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At a glance
- Vaccine preventable – check who’s eligible
- Nationally notifiable disease
About Japanese encephalitis
Japanese encephalitis is a rare but serious infection of the central nervous system. It is caused by the Japanese encephalitis virus (JEV) and is spread by mosquitoes.
For the vast majority of people, JEV infection is mild – only about 1% to 4% get any symptoms.
For those who get symptoms, it can be very serious and cause severe and permanent complications, or death.
Why it matters to public health
Japanese encephalitis is a serious disease with no specific treatment.
As many as 1 in 3 people who develop encephalitis die from the disease. Of those who survive, up to half suffer permanent cognitive, behavioural or neurological complications.
Because of these major impacts, we:
- work with colleagues in the animal and environmental sectors at the national and state and territory levels to ensure a One Health coordinated approach to monitoring and reporting of JEV
- plan for how to manage outbreaks.
Symptoms
If you’re looking for advice about your own health or treatment options, see healthdirect or speak with a qualified healthcare professional. Our role is to provide public health advice – information and guidance that helps prevent disease, protect communities and improve wellbeing at a population level.
Common early symptoms include:
Neurological symptoms might then develop over the following few days, including:
- confusion and agitation
- paralysis
- convulsions and seizures
- coma.
Read more about symptoms, diagnosis and treatment of Japanese encephalitis.
healthdirect’s symptom checker can help you decide whether to see a health professional.
Onset of symptoms
Symptoms usually start between 5 and 15 days after an infected mosquito bite. This is known as the incubation period.
How it spreads
JEV is spread through bites of certain species of mosquitoes after they have become infected from feeding on infected waterbirds or pigs.
These mosquitoes are usually active:
- from mid-spring to late autumn in south-eastern Australia
- all year in northern Australia.
The risks vary depending on location, season, weather and other local factors.
Humans cannot pass on the disease, as we do not develop high enough concentrations of JEV in our blood to infect mosquitoes.
Infectious period
JEV does not transmit from person to person.
Prevention
Vaccination
Japanese encephalitis is vaccine preventable.
See who is eligible for free vaccination in your state or territory.
Routine JEV vaccination is recommended for:
- laboratory workers who may be exposed the virus
- 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.
States and territories may provide free vaccination to eligible people who live or regularly work in areas of high JEV concern.
Free vaccination may also be available for people outside those areas who:
- work with or live close to pigs and waterbirds
- work with mosquitoes, such as environmental health officers or entomologists.
Read more about Japanese encephalitis vaccination.
Other prevention steps
The best protection against JEV is to prevent mosquito bites.
Read more about preventing Japanese encephalitis.
Priority groups and settings
People who work in certain settings – such as piggeries, pork abattoirs and pork rendering plants – are at greater risk of being exposed to infected mosquitoes.
If you are at greater risk, it is especially important to:
- get vaccinated, if eligible
- take steps to protect yourself from mosquitoes.
People at greater risk of severe disease
Anyone with JEV infection is at risk of severe disease, but those who might be at greater risk include:
- children aged under 5 years
- non-immune adults
- people who are immunocompromised
- pregnant people.
People at greater risk of exposure
You are at risk of exposure to JEV if you travel to, work or live in areas with JEV. You are more likely to be exposed if you:
- undertake outdoor work or leisure activities – like camping, fishing, hiking or gardening – in areas with JEV
- work with or live close to pigs and waterbirds
- work with mosquitoes, such as environmental health officers or entomologists
- travel to areas with JEV during the JEV transmission season
- live or work on the outer islands of the Torres Strait.
Diagnosis and treatment
Your health professional can diagnose JEV infection through tests that might include a:
- blood test
- spinal fluid test (lumbar puncture).
You can use healthdirect’s directory to find a health service near you.
There is no specific treatment for JEV infection. If you have symptoms, you will likely need to be cared for in hospital.
Read more about diagnosing and managing JEV infection.
Surveillance and reporting
JEV infection is a nationally notifiable disease – these are diseases that present a risk to public health.
Health authorities in each state and territory report new laboratory confirmed cases to us through the National Notifiable Diseases Surveillance System.
This is part of our surveillance activities, which help us monitor case numbers around the country and understand disease patterns.
We take a One Health approach to the surveillance of JEV. As well as human disease surveillance, we work with government agencies for agriculture and the environment, to monitor JEV in mosquitoes and animals (including wildlife).
We analyse the data, and report on case numbers through our data visualisation tool.
Outbreaks
The joint national Japanese encephalitis virus outbreak response plan provides a framework for a national One Health response to manage a JEV outbreak.
Control measures used during outbreaks focus on humans, animals and the environment, and include:
- animal surveillance to track where the virus is
- support action to reduce the immediate transmission risk
- mosquito control measures, including environmental, biological and chemical controls
- health education and promotion of mosquito bite prevention
- vaccination of people at high risk of exposure to JEV.
Read more about how the Australian Government defines and plans for outbreaks and pandemics.
Support
See prevention posters, videos and other resources on protecting yourself from JEV.
For information in your state and territory, including whether you are eligible for vaccination, see:
- Australian Capital Territory
- New South Wales
- Northern Territory
- Queensland
- South Australia
- Tasmania
- Victoria
- Western Australia.
For information on staying safe from JEV while travelling, see:
Quick links
Disease
Infectious agent
Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus closely related to Murray Valley encephalitis virus and West Nile virus.
Clinical presentation
Most human infections are asymptomatic.
Estimates of the proportion of infected people who develop symptoms vary in different populations, ranging from less than 1% to up to 4%.[1]
Of those infected with JEV, less than 1% develop neuroinvasive disease.
The most recognised clinical presentation of JEV infection is acute encephalitis. Milder presentations include non-specific febrile illness with headache and aseptic meningitis.
Initial symptoms are non-specific and typically include:
Neurological manifestations might then develop over the following few days, including:
- confusion and agitation
- focal neurological deficits, such as cranial nerve palsies and paralysis
- convulsions and seizures
- coma.
As many as 1 in 3 people who develop encephalitis die from the disease.
Of those who survive, up to half suffer permanent cognitive, behavioural or neurological complications.
Read about diagnosing JEV infection.
Public health importance
Japanese encephalitis is a serious, vaccine-preventable disease with no specific treatment.
JEV infection has a high rate of morbidity and mortality in people who develop encephalitis.
Because of these major impacts, we:
- work with colleagues in the animal and environmental sectors at the national and state and territory levels to ensure a One Health coordinated approach to monitoring and reporting of JEV
- plan for how to manage outbreaks.
Epidemiology
JEV infection is a major public health problem in many parts of Asia and the western Pacific.
In Australia, before 2021, occasional outbreaks occurred only in the Torres Strait and Cape York Peninsula.
During 2021 and 2022, an outbreak in south-eastern Australia resulted in 45 cases and 7 deaths.
JEV detections in feral pigs, mosquitoes and sentinel chickens show there is ongoing JEV transmission in animals in south-eastern Australia.
Studies using blood samples from people living in high-risk areas of Victoria and New South Wales have shown evidence of undetected spread to people.[2] [3]
The risk of JEV infection varies depending on location, season, weather and other local factors.
For the latest information on JEV infection cases in Australia, see the National Notifiable Diseases Surveillance System data visualisation tool.
Spread of infection
Transmission
JEV transmits through bites of infected mosquitoes after they have fed on infected waterbirds or pigs.
The primary host of JEV is believed to be wild birds, especially those in the Ardeidae family (including herons and egrets).
The main vector for JEV in Australia is Culex annulirostris, though several mosquito species are likely involved.
Culex annulirostris lives across Australia in permanent and semi-permanent freshwater bodies, usually in heavily vegetated sites.
Adult Culex annulirostris mosquitoes are active:
- from mid-spring to late autumn in south-eastern Australia
- all year in northern Australia.
Humans are incidental and dead-end hosts – this means we cannot pass on the disease, as we do not develop high enough concentrations of JEV in our blood to infect mosquitoes.
JEV does not spread through:
- contact with infected people
- eating meat from an infected animal.
Incubation period
Symptoms usually start between 5 and 15 days after a bite from an infected mosquito.
Infectious period
JEV does not transmit from person to person.
Priority populations
People at greater risk of severe disease
Anyone with JEV infection is at risk of severe disease.
Evidence about risk factors for severe disease is limited. Those who might be at greater risk include:
- children aged under 5 years
- non-immune adults
- people who are immunocompromised
- pregnant people.[4]
People at greater risk of exposure
People are at risk of exposure to JEV if they travel to, work or live in areas with JEV.
People are more likely to be exposed if they:
- undertake outdoor work or leisure activities – like camping, fishing, hiking or gardening – in areas with JEV
- work with or live close to pigs and waterbirds
- work with mosquitoes, such as environmental health officers or entomologists
- travel to endemic areas during the JEV transmission season
- live or work on the outer islands of the Torres Strait.
Settings at increased risk of spread
High-risk settings include piggeries, pork abattoirs and pork rendering plants.
These settings should actively promote measures people can take to protect themselves, including to:
- get vaccinated
- take steps to prevent mosquito bites.
Read more about:
- controlling mosquitoes around piggeries
- the prevention, control and public health management of outbreaks
Prevention
Vaccination
JEV infection is vaccine preventable.
Routine JEV vaccination is recommended for:
- laboratory workers who may be exposed the virus
- travellers spending 1 month or more in endemic areas during the JEV transmission season
- people who live or work on the outer islands of Torres Strait.
States and territories also provide free vaccination to eligible people who live or regularly work in areas of high JEV concern. Free vaccination may also be available for people outside those areas who:
- work with or live close to pigs and waterbirds
- work with mosquitoes, such as environmental health officers or entomologists.
See who is eligible in your state or territory:
- Australian Capital Territory
- New South Wales
- Northern Territory
- Queensland
- South Australia
- Tasmania
- Victoria
- Western Australia.
Read more about JEV vaccination.
Other prevention steps
The best protection against JEV is to prevent mosquito bites.
The mosquitoes that spread JEV are most active at dawn or dusk so people should avoid areas of high mosquito activity, especially at these times.
Diagnosis and clinical management
Diagnosis
JEV infection is usually diagnosed through laboratory nucleic acid amplification testing – most often using polymerase chain reaction (PCR). Samples of cerebrospinal fluid or blood are most often used.
Serology can also be used to diagnose JEV using a blood sample.
Laboratories need extensive experience in diagnostic testing for flaviviruses, as cross-reactivity with other flaviviruses is common in serological tests.
If JEV infection is part of a differential diagnosis, it’s important to specifically request JEV testing when referring patients to pathologists.
Read more about the diagnosis and treatment of Japanese encephalitis.
Laboratory case definition
Flavivirus – Laboratory case definition
The Public Health Laboratory Network (PHLN) has developed standard case definitions for the diagnosis of key diseases in Australia. This document contains the laboratory case definition for flavivirus.
Clinical management
There is no specific antiviral treatment for JEV infection. Clinical management consists of supportive care.
People with suspected JEV infection are generally referred to hospital for management and further investigation.
Notification and reporting
Surveillance case definition
Japanese encephalitis virus infection – Surveillance case definition
This document contains the surveillance case definition for Japanese encephalitis virus infection, which is nationally notifiable within Australia. State and territory health departments use this definition to decide whether to notify us of a case.
National notification and reporting
JEV infection is a nationally notifiable disease. This means certain health professionals must report diagnoses through their relevant health authorities.
Check how to report laboratory-confirmed JEV infection cases or a related death in your state or territory:
- Australian Capital Territory
- New South Wales
- Northern Territory
- Queensland
- South Australia
- Tasmania
- Victoria
- Western Australia.
State and territory health authorities report new cases to us through the National Notifiable Diseases Surveillance System, as part of our surveillance activities.
We take a One Health approach to the surveillance of JEV. As well as human disease surveillance, we work with government agencies for agriculture and the environment, to monitor JEV in mosquitoes and animals (including wildlife).
We report case numbers and activity through our data visualisation tool, where you can filter and search the latest information.
This helps us to:
- identify infections in animals and humans and their location
- monitor trends in spread of JEV
- plan and allocate resources
- assess the impact of JEV control programs.
Public health response
The joint national JEV outbreak response plan provides a framework for nationally co-operative response arrangements for managing JEV.
Public health authorities adopt a One Health approach when responding to locally acquired JEV infection cases. This recognises the connections between humans, animals and the environment that contribute to JEV outbreaks.
Public health actions focus on:
- finding the sources of exposure
- supporting local communities to control mosquitoes
- communicating advice on preventing mosquito bites
- offering vaccination to eligible people.
Animal health authorities, industry workers, landowners and work health safety officers can help identify and manage any domestic or wild pigs near likely exposure sites.
Local councils may be involved in mosquito control measures – such as fogging and spraying of insecticides – when there are large numbers of mosquitoes. They may also provide mosquito warnings and signage in high-risk areas.
Environmental health officers undertake mosquito surveillance and determine the need for extra mosquito control measures.
Management of cases
Public health units urgently investigate human cases of JEV, with a focus on determining the likely source of the infection.
The person affected, their family and any other people who might have been exposed to the same source should be provided with information about JEV.
Human cases do not need to isolate.
Management of contacts
Public health authorities provide information to people who might have been exposed about:
- how JEV spreads
- the signs and symptoms of JEV infection
- vaccination.
Outbreak response
How public health agencies respond to JEV infection cases and outbreaks depends on:
- state or territory legislation
- local reporting requirements
- the nature of the cases or outbreak
- available resources.
Control measures used during outbreaks focus on humans, animals and the environment, and include:
- animal surveillance to
- understand disease epidemiology
- support targeted measures to reduce the immediate transmission risk
- mosquito vector control measures, including environmental, biological and chemical controls
- health education and promotion of mosquito bite prevention and behaviour change measures
- vaccination of people at high risk of exposure to JEV.
For detailed guidance, see state and territory advice, including:
- New South Wales Health Japanese encephalitis control guideline
- Queensland Health guidelines for public health units
- South Australia Health information for health professionals
- Western Australia Department of Health public health management and case investigation form.
Special situations and high-risk settings
See guidelines for pig producers and horse owners to help protect animals from mosquito bites and reduce the risk of infection.
Resources
See:
- prevention posters, videos and other resources
- the Australian Immunisation Handbook
- the healthdirect Japanese encephalitis page
- Japanese encephalitis in animals
- Joint national Japanese encephalitis virus outbreak response plan.
For information relevant to your state or territory, see:
- Australian Capital Territory
- New South Wales
- Northern Territory
- Queensland
- South Australia
- Tasmania
- Victoria
- Western Australia.
For information on staying safe from JEV while travelling, see:
References
- 1 SL Hills, M Netravathi and T Solomon, 'Japanese encephalitis among adults: A review', American Journal of Tropical Medicine and Hygiene, 2023, 108(5):860–864, doi:10.4269/ajtmh.23-0036.
- 2 Z Baldwin, L Hueston et al., 'The seroprevalence of antibodies to Japanese encephalitis virus in five New South Wales towns at high risk of infection, 2022: A cross-sectional serosurvey', Medical Journal of Australia, 17 June 2024, 220(11):561–565, doi:10.5694/mja2.52320.
- 3 MJ Marsland, TN Thomson et al., 'Serosurvey for Japanese encephalitis virus antibodies following an outbreak in an immunologically naïve population, Victoria, 2022: A cross-sectional study'. Medical Journal of Australia, 2024, 220(11):566–572, doi:10.5694/mja2.52344.
- 4 AR Howard-Jones, D Pham et al., 'Arthropod-borne flaviviruses in pregnancy', Microorganisms, 2023, 11(2):433, doi:10.3390/microorganisms11020433.