Know the facts: mozzie-borne diseases in Queensland

It’s a warm afternoon in Queensland. The sun is setting, you’ve got a cold drink in hand, and life is good — until you hear it.

ZzzzzzZZzz.

Then you see it, smack it, and suddenly you’re scratching your arm or leg. You’ve been bitten.

Queenslanders know this drill all too well — mozzies are a part of life in the Sunshine State.

Their bites leave behind itchy, annoying welts, but here’s the real kicker: some mozzies can carry dangerous diseases that can be transmitted to humans with a single bite.

Every summer, particularly after wet weather and flooding, Queensland sees an increase in mosquito numbers. ^[1]

This brings with it an increased risk of mosquito-borne diseases.

Last year, Ross River virus cases spiked significantly with more than 2,000 cases reported – nearly six times the number of cases seen in 2023. ^[2]

This year, while Ross River virus cases are lower, we’ve seen the reappearance of a potentially serious mosquito-borne disease: Japanese encephalitis virus (JEV).

In January 2025, the first human JEV case since 2022 was detected in Queensland. ^[3]

Queensland has now recorded three human cases this year and detected the presence of JEV in mosquito samples and pigs across the state. Some of these detections are in new locations where JEV has never been detected before.

JEV is a rare, but potentially serious illness. While not everyone infected by JEV will get sick, it can cause serious illness in some people, including inflammation of the brain. ^[4] Of the three human JEV cases in Queensland this year, two have sadly passed away.

With JEV and other mosquito-borne diseases such as Murray Valley Encephalitis (MVE) making headlines, knowing the facts has never been more important.

Why are we seeing JEV now? How did it get to Queensland?

JEV likely hitched a ride to Queensland in migratory birds, with mozzies picking up the virus once it was introduced. ^[5]

Before 2021, JEV had only been found in far northern Australia, with locally transmitted human cases recorded in the Torres Strait Islands and Cape York Peninsula in the mid to late 1990s. ^[6]

Since 2022, the virus has spread further south, identified in pigs, mosquitoes, and people across multiple states — including New South Wales, Victoria, South Australia, and the Northern Territory in addition to Queensland. ^[7]

So why is JEV moving south and more prevalent? Some of the answer lies in ideal mozzie breeding conditions.

Mozzies need water to complete their life cycle — from egg to larva (which are aquatic) to adults which emerge from the water surface. ^[8]

Mosquitoes thrive in coastal areas with wetlands and marshes, but also inland in flood-prone regions, where standing water provides them the perfect larval habitat. The landscape in places like northwest Queensland means water sits around for prolonged periods, allowing mozzies to multiply and spread disease. ^[9]

When heavy rain and flooding hit, mosquito numbers and mosquito-borne diseases have the potential to surge — it’s a pattern we’ve seen before. ^[10]

And now, with JEV recently detected in mosquitoes east of the Great Dividing Range for the first time in Brisbane (Hemmant) and in a pig in Central Queensland (Banana Shire Council), it’s clear that mozzie populations are on the move, carrying the virus across the state. ^[11]

Ongoing extreme weather events are likely fuelling this spike, making mosquito bite prevention and public awareness more important than ever.

The only way a human can get infected with JEV is through the bite of an infected mosquito. 

How does JEV spread? Can people pass it to each other?

The only way a human can get infected with JEV is through the bite of an infected mosquito. It cannot be passed from human to human. ^[12]

It’s actually mosquito saliva that does the dirty work. When a mozzie bites (only the females bite), it spits a tiny amount of saliva into your skin — this helps them feed on your blood (and it’s also what makes the bite itchy!). ^[13]

But how do mosquitoes get infected in the first place? They pick up JEV from biting infected pigs or wading birds. Once the virus enters their system, it replicates and takes about four to seven days to reach their salivary glands. ^[14] Then, when they go in for their next bite — sometimes on an unsuspecting human — they pass the virus along through their spit.

No, not all mosquito species can carry JEV. JEV is generally transmitted by Culex species mosquitoes – however, they are one of the most common species in Queensland.

Not every mosquito will be infected with a virus but once a mosquito is infected, it is infected for the rest of its life.

Further, mosquitoes thrive in Queensland’s warm, wet climate, which means every mosquito has the potential to carry and transmit mosquito-borne diseases. ^[15]

Some mosquitoes might carry Ross River virus, while others could be carriers of Murray Valley encephalitis virus.

While not every single mosquito is infected with one of these viruses, it’s always smart to stay protected — because you never really know which mozzie is just annoying and which one could pose a real health risk.

Remember, any mosquito could carry a mosquito-borne disease at any time. And it could be a mosquito in your backyard, campground or local park.

How likely am I to contract JEV from a mosquito?

The chance of you contracting JEV may depend on the area you live in, areas you visit and if you are likely to get bitten by mosquitoes.

You’ll never know if a mosquito is carrying a virus, so the best thing to do is protect yourself against all mosquito bites.

If you're spending a lot of time outdoors, such as going camping, bushwalking, fishing or working outdoors, you'll be more at risk of getting bitten by mosquitoes. ^[16]

The overarching rule is don’t get bitten by mosquitoes. ^[17]

Those living in at risk JEV areas can also access the JEV vaccine for free to prevent serious illness from the virus.

Example of setting up a mosquito trap to monitor mosquito activity in public park wetlands.

How can I protect myself from JEV?

Queenslanders should always take precautions against mosquito bites.

There are simple steps all Queenslanders should do to prevent mosquito bites, including:

• applying effective insect repellents that contain DEET, Picaridin or Oil of Lemon Eucalyptus to exposed skin and reapplying as directed by the manufacturer
• wearing loose, light-coloured clothing to cover up arms, legs and feet
• using insecticide sprays, insecticide-based vapour dispensing units and mosquito coils, if outdoors in a well-ventilated area
• ensuring proper screening in tents or sleep under a mosquito net when camping to prevent mosquitoes entering.

While there is a vaccine against serious illness from JEV for at risk groups, not every mosquito-borne virus has a vaccine.

Because of limited JEV vaccine supply globally, Queensland Health is prioritising at-risk cohorts. We determine this based on JEV detections in mosquitoes and pigs, and locations of exposure of human cases.

Free vaccine eligibility will continue to expand based on surveillance activities and any further detections of JEV.

Those most at-risk of JEV can access the jab for free. Some at-risk cohorts include:

• people who work at, live near, or have a planned visit to:
  • a piggery, including, but not limited to, farm workers and their families (including children aged 2 months and older) living at the piggery, transport workers, veterinarians, students and others involved in the care of pigs
  • a pork abattoir or pork rendering plant.
• personnel (professional and volunteer) who may be required to work outdoors in at risk areas
• people who live or work in or have a planned visit to identified local government areas or specific locations and who are risk of mosquito bites. The full list of eligible local government areas and other locations is available here.

Remember, the vaccine helps to prevent serious illness from JEV. But prevention can start with avoiding mozzie bites in the first place. ^[18]

How does Queensland Health test mosquitoes for diseases?

Queensland Health works with local councils to routinely collect and test mosquito samples for viruses like JEV, Ross River virus, and Murray Valley encephalitis virus. ^[19]

Why do we do this? Because mozzies love Queensland’s climate just as much as we do. It’s important for us to know how many mozzies are carrying transmissible diseases, and where those mozzies are. It’s a proactive public health measure to keep Queenslanders safe.

How do we test mosquitoes? In many cases, we test the mosquito’s saliva – yep, their spit. Queensland is one of the few places in the world that uses a saliva-based method for tracking mosquito-borne viruses. ^[20]

Our public health units work with local governments to set up specialised traps that emit carbon dioxide to attract mosquitoes and which contain honey-soaked cards inside. As the mosquitoes collected by the trap feed on the honey, mosquitoes leave behind traces of saliva which scientists can test for the presence of viruses.

This whole testing process takes less than a week, meaning health authorities can act fast if there’s a risk to the community.

Positive samples of virus in mosquitoes provides evidence of increased virus activity and indicates an increased risk to humans.

If we know there’s an increased risk of mosquito-borne diseases in certain communities, we let the community know and may ramp up certain measures, such as mosquito surveillance, public messaging and availability to the vaccine.

Mosquitoes thrive in coastal areas with wetlands and marshes, but also inland in flood-prone regions, where standing water provides them the perfect larval habitat.

What are JEV symptoms in humans?

Most people infected with JEV won’t experience any symptoms or signs of illness. In fact, fewer than four per cent of people who catch JEV will experience symptoms. ^[21]

But for those that do get affected by JEV, it can result in serious illness and even death.

Those who do experience symptoms will often notice them about five to 15 days after being bitten by an infected mosquito. ^[22] Most people will experience a fever, headache, and/ or vomiting. However, those with a more severe infection (1 in 250) may experience:

• Neck stiffness
• Disorientation and/ or paralysis
• Tremors and/ or seizures
• Coma

What should I do if I think I have JEV?

If you’re experiencing severe JEV symptoms, visit your nearest emergency department or call Triple Zero (000). ^[23]

Which animals are affected by JEV?

JEV is maintained in transmission cycles between mosquitoes, pigs and wading birds.

When pigs become infected the virus replicates in their blood, and this may result in signs of disease. These signs typically only occur in pregnant sows and cause the birth of mummified, stillborn or weak piglets. Less commonly the disease may cause nervous signs in young piglets or infertility in boars. ^[24]

Through the bite of a mosquito, JEV may also spread to horses, humans, and rarely other species. Similar to humans, when horses are infected with JEV, only a small percent will become ill. For those that do, most show only mild signs with few infections leading to inflammation of the brain (encephalitis).

Check here for more detailed information on JEV symptoms in animals and what do to.

Can I eat meat from animals who were infected with JEV?

Yes, it is safe to eat meat of animals who have contracted the virus. ^[25] While a pig may be a host for the virus, people cannot contract JEV from eating their meat or any meat product.

What are JEV symptoms in other animals?

JEV can cause reproductive losses in pigs and brain inflammation in horses. Other animals can be infected but typically do not show signs of illness, including cattle, sheep, dogs, and cats. ^[26]

Check here for more detailed information on JEV symptoms in animals and what do to.

What should I do if I think my animals have JEV?

Because JEV poses a risk to animal and human health it is reportable in Queensland. If you suspect an animal is showing signs of Japanese encephalitis you must report it to:

• Your local vet, or
• Biosecurity Queensland on 13 25 23. ^[27]

More information is available here.

What other diseases can people get from mosquitoes?

Queensland is home to around 300 different types of mozzies, and there are plenty of mosquito-borne viruses too. The most common mosquito-borne illnesses in Queensland are Ross River virus and Barmah Forest virus – prevention from these diseases relies wholly on avoiding mosquito bites.

Queensland Health works with local councils to routinely collect and test mosquito samples for viruses like JEV, Ross River virus, and Murray Valley encephalitis virus.

What mosquito-borne diseases does Queensland Health monitor?

Queensland Health monitors a number of notifiable and other communicable conditions in the state. ^[28] Mosquito-borne related infections monitored by Queensland Health include:

• Barmah Forest virus infection
• Chikungunya
• Dengue
• Japanese encephalitis
• West Nile virus (Kunjin subtype)
• Malaria
• Murray Valley encephalitis
• Ross River virus infection
• Yellow fever
• Zika

Each disease is accompanied by fact sheets, clinical guidelines, notification/ surveillance forms, and epidemiological data (where available). The website is updated every week and is available here.