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 local mosquitoes can spread.
About 5,000 cases of mosquito-borne disease are reported in Australia each year. The vast majority of these are due to Ross River virus. The disease this virus causes is not fatal though it can be severely debilitating.
Disease caused by two other pathogens, Japanese encephalitis virus and Murray Valley encephalitis virus, are much rarer but potentially fatal.
The symptoms of human disease caused by these two viruses are similar.
Most people infected show no symptoms. 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.
The influence of weather patterns
Murray Valley encephalitis virus has been known in Australia for many decades. After a significant outbreak across the Murray Darling Basin region in 1974, activity has generally been limited to northern Australia.
Outbreaks in southeastern Australia often accompany flooding brought on by La Niña weather patterns. Floods provide ideal conditions for mosquitoes, as well as the waterbirds that harbour the virus.
Japanese encephalitis virus is closely related to Murray Valley encephalitis virus. Mosquitoes pick up both viruses by biting waterbirds. But Japanese encephalitis virus has only recently become widespread in Australia.
What’s different this summer?
This summer, Japanese encephalitis virus has been detected in mosquitoes and feral pigs in NSW. The virus has also been detected in environmental surveillance in northern Victoria, and we know at least one person has been affected there.
Meanwhile, Murray Valley encephalitis virus has been detected in sentinel chicken flocks – which health authorities use to test for increased mosquito-borne disease risk – in NSW and in the Kimberley region of Western Australia.
How can you reduce your risk this summer?
The public health alerts in Victoria and NSW 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 eligible for vaccination. 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 insect repellent 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.
Conclusion
Australian mosquitoes, such as Ringworm, can play an important role in the spread of viruses. This summer, Japanese encephalitis virus and Murray Valley encephalitis virus are active again, despite relatively dry conditions. There is no evidence that mosquito numbers are booming or that waterbird activity is increasing. It is unclear what is driving the resurgence of these viruses, but research is ongoing to better understand their spread.
FAQs
Q: What is Japanese encephalitis virus?
A: Japanese encephalitis virus is a mosquito-borne virus that can cause serious illness, including encephalitis (inflammation of the brain), in humans.
Q: How can I reduce my risk of getting Japanese encephalitis virus?
A: Apply insect repellent when outdoors, especially during dawn and dusk when mosquitoes are most active. Cover up with long-sleeved shirt, long pants, and covered shoes. Seek advice from your local health authority to see if you are eligible for vaccination.
Q: Is there a vaccine available for Murray Valley encephalitis virus?
A: No, there is no vaccine available for Murray Valley encephalitis virus or Ross River virus.
Q: What are the symptoms of Japanese encephalitis virus?
A: The symptoms of Japanese encephalitis virus are similar to those of Murray Valley encephalitis virus. They include fever, headache, and vomiting, and in more serious cases, neck stiffness, disorientation, drowsiness, and seizures.
Q: How many cases of mosquito-borne disease are reported in Australia each year?
A: About 5,000 cases of mosquito-borne disease are reported in Australia each year. The vast majority of these are due to Ross River virus.
