The Zika virus, the mosquito-born disease that has spread rapidly through South America to the United States, has been known to be transmitted at least on occasion through sex.
In May, health officials began urging women who have been in areas hit by the virus to take precautions with their sexual partners and wait longer to conceive.
Some new studies indicate the disease may spread more frequently than thought through sex, The New York Times reports.
"Two reports now suggest that women in Latin America are much more likely to be infected than men, although both are presumed to be equally exposed to mosquitoes," the Times writes. "The gender difference appears at the age at which sexual activity begins, and then fades among elderly men and women."
The implication of the reports is both that sex may have already led directly to more transmissions than previously believed, and that women are more vulnerable than men.
So far, all cases of sexual transmission have occurred when the male is symptomatic. It is not yet known if women or asymptomatic men can transmit the virus through sexual activity. The virus has been found to linger for months in men's semen.
Overall, nearly 800 cases of Zika have been reported in the 50 states and the District of Columbia. All were people who had traveled to outbreak areas, or who had sex with someone who had traveled to affected areas.
The virus has been found to cause microcephaly, a birth defect in which babies are born with abnormally small heads, and has been linked to a rare paralyzing condition called Guillain-Barré syndrome.