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Questions and Answers for Healthcare Providers on Sexual Transmission of Zika Virus

What kind of sexual activity puts someone at risk for Zika if their partner is infected?

A man with Zika can transmit the virus to his sex partner(s) through sexual intercourse, including vaginal and anal sex, and likely, oral sex (fellatio). At this time, there is no evidence that a woman with Zika can transmit the virus to her sex partner(s) during vaginal sex or cunnilingus (mouth-to-vagina oral sex). There is also no evidence that Zika can be transmitted through deep kissing. Available studies have detected Zika in saliva, urine, and breast milk, but not in vaginal swabs collected from women with Zika.

Can asymptomatically infected men have Zika in semen and transmit it to their sex partners?

We don’t know. In known cases of sexual transmission, the men had Zika virus symptoms. From these cases, we know the virus can be spread when the man has symptoms, before symptoms start, and after symptoms resolve.

Studies are underway to help us better understand when and under what circumstances Zika can be transmitted sexually. Specifically, scientists are examining whether there are differences between the semen of men with symptomatic and asymptomatic Zika infection in terms of the incidence of viral shedding, the concentrations of virus in semen, and the duration and pattern (e.g., steady decline, intermittent on/off) of viral shedding.  

How long can Zika be transmitted to sex partners after initial infection?

We don’t know. Zika virus RNA has been detected in semen up to 62 days after the onset of symptoms. CDC therefore recommends that men who have been diagnosed with Zika should consider using condoms or not having sex for at least 6 months. Ongoing studies are examining the incidence and duration of Zika virus shedding in the semen of men with symptomatic and asymptomatic Zika infection.

Should men take precautions to prevent Zika transmission to female and male sex partners?

Yes. Zika virus infection during pregnancy is a cause of microcephaly and other severe fetal brain defects. Men who live in or travel to areas with Zika should protect their sex partners from sexually transmitted Zika, particularly if their partner is pregnant or may become pregnant.

  • Men with pregnant partners should be counseled to use condoms every time they have vaginal, anal, or oral (mouth-to-penis) sex or abstain from sex for the duration of the pregnancy.  Following this advice is important for all men at risk of Zika infection, including men who do not have symptoms of illness because the infection is most often asymptomatic and we do not yet know the extent to which asymptomatically infected men shed infectious Zika virus in their semen.

For partners who are not pregnant, Zika infection rarely causes serious disease. Many infected people do not have symptoms. When symptoms appear, they are usually mild. For persons who want to prevent transmitting the infection, the risk that an infected man might pass Zika to his sex partners can be reduced by using condoms consistently and correctly, and can be eliminated by not having sex. To be effective, condoms must be used from start to finish, every time during vaginal, anal and oral (mouth-to-penis) sex.

  • The length of time that a man should consider using condoms or not having sex will depend on his circumstances, as well as his partners’.  
  • In helping male patients consider  condoms or abstinence,  you can discuss their personal risks and benefits, including:
    • The likelihood that he has been infected with Zika, which will depend on the length of time he spent in areas with Zika and whether he took steps to prevent mosquito bites while there
    • The fact that for most adults, Zika is a short-lived illness with non-life-threatening, generally mild symptoms
    • Plans for pregnancy (if appropriate)
    • Access to condoms and other contraception
    • Desire for intimacy, including willingness to use condoms or not have sex
    • Ability to use condoms (i.e., accessibility, experience putting on and taking off) or to not have sex
    • The chance of having a partner become pregnant and infected with Zika (even if the pregnancy is not planned).

What should I tell patients concerned about getting Zika through sex? 

Only people whose male sex partners have traveled to or live in an area with Zika need to be concerned about getting Zika virus through sex. Sexual transmission of Zika is of greatest concern for pregnant women with male partners who have had or are at risk for Zika virus infection. Pregnant women and women who could become pregnant should take the necessary precautions to prevent acquiring Zika sexually.

  • Pregnant women with male partners who live in or travel to areas with Zika should be counseled to use condoms every time they have vaginal, anal, or oral (mouth-to-penis) sex or abstain from sex for the duration of the pregnancy. Following this advice is important because the infection is most often asymptomatic, and we do not yet know the extent to which asymptomatically infected men shed infectious Zika virus in their semen.

All other patients should be informed that the chance of getting Zika from sex can be reduced by using condoms consistently and correctly, and can be eliminated by not having sex. To be effective, condoms must be used from start to finish, every time during vaginal, anal and oral (mouth-to-penis) sex.

When is Zika testing recommended to identify possible sexual transmission cases?

Zika virus testing is recommended for people who may have been exposed to Zika through sex and who have Zika virus symptoms. Testing is also recommended for a pregnant woman with possible sexual exposure to Zika virus if either she or her male partner develops one or more- symptoms of Zika.

At this time, testing a man’s blood, urine or semen is not recommended to determine his potential risk of sexually transmitting Zika virus for the following reasons:

First, a negative blood test or antibody test could be falsely reassuring. This can happen when:

  • The blood test is performed after the virus is no longer in the blood (detected by RT-PCR), but Zika virus remains in the semen.
  • The antibody test is performed early after infection when the antibody levels are not yet high enough to be detected, or later after infection when the antibody levels have fallen to undetectable levels.
  • The test is falsely negative.

Second, with regard to semen, we currently have limited understanding of how to interpret the results of semen testing. Zika shedding in semen may be intermittent, in which case a man’s semen could test negative but he still carries the virus and may shed it in the future. Studies are underway to better understand the pattern of Zika shedding. As we learn more, test of semen may become more helpful for determining the risk of sexual transmission of Zika.

For more information on diagnostic testing for Zika, see Diagnostic Testing.

What is the role for STD/HIV Programs in the Zika response?

STD and HIV programs have expertise in patient education, communication, and condom promotion and distribution efforts that may be relevant to preventing sexual transmission of Zika virus. CDC encourages state and local programs to work with their state health officials and link concerned STD/HIV clients who have had possible sexual exposure to Zika to primary care or reproductive health providers who can offer counseling and follow up.

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