Japanese encephalitis

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.

Since February 2022, JE cases have been detected in several Australian states and territories. While there have been no human cases of JE reported in WA, evidence of JEV activity was identified in the Kimberley region in late 2024 through the sentinel chicken surveillance program. It is possible that the virus may remain active at low levels in northern WA and could become more active if favourable environmental conditions support increased mosquito populations and animal hosts of the virus. For these reasons, WA continues to be considered a potential risk area.

JE is a vaccine-preventable disease. Persons eligible for vaccination are encouraged to get vaccinated against JE now. See Prevention section below for further details.

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.

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 essential for protecting yourself from JEV. Even if people are vaccinated, they should still take precautions to avoid mosquito bites, which will also protect them against other mosquito-borne diseases. No vaccine is 100 per cent 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
• use insecticide sprays, vapour dispensing units (indoors) and mosquito coils (outdoors) to clear rooms and repel mosquitoes from an area
• make sure accommodation, including tents, are properly fitted with mosquito nets or screens
• 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).

Vaccination

The WA Department of Health is currently offering free JE vaccine to eligible persons in the Kimberley and specific areas of the Pilbara. These areas are considered to be at highest risk of JEV transmission in WA, either because evidence of JEV activity has been detected nearby or there are habitats like wetlands, large numbers of waterbirds or feral pigs and JEV carrying mosquitoes nearby that could support JEV spread.

Eligible persons currently include:

• all residents in the Kimberley region
• all residents in the Pilbara region
• workers for mining companies with sites in the Kimberley and Pilbara region
• travellers to the Kimberley and Pilbara region.
• persons who work directly with mosquitoes in the Kimberley or Pilbara regions or handle live JEV (e.g. laboratory workers, entomologists).
• persons living or residing in specific postcodes in the Pilbara region who spend at least 4 hours per day outdoors for unavoidable activities.

There is limited supply of JE vaccines worldwide. Eligibility for vaccines will continue to be targeted to those at highest risk of JEV infection, taking into account vaccine supply availability.

Proof of eligibility

• Bring evidence of primary residence in an eligible postcode e.g. driver’s licence, Medicare card, utilities bill, or similar.
• Employees need to get a letter from their employers and bring it to their vaccination appointment as proof of eligibility. A template JE vaccine eligibility after employers in Kimberley and Pilbara are available for use.

Types of vaccines

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
• JEspect® (also known as Ixiaro) – a 2 – 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.

Where to get vaccinated

To report an adverse event following immunisation, contact the Western Australian Vaccine Safety Surveillance System (external site) by email wavss@health.wa.gov.au or phone (08) 6456 0208.

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

Further information

• 2023 WA JEV Vaccination Program Frequently Asked Questions (FAQs)
• Japanese encephalitis: Information for WA local government and industry
• Japanese encephalitis | Australian Government Department of Health and Aged Care
• Japanese encephalitis virus (JEV) vaccines | Australian Government Department of Health and Aged Care