With the warm, muggy weather of summer fast approaching and the spread of the Zika virus continuing to ascend northward from South America, many Americans are worried that mosquito-borne transmission of Zika may become a reality in the continental United States. And there is good reason for concern: Puerto Rico, the U.S. Virgin Islands, and American Samoa have already seen cases of Zika transmitted by local mosquitoes, and there have been several travel-associated cases of Zika in the 50 states.