunscreen, always apply insect repellent after sunscreen.
  • DEET
  • Picaridin (known as KBR 3023 and icaridin outside the US)
  • IR3535
  • Oil of lemon eucalyptus (OLE)
  • Para-menthane-diol (PMD)
  • 2-undecanone

Find the right insect repellent for you by using EPA's search tool.

• Insect Repellent Tips for Babies and Children
  • Dress your child in clothing that covers arms and legs.
  • Cover strollers and baby carriers with mosquito netting.
  • When using insect repellent on your child:
    • Always follow label instructions.
    • Do not use products containing oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD) on children under 3 years old.
    • Do not apply insect repellent to a child’s hands, eyes, mouth, cuts, or irritated skin.
      • Adults: Spray insect repellent onto your hands and then apply to a child’s face.
    • If also using sunscreen, always apply insect repellent after sunscreen.

Wear long-sleeved shirts and long pants

Treat clothing and gear with permethrin

• Use 0.5% permethrin to treat clothing and gear (such as boots, pants, socks, and tents) or buy permethrin-treated clothing and gear.
  • Permethrin is an insecticide that kills or repels mosquitoes.
  • Permethrin-treated clothing provides protection after multiple washings.
  • Read product information to find out how long the protection will last.
• If treating items yourself, follow the product instructions.
• Do not use permethrin products directly on skin.
• Watch the CDC video How to Use Permethrin.

Keep mosquitoes out of your hotel room or lodging

• Choose a hotel or lodging with air conditioning or window and door screens.
• Use a mosquito net if you are unable to stay in a place with air conditioning or window and door screens or if you are sleeping outside.

Sleep under a mosquito net

• Sleep under a mosquito net if you are outside or when screened rooms are not available. Mosquitoes can live indoors and bite during the day and night.
• Buy a mosquito net at your local outdoor store or online before traveling overseas.
• Choose a mosquito net that is compact, white, rectangular, with 156 holes per square inch, and long enough to tuck under the mattress.
• Permethrin-treated mosquito nets provide more protection than untreated nets.
  • Permethrin is an insecticide that kills mosquitoes and other insects.
  • To determine if you can wash a treated mosquito net, follow the label instructions.

If you are bitten by mosquitoes, avoid scratching the bites and apply over-the-counter anti-itch or antihistamine cream to relieve itching.

If you traveled and feel sick, particularly if you have a fever, talk to a healthcare provider, and tell them about your travel. Avoid contact with other people while you are sick.