The Zika virus is a flavivirus transmitted to humans primarily by the bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus). These mosquitoes are mainly daytime-active; however, they can also bite at night. Zika virus is named after the Zika Forest of Uganda, where the virus was first isolated in 1947. Zika means "overgrown" in the Luganda language. The virus is related to dengue, yellow fever, Japanese encephalitis, and West Nile viruses. Since the 1950s, the Zika virus has been located in a very narrow geographical area from Africa to Asia and is found primarily in tropical climates. From 2007 to 2017, the virus had spread eastward across the Pacific Ocean into the Americas. The first Zika outbreak in the United States occurred in 2016. However, from 2018 to the present (2022), Zika cases have been on a decline worldwide, with no current local transmission of Zika virus in the continental U.S.
Dengue, chikungunya, and Zika viruses are all transmitted by Aedes mosquitoes, found primarily in tropical locations. In addition, all three viruses can have overlapping clinical symptoms and may be found in the same geographic locations.
Although the Zika virus is primarily transmitted to humans through the bite of an Aedes mosquito, the virus can be transmitted from mother to child during pregnancy (resulting in congenital infection). The virus can also be spread via sexual activity, blood transfusion (not in the United States to date, but multiple reports in Brazil), and laboratory exposure. Although the Zika virus has been detected in breast milk and human tears, transmission through breastfeeding or contact with human tears has not been documented.
Regarding sexual transmission, scientists have learned that transmission of the Zika virus can occur via oral, anal, and vaginal sex. Moreover, the CDC has issued sexual guidance for Zika transmission, which includes the recommendations of no intercourse during the entire pregnancy, unless the couple can carefully and correctly practice safe sex. In addition, similar recommendations apply to couples trying to conceive.
