dengue fever

Two years ago Pakistan's Punjab province was hit with one of the world's worst dengue outbreaks. This year the number of recorded cases has plummeted. Many leaders credit a mobile phone app that tracks mosquito populations and city workers' efforts to contain them.

After decades without any reported cases, dengue fever seems to be getting a foothold in the U.S. In 2009, it surfaced in Key West. This year, 18 cases have been reported this summer in Martin County, Fla.