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What effect does the Zika virus have on fertility?
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A lot of the scare regarding the Zika virus in 2016 was about the disease’s potential effects on pregnant women. But a recent study shows it’s not just the ladies who should be concerned—Zika likely has some pretty serious effects on male fertility as well.

In October 2016, a group of researchers from Washington University in St. Louis, Missouri, released the results of their experiments on male mice infected with the Zika virus. According to their article in Nature, Zika wreaked havoc on the mice’s reproductive systems, including causing lasting cellular damage, lower levels of sex hormones, and reduced overall fertility.

That’s a bad sign for male humans exposed to the virus.

Obviously mice aren’t the same as humans, noted Dr. Michael Diamond, a study co-author and professor of pathology, immunology, and molecular microbiology at Washington. But he confirmed that the tests are definitely worth corroborating.

Previous research has shown that Zika can remain in the semen of infected men for up to six months, which led Diamond and his fellow researchers to wonder about the long-term effects of exposure to the testes.

After a week, exposed mice were showing some signs of the virus, but in general their testes were still in good health.

Fast forward three weeks, however, and the mice’s testes had shrunk to a tenth of their normal size. Worse, the internal structure was completely destroyed.

That internal structure—in particular the seminiferous tubules and Sertoli cells—is vital to the creation of sperm and the health of the testes. Lose that, and your fertility goes way down.

“This is the only virus I know of that causes such severe symptoms of infertility,” said Dr. Kelle Moley, a fertility specialist and study co-author.

Of course, the science still needs some work to confirm the connection between what’s being seen with the mice and how the virus could affect human males. Dr. Diamond and his team will continue to gather data and collaborate with researchers in South and Central America, particularly looking at things like sperm count, motility, and testosterone levels to see how the mice results tally with what’s being seen in humans.

But with no cure for Zika currently in sight, it’s definitely worth your while to take care when traveling internationally!