Dengue Fever Cases Underestimated by Scientists, Current Epidemic in Over 100 Nations

A recent study estimates that scientists may have been seriously underestimating the amount of dengue around the globe.

According to the study, there are as many as 400 million dengue infections each year worldwide, which make it more prevalent than malaria. This is four times higher than the current dengue prevalence estimate from the World Health Organization.

Dengue, usually described as an infections tropical disease that has even lately been popping up outside the tropics, has reported major outbreaks in such countries as Portugal, Russia and even some cases in the United States. Prior to 1970 the mosquito-borne disease had only been reported in nine tropical countries, according to the WHO. Now it's endemic in more than 100 nations.

Thomas Scott, an entomologist at the University of California, Davis, and the co-author of the study, notes that the problem is continuing to spread.

"Not only are the number of cases increasing, the geographic range is increasing," Scott said. "So [dengue] is spreading in to areas where it was not previously but we are also seeing more and more cases."

Previous efforts to count dengue cases were missing huge numbers of infections - mainly the less severe ones which might not lead to hospitalization or medical attention, the authors write.

Dengue appears to be attracted to overcrowded slums in the burgeoning cities of the developing world. Scott said the new report shows that poverty is a significant risk factor for dengue taking hold in a new environment.

"People living in substandard conditions where they're storing water and they don't have proper disposal of waste [are more at risk]," he said. "Rainwater accumulates in containers and the mosquito that transmits this virus, Aedes aegypti, then lays its eggs in those places."

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.

"You get these explosive epidemics," Scott said. "With large numbers of people getting infected in short periods of times, it really overwhelms the public health infrastructure."

The study was published in a new paper from the journal Nature.