Health conditions

Japanese encephalitis

Japanese encephalitis (JE) is a rare but serious disease that is caused by the Japanese encephalitis virus (JEV). JEV is spread to humans and other animals, such as waterbirds, pigs and horses, by infected mosquitoes. JEV cannot be transmitted (by contact) from person to person, from animal to person, nor transmitted by eating meat from an infected animal.

At risk groups

JEV is typically found throughout Asia and the Pacific region, with historically a small number of notifications in far north Queensland, the Torres Strait and the Tiwi Islands in the Northern Territory.

At risk groups are:

  • Laboratory workers who may be exposed to JEV
  • Travellers spending 1 month or more in endemic areas during the JEV transmission season
  • People who live or work on the outer islands of the Torres Strait.

Since February 2022, JE cases have been detected across several Australian states and territories. Following this outbreak, the Communicable Disease Network of Australia has identified additional at-risk groups as:

  • Persons with an occupational/residential exposure to, or a planned, non-deferable visit to a piggery or pork abattoir/rendering plant
  • Persons working directly with mosquitoes (surveillance, control, or management)
  • Persons working with sentinel animals (vertebrate mosquito-borne disease surveillance systems).
Signs and symptoms

Most people infected with JEV do not develop symptoms. However, in rare cases (less than 1% of infected people) encephalitis (swelling of the brain) may develop which can lead to death or long-term damage to the nervous system. Signs and symptoms of severe JE include headache, fever, convulsions, decreased consciousness (becoming drowsy or unresponsive), and disorders of the muscles, including paralysis.

Children under the age of 5 years and older people who are infected with JEV are at a higher risk of developing more severe illness, such as encephalitis. Infection during pregnancy can result in an increased risk of miscarriage and other complications.

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

If you are experiencing symptoms, especially if you have visited affected regions, please seek urgent medical assistance.

Diagnosis and treatment

JEV infection is usually diagnosed by testing blood or spinal fluid samples. Under the Public Health Regulations 2017 (WA) JE is an urgently notifiable infectious disease in Western Australia (WA).

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


Taking steps to avoid mosquito bites is the best protection against JEV. Even if people are vaccinated, they should still use precautions to protect against mosquito bites, which will also protect them against other mosquito-borne diseases. No vaccine is 100% effective and the JE vaccine takes a few weeks to provide protection.

Ways to protect yourself from mosquito bites include:

  • apply and regularly reapply an effective insect repellent on exposed skin, ensuring you follow the instructions on the label
  • wear long, loose fitting clothing when outside
  • make sure accommodation, including tents, are properly fitted with mosquito nets or screens
  • use insecticide sprays, vapour dispensing units (indoors) and mosquito coils (outdoors) to clear rooms and repel mosquitoes from an area
  • cover all windows, doors, vents and other entrances with insect screens
  • remove any water-holding containers where mosquitoes may breed.

Effective mosquito repellents contain diethyltoluamide (DEET), picaridin, or oil of lemon eucalyptus (OLE).


For persons at increased risk of exposure to JEV, there are two vaccines available in Australia which are safe and effective for both adults and children.

  • Imojev® – a single dose, live attenuated virus vaccine; cannot be given to those who are pregnant or breastfeeding, or people who are immunocompromised.
  • JEspect® – a two dose, inactivated vaccine (given 28 days apart)

If you are pregnant or immunocompromised, please consult with your immunisation provider to ensure you receive the right vaccine.

To report an adverse event following immunisation, contact the Western Australian Vaccine Safety Surveillance System (external site), email or phone (08) 6456 0208.

For more information about the JE vaccines, please refer to the Japanese encephalitis virus (JEV) vaccines | Australian Government Department of Health and Aged Care.

Further information

Where to get help

  • Find a GP/doctor
  • Consult with your GP, immunisation provider or HealthDirect on 1800 022 222 (available 24 hours)
  • For emergency or life-threatening conditions, visit your nearest emergency department or call 000 for an ambulance.


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.