Health conditions

Japanese encephalitis

Japanese encephalitis is a vaccine-preventable disease caused by the Japanese encephalitis virus (JEV). It is spread to humans and other animals, such as waterbirds, pigs and horses, by infected mosquitoes.

How do you get it?

JEV can only be spread to humans by the bite of an infected mosquito. Mosquitoes become infected with the virus after feeding on an infected pig or waterbird. The virus cannot be spread from human to human, or from animal to human either by direct contact or by eating meat from an infected animal.

The incubation period (i.e. the time from being bitten by an infected mosquito to developing the disease) in humans is from 5 to 15 days.

Who is most at risk?

JEV is found throughout Asia and the Pacific region. A few Japanese encephalitis cases have previously been notified in far north Queensland, the Torres Strait and Tiwi Islands in the Northern Territory.

In early 2022, JEV was detected in the southeast of Australia (New South Wales, Victoria, South Australia) for the first time.

People are at risk of getting infected if they visit or live areas where JEV has been detected. This includes:

  • Travellers who plan to stay for more than a month in regions of Asia and the Pacific where JEV is present.
  • In Australia:
    • people who live or work on the outer islands of Torres Strait
    • people who work or live near commercial piggeries which have tested positive for JEV
    • people who engage in outdoor activities (e.g. camping, fishing and hiking) in regions where JEV has been detected
  • Laboratory workers who work with potentially infected samples.
What are the signs and symptoms?

Most people (more than 99%) infected with JEV do not develop symptoms. Less than 1% of infected people develop severe disease in the form of encephalitis (inflammation of the brain). Early symptoms include sudden onset of headache, high fever and vomiting. It may also cause confusion and affect the nervous system.

Severe disease can result in permanent neurological complications or death.

If you think you may be infected with JEV please seek urgent medical assistance.

How is it diagnosed?

JEV infection is usually diagnosed by testing blood or spinal fluid samples.

How is it treated?

There is no specific treatment for Japanese encephalitis. Treatment usually involves management of symptoms.

How is it prevented?

You can prevent Japanese encephalitis by getting a vaccination or avoid being bitten by mosquitoes.

Protect yourself from being bitten by mosquitoes by:

  • covering yourself with loose-fitting, long-sleeved clothing when outside
  • ensuring infants and children are adequately protected against mosquito bites with suitable clothing, including shoes/socks, and bed or pram netting
  • applying an effective mosquito repellent, containing diethyltoluamide (DEET) or picaridin, evenly to all areas of exposed skin, according to the label instructions
  • avoiding being outdoors at peak times of mosquito activity, particularly around dawn and dusk
  • removing potential mosquito breeding sites from around the home
  • ensuring window and door screens are installed and in good working order, with no holes.

The management and control of mosquitoes is also very important to reduce the risk of being bitten by infected mosquitoes.

Read more about preventing mosquito bites.

Two vaccines are available for protection against JEV in Australia and are very safe and effective for both adults and children.

Vaccination for Japanese encephalitis is recommended for:

  • people living on the outer islands of the Torres Strait and people working on the outer islands of Torres Strait for 30 days or more during the wet season (December to May)
  • travellers who plan to spend one month or more in endemic areas of in Asia and Papua New Guinea
  • all laboratory workers who may be exposed to JEV
  • people with occupational exposure to pigs and/or mosquitoes, with prioritisation for areas where JEV has been detected.1

For more detailed advice about the Japanese encephalitis vaccines see the Australian Immunisation Handbook (external site) and the Australian Government of Health JEV vaccines website (external site)1 which includes priority groups for vaccination in JEV affected regions in Australia.

Where to get help

  • Find a GP/doctor
  • Visit healthdirect (external site) or call 1800 022 222
  • For emergency or life-threatening conditions, visit an emergency department or dial triple zero (000) to call an ambulance

Acknowledgements

Public Health


This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.