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The first case of Zika spreading sexually from a woman to a man has been documented in New York City, according to a new report from the U.S. Centers for Disease Control and Prevention. While Zika is also spread by mosquitoes, the news adds support to the evidence that sexual transmission of the virus is a threat in the United States.

Until Friday, it was unknown whether women could also sexually transmit the virus. The CDC had previously confirmed that a man can spread the disease to female and male partners via vaginal, anal or oral sex without a condom. The virus lasts longer in semen than it does in blood.

In the specific case in New York City, a woman in her 20s who was not pregnant reported that she had engaged in sex with a male partner when she returned to the city from a country with ongoing transmission of Zika. At the airport she had developed a headache and abdominal cramping, and later had a fever, fatigue and rash among other symptoms. Her doctor took samples of her blood and urine, and Zika was detected. A week after having sex, the male partner developed a fever, rash, joint pain and eye redness. He visited the same doctor as the woman, and Zika was identified in his urine sample. The man confirmed with health authorities that he had not traveled outside of the U.S. in the year before he got sick.

Health authorities have so far reported around 14 cases of sexual transmission of the virus in the U.S.

Current recommendations are based on the assumption that men are the ones who pass the virus on sexually, and the CDC says it is currently updating its advice for sexually active couples that are not pregnant or concerned about pregnancy who want to avoid an infection.

“CDC recommends that all pregnant women who have a sex partner who has traveled to or resides in an area with Zika use barrier methods every time they have sex or they should not have sex during the pregnancy,” the agency said in a statement. The CDC adds that while woman to woman transmission has not yet been documented, that advice applies to female sexual partners of women who are pregnant as well.

It’s unknown whether Zika can be passed during kissing through saliva, or if the virus has a different risk for birth defects if it’s passed to a pregnant woman via sex versus from a mosquito.

In the U.S. there are over 1,000 cases of Americans with Zika, including around 346 pregnant women. Over 300 additional pregnant women in U.S. territories are also infected. On Thursday Senate failed to pass any emergency Zika funding, and will recess until September.

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