PARIS (Reuters) - France has detected its first sexually transmitted case of Zika in a woman whose partner had traveled to Brazil, the epicenter of an outbreak of the virus, a senior health official said on Saturday.

U.S. officials said earlier this week they were investigating 14 reports of the mosquito-borne disease that may have been transmitted through sex, including to several pregnant women.

Francois Bourdillon, head of France's Institute for Public Health Surveillance (IVS), said the infected woman was the country's "first confirmed indigenous case of transmission".

"This was a woman who had never traveled. Her partner had come from Brazil, so she was tested," Bourdillon said in an interview broadcast on BFM TV, adding that both patients were doing well.

Marie-Claire Paty, who helps monitor diseases transmitted by insects for the IVS, told Reuters the current epidemic seemed to confirm sexual transmission, which was identified as a possibility during an earlier outbreak in Polynesia in 2013-14, when the virus was isolated in sperm.

Brazil has declared a public health emergency over Zika, which may be linked to thousands of cases of the microcephaly birth defect that is marked by undersized heads and underdeveloped brains.

There is no cure or treatment for the virus, which is usually transmitted by mosquitoes and has spread to more than 30 countries.

(Reporting by Yann Le Guernigou; Writing by James Regan; Editing by Helen Popper)