The Zika virus is primarily transmitted by the Aedes species mosquito, but it can also be passed through sexual contact. The duration of viral presence, known as viral shedding, varies significantly depending on the specific body fluid being tested. While the virus clears from the bloodstream relatively quickly, its persistence in reproductive fluids creates a prolonged risk for sexual partners and affects transmission risk.
Acute Phase Clearance in Blood and Urine
The initial phase of infection, known as viremia, involves the presence of the virus in the bloodstream. For most infected individuals, the virus is detectable in the blood for about a week following the onset of symptoms. Viral RNA, the genetic material of the virus, is present in the serum for an average of 10 days, and 95% of individuals clear the virus from their blood within 19 days of infection.
Viral RNA has been detected in urine samples for up to two to three weeks after the first symptoms appear, sometimes persisting slightly longer than in the blood. The median time to viral clearance from urine has been estimated to be around eight days.
For pregnant individuals, the clearance timeline from the blood can be notably extended. The virus’s genetic material has been detected in the serum of some pregnant women for up to 46 days after their symptoms began. Clearance from the blood and urine generally marks the end of the acute illness phase.
Prolonged Persistence in Reproductive Fluids
The Zika virus persists in reproductive fluids, particularly in semen, much longer than in other bodily fluids, including blood and urine. This prolonged persistence is the reason for the established risk of sexual transmission, which can occur even if the infected person has no symptoms.
For men, the genetic material of the virus can be detected in semen for a substantial period. The estimated mean time for viral RNA to clear from semen is about 54 days. While the majority of men clear the RNA within three months, detection has been reported for as long as nine months in isolated cases.
It is important to differentiate between the presence of viral RNA and the presence of infectious virus particles. Studies indicate that while the genetic material persists for months, the actual infectious virus is rarely detectable beyond 30 days after the onset of illness. This difference informs public health guidelines, which err on the side of caution regarding potential sexual transmission.
In contrast, the persistence of the virus in female reproductive fluids is much shorter. Viral RNA has been detected in vaginal fluids for a few days and in cervical mucus for up to 11 days after symptoms begin. The shorter duration correlates with a lower documented risk for female-to-male sexual transmission compared to male-to-female transmission.
Monitoring Timelines and Testing for Clearance
Confirmation of Zika infection and subsequent clearance relies on specific laboratory testing protocols. During the acute phase, within the first two weeks of symptom onset, real-time Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) testing is used to detect the virus’s genetic material in serum and urine. After this acute window, serology testing for antibodies, such as IgM and IgG, is necessary to determine if a recent or past infection has occurred.
Public health organizations provide distinct guidance for couples regarding waiting periods to minimize the risk of sexual transmission or congenital infection. These periods are based on the documented difference in viral persistence between men and women. The recommendations focus on the time after symptom onset or after the last possible exposure.
A person who has had confirmed Zika infection should wait specific periods before attempting conception or engaging in unprotected sex. Women who have had Zika are advised to wait at least eight weeks after symptom onset before trying to get pregnant. The longer precautionary period is recommended for men, who are advised to wait at least six months after the start of symptoms.
Couples with a pregnant partner where one partner has traveled to a Zika-affected area should use condoms or abstain from sex for the duration of the pregnancy. These guidelines are based on the known, albeit variable, duration of the virus in the system.