Space & Innovation

Zika Could Make It Harder For Men to Reproduce

The Zika virus targets the male reproductive system in mice, suggesting it could affect a man's ability to have children.


We are very aware of the effects Zika virus has on fetuses and pregnant women, but a new study from Washington University in St. Louis published Monday in the journal Nature, suggests that Zika may also interfere with a man's ability to reproduce.

During the study, male mice were infected with Zika and within one week the virus had traveled to their testicles and there was some inflammation observed. After two weeks, the testes had shrunk, their internal structure was collapsing and many cells were dying.

After the third week, researchers found the mice's testicles had shrunk to one tenth their original size, they had a reduced level of sex hormones and reduced fertility. Female mice were paired with both Zika infected and uninfected male mice, and the females mated with infected males were four times less likely to get pregnant than those mated with uninfected males.

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Six weeks later, even after the virus was cleared from the mices' bloodstream, their testicles did not heal. The structure of testes are dependent on Sertoli cells, which nourish developing sperm cells but do not regenerate.

Michael Diamond, MD, PhD, a co-senior author on the study and the Herbert S. Gasser Professor of Medicine said in a press release, "We don't know for certain if the damage is irreversible, but I expect so, because the cells that hold the internal structure in place have been infected and destroyed."

He added, "While our study was in mice - and with the caveat that we don't yet know whether Zika has the same effect in men -- it does suggest that men might face low testosterone levels and low sperm counts after Zika infection, affecting their fertility."

Currently, the Centers for Disease Control and Prevention recommend that men who have traveled to places with a known presence of Zika use condoms for at least six months afterward because the virus can persist in their semen for several months.

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"This is the only virus I know of that causes such severe symptoms of infertility," said co-senior author Kelle Moley, MD, the James P. Crane Professor of Obstetrics and Gynecology, in a press release. "There are very few microbes that can cross the barrier that separates the testes from the bloodstream to infect the testes directly."

So far there have been no reports published that directly link Zika to infertility in men, however, it's a difficult thing to diagnose, as many people don't discover they're infertile until they try to have children. "I think it is more likely doctors will start seeing men with symptoms of low testosterone, and they will work backward to make the connection to Zika," Moley added.

Both Diamond and Moley agree that human tests need to be conducted in areas with high rates of Zika in order to draw more concise conclusions about the affect it has on male infertility.

"Now that we know what can happen in a mouse, the question is, what happens in men and at what frequency?" Diamond said. "We don't know what proportion of infected men get persistently infected, or whether shorter-term infections also can have consequences for sperm count and fertility. These are things we need to know."