Japanese encephalitis - including symptoms, treatment and prevention

Japanese encephalitis is a rare but serious disease caused by the Japanese encephalitis virus.

It is spread to humans by infected mosquitoes.

Japanese encephalitis virus (JEV) has been detected in South Australia, including nine cases in people in SA. Prior to February 2022, Japanese encephalitis was not known to occur in southern Australia.

Japanese encephalitis has been detected in mosquitoes and animals in the following local government areas:

  • Loxton Waikerie
  • Murray Bridge
  • Coorong
  • Goyder
  • Clare and Gilbert Valleys
  • Light.

Japanese encephalitis is a notifiable condition1

How Japanese encephalitis virus is spread

The Japanese encephalitis virus is transmitted to humans through bites from Culex mosquitoes, which have been infected with Japanese encephalitis virus. Culex mosquitoes are commonly found in South Australia. The virus exists in a transmission cycle between mosquitoes, pigs and/or water birds.

Pigs are an important host for the virus. The virus can occur at high levels in their blood for 4-6 days. Mosquitoes that feed on infected pigs during this period can become infected with the virus and then transmit it to humans.

It cannot be transmitted by eating meat of infected animals. It cannot be spread from person to person.

Until recently, the risk for Japanese encephalitis virus infection for people living in Australia was only through overseas travel, or rarely by travel/residence in the far north of Australia. However, recently there have been cases acquired locally for the first time.

Signs and symptoms

Most people with Japanese encephalitis virus infection do not experience any illness. There may be mild symptoms such as fever and headache.

A small proportion will have encephalitis (inflammation of the brain). This may begin with symptoms such as:

  • tiredness
  • fever and headache
  • nausea
  • vomiting, or diarrhoea.

Confusion, unusual behaviour, sleepiness, seizures, weakness, and abnormal movements may develop. Encephalitis can cause permanent damage to the nervous system or death.

Diagnosis of Japanese encephalitis virus

Diagnosis is usually made by a blood test or sample from the spinal fluid. If you have been infected, you do not put others at risk.

if you have symptoms consistent with Japanese encephalitis, seek medical attention.

if you have any severe signs such as headache, vomiting, confusion, paralysis or seizures, you should call 000 immediately.

Incubation period

An incubation period is the time between coming infected, and developing symptoms.

Symptoms, if they occur, usually develop 5 to 15 days after being bitten by infected mosquitoes.

Treatment for Japanese encephalitis virus

There is no specific treatment for infection with Japanese encephalitis virus. Serious illness with encephalitis requires management in hospital.


Japanese encephalitis virus vaccination is recommended for persons at highest risk of infection, including certain occupations. SA Health is responding to the Japanese encephalitis outbreak by providing funded vaccines to priority groups as advised by the Communicable Diseases Network Australia, as well as other vulnerable members of the community.

For more information visit the Japanese encephalitis virus (JEV) vaccine page.

Vaccination for the Japanese encephalitis virus is also recommended for travellers spending one month or more in rural areas of countries with a high-risk for Japanese encephalitis.

Prevention of Japanese encephalitis virus

There are simple steps all people should take to protect themselves against mosquito bites and mosquito-borne diseases, including wearing long, loose fitting clothing; using insect repellent and eliminating the water the mosquitoes can breed in.

For more information visit the Fight the Bite page.

Immunisation against JEV will not protect people from other mosquito borne diseases.

Exclusion from childcare, preschool, school or work is not necessary.

All people who work with potentially infected animals, or work in areas in which infected mosquitoes may be present, should wear appropriate personal protective equipment (PPE). The PPE should be chosen based on the assessed level of risk and the task. 

Useful links

1 – In South Australia the law requires doctors and laboratories to report some infections or diseases to SA Health. These infections or diseases are commonly referred to as 'notifiable conditions'.