Any kind of sex can spread the Zika virus, federal health officials said Monday in updated guidance for pregnant women.
And doctors need to ask all pregnant women about any chance they could have been infected with Zika, either through sex, travel or via mosquito bite, the Centers for Disease Control and Prevention said in updated Zika guidelines.
Several recent new cases show that just about any kind of sexual contact can spread the virus, the CDC said. "Sexual exposure includes vaginal sex, anal sex, oral sex, or other activities that might expose a sex partner to genital secretions," it says in the new guidance.
"All other couples in which a partner (male or female) has been in an area with Zika can also reduce the risk of sexual transmission by using condoms or abstaining from sex. Sex includes vaginal, anal and oral sex, and may also include the sharing of sex toys."
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Zika virus has exploded across the Americas, carried mostly by mosquitoes but also, to the surprise of doctors, by person-to-person contact. Most people don't even get sick, but there is a huge risk to unborn babies.
The virus can cause severe birth defects if a pregnant woman gets infected -- all the way from extreme brain damage to subtler defects that experts say may not show up until a child starts to grow older.
There's no known way to protect an infected fetus, so the CDC says it's vital for women to avoid being both pregnant and infected with Zika if at all possible.
"Pregnant women with sex partners (male or female) who live in or who have traveled to an area with active Zika virus transmission should consistently and correctly use barriers against infection during sex or abstain from sex for the duration of the pregnancy," the CDC advises.
CDC's been watching more than 400 known cases of Zika-affected pregnancies in the U.S., plus another 378 in U.S. territories such as Puerto Rico. Twelve babies have been born in the U.S. with Zika-related defects and another six pregnancies were miscarried or aborted because of severe defects.
So far, all the women were in Zika-affected areas when pregnant, but more and more cases of sexual transmission are turning up. Health experts can say they're sexually transmitted because Zika is not yet known to be spreading in the U.S. and they've found Zika in the semen of men and in other bodily fluids.
"As of July 20, 2016, 15 cases of Zika virus infection transmitted by sexual contact had been reported in the United States," the CDC report reads.
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"Sexually transmitted Zika virus infection has also been reported in other countries. In published reports, the longest interval after symptom onset that sexual transmission from a man might have occurred was 32-41 days."
Evidence of Zika in semen has been found as long as three months after a man was infected.
Men are at risk, too, but Zika's not much threat to men. It rarely causes neurological complications such as Guillain-Barre syndrome, just as other infections can.
"For sex partners of infected women, Zika virus might be transmitted through exposure to vaginal secretions or menstrual blood," the CDC said.
"Men and women who want to reduce the risk for sexual transmission of Zika virus should use barrier methods against infection consistently and correctly during sex or abstain from sex when one sex partner has traveled to or lives in an area with active Zika virus transmission."
The CDC also says pregnant women can get a blood test for Zika for as long as two weeks after possible infection. Zika usually only stays in blood for about a week but it seems to last longer in pregnant women.
Researchers reported Monday that as many as 1.65 million women in Latin America could be infected with Zika while pregnant, meaning tens of thousands of pregnancies could be at risk.
The CDC's very concerned about the risk in the U.S. because half of all U.S. pregnancies are unplanned. That means men and women might not be thinking about Zika risk when they have unprotected sex.
Florida officials are investigating two cases there that may have been transmitted by mosquitoes, because there is no other apparent explanation. Florida, Texas, Arizona and other southern states all have the Aedes mosquitoes that carry and spread Zika, so the CDC expects some limited outbreaks.