Japanese encephalitis virus (JEV) infection

Japanese encephalitis virus (JEV) spreads to humans and other animals through infected mosquitoes. Most people don’t get any symptoms. For the small number who do, it can cause severe illness or even death. The best protection is to avoid getting bitten by mosquitoes and getting vaccinated.

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What Japanese encephalitis is

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:

Symptoms

If you have serious symptoms – such as seizures, muscle weakness, paralysis or confusion – call 000 immediately.

Common early symptoms include:

  • fever
  • diarrhoea
  • headache
  • vomiting
  • muscle weakness.
  • confusion and agitation
  • paralysis
  • convulsions and seizures
  • coma.

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 doctor. 

Check your symptoms

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

The best protection against JEV is to avoid mosquito bites by:

  • using insect repellents that contain diethyltoluamide (DEET), picaridin or oil of lemon eucalyptus (OLE) – always follow the instructions on the label
  • wearing long, loose-fitting, light-coloured clothing and enclosed footwear 
  • using mosquito netting or screens on windows, doors and vents, and patching any splits or tears
  • using insecticide sprays, vapour-dispensing units (indoors) and mosquito coils (outdoors) to repel mosquitoes 
  • removing standing water where mosquitoes may breed, such as plant trays or saucers, buckets or kiddie pools
  • regularly cleaning out permanent water containers – such as ponds and pet water bowls 
  • keeping gutters clear
  • covering openings to water storage – like rainwater and sceptic tanks – with mosquito-proof mesh
  • avoiding areas of high mosquito activity at dawn and dusk.

Read more about preventing Japanese encephalitis.

Vaccination

Japanese encephalitis 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 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.

See who is eligible in your state or territory. 

Read more about Japanese encephalitis vaccination. 

High-risk 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: 

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 doctor can diagnose JEV infection through tests that might include a:

You can use healthdirect’s directory to find a health service near you. 

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There is no specific treatment for JEV infection. If you have symptoms, you will likely need to be cared for in hospital.

Antibiotics are not used to treat JEV infections, because they do not work for viral infections. Taking antibiotics when you don’t need them can increase the risk of antibiotic resistance.

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. 

We take a One Health approach to surveillance of JEV. As well as human disease surveillance, we work with other government departments to monitor JEV in mosquitoes and animals, including wildlife.

This helps us to:

  • identify areas where JEV may be present in animals
  • monitor trends in spread of JEV
  • plan and allocate resources
  • assess the impact of JEV control programs.

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 we define and plan 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:

For information on staying safe from JEV while travelling, see:

We regularly add new content to this website. This will include more topics and diseases. In the meantime, information about other diseases in Australia is on the Department of Health and Aged Care’s website. 

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