A New York City woman has infected her male partner with the Zika virus through sex.
It is the first time female-to-male transmission of the germ has been documented.
Zika is usually spread by mosquitoes, and multiple studies have found the virus can survive two months or more in semen - even after symptoms fade.
However, there is little research on Zika's presence in women, and how they pass it on.
The new finding prompted the Centers for Disease Control and Prevention to update its advice in a report issued on Friday, urging female partners of pregnant women to wear protection, not just male.
According to the report, the New York woman - who was not pregnant - had recently returned from a Zika-infected country.
On returning, she had a fever, fatigue, a rash, and numbness in her hands and feet.
A blood and urine test confirmed she had Zika.
But at the time, doctors did not believe women could pass the virus to men.
Six days later, however, her male partner started to develop symptoms despite not having been abroad.
Concerned, he got tested - and it was confirmed that he had developed the virus.
Updating the official guidelines on Friday, the CDC said it now advises pregnant women to use protection with a partner that has traveled to a Zika-infected region, whether they are a man or a woman.
'Although no cases of woman-to-woman Zika transmission have been reported, these recommendations now also apply to female sex partners of pregnant women,' the CDC said in a statement on Friday.
Source: Daily Mail