Sexual Transmission of Zika Virus

Zika virus transmission through sexual activity

A person with Zika virus infection can transmit the virus to their partner(s) through vaginal sex, anal sex, and possibly oral sex. Sharing sex toys may also put someone at risk. Zika virus has been detected in semen, vaginal fluids, saliva, urine, and breast milk. There is no evidence that Zika virus can be transmitted through saliva during deep kissing.

There is documented evidence of sexual transmission of Zika virus from male-to-female, male-to-male, and female-to-male sex partners. Female-to-female sexual transmission has not yet been reported but is biologically plausible. Females with Zika infection may pass the virus to sex partners through vaginal fluids or menstrual blood.

Sexual transmission from an asymptomatically infected male has been reported. Limited data suggest the incidence of Zika virus RNA shedding in semen and its persistence after infection are likely similar for symptomatic and asymptomatic men infected with Zika virus. People with symptomatic illness have transmitted Zika virus before they had symptoms, while they had symptoms, and after symptoms resolved.

Using condoms or abstinence is recommended to protect sex partners concerned about Zika virus infection.

Duration of risk of sexual transmission

Among the currently available reports of sexual transmission of Zika virus, the longest period from symptom onset in the index case to potential sexual transmission to a partner was between 32–41 days. However, most reports indicate shorter intervals.

The longest reported period after symptom onset at which potentially infectious virus has been detected in semen by culture or cytopathic effect was 69 days. No other studies reported potentially infectious Zika virus in semen specimens obtained more than 40 days after symptom onset.

Many publications have also reported on detection of Zika virus RNA in semen. However, this might not indicate presence of infectious virus at the time of sampling or correlate with the potential for sexual transmission of infectious virus. In the largest cohort study to date, Zika virus RNA shedding declined during the 3 months after symptom onset. At >90 days after illness onset, less than 7% of participants had detectable Zika virus RNA in semen. The estimated mean time to clearance of Zika virus RNA from semen was 54 days. Similar findings have been observed in smaller cohort studies.

Counseling travelers

Healthcare professionals should review CDC's Zika travel guidance with people who are pregnant, their partners, and people who are planning pregnancy before travel. CDC does not have accurate information on the current risk of Zika virus exposure in many geographic areas. Recommendations are based on whether travel is to a geographic area with an active CDC Zika Travel Health Notice or with current or past Zika virus transmission.

Pregnant travelers

Because Zika infection during pregnancy can cause severe birth defects associated with congenital Zika syndrome, advise people who are pregnant to avoid travel to areas with an active Zika Travel Health Notice. If a person who is pregnant chooses to travel, they should be advised to strictly follow recommendations to prevent mosquito bites and sexual transmission during and after travel. Travelers with a pregnant partner should consider the reasons for travel, ability to prevent mosquito bites and potential risk of transmitting Zika to their pregnant partner. If they choose to travel to an area with an active Zika Travel Health Notice, advise them to prevent mosquito bites and sexual transmission during and after travel.

Inform people who are pregnant and their partners of the possible risks to the fetus when considering travel to areas with current or past spread of Zika virus. In deciding to travel, they should consider the destination, reason for traveling, and their ability to prevent mosquito bites. If a person who is pregnant or their partner choose to travel, counsel them to prevent mosquito bites during and after travel. Also advise them to consider preventing sexual transmission during and after travel if they are concerned about the possible risks of Zika to the fetus.

Travelers planning pregnancy

Advise people planning to become pregnant and their partners who travel to areas with an active Zika Travel Health Notice to prevent mosquito bites and sexual transmission during and after travel. Additionally, advise them to delay pregnancy following travel using the timeframes to prevent sexual transmission specified above.

Advise people planning to become pregnant and their partners who travel to areas with current or past Zika virus transmission to prevent mosquito bites during and after travel. If they are concerned about the risk of Zika, advise them to consider preventing sexual transmission during and after travel, and delaying their pregnancy according to the timeframes to prevent sexual transmission. CDC supports shared patient-provider decision making to determine timeframes to wait before trying to conceive after possible Zika virus exposure. Some couples might choose to wait shorter or longer periods depending on individual circumstances (e.g., age, fertility, or details of possible exposure), healthcare provider judgement, and an assessment of risks and possible outcomes.

Counseling people living abroad

Healthcare providers should review CDC's Zika guidance for people living abroad with people who are pregnant, their partners, and people planning pregnancy living in areas with an active Zika Travel Heath Notice or in an area with current or past Zika virus transmission.

Advise people who are pregnant and their partners living in an area with an active Zika Travel Heath Notice to strictly prevent mosquito bites and sexual transmission during their entire pregnancy.

Counsel people who are pregnant, people planning pregnancy, and their partners living in areas with current or past Zika virus transmission about their risks in the context of the local situation and the potential need to prevent sexual transmission. Emphasize the importance of preventing mosquito bites.

Educate people who are planning pregnancy and their partners living in an area with an active Zika Travel Heath Notice about their risk of ongoing exposure to Zika virus, the possible risks of Zika to the fetus, and ways to protect themselves. Delaying pregnancy until the transmission risk decreases should be considered.

Communicate the risks of Zika in the context of the local epidemiologic situation to people who are planning pregnancy and their partners living in an area with current or past Zika virus transmission. Counsel on the need to prevent sexual transmission and mosquito bites.

Testing to determine risk of sexual transmission

At this time, testing a person's blood, urine, or genital secretions to determine their potential risk of sexually transmitting Zika virus is not recommended 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 RNA NAAT [nucleic acid amplification testing]) but could still be present in other bodily fluids (e.g., 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, there is a limited understanding of Zika virus shedding in genital secretions, or of how to interpret the results of tests of semen or vaginal fluids. Zika shedding in these secretions may be intermittent, in which case a person could test negative at one point but still carry the virus and shed it again in the future.