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Not who you want to meet on your tropical vacation.

USDA/AP

Not who you want to meet on your tropical vacation.

If winter has you daydreaming of a vacation to sunny lands, you might want to consider the risk of dengue fever in your plans.

The number of cases of the disease, a severe flu-like illness with excruciating headaches, joint and muscle pain, is soaring, according to an update from the World Health Organization.

Now more than 40 percent of the world's population is at risk â€" 2.5 billion people, according to the group. In 2010, there were 1.6 million cases in the Americas alone.

"Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are occurring," WHO warned in a statement on its website.

 

Europe can expect a dengue outbreak soon, the WHO statement says. In 2010, locally acquired cases were reported in Croatia and France for the first time.

Closer to home, last year Miami logged two cases of dengue fever, both of which were locally acquired.

When it comes to infectious disease, this is bad news. Until now, most cases of dengue in the United States have been in people returning from places like the Caribbean, South America or Asia, where the disease is common.

"It means it's in our area, not an imported disease," Vincent Conte, deputy director of epidemiology for the Miami-Dade County Health Department, told the Miami Herald last September.

In 2010, there was a dengue outbreak in the laid-back vacation haven of Key West, the first sizable outbreak of the disease in the U.S. in more than 50 years. Federal health officials said at the time that the Southern U.S. should brace for more. (NPR's Richard Knox reported on that outbreak.)

Dengue is caused by a virus, and the virus is spread by the Aedes aegypti mosquito. It lives in urban areas, likes to breed in flowerpots and similar containers, and bites during the day, when people are out and about. There's no vaccine to prevent dengue. The best way to avoid it is to avoid getting bitten by a mosquito.

With no new cases in Miami since September, earlier this month the health department lifted its dengue advisory.

But the authorities there are still urging people to dengue-proof by draining standing water from flowerpots and pool covers, covering up with clothing and repellent, and repairing window screens.

The global surge of dengue has not gone unnoticed by scientists, who are trying to figure out how to halt transmission.

NPR's Dan Charles reported last year on efforts to study dengue in Peru, while scientists in England are working on genetically modified sterile male mosquitoes. And in Australia, scientists are feeding mosquitoes bacteria in the hope that they'll be too sick to bite. Here's Joe Palca's report.