Mosquito-borne viruses triple in Queensland as La Niña provides ideal breeding conditions

In short:

2024 saw the highest number of mosquito-borne virus cases in Queensland in four years, according to the state health department.

Cases of Ross River virus and the potentially deadly dengue fever more than tripled

What's next?

The state government will provide free Japanese encephalitis virus vaccines to at-risk residents and people are urged to take precautions to avoid getting bitten.

Mosquito-borne virus cases almost tripled across Queensland in 2024 amid surges in cases of Ross River virus and potentially deadly dengue fever.

Queensland Health recorded 3,225 cases, including one of Japanese encephalitis virus (JEV) – the first since 2022 – in the Wide Bay region.

Outside of Brisbane the Sunshine Coast recorded the most cases of mosquito-borne viruses with 495 and the Gold Coast and Darling Downs more than doubled the numbers on previous years with more than 200 cases each.

The CSIRO said hot and wet weather around the state off the back of La Niña conditions over the last few years had created a haven for mosquito breeding.

"This means an increased number of mosquitoes and unfortunately more opportunity for mosquitoes to transmit viruses," principal research scientist Prasad Paradkar said.

"The warm temperatures shorten the time it takes for viruses to multiply, which means the mosquitoes become infective more quickly."

He said climate change was increasing the risk of mosquito-borne viruses.

"As temperatures rise mosquitoes can also move to different areas which were considered previously uninhabitable to them," Dr Paradkar said.

"Also with climate change there are extreme weather conditions which can introduce new species of mosquitoes into new areas."

Regional concern

The Goondiwindi community in the Queensland's south is on high alert after a middle-aged Townsville man was hospitalised with JEV after travelling to the area last week.

A Townsville man diagnosed with dengue fever has recently been discharged from hospital.

The state government has listed 23 local government areas that are at risk and is offering free JEV vaccines for eligible residents.

Goondiwindi GP Matthew Masel said the vaccine supply was used up quickly but more was expected to arrive in the coming weeks.

"We've been informed that supply levels are very good and that the supply chain [is] intact," he said.

"A regular check-up with your GP that includes a discussion about what vaccines are available and you might be eligible for is an import part of any check-up with your GP."

Ross River Virus

Total cases: 2,475

Sunshine Coast: (392), Townsville (190), Gold Coast (187)

Fatal: No

Vaccine: No

Ross River virus made up the majority of mosquito-borne virus cases in Queensland in 2024, more than tripling from the previous year to almost 2,500 cases.

Mosquitoes can contract the virus from an infected animal and there is no vaccine available.

The virus is not life-threatening but can cause muscle and joint inflammation and pain, fever, chills, rashes and fatigue.

Queensland Health recommends treating it with rest and gentle exercise to keep joints moving.

Medication may be needed in severe cases.

Dengue fever

Total cases: 371

Gold Coast (69), Torres and Cape (56), Sunshine Coast (42)

Fatal: In severe cases

Vaccine: No

Dengue fever was the most infectious of the potentially deadly mosquito-borne viruses in Queensland last year.

It usually spreads between people via bites from the Aedes aegypti mosquito.

The species is common in central and northern Queensland and can occur in southern parts of the state, usually breeding in containers and junk scattered around urban areas rather than in bushland.

Dengue fever is most notable for causing a red rash, which can lead to itching, peeling skin and hair loss.

Other symptoms include fever, extreme tiredness, intense headaches, muscle and joint pain, loss of appetite, vomiting, diarrhoea, abdominal pain, a metallic taste in the mouth, minor bleeding from the nose or gums and and heavy menstruation in women.

In severe cases dengue can lead to shock from internal fluid loss and haemorrhaging, which can be fatal.

In Australia there is no vaccine that can prevent the four strains of dengue fever.

Queensland Health recommends anyone experiencing symptoms to immediately see a doctor.

Japanese encephalitis virus

Total cases: 1

Wide Bay (1)

Fatal: In severe cases

Vaccine: Yes

Last year Queensland recorded its first cases of JEV in two years.

In 2022 there were 41 cases, which resulted in seven deaths, including one in Queensland.

The virus is contracted from pigs and waterbirds.

Humans are they care classified as "dead-end" hosts, meaning mosquitoes cannot pick up JEV by biting them.

Most people with JEV show mild or no symptoms, though some – particularly children – experience a high fever, headache, abdominal pain and vomiting.

Health authorities are particularly concerned for the one per cent of cases involving acute encephalitis (inflammation of the brain).

Symptoms include neck stiffness, disorientation, convulsions, paralysis, and coma.

There is an approximate mortality rate of one third in severe cases, and one third are left with permanent disabilities, according to Queensland Health.

A vaccine is available for JEV, which the state government has made free for at-risk people.