Zika virus can pass through sex from an infected person to their partners — even if the infected person has no symptoms. It persists longer in semen than in other body fluids. Condoms or abstinence are recommended to protect partners concerned about Zika.
How it spreads through sex
- Zika can spread through vaginal and anal sex, possibly oral sex, and possibly shared sex toys.
- The virus has been found in semen, vaginal fluids, saliva, urine and breast milk, but there's no evidence it spreads through saliva in deep kissing.
- Transmission has been documented male to female, male to male and female to male. Female-to-female transmission hasn't been reported but is biologically plausible; women can pass the virus through vaginal fluids or menstrual blood.
- Men without symptoms have transmitted it, and limited data suggest viral RNA in semen appears and lasts about as long in men with and without symptoms. People with symptoms have spread it before, during and after their illness.
How long the risk lasts
| Measure | Finding |
|---|---|
| Longest reported time from symptom onset to possible sexual transmission | 32–41 days (most reports shorter) |
| Longest time potentially infectious virus was found in semen | 69 days (no other study found it beyond 40 days) |
| Men with Zika RNA in semen more than 90 days after illness | Under 7% in the largest study |
| Estimated average time for RNA to clear from semen | 54 days |
Viral RNA in semen doesn't necessarily mean infectious virus is present.
Timeframes to prevent sexual transmission
The clock starts on return from travel — even without symptoms — or at the start of symptoms or diagnosis:
| Use condoms or don't have sex for | |
|---|---|
| Males | At least 3 months |
| Females | At least 2 months |
Why testing isn't recommended to judge risk
Testing blood, urine or genital fluids to decide whether someone can still transmit Zika sexually isn't recommended:
- A negative blood or antibody test can be falsely reassuring — the virus may have left the blood but remain in semen; antibodies may be too low to detect early or late in infection; or the test may simply be wrong.
- Little is known about how Zika is shed in genital fluids or how to interpret semen and vaginal fluid tests. Shedding may be intermittent, so someone could test negative and later shed virus again.
Sources
Based on "Sexual Transmission of Zika Virus," Centers for Disease Control and Prevention; a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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