A Victorian man is reportedly in hospital after contracting Japanese encephalitis from a mosquito bite.
Author
- Cameron Webb
Clinical Associate Professor and Principal Hospital Scientist, University of Sydney
This news comes after both and issued public health alerts in recent weeks warning about the virus.
So what is Japanese encephalitis, and how can you protect yourself and your family if you live, work or are holidaying in mosquito-prone regions this summer?
Mosquito-borne diseases in Australia
Relative to other parts of the world, Australia has traditionally been very low risk for potentially life-threatening mosquito-borne diseases.
There’s no widespread dengue, yellow fever or malaria. But there are still many viruses that .
About are reported in Australia each year. The vast majority of these are due to . The disease this virus causes is , though it can be severely debilitating.
Disease caused by two other pathogens, virus and virus, are much rarer but potentially fatal.
The symptoms of human disease caused by these two viruses are similar.
Most people infected . In mild cases, there may be fever, headache and vomiting. In more serious cases, people may experience neck stiffness, disorientation, drowsiness and seizures. Serious illness can have lifelong neurological complications and, in some cases, the disease is life-threatening.
There’s no specific treatment for either disease, though there is a vaccine for which may be appropriate for certain people at high risk (more on that later).
The influence of weather patterns
has been known in Australia for many decades. After a significant outbreak across the Murray Darling Basin region in 1974, activity has generally been .
Outbreaks in southeastern Australia often accompany flooding brought on by . Floods provide ideal conditions for mosquitoes, as well as the that harbour the virus.
is closely related to Murray Valley encephalitis virus. Mosquitoes . But Japanese encephalitis virus has only recently become widespread in Australia.
After flooding rains brought on by La Niña in 2020, conditions that , returned and arrived for the first time.
Japanese encephalitis virus was initially discovered in southeastern Australia during , and the that followed flooding at the time contributed to its spread.
There have been around caused by these two viruses combined over the past four years. This includes across .
Additional deaths have been reported due to Murray Valley encephalitis in recent years – two each in and the .
In the summer of 2023-24, , mosquito numbers declined, and the of disease caused by Japanese encephalitis virus and Murray Valley encephalitis dropped.
Now . So what’s going on?
What’s different this summer?
This summer, Japanese encephalitis virus has been detected in in NSW. The virus has also been detected in in northern Victoria, and we know at least one person there.
Meanwhile, Murray Valley encephalitis virus has been detected in sentinel chicken flocks – which to test for increased mosquito-borne disease risk – in and in the Kimberley region of .
It’s unusual to see activity of these viruses when conditions are relatively dry and mosquito numbers relatively low.
Some regions of Australia may have experienced , but for many regions of the country, conditions have been hot and dry. This is bad news for mosquitoes.
There is no evidence that mosquito numbers are booming like they did back when La Niña brought .
There also isn’t any evidence of more waterbird activity. In fact, .
So why are Japanese encephalitis virus and Murray Valley encephalitis virus active again when the conditions appear to be less favourable?
Despite predictions of a , there’s still speculation about what this means for . We may not see flooding, but there is still likely to be enough water around for mosquitoes.
For Japanese encephalitis virus, it may be that are playing a more important role in its spread. We know and with drier conditions, perhaps mosquitoes and feral pigs, , are gathering together where they can find bodies of water.
After its unexpected arrival, it now seems Japanese encephalitis virus is here to stay. But how this virus interacts with local mosquitoes and wildlife, under the influence of increasing unpredictable climatic conditions, requires more research.
How can you reduce your risk this summer?
The public health alerts in and focus especially on specific regions in northern Victoria and around Griffith and Narromine in NSW where the virus has been detected.
If you live or work in areas at risk of Japanese encephalitis, seek advice from your local health authority to see if you are . Residents in specified local government areas in affected regions in both states are currently eligible for a free vaccine.
But there is no vaccine available for Murray Valley encephalitis or Ross River viruses.
Wherever you live, mosquito bite prevention is key. Apply when outdoors, especially during dawn and dusk when mosquitoes are most active or at any time of the day if you’re in bushland or wetland areas where numbers of mosquitoes may be high.
You can get better protection by also covering up with a long-sleeved shirt, long pants, and covered shoes.
