A Zika virus researcher at the NIAID Vaccine Research Center loads samples into a microcentrifuge. Zika virus is spread by daytime-active Aedes mosquitoes. Its name comes from the Zika Forest of Uganda, where the virus was first isolated in 1947. Zika virus is related to dengue, yellow fever, Japanese encephalitis, and West Nile viruses. Since the 1950s, it has been known to occur within a narrow equatorial belt from Africa to Asia. From 2007 to 2016, the virus spread eastward, across the Pacific Ocean to the Americas, where the 2015-16 Zika virus epidemic reached pandemic levels. The infection often causes no or only mild symptoms, similar to a very mild form of dengue fever. As of 2016, the illness cannot be prevented by medications or vaccines. Zika can also spread from a pregnant woman to her fetus. This can result in microcephaly, severe brain malformations, and other birth defects.