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. The best protection against JEV is to avoid mosquito bites. Even people vaccinated against JEV should protect themselves against other mosquito-borne diseases. No vaccine is 100 per cent effective and the JEV vaccine takes a few weeks to provide protection.

Ways to protect yourself from mosquito bites are to:

• Cover up and wear long, loose-fitting, light-coloured clothing that covers as much of the body as possible. Cover all windows, doors, vents, and other entrances with insect screens, and use mosquito nets when camping or in areas with high mosquito activity.
• Repel by evenly applying to exposed skin an effective insect repellent containing DEET (diethyltoluamide), picaridin or oil of lemon eucalyptus (OLE, also known as PMD). Use insecticide sprays, vapour dispensing units (indoors), and mosquito coils (outdoors) to clear rooms and repel mosquitoes from an area.
• Clean up by removing, emptying or covering water-holding containers. Keep your grass short to stop mosquitoes hanging around your home.