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Japanese encephalitis

Page last updated on 17 February 2021

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

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 and one on the Cape York Peninsula. There have been no outbreaks in Australia since 1998.

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 mosquitos 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.1  However, in a small number of cases, severe neurological (nervous system) symptoms may be experienced, and may be fatal in 25-30% of these cases.

Key disease information

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 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 (approaching 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.

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 five 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.

How Japanese encephalitis can be prevented?

There are two main methods for preventing infection with Japanese encephalitis: vaccination and avoiding mosquito bites.

The Australian Government recommends vaccination for people (older than 1 year) traveling for one month or longer to high-risk countries. This especially if travelling in the wet season, participating in any outdoor activities, or visiting rural areas. Vaccination should be completed at least 1-2 weeks before travelling. For further information regarding vaccination, speak with your healthcare professional.

Recommended ways to decrease the likelihood of mosquito bites include:

  • Wearing loose-fitting, long-sleeved shirts and long pants
  • Using high strength mosquito repellent on exposed skin and clothes
  • Being extra vigilant from dusk to dawn (peak mosquito biting hours for species which transmit Japanese encephalitis)
  • Removing or covering still water, e.g. water buckets
  • Ensuring windows and doors are closed or screened
  • Using a mosquito net over sleeping areas, and spraying it with mosquito repellent or insecticide.

VaccineHub offers general information only. Please see a healthcare professional for medical advice

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Sources & Citations

  1. Australian Government, Department of Health. The Australian Immunisation Handbook. Japanese encephalitis. Available at: (accessed 10 March 2020).
  2. NSW Government, Department of Health. Japanese encephalitis fact sheet. Available at; (accessed 10 March 2020).
  3. National Notifiable Diseases Surveillance System. Number of notifications of Japanese encephalitis, Australia, in the period of 1991 to 2019 and year-to-date notifications for 2020. Available at: (Accessed 19 March 2020).
  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. Northern Territory Government. Japanese encephalitis. Available at: (accessed 10 March 2020).
  7. Centers for Disease Control and Prevention. Japanese encephalitis – symptoms & treatment. Available at: (accessed 10 March 2020).
  8. Centers for Disease Control and Prevention. Japanese encephalitis – transmission. Available at: (accessed 10 March 2020).
  9. Centers for Disease Control and Prevention. Chapter 4 – Travel-related infectious diseases - Japanese Encephalitis. Available at: (accessed 10 March 2020).
  10. Centers for Disease Control and Prevention. Japanese encephalitis – prevention. Available at: (accessed 10 March 2020).

SPANZ.IMOJ.18.04.0141(1) - Date of preparation March 2020