Health officials have warned people in recently flooded areas of the country to protect against mosquito-borne diseases after a new case of Japanese encephalitis was detected in New South Wales.
Japanese encephalitis is a viral infection that can cause severe illness and sometimes death, according to the World Health Organization (WHO).
NSW Health said a man in his 20s had become the fifth person to contract Japanese encephalitis in the state this season after travelling to northern NSW.
An ACT man died from Japanese encephalitis earlier this month after contracting the disease while holidaying in the Murrumbidgee region — the second death from the virus in NSW this year.
In Queensland, the first locally-acquired human case of the disease was detected in January of a person who likely caught the disease on the NSW-Queensland border.
Earlier this month, Queensland Health confirmed that the virus had been detected in mosquitoes in Brisbane.
What is Japanese encephalitis and why are cases rising?
Japanese encephalitis is a mosquito-borne viral infection that belongs to the same class of other common infections, such as dengue, Zika, yellow fever and Wester Nile viruses.
University of Queensland infectious diseases physician Paul Griffin said the virus had a complicated life cycle that moved between different animals.
“It has quite a complex life cycle that involves birds and pigs and is being transferred from mosquitoes, sometimes into humans,” Dr Griffin said.
QIMR Berghofer Medical Research Institute Emerging Viral Diseases Lab head Daniel Rawle said the virus was first detected in Australia in the Tiwi Islands.
Dr Rawle said the virus spread south in 2022 in what he described as an “unprecedented incursion” through the eastern states and other parts of the country.
“There was lots of flooding that year so we think that the flooding, which is perfect [for] mosquito breeding and then wading bird migration, with the birds being the key carriers, pushed that virus down south to the Murray River region,” he said.
It became dormant until this year and has now become endemic, Dr Rawle said.
“It’s certainly on the rise in the way that we’re seeing cases in areas that we’ve never seen them before in Australia,” he said.
He said while it was unclear why Japanese encephalitis had taken hold in southern parts of Australia, climate change and animals could be a factor.
“As climate change occurs, we know that mosquitoes are adapting to survive in hotter conditions so they may start being able to populate areas that they wouldn’t before.”
What are the symptoms and how can it be transmitted?
Japanese encephalitis is spread to humans by the Culex tritaeniorhynchus mosquito, according to the WHO.
Dr Rawle said the virus was transmitted between pigs and birds — which act as amplifying hosts — and occasionally to humans through mosquitoes.
“Pigs and birds are the key ones for JE (Japanese encephalitis), and then every now and then an infected mosquito can infect a human,” he said.
Dr Griffin said most people developed a mild case of the virus but others could become seriously ill.
He said people could develop symptoms such as confusion, severe headaches, changes in conscious state and even seizures.
“In a small number it can be very severe, lead to encephalitis or brain infection and inflammation, and unfortunately a proportion of those people won’t survive,” he said.
“A lot of people will know about things like Dengue or Murray Valley encephalitis which is a virus we’ve had in Australia for a long time, but this is one that’s a bit more on the severe side.”
Dr Griffin said it was important for anyone experiencing those symptoms to seek urgent medical attention.
“If there’s any of those sorts of features, of course, people need to seek medical attention promptly and if they’ve been in an area where this virus exists, it’ll be something that’s considered,” he said.
How can flooding impact mosquito-borne diseases?
Dr Rawle said flooding and other large bodies of water could increase mosquito numbers because they lay their eggs in stagnant water.
“One to two weeks after the eggs are laid, they emerge as adults and then female adults go looking for blood, which is where the risk of disease comes from,” he said.
NSW Health’s executive director of health protection Dr Jeremy McAnulty said people needed to take precautions as they cleaned up from the floods.
“Standing water, like that left after mass rainfall and floods, makes for ideal breeding grounds for mosquitoes. This increases people’s risk of being bitten, especially if they’re working outdoors,” he said.
Dr Griffin added that areas close to pig populations were also at risk of harbouring mosquitoes infected with Japanese encephalitis.
“That means there’s a fairly small geographical location where that can happen and people that are at highest risk, that might be visiting or working in those sorts of locations, we can target for vaccinations,” he said.
Dr Griffin said long-sleeved shirts and long pants, chemical repellents, and fly screens were important measures that could help prevent people from being bitten by mosquitos and reduce their risk of infection.
“There are stronger versions of things like DEET which are very effective at preventing people being bitten, so preventing exposure to the vector, which in this case is a mosquito,” Dr Griffin said.
NSW Health said people living in high-risk areas could be vaccinated against Japanese encephalitis through their general practitioner or Aboriginal Medical Service.
I find it really amazing that some time last year Bill Gates said he would use his latest idea on Australia’s mosquito population because this was becoming a problem .After doing a little research I found this was not true ,And now of course its becoming a real thing .Strange that I suppose its another one of those gifts that keep on giving from the liked of Gates and Soros etc.