Zika virus particles, animation. Zika virus is an RNA (ribonucleic acid) virus from the Flaviviridae family. The virus has an icosahedral capsid containing the genetic material, surrounded by a protein envelope. It is transmitted to humans via the bites of infected Aedes mosquitoes, and there have been reports of sexual transmission. It causes Zika fever, a mild disease with symptoms including rash, joint pain and conjunctivitis. In 2015 a previously unknown connection between Zika infection in pregnant women and microcephaly (small head) in newborns was reported. This can cause miscarriage or death soon after birth, or lead to developmental deficits.