Once harmless, the Zika virus became lethal after a single genetic mutation

When the Zika virus was first isolated from an Ugandan forest monkey in 1947 and found in mildly ill humans a few years later, it was hardly worth a mention in the annals of human disease. What a difference a mutation can make. In a new round of genetic sleuthing, Chinese researchers have pinpointed the single genetic change that has made the Zika virus a fearsome plague to pregnant women and their babies in Brazil and across the Americas, responsible for thousands of cases of microcephaly and other grievous brain abnormalities that sometimes result in death. The Chinese researchers also came close to pinpointing the time at which the Zika virus graduated from unwelcome pest status to international scourge. That change, they surmised, occurred in about May 2013, a few months before the start of a two-year outbreak in French Polynesia and three other Pacific islands. By March 2015, the Zika virus had arrived...