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 is suspected of causing 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 what illnesses the virus is truly responsible for and why more people are getting sick.
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