A rare case of the Zika virus being transmitted through sex, not a mosquito bite, has been reported in the US.
The Centers for Disease Control and Prevention confirmed a patient was infected in Dallas County, Texas.
A patient was apparently infected after having sexual contact with someone who returned from a country where the disease is present.
Zika is carried by mosquitoes and has been linked to thousands of babies being born with underdeveloped brains.
It is spreading through the Americas and the World Health Organization has declared the virus a global public health emergency..
This case in Dallas would be the first known infection to take place in the mainland US, though Texas has seen seven other Zika cases all related to foreign travel.
"Now that we know Zika virus can be transmitted through sex, this increases our awareness campaign in educating the public about protecting themselves and others," said Zachary Thompson, director of Dallas County Health and Human Services, in a news release.
"Next to abstinence, condoms are the best prevention method against any sexually-transmitted infections."
The case is "significant" if it was definitely transmitted through sexual contact, Alaka Basu, a senior fellow for public health at the UN Foundation, told the BBC.
"This significance is parallel with the HIV/Aids case. It's worse in some ways, because there are two modes of transmission."