Queensland has recorded its first human case of mosquito-borne Japanese encephalitis in more than two decades.

It has triggered warnings for people to take precautions against getting bitten by the insects, particularly as the state's south-east cleans up after the floods.

Here's what you need to know about the discovery of the case.

What do we know about the person who contracted the virus?

The woman is in her 60s and is in a critical condition on life support in Brisbane's Prince Charles Hospital after a campervan trip to southern Queensland.

Her diagnosis follows the recent detection of Japanese encephalitis in animal samples taken from a Goondiwindi commercial piggery, in the state's south.

The virus, which transmits through mosquito bites and not human-to-human contact or through eating pork — has also been found recently in piggeries in Victoria and NSW, including one near the Queensland border at Tenterfield.

Earlier this week, four Victorians were diagnosed with the virus, believed to be the first cases recorded in southern Australia.

How serious is Japanese encephalitis?

Brisbane-based infectious disease physician Paul Griffin said while most people who developed Japanese encephalitis would only experience mild symptoms, in rare, severe cases, it could result in encephalitis — inflammation of the brain — which is potentially deadly.

Symptoms can include sudden onset of fever, vomiting, severe headache, neck stiffness and sensitivity to light.

"The main thing everyone needs to know is that not everyone who gets this virus ends up with severe encephalitis or the severe manifestations — in most people that's not the case," Dr Griffin said.

"It is something that we should take seriously enough to take some simple steps to reduce our chance of it being a big problem."

What precautions should be taken?

Dr Griffin, an associate professor at the University of Queensland, said people should take measures to prevent mosquito bites.

This includes the use of repellents containing diethyl toluamide (DEET) and through wearing closed-in shoes and loose, light-coloured clothing to cover arms and legs.

Is it related to the flooding?

No, but Dr Griffin said the timing of Japanese encephalitis being found in eastern Australia coinciding with a major flood event was "unfortunate", given the potential for increased mosquito breeding in the coming days.

"The virus has been there before these immense rainfall events and obviously it will be the right breeding ground for the mosquitoes now … so the timing is pretty terrible," Dr Griffin said.

"The usual things we say about having pooled water around households will become increasingly relevant as we start to get the bulk of the floodwater receded and a lot of the clean-up happening.

"If there's any residual water sources in pot plants or other small containers, make sure there's no pooled water anywhere that can facilitate the growth of mosquitoes."

What about vaccinations?

Australia's Acting Chief Medical Officer Sonya Bennett said earlier this week work was underway for targeted vaccinations to protect against Japanese encephalitis.

But Dr Griffin said a widespread vaccination campaign, such as the COVID-19 vaccine rollout, would not be necessary.

"It's more likely something we'd do on a particular risk basis and so people who work with pigs, in particular, would be highest on the list," he said.

What else is being done to stop more cases?

Queensland Health Minister Yvette D'Ath said she had spoken to local government leaders about spraying for mosquitoes in the coming weeks to reduce the risk of Japanese encephalitis.

The last Queensland cases of Japanese encephalitis are believed to have occurred in 1998 — in a 12-year-old boy on Badu Island in the Torres Strait and a man working at the mouth of the Mitchell River at Cape York.