The Zika virus seems to have come out of nowhere, but health officials now worry the disease could infect as many as 4 million people worldwide in 2016 alone. The World Health Organization says the disease is “spreading explosively.” But where did Zika come from? And how did it spread so fast? Click below to begin.
Content retrieved from: http://www.pbs.org/wgbh/frontline/article/map-how-zika-spread/.