Zika Resource Center

Zika Resource Center

April 11, 2018
2 min read

Zika may be infectious in semen for only a few weeks

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New study findings indicate there is a short period of time that men infected with Zika virus can sexually transmit it to others — perhaps just a few weeks after they become ill.

Based on the findings, which were published in The New England Journal of Medicine, the CDC will re-evaluate its guidance for the prevention of sexual transmission of Zika virus, an agency spokeswoman told Infectious Disease News.

Scientists have known that Zika can be sexually transmitted by both men and women, potentially even from asymptomatic men. Past cases have suggested that Zika virus RNA can persist in semen for more than 180 days — longer than the 6-month period the CDC recommends that male patients wait before trying to conceive a child or have unprotected sex — guidance that is especially aimed at preventing birth defects in children who were born to infected mothers, including microcephaly.

To help clarify the risk, Paul S. Mead, MD, MPH, epidemiologist in the CDC’s National Center for Emerging and Zoonotic Infectious Diseases, and other colleagues at the government agency, tested semen and urine samples from 185 symptomatic Zika-infected men in the United States “to determine the frequency and duration of [Zika virus] shedding in semen and urine and to identify risk factors for prolonged shedding in these fluids.” They used RT-PCR to detect Zika virus RNA and culture to determine infectious Zika in 1,327 semen and 1,038 urine samples taken 14 to 304 days after illness onset.

According to the study, Zika RNA was isolated from 14% of all tested semen samples. By contrast, Mead and colleagues reported that just 1% of urine samples yielded evidence of Zika RNA. Detectable Zika RNA was found in 61% of men who submitted samples within 30 days after illness onset, with the proportion decreasing to 7% or less in men who submitted samples after more than 90 days after illness onset.

“The divergent results generated by culture and RT-PCR can be adjudicated by comparing them with epidemiologic data about known instances of sexual transmission,” Mead and colleagues wrote. “Among documented cases of male-to-partner sexual transmission, all have occurred within 41 days after illness onset in the source male partner, and most have occurred within 20 days. The absence of reported events occurring at later time points suggests that transmission events coincide with the period during which the virus can be cultured and that detection of [Zika virus] RNA by RT-PCR may overstate the duration and magnitude of the risk of sexual transmission.”


In a related editorial, Heinz Feldman, MD, chief of the virology laboratory in the NIH’s National Institute of Allergy and Infectious Diseases, agreed the study offers evidence that there is a short period of time during which Zika-infected men might transmit the virus through sexual contact and said molecular detection alone is not enough to understand transmissibility. – by Gerard Gallagher

Disclosures: The authors report no relevant financial disclosures.