Zika virus. Computer illustration of a zika virus particle (virion). Zika is an RNA (ribonucleic acid) virus that causes zika fever, a mild disease with symptoms including rash, joint pain and conjunctivitis. It is transmitted to humans via the bite of an infected Aedes sp. mosquito. 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 delays and disorders.