Four out of 5 people who get Zika virus have no symptoms. If symptoms do develop, they typically include a rash, fever, joint pain or red eyes. An infection usually lasts about a week, but the virus may hang out for longer in some people. For pregnant women, scientists now believe that Zika virus can affect a developing baby. Evidence shows that Zika can cause microcephaly—a birth defect where the baby’s brain and head are underdeveloped. Zika during pregnancy also appears to be linked to Guillain-Barré syndrome in babies—a rare condition in which the body attacks its own nerves.