From the Background: "Zika is a virus that is primarily spread by Aedes mosquitoes--the same mosquitoes that transmit dengue, chikungunya, and yellow fever. Zika transmission has also been documented from mother to child during pregnancy, as well as through sexual intercourse, blood transfusions, and laboratory exposure. Scientists first identified the virus in 1947 among monkeys living in the Ugandan Zika forest. Five years later, human cases were detected in Uganda and Tanzania. The first human cases outside of Africa were diagnosed in the Pacific in 2007 and in Latin America in 2015. The ongoing outbreak in Latin America began in Brazil in May 2015 and has since spread to 22 countries and territories in the region. Health experts predict that the virus will likely spread to all countries in the Western Hemisphere except Canada and Chile, the only countries in the region without Aedes mosquitoes. No instances of local transmission have been reported in the continental United States, but cases have been reported among travelers who visited Central and South America, and transmission is ongoing in Puerto Rico. Outside of Latin America, Cape Verde --islands off the West African coast--has ongoing transmission and Samoa--islands in the Western Pacific--has reported less than a dozen imported cases."
CRS Insight, IN10433
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html