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Health care professionals are being urged to be vigilant after a resurgence of Japanese encephalitis virus (JEV) has been reported across New South Wales and Victoria.
Mosquitoes infected with the virus have recently been detected in the Moira Shire in Victoria’s north. This follows a reported case of the virus in a Victorian man who is fighting for his life.
The virus has also been detected for the first time in chickens in Moree in NSW’s west. JEV was detected in mosquitoes in December 2024 in the Griffith area, and in feral pigs in the Narromine Shire local government area (LGA).
Japanese encephalitis in Australia
Japanese encephalitis is a vaccine-preventable disease caused by infection of JEV. It is spread by mosquitoes that have become infected through biting infected pigs and waterbirds.
Most people don’t show any symptoms once infected with JEV; however, rarely, it can result in severe disease or even death. It’s endemic to parts of Asia and the Torres Strait region of Australia.
A perspective recently published in the MJA highlighted the challenges of managing Japanese encephalitis in Australia. The authors explained its recent history in Australia.
“JEV emerged again in 2021 with a fatal case in the Tiwi Islands, and shortly after was detected on an unprecedented scale and geographical spread in 2022: cases in humans and piggeries were detected across four states in south-eastern Australia (New South Wales, Victoria, Queensland, South Australia),” the authors wrote.
The Australian Government declared it a communicable disease of national significance in March 2022.
“Over the following months, a total of 46 cases (including 7 deaths) were identified in humans (as of 13 February 2023). The end of the JEV emergency response was announced on 16 June 2023, although concern remains regarding potential endemicity in Australian waterbird, pig and mosquito populations,” the authors continued.
Rainfall and flooding are usually risk factors for increasing numbers of mosquitoes and subsequently JEV infections. The end of La Nina in 2023 meant that the number of JEV infections dropped off and no locally acquired cases were reported in the national communicable diseases surveillance database in 2023 and most of 2024 (two recent cases reported in Queensland were acquired overseas).
However, the recent detection of the virus in animals and the reported locally acquired case in Victoria has public health experts on alert.
Co-author of the MJA paper, Professor Wenbiao Hu, told InSight+: “The recent emergence of JEV in Australia, particularly in regional areas like northern Victoria, has significantly increased the risk for local populations.
“The resurgence of JEV in northern Victoria this summer, despite no significant increase in flooding or mosquito numbers, may be due to a higher proportion of infected mosquitoes and increased viral circulation in amplifying hosts like pigs and wading birds. Localised water sources, subtle climate variations, and changes in human activity or land use could also have sustained the transmission cycle.
“These factors highlight the need for enhanced surveillance and proactive measures to mitigate the risk of JEV outbreaks,” he said.
Current surveillance in Australia
The authors of the perspective believe the current reactive “surveillance and response” approach to JEV monitoring isn’t adequate.
“The prevailing, passive surveillance system proved futile in detecting JEV circulation in Australia, resulting in cases being detected in pigs and humans at a similar time,” they wrote.
“There is a pressing need to shift from a reactive “surveillance and response” approach to a more proactive, comprehensive “predict and prevent” strategy, particularly in regional areas of Australia where populations are at greater risk,” they continued.
According to Professor Hu, it is essential to strengthen mosquito monitoring and JEV transmission prevention in urban and rural areas.
“This could involve implementing more advanced surveillance technologies and predictive modelling to identify high-risk areas before an outbreak occurs,” he told InSight+.
In addition, “the coordination between federal, state and local health authorities must be enhanced, with clearly defined protocols for the rapid deployment of vaccines, resources and public health interventions when outbreaks are detected,” he said.
Professor Hu highlighted the One Health approach, which would help Australia prepare and respond to zoonotic disease such as JEV.
“This approach would involve closer collaboration between human health, veterinary and environmental sectors to monitor and manage JEV transmission, particularly in regions where wildlife and livestock play a key role in the amplification of the virus,” he said.
The interim Australian Centre of Disease Control (CDC) has acknowledged this approach and are expanding Australia’s ability to implement it.
“A One Health perspective would enable more comprehensive risk assessments, timely responses to emerging outbreaks, and more effective prevention strategies, as it accounts for the broader ecosystem and potential sources of transmission,” Professor Hu explained.
Keeping the public informed
Crucially, there also needs to be increased public health communication to make sure the general population understands the risks and prevention measures.
This is where GPs play a vital role.
“As trusted health care providers within local communities, they can raise awareness, especially among at-risk populations. GPs can inform patients about the symptoms of JEV, prevention methods like mosquito control, and the importance of vaccination,” Professor Hu said.
The Japanese encephalitis vaccine is available and free for specific groups at higher risk of exposure to the virus. This includes eligible people in 24 high risk LGAs in northern Victoria and 55 high risk LGAs in inland NSW.
Doctors should consider the possibility of JEV infection or a compatible illness in patients who have spent time in the affected areas and present with symptoms including sudden onset of fever, headache and vomiting.
Other symptoms, including mental status changes, focal neurological deficits, seizures, generalised weakness, movement disorders, loss of coordination and coma, may develop over the next few days. Milder forms of disease, such as aseptic meningitis or undifferentiated febrile illness, can also occur.
Patients should be reminded about taking steps to limit exposure to mosquitoes, by following these tips from Victoria’s Department of Health:
- 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 the home or campsite.
Read the perspective in the Medical Journal of Australia.
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