A NSW man who died last month had Japanese Encephalitis, the mosquito-spread virus recently detected in the state for the first time.

NSW Health announced on Wednesday afternoon a post-mortem of the Griffith man in his 70s confirmed he had Japanese Encephalitis when he died in a Sydney hospital on February 13.

Health authorities are warning people to take precautions against mosquito bites that can transmit the disease, which can cause severe neurological illness.

Mosquitoes can infect animals and humans but it does not spread from humans to humans.

There are now three known cases of the disease in NSW, where locally acquired cases have never previously been identified.

A NSW man and a child previously confirmed with the virus are being treated in Victorian hospitals and several more are awaiting test results to confirm whether they have it.

The virus was detected in samples from pig farms across the east coast and South Australia last month.

Health authorities around the country are working to determine the circulation of the virus.

NSW Health has secured vaccines and is prioritising workers on the affected pig farms and their family members who live there.

NSW HEALTH ADVICE FOR AVOIDING MOSQUITO BITES

* Avoid going outdoors during peak mosquito times, especially at dawn and dusk, and close to wetland and bushland areas.

* Wear long sleeves and pants outdoors, shoes and socks where possible to minimise skin exposure.

* Apply repellent to all areas of exposed skin and reapply repellent after swimming.

* Infants aged less than three months can be protected from mosquitoes by using an infant carrier draped with mosquito netting that is secured along the edges.

* If camping, ensure the tent has fly screens to prevent mosquitoes entering.

* Reduce all water holding containers around the home where mosquitoes could breed. Mosquitoes only need a small amount of liquid to breed.