Experts are warning people to guard against mosquito bites over the next few months, with the spread of the pest that carries the Ross River virus and Barmah Forest virus.
The National Notifiable Disease Surveillance System reports that so far this year there have been 3500 cases of Ross River (4684 cases in 2012) around Australia.
There has been a big increase in Barmah Forest virus, with 3465 cases (1722 cases in 2012).
In its warning, the medical travel service Travelvax has singled out grey nomads, campers and visitors to bush areas as widespread as south-eastern Australia, tropical Queensland and south-western Western Australia.
But the service director, Eddy Bajrovic, said people in urban areas were also vulnerable.
"You don't have to be on holiday in the bush any more to be at risk," he said. "We are seeing increased reports of Ross River and Barmah Forest virus from the capital cities too."
A mosquito specialist, Cameron Webb, an entomologist based at the University of Sydney, said: "Ross River and Barmah Forest viruses are now commonly reported from southern states.
"In fact, outbreaks are increasingly occurring on the fringes of cities such as Sydney, Melbourne and Perth." Perth is expecting a spring surge of Ross River virus, with 31 people contracting it in the metro area and eight in the fringes in the month to August 19. Sydney, with forecasts of warm weather and above-average rainfall for the next three months, may also have a surge in mozzies.
Dr Bajrovic said the migration and spread of the disease-carrying mosquitoes could be linked to global warming and climate change. Cities are also expanding into mosquito habitats. The viruses are not fatal, but there are no specific treatments or vaccines.
Symptoms can be severe and prolonged, including painful and swollen joints, sore muscles, skin rashes, fever, tiredness, headaches and swollen lymph nodes.
In one case, a Japanese tourist in Melbourne in January was unable to walk after coming down with Ross River virus contracted in the city.
A Perth woman bitten in her backyard seven months ago has suffered fever and joint pain and is still unable to fully move her fingers.
Dengue fever, with similar symptoms to Ross River and Barmah Forest viruses, is another mosquito-borne danger, present north of Townsville.
But most of Australia's reported cases (1238 so far this year) are brought back from overseas.
"There is a risk of dengue fever and chikungunya virus in Indonesia, particularly Bali, where a lot of Australians travellers are going because of cheap prices," Dr Webb said.
"The mosquitoes there have a different bite pattern [attacking during the day] and Australians are not going with the right mindset to take the necessary precautions, like they would if they were holidaying on the coast here.
"If there is a take-home message for travellers, it is that they should use a repellent with DEET or Picaridin."