Zika is a disease caused by the Zika virus, which is spread to people primarily through the bite of an infected Aedes species mosquito. It can also be spread by a man to his male or female sex partners during vaginal, anal, or oral (mouth-to-penis) sex. The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting for several days to a week after being bitten by an infected mosquito. People usually don’t get sick enough to go to the hospital, and they very rarely die of Zika. For this reason, many people might not realize they have been infected. However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly, as well as other severe fetal brain defects. Once a person has been infected, he or she is likely to be protected from future infections.