Explainer: Health authorities on alert as mosquito-borne virus spreads across eastern Australia

NSW authorities on Wednesday confirmed a man in his 70s had died from Japanese encephalitis, a rare disease spreading along the Murray-Darling basin.

It came just a day after Victoria revealed a man in his 60s had succumbed to the virus.

There are nine confirmed human cases in Australia, spread across the country's eastern seaboard and SA, but authorities are looking into another dozen cases strongly suspected to be JEV.

A national health alert was also issued last week after 14 Australian piggeries confirmed outbreaks.

There is no treatment for JEV. But how much of a concern is it?

Here's what you need to know.

Mosquito bites.

Certain types of mosquitoes are susceptible to the virus. If they're infected, their bites can transfer it to humans.

Mosquitoes typically contract JE from water birds.

But it can't move from person-to-person, reducing the speed it can travel at.

It's particularly common in pigs, but you can't contract it from eating pork products.

Mostly nothing.

The vast majority of infected people - 99 per cent - will not experience any symptoms.

But those who do report fever, sudden vomiting, headaches, neck stiffness, tremors and disorientation. Children are most likely to suffer from convulsions.

Extreme cases can lead to comas.

The very old and the very young.

Obviously, people living in areas with large numbers of mosquitoes.

Given horses and pigs are also susceptible to the virus, people who work with animals - particularly in piggeries - are also at risk.

People aged 75 and over, or under five, are most likely to experience severe symptoms.

Yes, it's effective but pricey.

If you've travelled to south-east Asia, there's a good chance you've already received it.

The federal government is working with all states and territories to support distribution to at-risk groups. Victoria is already working on rolling it out to high-risk communities.

But a single course will typically cost around $300 - a huge amount for most people, let alone families.

Children as young as one year old can receive their jab.

But those who have been vaccinated are still urged to take precautions.

Common sense.

Wear long sleeves and long pants if you're outside.

Anything to keep mosquitoes away - repellent, removing breeding sites from near your doors and windows - will help.

Take care when you're in peak biting times - dusk and dawn - and avoid areas likely to have a large mosquito populations.

If you're sleeping outside where you might be exposed, use a bed net.