Until recently, Zika—once considered a mild disease—was hardly a cause for global panic. But as early as August 2015, doctors in northeast Brazil began to notice a trend: many mothers who had recently experienced symptoms of the Zika virus were giving birth to babies with microcephaly, a serious disorder characterized by unusually small heads and brain damage.By early 2016, Zika was making headlines as evidence mounted—and eventually confirmed—that microcephaly is caused by the virus, which can be contracted through mosquito bites or sexually transmitted.The first death on American soil, in February 2016, was confirmed in Puerto Rico in April. The first case of microcephaly in Puerto Rico was confirmed on May 13, 2016. The virus has been known to be transmitted by the Aedes aegypti or Yellow Fever mosquito, but now Aedes albopictus, the Asian Tiger mosquito, has been found to carry it as well, which means it might affect regions as far north as New England and the Great Lakes. Right now, at least 298 million people in the Americas live in areas “conducive to Zika transmission,” according to a recent study. Over the next year, more than 5 million babies will be born.In Zika: The Emerging Epidemic, Donald G. McNeil Jr. sets the facts straight in a fascinating exploration of Zika’s origins, how it’s spreading, the race for a cure, and what we can do to protect ourselves now.