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Japanese encephalitis in Australia: Lessons from the region?

Researchers react to recent JEV cases in Australia
The Japanese encephalitis virus has been detected in parts of Australia for the first time. But across much of Southeast Asia, the virus has long been a concern.

The Japanese encephalitis virus (JEV) has been detected in pigs in New South Wales, Victoria, South Australia and Queensland over the past few weeks, prompting the Australian Government Department of Health to declare the situation a communicable disease incident of national significance.

It is the first time the rare tropical virus, spread to humans by mosquito bites, has been locally detected beyond far north Queensland and the Torres Strait region. While the overwhelming majority of JEV cases are asymptomatic in humans, in rare but serious cases the virus can cause encephalitis, or swelling of the brain. 

JEV in Southeast Asia

While parts of Australia grapple with their first ever local detections, JEV is endemic across much of Southeast Asia, where transmission most frequently occurs in rural areas. The virus spreads through mosquitoes that carry it from pigs or water birds.

“I previously worked in the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam, where we had an encephalitis ward and saw occasional cases of JEV there. For those who get symptoms, it’s a scary disease,” said Dr Justin Beardsley, Senior Lecturer in Infectious Diseases at the Sydney Institute for Infectious Diseases.

“Now I work in Sydney, it’s strange to suddenly consider and look for homegrown cases in people who have only been in Victoria, Queensland, or NSW. Until JEV was discovered here we only had to consider this diagnosis in returned travellers. Everyone is now on high alert.”

According to the World Health Organization (WHO), 24 countries across Asia and the Pacific are at risk of transmission, including the whole of Southeast Asia. There are an estimated 68,000 clinical cases each year.

“Since the vectors are mosquitoes and the intermediate hosts are waterfowl and mammals, areas with lots of standing water (e.g. rice farming areas) are especially high risk,” Dr Beardsley said.

“In normal circumstances, we only recommended JEV vaccination for travellers anticipating prolonged stays in rural areas.”

Climate factors

Experts point to the role of climate change in the spread of the virus, with weather that is warmer and wetter providing an ideal climate for mosquitoes to prosper.

Close-up of mosquito and its reflection on a body of water

Areas with lots of standing water, such as rice farming areas, or recently flooded areas, are the perfect breeding ground for mosquitoes, and represent high risk areas for the spread of Japanese encephalitis.

We have long been concerned that [Japanese encephalitis] would inevitably arrive in Australia, as climate change impacts worsen.
Emeritus Professor Peter Windsor

“As [JEV] is spread by mosquito vectors and is endemic to several parts of Asia and the Torres Strait region of Australia, we have long been concerned that it would inevitably arrive in Australia, as climate change impacts worsen,” said Professor Emeritus Peter Windsor of the Sydney School of Veterinary Science.

“We commonly get arboviruses [viruses that can be spread to humans by mosquitoes] from Southeast Asia, including Bluetongue virus. In fact, we have a sentinel herd & insect collection scheme that annually produces maps of insect & pathogen distribution.”

Dr Victoria Brookes is an epidemiologist whose research focuses on emerging and neglected infectious diseases. Her work has included research on disease preparedness in Southeast Asia.

“We know that the distribution of arboviruses can wax and wane with climate factors such as increased rainfall – so increased habitat for mosquito larvae to develop – and warm weather,” Dr Brookes said.  

“To come this far south really is an indicator of a massive increase in distribution and obviously the recent weather events [across the southeast of Australia] – warm weather coupled with La Niña conditions – will have contributed to that.”

Managing the spread

For the pig industry in Australia, the virus has always been a concern, according to Dr Brookes. But it hasn’t been high on the list for an industry generally concentrated in more southern regions of the country.

“We also have feral pigs in Australia so understanding the risk from them will be important. In northern Australia, we do know that mosquitoes feed on feral pigs, so whether they could form a reservoir host for the virus more long-term would definitely be something of importance to consider,” Dr Brookes said.

“Another aspect that needs to be addressed is, we’re talking a lot about the pig industry on the commercial side, but there are people keeping backyard pigs in Australia and we don’t know where all of those people are. It’s important for us to make sure those people are aware that the disease is around and that they are taking precautions.”

In combatting the virus, Dr Beardsley says that Australia could turn to clinical colleagues and experts in Southeast Asia for support.

“Diagnosis and management of cases is an area where we can learn a lot from our colleagues in Southeast Asia,” he said.

“Clinicians in Southeast Asia have much more experience in identifying, diagnosing, and managing cases. There are currently no JEV-specific treatments, but we could potentially learn a lot about supportive care and rehabilitation. There may also be significant opportunities to collaborate on research.”

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