A single genetic glitch may explain how Zika became so dangerous

By Julie SteenhuysenCHICAGO (Reuters) - A single genetic change that occurred in 2013 may explain how Zika acquired the ability to attack fetal nerve cells, causing a severe birth defect in babies whose mothers were infected while pregnant, Chinese and U.S. researchers reported on Thursday.Scientists have posited many theories about why Zika, a mosquito-borne virus that had been linked with only mild symptoms since its discovery in 1947, could suddenly be associated with thousands of cases of th