How Many Viruses Can Get into Men’s Semen?

During recent outbreaks of the Zika virus, researchers discovered that the virus could find its way into men’s semen and stay there for months. But how many other viruses can get into semen?

To find out, researchers at the University of Oxford in the United Kingdom searched the scientific literature for reports of “viremic” viruses — ones that get into the blood —  that have also been found in semen.

The results showed that at least 27 viruses can make their way into human semen.

“The presence of viruses in semen is probably more widespread than currently appreciated,” the researchers wrote in the October issue of the journal Emerging Infectious Diseases. [10 Deadly Diseases That Hopped Across Species]

The list includes a number of well-known viruses, such as Ebola, HIV, hepatitis C, chickenpox, herpes, mumps and chikungunya (a mosquito-borne virus), as well as some lesser-known viruses, such as JC virus, simian foamy virus and Rift Valley fever.

In addition, some of these viruses, such as HIV and herpes, are known to spread sexually. But for many of the viruses on the list, it’s unclear whether they can be spread through sex, the researchers said.

The results raise a number of questions, including how long the viruses remain in semen, at what concentrations they are present, and whether the viruses remain “viable” or capable of causing disease, the researchers said. The answers to these questions will help researchers better understand the risk for sexual spread of these viruses, the study said.

More research is also needed on whether these viruses can infect sperm, the researchers said. (Sperm are men’s reproductive cells, whereas semen is usually a mixture of sperm and fluids.) This is an important question, because infections in sperm could cause mutations in the sperm DNA that might be passed on to the next generation, and possibly increase the risk of conditions such as cancer, the researchers said.

It’s thought that some viruses persist in semen — even when they’ve been cleared from the rest of the body — because the testes are an “immunologically privileged” site in the body, meaning they are protected from attack by the body’s immune system.

The findings also highlight the need for researchers to consider whether treatments being developed for virial diseases can be effective against viruses in all parts of the body, including the male reproductive tract, the researchers said.