Department of Health

Health alert

Alert number:
Date issued:
29 Dec 2022
Issued by:
Associate Professor Deborah Friedman, Deputy Chief Health Officer (Communicable Disease)
Issued to:
Health professionals and the Victorian community

Key message

  • A case of Japanese encephalitis (JE) virus infection has been identified in a Campaspe LGA resident, the first identified case of JEV infection in Victoria this mosquito season.
  • JE virus can cause a rare but potentially serious infection of the brain and is spread to humans through mosquito bites.
  • New South Wales and South Australia have also recently reported their first case of JE virus infection.
  • Most JE virus infections are asymptomatic. A small proportion may present with a febrile illness, however less than one per cent may experience severe infection manifested by headache, vomiting, disorientation, seizures, coma, and more rarely, permanent neurological complications or death.
  • Anyone experiencing these symptoms, should seek urgent medical attention.
  • Clinicians must consider and test for JE virus in patients with a compatible illness
  • Clinicians should notify the Department immediately of suspected cases by calling 1300 651 160 (24 hours).
  • Avoid mosquito bites by using mosquito repellent containing picaridin or DEET on all exposed skin. Wear long, loose fitting clothing when outside, and ensure accommodation, including tents are properly fitted with mosquito nettings or screens.

What is the issue?

A case of JE virus infection has been identified in a Campaspe LGA resident, the first identified case of JE virus infection in Victoria this mosquito season.

Recent weather conditions have been favourable for mosquito breeding and biting and mosquito numbers are high across many parts of Victoria. There is ongoing concern over JE virus transmission in inland riverine regions and extending up towards the Murray River.

Not all mosquitoes carry diseases – most are just a nuisance. However, the types of mosquitoes that are known to spread disease are increasing in number. The risk of JE virus infection is expected to increase as summer temperatures rise and lingering flood waters become more stagnant.

Taking measures to avoid mosquito bites is critical to protect against infections.

JE virus has not been identified in mosquitoes or animals in Victoria this mosquito season. Ongoing mosquito testing is being carried out to help identify high risk areas.

Who is at risk?

Anyone is potentially at risk of being bitten by mosquitoes and while most bites will only cause minor swelling and irritation, an infected mosquito can transmit potentially serious diseases, including JE virus infection. People with increased exposure to mosquitoes may be at a higher risk of JE virus infection, particularly people camping, or working or spending time outdoors in inland riverine regions and extending up towards the Murray River.

Children aged under 5 years old and older people who are infected with JE virus are at a higher risk of developing more severe illness, such as encephalitis.

Symptoms and transmission

JE virus is transmitted to humans through the bite of an infected mosquito. There is no evidence of transmission from person to person.

More than 90 per cent of JE virus infections are asymptomatic. Less than one per cent of people infected with JE virus develop neurologic illness.

Encephalitis is the most serious clinical consequence of JE virus infection. Illness usually begins with sudden onset of fever, headache and vomiting. Mental status changes, focal neurological deficits, generalised weakness, movement disorders, loss of coordination and coma may develop over the next few days. The encephalitis cannot be distinguished clinically from other central nervous system infections. Milder forms of disease, such as aseptic meningitis or undifferentiated febrile illness, can also occur.

The incubation period is usually 6-16 days.


Clinicians should consider the possibility of JE virus infection in patients presenting with encephalitis or a compatible illness, and particularly in those who have spent time within rural or regional Victoria or have had extensive mosquito exposure or contact with pigs within the few weeks prior to symptom onset.

JE virus infection is an urgent notifiable condition and must be notified immediately to the department if suspected or confirmed by medical practitioners and pathology services by phoning 1300 651 160 (24 hours).

Recommended testing for patients with encephalitis, particularly those without another pathogen identified, and with compatible MRI or CT findings, in adults and children is as follows:

  • Blood (serum tube – 2 mL from children, 5-8 mL from adults)
    • Acute and convalescent (3-4 weeks post onset) for flavivirus and JEV IgG, IgM and Total Ab
    • Culture/PCR on acute sample
  • CSF (at least 1 mL)
    • Flavivirus and JEV PCR and culture
    • Flavivirus and JEV IgG, IgM and Total Ab
  • Urine (2-5 mL in sterile urine jar)
    • Flavivirus and JEV PCR and culture

Specimens should be sent urgently (same or next day) to Victorian Infectious Diseases Reference Laboratory (VIDRL) for flavivirus serology, PCR and culture and transported at 4 degrees Celsius. Request forms should be appropriately labelled and the on-call pathologist at VIDRL should be contacted to provide information on samples being sent.

Victorians should be aware of the risk of mosquito-borne diseases including JE virus infection and take steps to significantly limit their exposure to mosquitoes. There are simple steps to protect against mosquito-borne diseases:

  • Cover up – wear long, loose-fitting, light-coloured clothing.
  • Use mosquito repellents containing picaridin or DEET on all exposed skin.
  • Limit outdoor activity if lots of mosquitoes are about.
  • Remove stagnant water where mosquitoes can breed around your home or campsite.
  • On holidays make sure your accommodation is fitted with mosquito netting or screens.
  • Don’t forget the kids – always check the insect repellent label. On babies, you might need to spray or rub repellent on their clothes instead of their skin. Avoid applying repellent to the hands of babies or young children.
  • Use ‘knockdown’ fly sprays and plug-in repellent devices indoors.
  • Sleep under mosquito nets treated with insecticides if you don’t have insect screens on windows on your home or are sleeping in an untreated tent or out in the open.
  • Mosquito coils can be effective in small outdoor areas where you gather to sit or eat.

A Japanese encephalitis vaccine is available. See JEV vaccine eligibility criteria for further details.

Supply of JE vaccine continues to be severely constrained in Australia. Nevertheless, people listed in the specific priority groups are advised to contact their general practitioner, local public health unit, local council or community pharmacy to confirm eligibility and arrange a vaccination appointment. Additional vaccines are expected to arrive in the first part of 2023.

Reviewed 24 February 2023


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