Japanese encephalitis virus threat

montage of war time mosquito prevention images
Japanese encephalitis is a viral brain infection, spread via mosquito bites.

The virus threat that Australians need to worry about now is Japanese Encephalitis.

It has already claimed the lives of one man in Victoria and another man in NSW.

What is Japanese encephalitis?

Japanese encephalitis is a viral brain infection. Spread via mosquito bites, it is the most serious clinical consequence of a Japanese encephalitis virus (JEV) infection.

JEV is a Flavivirus – as are the Kokobera virus, West Nile virus, and Murray Valley encephalitis virus.

There are around 68,000 cases of Japanese encephalitis worldwide each year according to WHO (World Health Organization) estimates and, in February 2022 JEV spread its wings into mainland Australia.

To date, 9 cases have so far been recorded across Queensland, NSW and Victoria, with 3 cases recorded in South Australia.

A number of other cases in humans are under investigation. Testing for the virus is not straightforward and confirmation of further cases is expected in the coming days.

Flood waters on the Murrumbidgee flood plains in North Wagga
Excessive rainfall and flooding events, due to La Niña weather conditions, are blamed for the sudden southward spread of JEV.

How JEV spreads

JEV has been present in parts of far northern Australia since the 1990s. JEV outbreaks have occurred in the Torres Strait. But this is the first time the virus has been recorded in people further south.

The distance it has travelled undetected has surprised the experts. Excessive rainfall and flooding events, due to La Niña weather conditions, are blamed for its sudden southward velocity.

The conditions allowed the virus to thrive and infect waterbirds.

"The waterbirds develop a lot of virus in their bloodstream," says University of Queensland virologist Jody Peters, "then they subsequently infect another mosquito and that drives this transmission cycle."

Infected pigs contribute to transmission, developing enough virus in their bloodstream to pass it on to another mosquito that bites them.

JEV is not transmitted human to human.

“This virus is transmitted to humans through the bite of an infected mosquito,” says Deputy Chief Medical Officer Sonya Bennett.

Japanese encephalitis is a viral zoonotic disease – an infectious disease that is able to jump from a non-human animal to humans.

Australia's Chief Veterinary Officer Mark Schipp, said "We're mapping the presence of waterbirds, feral pigs or piggeries and people that have contracted the infection."

The purpose of the mapping is prioritise and roll out vaccinations.

Infections at more than 40 piggeries across Victoria, New South Wales, Queensland, and South Australia, have already been noted. Mosquito surveillance and control have been introduced.

Importantly, in Australia, JEV is a nationally notifiable disease, which means any animal showing signs of the disease must be reported to either a local veterinarian or the national Emergency Animal Disease Watch Hotline on 1800 675 888.

Is Japanese encephalitis curable?

There is no known cure for Japanese encephalitis. Treatment is aimed at relieving symptoms and supporting the functions of the body as it tries to fight the infection.

An infected person would usually be admitted to hospital for treatment so they can receive fluids, oxygen and medication.

In severe cases, medications are used to help control swelling in the brain. The patient may need heavy sedation and a breathing tube until swelling in the brain begins to improve.

Parents and caregivers need to be cautious. Children under 5 years are particularly at risk of developing encephalitis from the virus.

Prevention is the best form of treatment for Japanese encephalitis.

Antibiotics are not effective against viruses.

Anti-viral drugs are available and vaccination against the infection is an excellent way to prevent Japanese encephalitis.

The vaccine, usually available only privately, gives effective protection against JEV in more than 9 out of 10 people who receive it. The vaccine is given as an intramuscular injection. Two doses are needed for full protection, the second is given 28 days after the first.

Infants between 2 months and 3 years of aged can receive 2 doses of the JEspect vaccine, each of 0.25 mL, 28 days apart. Children over 3 years of age, and adults, should receive 2 doses of JEspect, each of 0.5 mL, 28 days apart.

In Australia, JEspect and Imojev are available. Imojev is not suitable for children under 9 months.

Booster doses of the vaccine for those in at-risk situations, are given 12 to 24 months after the initial vaccination.

Further details about Japanese Encephalitis vaccines in Australia.

Chris Lease from S.A. Department of Health, says some vaccines are available, but recommends avoiding infection by not being bitten in the first place.

A vaccine for horses and pigs is available in countries where JEV is endemic but no JE vaccine for animals is currently registered for use in Australia.

Mosquito - Subfamily Culicinae
Seek urgent medical assistance if you believe you have contracted Japanese encephalitis

Symptoms of Japanese Encephalitis (JEV)

Illness usually begins with symptoms such as sudden onset fever, headache, and vomiting.

Seek urgent medical assistance if you believe you have contracted Japanese encephalitis. The serious consequences of this include severe disease and even death.

Around 1 in every 250 people with JEV infection develop more severe symptoms as the infection spreads to the brain. In such cases, this would happen 5 to 15 days after infection.

Symptoms can include:

  • high temperature (fever)
  • confusion
  • inability to speak
  • muscle weakness or paralysis
  • seizures (fits)
  • stiff neck
  • uncontrollable shaking (tremor)


For infected people who develop these more serious symptoms, as many as 1 in every 3 will die.

In survivors, symptoms tend to improve slowly. It can take several months for full recovery.

Up to half of those who survive will suffer permanent brain damage. Typically, they would have long-term problems, including tremors and muscle twitches, or personality changes, muscle weakness, learning difficulties, and paralysis in 1 or more limbs.

For most people, the symptoms of JEV infection thankfully, go either unnoticed or are mild, short-lived, and often mistaken for the common flu.

In animals, the disease can be observed in horses and pigs. Other animals – e.g. cattle, sheep, goats, dogs, cats, bats, rodents, reptiles, amphibians, birds – can be infected but typically show no signs of disease.

Empty shells of mosquito larvae
Empty shells of mosquito larvae

Which mosquito carries Japanese Encephalitis?

The bite of infected Culex species mosquitoes, particularly Culex tritaeniorhynchus, is how JEV is transmitted to humans.

How JEV is transmitted

Mosquitoes pick the virus up from animals and birds, then spread it through mosquito bites.

It cannot be transmitted from human to human. Mosquitoes can bite an infected person but cannot then spread JEV to another person.

It cannot be contracted by eating meat from an infected animal.

"Pigs are an amplifying host, so they produce a lot of virus," Chief Veterinary Officer Mark Schipp explains. "Mosquitoes pick that up and carry it forward into humans and horses."

Pork producers are being urged to report suspected cases.

Farms would be issued a movement permit that allows them to continue business if there's a or positive suspect case. JE is not transmitted by eating pork products, so there's no reason to prevent producers transporting livestock to abattoirs.

Mr Schipp believes JEV will have a significant impact on human health and industry, including tourism. "We're doing everything we can," he says, "to try and minimise its spread and ensure that people are vaccinated."

Feral pigs coming to water at Jardines Lagoon, near Einsleigh, North Queensland
If infection spreads to Australia's large population of wild pigs, not just farm animals, stamping out the virus reservoir would be far from easy

How can we stop JEV?

Aside from vaccination, which is better than 90% effective, Professor of microbiology at the Australian National University, Peter Collignon says, "If pigs are the major reservoir (of JEV), we can possibly get rid of it.

"The problem with mosquito-borne viruses, like Ross River virus, is kangaroos and marsupials are the reservoir, and they’re everywhere."

Acknowledging Australia's large population of wild pigs, he warns that stamping out the virus reservoir would be far from easy if JE is in those animals, not just in farm animals.

Protecting yourself against mosquitoes is best done by preventing the insects from coming indoors. After the recent rainy weather, mosquitoes will breed in water around the house. Clear these breeding waters if possible and make sure mosquito-proof mesh on your doors and windows is installed and intact.

Other mosquito repellent devices can be used inside and outside the home.

Use insect repellant containing DEET or picaridin. Oil of lemon eucalyptus is an alternate repellant. Reapply insect repellant as necessary. Always check the label for reapplication times.

Wear long, loose-fitting clothing and enclosed footwear.

What are our officials doing about it?

Federal Health Department

We are monitoring the unfolding situation in Australia concerning the Japanese encephalitis virus (JEV). It has been declared a Communicable Disease Incident of National Significance. We will update this alert with the latest medical advice and official reports.

Animal Health Australia

AUSVETPLAN contains the nationally-agreed approach for the response to emergency animal disease (EAD) incidents in Australia.
Direct link to the PDF for managing response to Japanese encephalitis.

ABC News footage

See ABC News video.

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