A deadly mosquito-borne virus is spreading across three states, with a second confirmed case identified in Victoria.

Japanese encephalitis has infected a second northern Victorian resident this mosquito season, Chief Health Officer Tarun Weeamanthri said.

The person is likely to have been exposed to the disease in the vicinity of the Murray River along NSW's Riverina region.

The virus has been detected along the Murray River from Mildura in the state's northwest to Moira in central Victoria and in piggeries across all three eastern states.

Across the border, five human cases of Japanese encephalitis have also been reported in NSW and Queensland.

Japanese encephalitis, a flavivirus related to dengue and yellow fever,  is transmitted by mosquitoes and can cause serious infection of the brain.

Most people do not become sick but symptoms can include a fever, vomiting and headaches.

In more severe cases patients can experience seizures, paralysis, permanent disability or even death.

Residents and visitors to northern Victoria and inland riverine regions of eastern Australia, particularly near the Murray River, are potentially at higher risk of infection and should take measures to prevent mosquito bites.

These include using repellent on exposed skin and wearing long, loose fitting clothing when outside, and ensuring accommodation, including tents are properly fitted with nets.

The first Victorian confirmed case this summer also occurred in the state's north.

Risk of infection increases in the warmer months from November to March due to a higher number of mosquitoes.

Children aged under five and older people who are infected with the virus are at a higher risk of developing more severe illness, such as encephalitis.