Increasing heat and unusual rain patterns are driving mosquitoes into new parts of Australia, and the insects are carrying a concerning disease with them.
Japanese encephalitis, once thought to be mostly confined to the more remote parts of the country, is now appearing in Australian towns and pig farms where people live and work.
Rising global temperatures are doing more than exacerbating extreme weather and impacting food supplies. They’re also altering wildlife activity and spreading potentially deadly diseases.
What’s happening?
Japanese encephalitis virus has been detected in mosquitoes, feral pigs, and commercial piggeries across multiple Australian states. This year, for the first time, it has also been identified in Brisbane, according to a report from Medscape Medical News in mid-August.
By that point, the virus had already claimed two lives in 2025. “In some parts of the country, [mosquitoes] can kill you,” Cameron Webb, an associate professor of medical sciences at the University of Sydney, told Medscape.
Sarah McGuinness, a physician in the Department of Infectious Diseases at Melbourne’s Alfred Hospital, said that warmer temperatures and changes in rainfall patterns are expanding mosquito breeding grounds and increasing the likelihood of disease spread.
“Altered rainfall patterns and warmer temperatures affect mosquito breeding habitats and the distribution of reservoir hosts,” she said in the Medscape report. “These conditions can extend the mosquito season and expand the geographic range of mosquito vectors.”
The spread to Brisbane may be particularly concerning. As the country’s third-largest city, population density there could aggravate infection rates.
Why is this concerning?
While most Japanese encephalitis infections are mild, they can also be lethal. In general, 1 in 250 cases lead to severe illness, and in up to 30 percent of those severe cases, people die or suffer lifelong brain and behavioral problems, according to the report.
Meanwhile, researchers say that rising global temperatures are making places once too cold for mosquitoes now more hospitable to the insects, thereby increasing the months and areas where transmission can happen. According to the World Mosquito Program, warmer climates and longer warm seasons are expanding the habitats where mosquitoes thrive, worsening the risk of practically all mosquito-borne viruses, including dengue and Zika, in various parts of the world.
“We’re very lucky in that we are generally free of some of the serious mosquito-borne diseases that impact many countries, like malaria and dengue,” McGuinness said. “But we need to remind the community that it’s important to take extra measures in some parts of the country to avoid mosquito bites.”
What’s being done about this outbreak of Japanese encephalitis?
Fortunately, an effective vaccine is available to help mitigate the spread and severity of this infection.
The Australian government offers free Japanese encephalitis vaccinations to those in high-risk zones and is closely tracking the virus by monitoring monkeys, pigs, and birds. States have also incorporated the virus into their existing arbovirus surveillance efforts with the goal of enabling quicker responses, according to David Williams, a researcher at the Australian Centre for Disease Preparedness.
Williams says researchers are not entirely sure whether the infection is being reintroduced from somewhere in Northern Australia or if it remains dormant during the winter, only to reemerge when mosquitoes increase. However, Australians can expect to see more outbreaks.
The growth of infections from Japanese encephalitis in parts of Australia highlights another threat posed by the overheating of our planet. Strengthened surveillance efforts, equitable vaccine access, and community awareness can mitigate this threat — but only if they can keep pace with the changing environment. In the big picture, reducing the heat-trapping pollution that warms our world could also be viewed as a component of disease prevention.
Join our free newsletter for good news and useful tips, and don’t miss this cool list of easy ways to help yourself while helping the planet.