Research: Dengue Underestimated By World Health Organization

The tropical disease dengue is far more widespread than previously thought, according to an article in the journal Nature. The study estimates there are three to four times more dengue infections each year than the number currently tallied by the World Health Organization.

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The tropical disease dengue is on the move, spreading far outside the tropics. There have been major outbreaks in places like Portugal, Russia and Australia. It even popped up in Florida. Now, according to a new paper in the journal Nature, scientists have been seriously underestimating the amount of dengue around the globe. The study estimates that there's three to four times more dengue infections each year than what was reported by the World Health Organization. NPR's Jason Beaubien has more.

JASON BEAUBIEN, BYLINE: Dengue is a nasty virus. There's no vaccine, no way to treat it. Usually, it doesn't kill you, but it can. Its effects can be so intense, that at times, it's called break-bone fever.

THOMAS SCOTT: You just have aches and pains. There's post-orbital pain, where your eyes ache. Your bones and joints ache.

BEAUBIEN: Thomas Scott is professor at the University of California Davis and one of the authors of the new report on the global spread and burden of dengue.

SCOTT: Not only are the number of cases increasing, the geographic range is increasing. So, it is spreading into areas where it was not previously, but we're also seeing more and more cases.

BEAUBIEN: Scott and his colleagues estimate that there are roughly 400 million dengue infections around the world each year, making it more prevalent than malaria. The World Health Organization puts the number of dengue infections globally at just a fraction of that, in the range of 50 to 100 million per year. Over the last few decades, there's been an explosion of dengue around the world. Prior to 1970, the mosquito-borne disease had only been reported in nine countries, according to the WHO. Now it's endemic in more than 100, and it continues to spread. Dengue appears to be attracted to overcrowded slums in the burgeoning cities of the developing world. Scott at UC Davis says this new report shows that poverty is a significant risk factor for dengue taking hold in the new environment.

SCOTT: People living in substandard conditions, where they're storing water and they don't have proper disposal of waste and rainwater accumulates in containers. And the mosquito that transmits this virus Aedes aegypti, lays its eggs in those places.

BEAUBIEN: Scott says not only is dengue making more and more people sick in some of the poorest countries in the world, it's straining already-fragile health care systems.

SCOTT: You get these explosive epidemics with large numbers of people getting infected in short periods of time, and it really overwhelms the public health infrastructure.

BEAUBIEN: Scott says one of the key findings of their new report is that there are possibly hundreds of millions of dengue infections each year in which people are carrying the virus, but don't get extremely sick. This means that there's far more virus circulating in the environment than previously thought, and this could mean that containing dengue, or at least stopping its current rampant growth, is going to be difficult. Jason Beaubien, NPR News, Washington.

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