Zika virus, a mosquito-borne flavivirus that causes febrile illness associated with rash, has been rapidly emerging in the Western Hemisphere over the past few months. The virus was rarely identified until outbreaks occurred on Yap Island in the Federated States of Micronesia in 2007, French Polynesia in 2013, and Easter Island in 2014. It was initially detected in Brazil in 2015, in the northeast, and was subsequently identified in other states and several South American countries, including Colombia, Ecuador, Suriname, Venezuela, French Guyana, and Paraguay (1). Local transmission has been documented in Central America (Panama, El Salvador, Honduras, and Guatemala), the Caribbean (Martinique, Puerto Rico, Dominican Republic, and Haiti), and Mexico. Transmission has also occurred in travelers returning from the infected regions to nonendemic countries, including the United States, Canada, Japan, and Western Europe. As of 22 January 2016, a total of 20 countries and territories in the Americas have Zika virus circulation (1). The explosive spread mirrors the emergence of chikungunya, which was first detected in the Americas (St. Martin) in 2013 and rapidly disseminated throughout the region (2).