Three years ago, the Zika virus was nowhere to be found in the Western Hemisphere. To date, the largest outbreak occurred in French Polynesia in 2013 with 383 reported cases. But in 2015, Brazil suddenly found itself with an unprecedented Zika outbreak. More than a million people have been infected by the mosquito-transmitted—and potentially sexually transmitted disease.
The mosquito-borne virus doesn’t seem to harm most of its victims. But there’s increasing evidence that it can cause serious damage to the brains of fetuses and, in rare instances, devastating neurological problems in adults.