Japanese encephalitis current situation

December 2023

Japanese encephalitis first appeared in Victoria in early 2022 with 23 piggeries reporting the infection that summer. While no cases were detected in the 2022-23 summer, concerns remain for the coming summer seasons.

The disease is now considered to be sporadically and seasonally endemic in mainland eastern Australia.

Japanese encephalitis virus is spread by mosquitoes in a complex cycle that can involve birds, pigs and spillover hosts like horses, humans and many other animals. This transmission cycle means it is not possible to eradicate Japanese encephalitis in Victoria.

Agriculture Victoria continues to closely monitors the situation, actively continuing to investigate and test horses and pigs or other livestock (for example, alpaca) presenting with clinical signs consistent with JE virus infection.

Agriculture Victoria is supporting the Victorian Department of Health in its ongoing public health response activities.

JE is spread by mosquitoes. Pigs, horses and wild birds are not responsible for spreading the disease, and they do not pass it onto people.

Earlier this year, Japanese encephalitis was reclassified under the Livestock Disease Control Act 1994 as a notifiable “disease” rather than a notifiable “exotic disease”, reflecting the position of the other states.

If you suspect an animal is showing signs of Japanese encephalitis, you must report it within 12 hours either to your local veterinarian, via the 24-hour Emergency Animal Disease Hotline on 1800 675 888, via the Notify Now app or to Agriculture Victoria animal health staff.

The Victorian Department of Health conducts mosquito surveillance and provides weekly mosquito-borne disease reports throughout the mosquito breeding season. In inland areas this typically occurs from early November through to late April the following year, with coastal areas typically starting earlier and ending later.


Japanese encephalitis was detected in piggeries across Victoria, NSW, Queensland, and South Australia in February 2022.

There were 23 infected pig properties confirmed in Victoria in the following Victorian local government areas: Gannawarra, Campaspe, Moira, Loddon, Wangaratta, Greater Shepparton, Greater Bendigo and Northern Grampians.

Japanese encephalitis is a notifiable disease under the Livestock Disease Control Act 1994.

  • Be vigilant for signs of mosquito activity and Japanese encephalitis.
  • Continue to use effective biosecurity measures including mosquito control to limit the spread of Japanese encephalitis and to protect people and your livestock.
  • All livestock owners including pig and horse owners must ensure their Property Identify Codes (PICs) are current and update them when required.
  • If you suspect Japanese encephalitis on your property, call the 24-hour Emergency Animal Disease Hotline on 1800 675 888, or contact your local vet.

For advice on health and vaccinations, visit the Victorian Department of Health website or to find more information about how you can Protect yourself from mosquito-borne disease on the BetterHealth channel website.

What to do if I suspect Japanese encephalitis in my animals?

Japanese encephalitis is a notifiable disease in Victoria. If you suspect Japanese encephalitis in any animal, but especially in pigs or horses showing any clinical signs, immediately contact your local Agriculture Victoria staff or phone the all-hours Emergency Animal Disease Hotline on 1800 675 888.

If you suspect you have Japanese encephalitis, contact your doctor and refer to the Victorian Department of Health website.

Protect yourself and your family

In Victoria mosquitoes can spread a number of mosquito-borne diseases including Ross River virus, Barmah Forest virus and rarely Murray Valley encephalitis virus.

Ross River and Barmah Forest virus cause similar symptoms including joint swelling and pain, fever, muscle aches, and a rash.

Now most people recover completely from these infections, but some people can go on to had symptoms for very many months.

I contracted the Ross River virus in mid-January 2017.

It caused quite a significant effect in the way I was able to conduct my normal daily life. It was significant joint pain particularly in my legs. I still feel numbness in my hand, my right arm; and I went to get into the car one day and had to physically lift my leg into the car. That's at the point when I went to the doctor.

The best way to avoid mosquito-borne disease is to beat the bite.

There are simple things you can do to protect yourself and those in your care. Wear loose-fitting clothing and cover up as much as possible when outdoors.

Use a mosquito repellent that contains Picaridin or DEET on all exposed skin and make sure your house, caravan, or tent has properly fitted mosquito nets or screens; and remember to use knockdown fly sprays it there are any mosquitoes flying inside the home.

Mosquitoes can breed quickly and in tiny amounts of water, so remove as much stagnant water as possible. Get rid of old tyres, and containers the mosquitoes love to breed in. Change the water in outdoor pets drinking bowls, and bird baths at least once a week.

For more information visit


If you have any health concerns see your doctor or phone NURSE-ON-CALL on 1300 60 60 24

Mosquito borne diseases and surveillance

CATHERINE ELLIS, REPORTER: There are more than 3500 species of mosquitoes in the world and more than 300 in Australia, but most don't bite humans and only a small number are dangerous because they can spread disease.

The trouble is the two most common species found during the height of summer in Victoria are disease spreaders.

A/PROF DEB FRIEDMAN, VICTORIA’S DEPUTY CHIEF HEALTH OFFICER: We're most concerned about those infections that can be fatal or that can cause lifelong disability, and so those infections that can cause encephalitis.

REPORTER: To try to protect us and warn us of any potential risk mosquito surveillance takes place across the state.

DEB FRIEDMAN: Surveillance is our best preventative measure. If we know that it's present in mosquitoes or present in other animals, that gives us an insight into what to expect among humans.

REPORTER: About 20 councils are involved in setting around 70 mosquito traps across the state each week. Doug has been a mosquito officer for Shepparton Council for more than two decades and he says it's always a bit of a laugh when people ask him what he does.

DOUG COUSINS, MOSQUITO OFFICER: And they’re like what you, you trap mosquitoes. Why?

REPORTER: Like humans, the traps release CO2 which can be detected by the mosquitoes from up to 50 meters away.

DOUG COUSINS: And the mosquitoes come in following that CO2 trail and when they get closer, there's a little light. They see the light as a patch of bare skin so they move in closer to have a feed, get sucked down by the draft of the fan and get caught in the trap and that's where they stay until we pick them up in the morning.

REPORTER: The traps are set at dusk when mosquitoes are most active in areas that represent different breeding types and they're collected the next morning.

DOUG COUSINS: We catch probably about 500 on a quiet week and perhaps 15,000 on a big week.

DEB FRIEDMAN: We trap mosquitoes for a very prolonged period that starts well before the mosquito season and extends beyond the mosquito season to make sure that we've captured information for as much of the year as is possible.

REPORTER: The mosquitoes are packaged up and sent by post to a lab in Melbourne.

During peak weeks, more than a million mosquitoes arrive here from across the state. They’re then carefully counted and sorted into species.

DR PETER MEE, SENIOR RESEARCH SCIENTIST, AGRICULTURE VICTORIA: So the mosquitoes arrive, we count and identify them, we put them in a tube and puree them into a soup or a liquid from that liquid or soup we can extract the DNA and from that, we can actually test it with PCR via different assays for those five main virus species.

REPORTER: It takes just two days from when they arrive to determine if a virus is present and to warn the public.

Mosquito surveillance began in Victoria almost 50 years ago after the 1974 floods.

There was an outbreak of Murray Valley encephalitis where several people died and many more were left with long term brain damage.

The virus hasn't been detected in humans in Victoria since, but it was found in chickens in 2011 and in recent months it's been found in trapped mosquitoes across the north of the state.

DEB FRIEDMAN: And on both of those occasions, both in the seventies and in 2011 it followed heavy flooding and obviously that concerns us greatly because we've had a lot of flooding recently.

REPORTER: Japanese encephalitis virus causes a similar illness. It was first discovered in Australia last year in pigs and later in humans.

Like Murray Valley encephalitis it's believed to have been spread here by waterbirds.

DEB FRIEDMAN: And these waterbirds are typically what we call migratory so we know that they fly long distances, and that migration of waterbirds can account for movement of these viruses from potentially country to country and definitely from state to state.

REPORTER: Mosquitoes usually feed on flower nectar. It's only the females that bite us because they need protein from our blood to make their eggs.

They stick their long, tubular mouthpiece into your skin to extract blood and at the same time inject saliva which contains chemicals to make your blood flow smoothly.

The itchy lump you get is your body's reaction to the saliva but if they have a virus, you can also get that and that's what makes mosquitoes the deadliest animals on Earth.

While most of us are terrified of sharks, crocodiles and snakes, it's the tiniest bite of all that kills the most number of humans. Around three quarters of a million people die each year from Mosquito borne diseases but that's mainly from malaria, which doesn't exist here.

DEB FRIEDMAN: The viral infections that we're concerned about are Ross River virus, Barmah Forest virus, Japanese encephalitis virus, Murray Valley encephalitis and West Nile/Kunjin viruses.

REPORTER: While all five viruses may result in no symptoms at all, the bottom three can be fatal.

DEB FRIEDMAN: Any of those symptoms that might point to an inflammation of the brain like seizures, confusion or weakness really mean immediate medical attention is required in a hospital.

REPORTER: This mosquito culex annulirostris is able to spread all the five viruses.

She likes to breed in fresh water across inland Victoria during the summer months.

DOUG COUSINS: There'll be culex annulirostris in every trap that we set.

PETER MEE: And that can be in those traps 80 to 90% of the actual insects in that trap.

REPORTER: Along the coast a salt water loving mosquito is able to spread Ross River and Barmah Forest viruses.

Humans can't catch these viruses from other humans or animals. They can only catch them from infected mosquitoes.

DEB FRIEDMAN: The problem with diseases transmitted by mosquitoes is that there are very few for which there's a vaccine. The only infection for which we have a vaccine is Japanese encephalitis virus.

REPORTER: And so the best form of protection is to avoid getting bitten in the first place.

DEB FRIEDMAN: First of all, use of repellent and not just any repellent, but repellent that includes one of two ingredients, either DEET or picaridin. Wearing long, loose fitting clothing, typically lighter coloured clothing.

REPORTER: Culex annulirostris likes to rest in shady areas, so cleaning up backyards can help, along with removing any stagnant water where other mosquitoes like to breed.

DEB FRIEDMAN: In any neighbourhood home, there can be areas in the garden that collect water.

REPORTER: Despite being a nuisance and a risk to humans, mosquitoes are an important food source for other wildlife, but work is done to control their numbers.

DOUG COUSINS: We've got a larvicide that will inhibit the mosquito larvae from becoming adults. It doesn't harm fish or all the other predators of mosquito larvae in the water.

REPORTER: Climate change is likely to increase the number and spread of mosquitoes, along with the risk of disease.

DEB FRIEDMAN: We are very concerned about the establishment of Murray Valley encephalitis and Dengue virus over the coming years, especially with climate change.

REPORTER: And so Doug's work and the rest of the mosquito surveillance program will become increasingly important to ensure we're aware of what the next threat might be.

Page last updated: 07 Dec 2023