Understanding Japanese Encephalitis

Generally speaking, encephalitis refers to an inflammation of the brain tissue.  Japanese encephalitis refers to a type of encephalitis that is caused by a virus and is the leading cause of encephalitis in Asia and the western Pacific. This type of encephalitis is vaccine-preventable, and the risk of contraction is low, but still a concern for those traveling to Asia.  The risk for exposure varies by destination, season and the types of activities someone is involved in.


The virus is primarily carried by mosquitoes and infection happens when a human is bitten by an infected mosquito.   The mosquitos often become carriers for the virus from hosts like pigs and wading birds. Humans can be infected when bitten by an infected mosquito. Most often, when a human is infected, either no symptoms or only mild symptoms result.  The percentage of people who develop encephalitis, or the brain inflammation is very low, but still possible.  If the infection does develop, 1 in 4 cases result in death. As there is no specific treatment of Japanese encephalitis, preventing the disease is our best protection against it. 

What are the symptoms of Japanese encephalitis?

Initial symptoms:

·         Headache

·         Muscle aches

·         Fever

More severe infection symptoms:

·         Headache

·         High fever

·         Stiff neck

·         Stupor

·         Disorientation

·         Coma

·         Tremors

·         Seizures

·         Spastic paralysis

How do you prevent Japanese encephalitis?

Anyone travelling to Asia, and the western Pacific, where Japanese encephalitis is endemic should be mindful and take the appropriate precautions to avoid mosquito bites.  This will serve to greatly reduce the risk for the disease, as well as for other vector-borne infectious dis­eases. Alternatively, a vaccine is available for those who are at high risk for contracting Japanese encephalitis.  A traveler can be at higher risk for the disease depending on what season they are traveling, where they are traveling and how long they will be staying.   

Here are some quick recommendations to remember and reduce your risk for contracting the infectious disease:

  • Avoid mosquitos:
    • Use insect repellant
    • Wear proper clothing, to reduce exposed skin
    • Minimize outdoor activities during peak mosquito hours
  • Get the vaccine:
    • If you plan on spending over a month in endemic area
    • If you plan on traveling to an endemic area during transmission season
    • If you plan on spending extensive amount of time outdoors
    • If you plan on traveling to an area with an ongoing Japanese encephalitis outbreak

 Here are some quick facts to remember about Japanese Encephalitis:

·         Less than 1% of people infected with Japanese encephalitis virus develop the illness

·         Those who do develop symptoms, usually do not develop them until about a week after being infected as the incubation period is typically 5-15 days

·         Initial symptoms include: fever, headache, and vomiting

·         More severe symptoms include: mental status changes, neurologic symptoms, weakness, and movement disorders

·         Seizures are common, especially among children.