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Japanese Encephalitis: What to Know

Medically Reviewed by Neha Pathak, MD on March 09, 2022

What Is Japanese Encephalitis?

Japanese encephalitis is a viral infection spread by mosquitoes in Asia and the western Pacific. It’s the top cause of viral encephalitis (a potentially deadly brain inflammation) in these parts of the world.

If you’re traveling to countries in Asia or the western Pacific, you can take steps to lower your chances of getting Japanese encephalitis. Here’s what you need to know about this disease, including its possible symptoms, treatments, and more.

What Causes Japanese Encephalitis?

A bite from an infected mosquito causes it. Culex species mosquitoes usually get the Japanese encephalitis virus from pigs and wading birds before they pass the virus to people.

The virus doesn’t spread from person to person.

What Are the Symptoms of Japanese Encephalitis?

It’s rare to get symptoms from it. Less than 1% of infected people get sick.

If you do get symptoms, they usually start about 4 to 15 days after you were bitten. Many people who develop symptoms get a mild headache and fever. A child may throw up or tell you their stomach hurts.

The infection makes about 1 in 250 severely ill, though. Severe disease can bring on:

  • High fever
  • Headache
  • Neck stiffness
  • Confusion
  • Weakness
  • Trouble moving
  • Coma
  • Seizures (especially in children)

Call your doctor right away if you think you or a loved one is having symptoms of Japanese encephalitis.

About 1 in 4 people who develop severe disease die. Anywhere from 20% to 50% of people who get ill and survive have lasting symptoms, which could include paralysis, seizures, or loss of the ability to speak.

Where Has Japanese Encephalitis Spread?

There have been cases of Japanese encephalitis in these Asian and western Pacific countries. For most people traveling to Asia, the risk of getting it is low.

Your chances of getting bitten by an infected mosquito are higher in rural agricultural areas, usually ones where rice production and irrigation by flooding happens. But sometimes the mosquitoes can show up near urban areas.

Japanese encephalitis is seasonal in temperate parts of Asia, with more infections in the summer and fall. The disease can spread year-round in the subtropics and tropic areas. Most cases usually happen during the rainy season.

How Is Japanese Encephalitis Diagnosed?

Doctors diagnose it based on any symptoms you have, and they do blood or spinal fluid tests. Those tests can spot antibodies that your immune system makes to fight the infection.

How Is Japanese Encephalitis Treated?

Doctors don’t have a specific treatment for it. If you get severely ill, you may need to go to the hospital and get fluids through an IV or help breathing. Your care team will ease your symptoms and try to keep you comfortable while the virus runs its course.

Is There a Vaccine for Japanese Encephalitis?

Yes. In the United States, the Japanese encephalitis vaccine is a two-dose shot called Ixiaro. It’s approved for people 2 months old and older. Vaccines made in other countries aren’t licensed for use in the U.S.

From 1993 -- when a vaccine for Japanese encephalitis became available in the U.S. -- through 2017, doctors have reported 12 cases of Japanese encephalitis among American travelers.

The CDC recommends you get vaccinated with Ixiaro if you’re:

  • Moving to an Asian or western Pacific country where Japanese encephalitis is endemic (commonly found)
  • Traveling there for a month or longer, or visiting often
  • Traveling there for less than a month but facing a higher risk for infection, based on things like the season, your exact destination, the places you’ll be staying, and the things you’ll be doing

Ask your doctor if you should get vaccinated even if you’re not sure about the specifics of how long you’ll be traveling to an endemic area, the exact areas you’ll be visiting, or the activities you’ll be doing.

The CDC doesn’t recommend the Japanese encephalitis vaccine if you’re taking a short trip to urban areas or traveling during a season where the virus isn’t spreading as much. If you’re not sure whether you need to get the vaccine, check with your doctor and tell them about your travel plans.

If you get vaccinated with Ixiaro, you’ll need two doses. People 18 to 65 years old can get their second dose as early as 7 days after the first. Everyone else should get their second dose 28 days after the first.

You should get the second dose of the vaccine at least 1 week before you travel. And you should get a third (booster) dose if you got your first two shots a year ago or longer and you’re still at risk of catching the Japanese encephalitis virus.

In general, the vaccine can bring on mild side effects like:

  • Pain and tenderness around where you got the shot
  • Headache
  • Muscle aches
  • Low-grade fever

A dose of Ixiaro (0.5 milliliters, the amount that people 3 years old and up get) may cost anywhere from $250 to $340 or more without insurance, depending on which pharmacy you buy it from and what discounts you can get. If you have health insurance, you can call your insurer and ask if they cover any or all of the cost.

How Can You Prevent Japanese Encephalitis?

Aside from getting the Japanese encephalitis vaccine, your best defense against the virus is to avoid mosquito bites. These tips can help:

Use insect repellent. Choose one that’s registered by the EPA and has one of these active ingredients:

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

When you use EPA-registered bug repellents as directed, they’re safe and effective even if you’re pregnant or breastfeeding.

If you’re putting insect repellent on a child, take extra care to follow the instructions on the label exactly. Don’t use products that have oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD) on a child under 3 years old. Also, don’t put repellent on a child’s hands, eyes, or mouth, or on cuts or irritated skin. Spray repellent on your hands, then gently rub it on your little one’s face.

Wear long-sleeved clothes. If your child is traveling with you, dress them in long-sleeved pants and shirts, too.

You could consider treating your clothes and gear (like tents) with an insecticide called permethrin. You’d need to use a 0.5% solution of it and follow the product’s instructions exactly. Never put permethrin directly on your skin.

Keep bad bugs at bay. To help keep mosquitoes away, make sure the place where you’re staying has screens for its windows and doors. Get any holes in the screens fixed.

If you use a stroller or baby carriage for your little one, cover it with mosquito netting.

Use air conditioning if you can, rather than keeping windows and doors open.

Also, keep mosquitoes from laying their eggs in or near water. Once each week, empty and scrub, turn over, cover, or toss out any items that hold water (like tires, buckets, flowerpots, and outdoor trash cans). Also, look around indoors and outdoors for any containers where water could collect.

Show Sources

SOURCES:

CDC: “Japanese Encephalitis,” “Geographic Distribution of Japanese Encephalitis Virus .”

World Health Organization: “Japanese encephalitis.”

Up to Date: “Japanese encephalitis.”

Mayo Clinic: “Encephalitis.”

Cleveland Clinic: “Encephalitis.”

National Health Service: “Japanese encephalitis.”

Healthychildren.org: “Japanese Encephalitis Vaccine: What You Need to Know (VIS).”

FDA: “Ixiaro Prescribing Information.”

Drugs.com: “Ixiaro Prices, Coupons and Patient Assistance Programs.”

GoodRx: “Ixiaro.”

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