Four Japanese encephalitis cases in Vic

AAP understands that since Sunday's alert four Victorians have contracted the virus.

All four were admitted to hospital and one has since been discharged.

Japanese encephalitis spreads through mosquito bites and people in regional areas who are in contact with pigs may be at particular risk.

Anyone working or camping in country Victoria is being warned to use mosquito repellent and cover up with loose-fitting clothing. 

Older people and those aged under five who are infected have a higher risk of developing a serious illness.

Chief Health Officer Brett Sutton says anyone who developed a sudden fever, headache and vomiting should see their doctor immediately.

"People with these symptoms can deteriorate over just a few short days, including suffering a loss of coordination, disorientation, generalised weakness and in some cases issues with movement which can last for years," he said on Sunday.