Before 2015, Zika virus (ZIKV) was a little-known flavivirus that caused sporadic symptomatic infections in humans (under 20 reported cases, but likely many more unreported asymptomatic cases) in the decades following its discovery during 1947 in Africa. Infections with ZIKV result in a mild acute illness including a self-resolving fever and rash, and no fatalities have been attributed to acute ZIKV fever. Carried by Aedes mosquitoes, the virus spread through Oceania and then Latin America over the past 10 years, culminating in the recent 2015–16 ZIKV epidemic with tens of thousands of laboratory-confirmed cases. Of note, ZIKV infections during pregnancy are linked with severe congenital brain anomalies, including microcephaly. These observations suggest that ZIKV may have become more pathogenic, and phylogenetic data shows that 2015–16 epidemic ZIKV isolates have evolved as a new cluster from previous isolates [1].