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Japanese encephalitis

Page last updated on 21 February 2020

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, although there have been cases reported in Australia, namely Northern Queensland and the Torres Strait. The first ever outbreak of JE in Australia occurred in the Torres Strait region (4 cases) and Cape York Peninsula (1 case) in 1995. Of this total of 5 cases, 2 were fatal.

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.  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 the associated symptoms, including headache, high fever, disorientation, coma, tremors and convulsions. 

How and when is Japanese encephalitis spread?

Japanese encephalitis (or JE) is spread 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.

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


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.

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Sources & Citations

  1. South Australian Government. Department of Health. Japanese Encephalitis. Available at (accessed 28 March 2018).
  2. Queensland Government. Department of Health. Communicable Disease Control Guidance. Japanese Encephalitis (v1 March 2010; v1.1 April 2011). Available at: (accessed 28 March 2018).
  3. NSW Government, Department of Health, Communicable Diseases Factsheet – Japanese Encephalitis. Available at; (accessed 28 March 2018).
  4. Centers for Disease Control and Prevention. Japanese Encephalitis. Available at: (accessed 28 March 2018).
  5. The Australian Immunisation Handbook 10th Edition. 4.8 Japanese Encephalitis. Available at (accessed 28 March 2018).
  6. Centers for Disease Control and Prevention. Japanese Encephalitis Prevention. Available at: (accessed 2 April 2018).
  7. Centers for Disease Control and Prevention. Japanese Encephalitis Geographic Distribution. Available at: (accessed 2 April 2018).
  8. Australian Government. Department of Health. National Notafiable Diseases Surveillance System. Number of notifications for all diseases by year, Australia, 1991 to 2017 and year-to-date notifications for 2018. Available at: (accessed 3 May 2018).
  9. NT Government. Japanese encephalitis. Available at: (accessed 11 May 2018).

SPANZ.IMOJ.18.04.0141 - Date of preparation May 2018