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Japanese encephalitis

Japanese encephalitis (JE) is a viral infection of the brain spread by the bite of an infected mosquito.

Page last updated 18 January 2024

JE is commonly found in many Asian countries, including Southeast Asia, India and China. Most cases reported in Australia are in travellers to these countries, however, occasional outbreaks have occurred in the very North of Australia, with 4 cases occurring in the Torres Strait Region, one on the Cape York Peninsula and one on the Tiwi Islands.

Pigs and wild water birds (breeds not found in Australia) play an important role in the spread of JE. The virus multiplies in infected pigs, causing very high levels of the virus in their bloodstream. When a mosquito ‘feeds’ on an infected pig they are able to pick up the virus and spread it on to humans.

The risk of JE to humans is highest during or just after the wet season, when large numbers of mosquitoes are present and are able to live longer, thus increasing the chance of virus transmission.

In the majority of cases, an infected person does not experience any illness.  However, in a small number of cases, severe neurological (nervous system) symptoms may be experienced, and may be fatal in 10 - 30% of these cases.

For further information regarding vaccination against Japanese Encephalitis, speak with your healthcare professional.

Commonly asked questions

What is Japanese encephalitis?


Japanese encephalitis (or JE) is a rare but serious viral infection of the human brain caused by the bite of a particular type of infected mosquito. The disease is rarely found in mainland Australia, however, it is relatively common in many parts of Asia (e.g. Southeast Asia, India, China).

In the vast majority of cases (about 99%), people will experience very mild or no symptoms from an infection. In a small number of cases, infection may lead to swelling of the brain (encephalitis) and its associated symptoms, including headache, high fever, disorientation, coma, tremors and convulsions.  In people who do develop the disease, 10-30% will die and 50% will have a permanent disability.

How and when is Japanese encephalitis spread?

Japanese encephalitis (JE) is spread to humans by the bite of an infected mosquito. The disease cannot be spread from person to person.

Transmission of JE mainly occurs in rural, agricultural areas of Southeast Asia where standing water is used for rice production and flooding irrigation. In some areas of Asia, these conditions can occur near urban centres.

JE transmission is seasonal in some areas of Asia, with the disease peaking around summer and autumn. In the more tropical and subtropical regions, such as Thailand, Cambodia and Vietnam, transmission can occur all year round, with a peak during the rainy season from May to October/November. In Indonesia, peak season varies by island.

In the outer Torres Strait islands, transmission season is December to May.

Is Japanese encephalitis contagious?

While Japanese encephalitis cannot be spread from person to person, the disease can be spread by the bite of certain types of (infected) mosquitoes.

What are the symptoms of Japanese encephalitis?

For most people (around 99%), there will be no symptoms of infection. However, in a small number of cases, symptoms of Japanese encephalitis may begin 5-15 days after infection from a mosquito bite.  

The initial symptoms may be severe shivering and chills, fever, headache, nausea and a stiff neck. Neurological (nervous system) symptoms may include disorientation, unconsciousness, tremors, seizures, convulsions, paralysis, coma, and death. Recovery can take a long period of time, and carries a high likelihood of on-going neurological symptoms, including deafness and partial paralysis.




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

What countries are affected by Japanese encephalitis?

Japanese encephalitis is found mostly in Asia - from India in the west to North and South Korea, and Japan in the northeast. It is also found from Thailand, Singapore, and Malaysia in the south, to Indonesia, Timor, and Papua New Guinea in the southeast.

Only six cases have been identified as acquired in Australia; and none have been identified since 1998. All other cases diagnosed in Australia have been acquired overseas.

Sources & Citations

  1. Australian Government Department of Health. The Australian Immunisation Handbook. Japanese encephalitis. Available at: (accessed 16 November 2021).
  2. NSW Government Department of Health. Japanese encephalitis fact sheet. Available at: (accessed 16 November 2021).
  3. Northern Territory Government. Japanese encephalitis. Available at: (accessed 16 November 2021).
  4. Hanna JN et al. Med J Aust 1996;165(5):256–60.
  5. Hanna JN et al. Med J Aust 1999;170(11):533–6.
  6. Centers for Disease Control and Prevention. Japanese encephalitis – symptoms & treatment. Available at: (accessed 16 November 2021).
  7. Centers for Disease Control and Prevention. Japanese encephalitis – transmission. Available at: (accessed 16 November 2021).
  8. Centers for Disease Control and Prevention. Chapter 4 – Travel-related infectious diseases - Japanese Encephalitis. Available at: (accessed 16 November 2021).
  9. Centers for Disease Control and Prevention. Japanese encephalitis – prevention. Available at: (accessed 16 November 2021).

MAT-AU-2102453  Date of preparation  December 2021