1st major outbreak of Japanese encephalitis hits Australia

close-up of a mosquito of the genus culex, against a white background
(Image credit: samxmeg via Getty Images)

Australia's first-ever major outbreak of the viral disease Japanese encephalitis (JE) may be a consequence of climate change, according to some scientists. 

JE is caused by a flavivirus, which belongs to the same genus of viruses as those that cause yellow fever, dengue fever and West Nile fever, according to the Centers for Disease Control and Prevention (CDC). The virus gets transmitted to humans through the bites of infected mosquitoes of the Culex genus, and the mosquitoes initially pick up the virus from infected vertebrates, mainly pigs and wading birds, according to the CDC

Less than 1% of people infected with the JE virus develop severe illness, but in some, the pathogen can trigger inflammation of the brain, called encephalitis, which can cause coma, tremors and convulsions, according to the CDC. An estimated one-quarter to one-third of these cases are fatal. In Australia's current JE outbreak, two people have died, New Scientist reported Wednesday (March 16).

JE mostly affects people in Asia and parts of the Western Pacific, particularly in agricultural areas, according to the CDC. However, the virus is now infecting people as far south as the Australian state of Victoria. In all, 19 people in Victoria, New South Wales, South Australia and Queensland have tested positive for the virus, according to New Scientist. The two fatal cases occurred in Victoria and New South Wales.

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In the past, cases of JE in Australia have only cropped up in very northern regions of the country, including the Torres Strait Islands, the tip of Cape York and the Tiwi Islands, Dr. Dominic Dwyer, a medical virologist and director of public health pathology at New South Wales Health Pathology, wrote in The Sydney Morning Herald on March 10. "But this has now dramatically changed and could be a catalyst for revisiting vaccination strategies," he wrote.

How did the JE virus spread all the way down to Victoria? Climate change may be to blame, experts suggested.

"It has not come by boat or plane like COVID-19, but probably by migratory birds visiting inland waterways and then mosquitoes, whose numbers have increased in eastern Australia with the wetter conditions, heavy rains and floods," Dwyer wrote in the Herald.

In recent weeks, eastern Australia was inundated with heavy rains and floods that resulted in the deaths of more than 20 people, AFP reported March 10. These horrific floods also may have drawn migratory birds to the newly formed wetlands, Roy Hall, a professor in the School of Chemistry and Molecular Biosciences at the University of Queensland in Brisbane, told New Scientist. "We know these birds often follow flooded watercourses."

These birds may have carried the JE virus deep into Australia, where mosquito populations have recently increased due to the unusually warm, wet weather. Once laden with virus, these mosquitoes likely passed the pathogen to pigs, causing an "amplifying effect," Hall said. The JE virus has now been detected in pigs on more than 20 Australian farms, New Scientist reported.

"We don't know if feral pigs have a role in its spread" as well, Dwyer wrote in the Herald.

"A national surveillance plan is being developed to identify and locate infected mosquitoes, birds, pigs — including feral pigs — horses, and humans," Australia's agriculture minister, David Littleproud, said in a statement, according to AFP. 

Australia's health and agriculture ministries have also announced that they'll be stocking up on JE virus vaccines, adding 130,000 doses to the 15,000 currently stockpiled, AFP reported. These shots will become available in late March and will initially be given to high-risk groups, such as pig farm workers and veterinarians, New Scientist reported. 

Besides vaccination, the best way to prevent JE virus infection is to take precautionary measures to prevent mosquito bites, by using insect repellent and wearing long-sleeved shirts and pants when outdoors, for instance, according to the CDC

"Only time will tell if this virus is a one-off problem or will become an endemic in eastern Australia, turning up again next summer," Dwyer wrote in the Herald. "We do expect that the arrival of winter temperatures will see a decline in the mosquito population."

Originally published on Live Science.

Nicoletta Lanese
Channel Editor, Health

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.