Dengue fever cases in Australia reached a 20-year high last year, driven by travellers being infected in tropical areas such as Bali and bringing the virus back with them.
More than 2000 cases of the mosquito-borne disease were confirmed in Australia last year, federal Health Department data shows.
University of Sydney mosquito expert Cameron Webb said dengue fever cases were increasing globally, and travellers were bringing the disease back to Australia. But, he said, if a person brought dengue fever back as an unwanted souvenir, they were unlikely to pass it on because most local mosquito species could not transmit the disease.
Microbiology professor Cameron Simmons, of the Peter Doherty Institute, said dengue fever was endemic (constantly being transmitted) throughout much of south-east Asia and the western Pacific, which were popular destinations for Australian travellers.
"Dengue has been a problem globally for 20 years, and in the last 10 years we have seen epidemic spread of the virus through many countries in our neighbourhood," he said. "The chance of travellers being infected may well be increasing."
But he said the increased number of dengue fever cases in Australia could also be because more doctors were running tests that determined whether returned travellers were infected with the disease.
The disease takes between three and 10 days to incubate, and causes flu-like symptoms that last for about a week. "It can be a pretty miserable week of your life, and it sometimes takes a few weeks to fully recover," Dr Simmons said.
An estimated 390 million people are infected with the dengue virus each year.
Dengue fever does not recur after the initial bout of the disease. However, if someone is infected a second time from another mosquito bite, the risk of potentially deadly complications, such as internal bleeding or hemorrhaging from the nose and gums, greatly increases, Dr Simmons said.
He said it was unlikely a person would be bitten by a dengue-carrying mosquito at a five-star resort in Bali, but anyone staying at a backpacker hostel that did not have a pest control plan would be more at risk.
Dengue fever cases hit a 20-year high in Victoria and New South Wales last year, with the states recording 461 and 450 cases, respectively.
Western Australia was the state with the most cases, at 553. It also had one of the highest infection rates of the disease of all the states and territories.
Dr Simmons said this could be because fly-in-fly-out workers in WA could easily travel to Bali, thanks to cheap four-hour flights from Perth.
Younger people were over-represented in the figures for dengue infections last year. Those aged 25 to 34 accounted for about one in four of the 2129 cases, despite making up just 15 per cent of the Australian population. There was a roughly even split of men and women contracting the disease.
Queensland has had by far the most dengue cases of any state over the past two decades, experiencing sudden rises in cases in 1993, 1998, 2003 and 2009 (when more than 1000 were confirmed).
Dr Simmons said that was because far north Queensland was one of the few parts of Australia with mosquitoes capable of spreading the virus, and local outbreaks had occurred after infected travellers brought the disease back with them from overseas.
However, infection numbers in Queensland have been down in recent years, in part because of the Eliminate Dengue program, which effectively immunised the local mosquito population in tropical areas against the dengue virus.
The mosquito that spreads dengue, Aedes aegypti, is also capable of transmitting the Zika virus, which led to warnings of similar outbreaks in far north Queensland if an infected traveller were to bring the disease into the country.
There were 59 confirmed Zika cases in Australia last year, all of which were from travellers who were infected overseas.
Dr Webb said travellers to Bali could reduce their risk of dengue infection by applying mosquito repellent in the morning as well as at other times. He said Australian tourists assumed overseas mosquitoes were only active in the afternoon and evening, but the bugs in Bali bite throughout the day.
