An analysis of data from hundreds of studies identified 22 viruses capable of persisting in human semen after infection, with nine showing evidence of sexual transmission.

Scientists have for decades understood that chronic infection-causing viruses like HIV and herpes can persist in semen, posing a risk for sexual transmission. More recently, viruses like Ebola and Zika have been found to infect the male reproductive tract, evading immune system clearance and sometimes spreading long after the acute phase of infection.

The new findings, published this week in The Lancet Microbe, expand the list of viruses that can persist in semen after acute infections. The research also highlights additional potential sources of reproductive complications and underscores new challenges for researchers developing vaccines and antiviral treatments against these pathogens.

“Establishment of latent infection in the male reproductive tract and virus shedding in semen is probably more common than currently considered,” said Caitlin Pley, a researcher at the Charité Center for Global Health in Berlin, and her co-authors. “An improved understanding of the role of semen in virus transmission is of great value for public health, most notably in the response to outbreaks of high-consequence viral pathogens.”

Among the viruses detected in semen and known or suspected to be sexually transmissible are Marburg, Mpox and West Nile. Although no evidence yet supports the presence of Crimean-Congo hemorrhagic fever or hepatitis A in semen, both may still be sexually transmissible. In contrast, SARS-CoV-2, the virus responsible for Covid-19, has been found in male reproductive tissues such as the testis and prostate, but it hasn’t been shown to transmit through sexual contact, the authors noted.

The study also revealed significant variability in how long viruses persist in semen, with both individual factors and the type of virus influencing the duration. Men with weakened immune systems tend to experience longer viral persistence. While Ebola and Zika have been known to persist for over two years, viruses like West Nile and dengue remain detectable in semen for just three to five weeks.

Virologists reported this month the presence of replication-competent Oropouche virus in semen, suggesting a potential risk for sexual transmission of the virus. This infection, which has been linked to fetal development issues, caused an explosive outbreak this year in Central and South America.

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