Japanese encephalitis in Victoria this summer

What is the issue?

A probable case of JE virus infection has been identified in a resident of northern Victoria, the first identified case of JE in Victoria this mosquito season. JE virus has also been detected through environmental surveillance in northern Victoria, and in mosquitoes and feral pigs in New South Wales this summer. These findings indicate that JE virus is likely circulating in northern Victoria this summer.

Mosquito numbers tend to increase at this time of year. Mosquitoes can spread diseases such as JE, Murray Valley encephalitis (MVE), and West Nile (Kunjin) virus infections, as well as Ross River and Barmah Forest viruses. The risk of mosquito-borne diseases remains high in the coming weeks. Taking measures to avoid mosquito bites is critical to protect against infections.

In Victoria, cases of JE were reported for the first time in 2022 while cases of MVE were last reported in 2023.

Mosquito testing is being carried out over the summer period 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. People with increased exposure to mosquitoes may be at a higher risk of infection, particularly people camping, working or spending time outdoors in inland riverine regions and along 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 (inflammation of the brain).

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 5-15 days after exposure with sudden onset of fever, headache and vomiting. Mental status changes, focal neurological deficits, seizures, 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.

Recommendations

For health professionals

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 in 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.

For the public

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 diethyltoluamide (DEET) on all exposed skin.
• 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.
• Limit outdoor activity if lots of mosquitoes are about, especially around dawn and dusk when mosquitoes are most active.
• Remove stagnant water where mosquitoes can breed around your home or campsite.

Residents and visitors to high-risk areas of Northern Victoria are advised to take additional preventative measures, including:

• Make sure your accommodation is fitted with mosquito netting or screens.
• Close doors and tent flaps to stop mosquitoes getting inside.
• Sleep under a mosquito net if mosquito screens are not available.
• Try to avoid camping near wetland habitats where mosquitoes are likely breeding.
• Mosquito coils can be effective in small outdoor areas where you gather to sit or eat.

JE vaccination

There is significant global demand for the JE vaccine and therefore access is restricted to those most at risk.

JE vaccine is available free-of-charge for specific groups at higher risk of exposure to the virus, including eligible people in 24 high-risk LGAs in northern Victoria. Eligibility criteria will continue to be monitored.

The free JE vaccine is available for eligible people through GPs, Aboriginal health services, community pharmacies and some local councils.

See JE vaccination for further detailed information on vaccine eligibility criteria and access.