The CDC's already advised travelers to be aware of the risk, recommending that men who have traveled to Zika-affected zones should use a condom if they want to be absolutely sure they don't infect sex partners.
CDC issued a travel advisory last month telling pregnant women to stay away from countries where Zika is circulating.
The Zika epidemic is a real-life science experiment. The virus is infecting millions of people who have never had it before and it's giving doctors a chance to use modern tests and techniques to see how new infections move across a population.
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Zika's clearly a mosquito-borne virus, spread as female Aedes mosquitos sip blood from one person after another, often in the same room. Other viruses are spread this way, too: yellow fever, dengue, West Nile and chikungunya. And the malaria parasite is also spread by mosquitoes.
"It's not likely that sexual transmission is anywhere close to the frequency of mosquito-borne transmission. The mosquito is the most dangerous animal on the planet," said Dr. William Schaffner of Vanderbilt University, past president of the National Foundation for Infectious Diseases.