The following piece was published 16 September 2013, SBS World News Australia Radio.
By Ildi Amon
Mosquito-borne viruses typically associated with tropical climates are spreading to the southern parts of Australia - even as far south as Tasmania.
And experts are now calling on Australians to be more vigilant, both at home and abroad.
Holiday-makers heading to popular tourist spots such as Bali are being asked to be particularly careful after a jump in the number of infections of the lesser known virus chiikungunya.
Ildi Amon investigates.
Mosquito-spread viruses such as Ross River virus, Barmah Forest virus and dengue infect thousands of people in Australia each year.
The number of people with these viruses are recorded on the National Notifiable Disease Surveillance System.
These records indicate that so far this year over 3000 people have been infected with Ross River virus while over 3500 have had the Barmah Forest virus.
Entomologist and mosquito researcher from the University of Sydney, Cameron Webb, says while these viruses are typically associated with tropical far north Queensland, Ross River and Barmah Forest are actually present Australia-wide.
Doctor Webb says it's not entirely clear why these mosquito-related viruses can sometimes flare up in cooler climates.
But he says climate change as well as changes in native wildlife populations may influence the outbreaks.
"We're starting to see an increase in particularly things like Ross River virus on the fringes of the cities and one of the reasons for that is that mosquitoes don't hatch out of the wetlands already infected with the virus. They have to bite an animal first to become infected and in the case of Ross River Virus that's mostly kangaroos and wallabies. So as we're doing a better job of conserving our wetlands around our cities but also creating better conditions for native wildlife, we're inadvertently increasing the risk of mosquito-borne diseases in some places and we're kind of seeing that on the outskirts of Sydney and Perth in recent years."
Doctor Webb says symptoms appear about a week after a bite by an infected mosquito and while the virus isn't contagious between people, there's no cure or vaccination.
He says that while the Ross River and Barmah Forest viruses aren't fatal they can cause joint pain, rash, fatigue and fever.
"The symptoms can sometimes be incredibly severe and last for many months. And so for people that have a severe case of Ross River virus it actually can be seriously debilitating. Some cases are much milder and you may not even know you've been infected but for those severe cases it can really be a significant impact on your lifestyle."
Perth man, Brad Davidson, was diagnosed with Ross River and he suspects he was bitten by a mosquito while on holidays just north of Perth in the months leading up to Christmas in 2011.
He's likened it to a really bad flu but says some of the symptoms still persist, even two years later.
"You just feel very achey, your joints just feel very, very sore and I noticed my joints were actually quite swollen. So I guess it would feel like what rheumatoid arthritis- from what I've read, I've never had it - but from what I've read it sounds very similar to how that would feel. Also very lethargic and tired, albeit for myself it was only half a dozen days where I had that feeling but the actual rheumatic feelings went on for six months to a year, at least."
An organisation that advises travellers on medical risks says many Australians underestimate the risk of viruses such as dengue and the lesser known Chiikungunya virus when travelling to South East Asia, particularly to Bali.
The National Notifiable Disease records show there's been a jump in the number of Australians with the Chiikungunya virus -- a virus that's present in Indonesia but not in Australia.
There were only about 20 cases of chiikungunya last year, but so far this year there have already been just over 100 cases.
Medical Director of the Travelvax company, Eddy Bajrovic says this could be because of the high number of Australian tourists heading to Bali coupled with the increasing prevalence of Chiikungunya in Indonesia.
"Chiikungunya is not new. It was first described in Africa. Chiikungunya comes from an old, I think, Swahili word in means "bent over" or "that who is bent over" obviously from the arthritis they get from the infection. But it's more recently found its way into South East Asia and with all of the tourism we're seeing cases come back to Australia now."
Cameron Webb from the University of Sydney says it's not known whether some people are more susceptible to these viruses but he says it's likely some people may be more attractive to mosquitoes than others.
"Probably has something to do with the chemical cocktails, smells on our skin that determine how many mosquitoes are likely to bite us. Some people also react a little bit worse just to the bite, so the type of itchy bite after they've been bitten can vary quite a bit and can give you the misconception you've been bitten more or less than your friends. But at the end of the day it only takes one bite from a mosquito to transmit some of these viruses so avoiding bites wherever possible is really the best line of defence."
Dr Webb believes there's a common misconception that mosquitos only bite at dusk or at night.
He says the mosquitoes that spread chiikungunya and dengue actually feed during the day.
So he says the only way to avoid these viruses is to avoid mosquito bites by wearing covering clothing and using powerful insect repellents.