Zika virus (ZIKV) is a member of the Flaviviridae virus family and the Flavivirus genus, transmitted by Aedes mosquitoes. In humans, it causes a mild illness known as zika, Zika disease, or Zika fever, which since the 1950's has been known to occur within a narrow equatorial belt from Africa to Asia. In 2007, it emerged further east in Micronesia, South America, Central America, and the Caribbean. There, it is considered an explosive pandemic. The illness is like a mild form of dengue fever, is treated by bed rest, and cannot be prevented by drugs or vaccines. Zika disease is related to yellow fever and West Nile disease, which are caused by other flaviviruses. A link to microcephaly in fetuses born to infected mothers is suspected, but is still being investigated.