To the Editor: Zika virus, genus Flavivirus, has spread nearly uncontrolled since its introduction into the Western Hemisphere; autochthonous spread has occurred in >39 countries and territories, including several US territories. Transmission of Zika virus is usually by the bite of infected mosquitoes, and potential for emergence in areas with competent mosquito vectors is high (1). Future spread of Zika virus is unpredictable; however, eventual local spread in the United States is possible. As of July 13, 2016, a total of 1,306 travel-associated cases had been reported (ArboNET, https://www.cdc.gov/zika); substantial populations of Aedes (Stegomyia) aegypti (Linnaeus) mosquitoes exist in >16 states in the eastern, southeastern, and southwestern United States; and Ae. (Stegomyia) albopictus (Skuse) mosquitoes inhabit >28 states and continued expansion throughout the northern United States is probable (2). Mosquitoes of these 2 species have demonstrated the ability to transmit Zika virus (1).