Six people have been infected with Ross River virus in Melbourne amid a state-wide outbreak, sparking a warning from authorities.
The infections were detected in Frankston and Casey and none of those diagnosed had travelled to areas where mosquitoes carrying the virus are usually found.
Recent heavy rainfall and warn weather have made ideal breeding grounds for mosquitoes, which pass the infection to humans with their bite.
Symptoms include fever, headache, aching muscles, joints and fatigue. Some people will also develop a rash. While the virus is not considered fatal, in rare cases a person can experience symptoms for more than a year.
A spokesman for the department of health said it was rare for the virus to be detected in Melbourne.
He did not have historical data, but said one mosquito in an outer Melbourne suburb tested positive for it in 2009. It was possible this insect had travelled in a car to the city the spokesman said.
Health Minister Jill Hennessy urged Victorians to cover up with loose fitting cotton clothing, use repellents and remove any stagnant water from around their homes.
"If anyone is feeling unwell we do want to urge them to contact their GP," Ms Hennessy said. "It's not necessarily a fatal illness but it is a really uncomfortable one to have."
There have been 857 cases in Victoria since January 1, a period during which the state would usually expect to see 20 to 50, said Victoria's chief health officer Charles Guest.
Over the past four months 18 local councils have been battling the spread in Victoria's north-west and north-east, using fobbing and larvacides.
Professor Guest said virus symptoms appear between two to 14 days after the mosquito bite and that there will be many people infected who won't experience any symptoms.
People may experience chronic imflammation in the small joints of their hands and feet, he said.
"It's usually a mild infection that can be prevented by avoiding the mosquito bite," Professor Guest said.
The virus is also found in a wide variety of animals, including horses.