Editor's note: As of Oct. 1, we're no longer updating this timeline.
Since it was first discovered in Uganda in 1947, Zika virus was known mostly as a short-lived and mild illness. In 2015, that all changed. An outbreak in Brazil has been linked to cases of a serious birth defect, microcephaly, and a potentially crippling disease, Guillain-Barre syndrome.
As the mosquito-borne illness spreads across the Americas, scientists are trying to figure out which illnesses the virus is truly responsible for and why more people are getting sick.
We've put together a timeline to track the global response to Zika virus and scientists' understanding of how it affects people, with the most recent events at the top. (Find NPR's ongoing coverage here.) Check back, as we're regularly updating this list.