A mosquito is seen under a microscope at the Greater Los Angeles County Vector Control District in Santa Fe Springs, California.Lucy Nicholson / Reuters

So far, all known cases of sexually transmitted Zika have involved a man spreading it to a partner. The virus thrives in semen, and lives there longer than it does in blood, which is why experts recommend that men use condoms if they’ve been in areas where Zika is spreading—for six months if they’ve had symptoms, and eight weeks even if they haven’t.

Currently, the website of the Centers for Disease Control and Prevention states, “We don’t know if a woman with Zika can pass the virus to her partners, during vaginal or oral (mouth-to-vagina) sex.” But now there’s reason to suspect that women might be able to.

In a new case study published in The Lancet Infectious Diseases, doctors at Pointe à Pitre University Hospital, in Guadeloupe, treated a woman with Zika in May, and detected the virus in her genital tract. When she first came in, her blood tested positive for Zika, though her urine did not. Three days after the onset of her symptoms, doctors did a genital swab, a swab around the opening of the cervix, and also took a sample of cervical mucus. All three samples tested positive for Zika virus RNA. They did another round of tests 11 days after her symptoms started—of blood, urine, and cervical mucus—and while the blood and urine were clear, the virus was still in the mucus.

This doesn’t prove anything, but it does raise the possibility that sexual transmission of Zika could come from anyone. And it seems there’s something about sexual fluids that helps Zika survive longer in the body. How long is unclear; apparently at least 11 days in a woman is possible.

The researchers speculate that this discovery could open the door to a much more serious one. “Our findings raise the threat of a woman potentially becoming a chronic Zika virus carrier, with the female genital tract persistently expressing the virus RNA,” the study reads. For women hoping to have children, given the risks of Zika to fetuses, that could be a huge threat.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.