Zika was a mild bug. A new discovery shows how it turned monstrous.
When the Zika virus became a global terror two years ago — inflicting severe birth defects on the babies of pregnant women who were infected with the virus and alarming health officials worldwide — scientists were mystified. How did such an obscure, relatively harmless pathogen that had been known for more than half a century suddenly blossom into a monster virus? Was it something about Zika’s new hunting grounds when it spread from Africa to South America and the Caribbean?