K_E_N/ShutterstockYou know that protected sex is wise if you want to prevent sexually transmitted infections like herpes and HIV—especially given that STDs are on the rise. But recently, researchers discovered that the Zika virus could be transmitted sexually. And now a team of British researchers have found traces of the deadly Ebola virus in the semen of survivors—up to two years after they got sick. And Ebola’s not the only one, which is why they’re calling for the World Health Organization to update its guidelines on sexual transmission of disease.
First, a little history: In 2016, Italian researchers explored the spread of a common, mostly harmless virus known as BKV. The theory had been that BKV spread through respiratory fluids; the researchers discovered it could also be transmitted through semen—muddling our notion of what can be defined as an STD. (This dangerous sex trend could also give you an STD.)
In the new study, published in the journal Emerging Infections Diseases (a publication of the Centers for Disease Control and Prevention), University of Oxford researchers scoured the scientific literature for evidence of viruses being found in semen. They found that there are at least 27 viruses that can be found in semen: Typical STDs like HIV and herpes, of course, but also diseases you wouldn’t expect, such as Ebola, Marburg, and mumps.
“Detection means that evidence of viral genetic material or viral protein was found in semen,” lead researcher Alex Salam told WebMD. “It’s important to note that this does not mean that the virus is viable, i.e., capable of replicating. To prove this, the virus needs to be isolated and grown in cells or animals. For many of the viruses, this test has not been done, so we don’t know whether virus is viable or not.”
Although the viruses may not be capable of replicating, they can live in semen for significant stretches of time. How? The reason is called immune privilege: The immune system is on constant alert for invaders, but it’s shielded from certain parts of the body—including the testicles. (One theory for immune privilege is that it protects sperm and eggs.) “That means the immune system doesn’t police the testicles as well as other organs,” Dr. Amesh Adalja told NPR. “So the testes kind of serve as this sanctuary site where viruses can kind of steer clear of the immune system.”
If a viral epidemic breaks out, experts and the public will now have to monitor blood, saliva, and sexual transmission. Even more troubling is that semen can remain infected for up to two years, the researchers found. We may have new reasons to practice safe sex—even with longtime partners. (Here are five surprising things you didn’t know were contagious).