The Zika virus, discovered in 1947 in Africa, is related to the viruses that cause yellow fever, West Nile, dengue and chikunguna, and it is spread by bites of the mosquitos Aedes aegypti and, to a lesser extent, Aedes albopictus. In the past the virus was found principally in Africa, southeast Asia, and parts of the Pacific, but over the past several years and especially in the last 6-9 months it has grown 鈥渆xplosively鈥 in the Americas. Brazil has been especially hard hit, and there is concern that the coming Olympics in Rio de Janeiro may cause further expansion of the virus鈥 territority.