When it comes to Ebola, new research suggests that the risk of catching the virus from a survivor is very low.

The recent Ebola outbreak happened at an unprecedented scale. Previously only seen in comparatively small clusters of cases, the virus erupted in a significant fashion in 2014, affecting thousands and easily launching the largest Ebola epidemic on record. Until now, the limited data regarding the disease had restricted the number of questions scientists could hope to answer about the infection. Simply put, cases of Ebola were so rare that we really hadn’t gotten the chance to learn a whole lot about it.

But 2014 changed that.

With the enormous influx of cases that occurred during the West African outbreak, scientists have started mining the resulting data for answers to questions critical to public health safety now and in the future. And, without reservation, one of the most important questions to be addressed is this: How likely is it for an Ebola survivor to spread the virus in the long-term, specifically, the period of time after the person is no longer actively sick with Ebola?

A new study published Monday in PLOS Neglected Tropical Diseases examined the presence and persistence of Ebola virus in various bodily fluids of survivors. Researchers from the University of East Anglia’s Norwich Medical School compiled patient data from nearly 6,000 articles, papers and case reports from the outbreak. They pulled test results relating to the presence of Ebola virus in various bodily fluids, such as blood, sweat, urine, breast milk, semen, vaginal secretions, feces and vomit.

And what they found is fairly good news: It appears that the risk of catching Ebola from survivor bodily fluids is very rare, with the exception of sexual transmission via semen. (There was not enough data regarding the infectivity of breast milk to make a definitive conclusion.)

The results of the study are promising, though the data was difficult to compile. Testing methods for the presence of the virus varied due to discrepancies in technological capabilities among treatment centers, which spanned everything from bare-bones field hospitals to state-of-the-art medical facilities.

As expected, infected blood appears to be the most infectious body fluid for Ebola, virtually teeming with the virus while the patient is in the throes of the disease. However, 95 percent of the patients included in the study who survived had cleared the virus from their blood by day 16 — though personal-protection measures for handling potentially contaminated blood might still be recommended.

A majority of other fluids tested appear to pose low infectious risk, with one glaring exception: semen. In fact, 70 percent of semen samples from survivors tested positive for the virus in the first seven months after the illness.

This may have had serious implications during the latter days of the epidemic, when areas thought to be clear of the virus saw new cases of the disease cropping up.

“It’s certainly plausible that some of the cases that occurred after the outbreak was over were the result of sexual contact,” said Paul Hunter, professor of health protection at the Norwich School of Medicine and lead author on the paper.

The current WHO recommendation is that survivors use barrier protection for sexual activity for a year post infection, up from the previous recommendation that condoms be used for the first six months.

These findings raise another interesting question: Why is the Ebola virus persisting in semen, especially when it seems quick to leave other fluids?

Hunter shared his purely speculative take on the matter, stressing that this was his personal theory based on pattern recognition, rather than an expansive expertise in physiology. He explained that semen (along with some of the other bodily fluids that Ebola is found in during the illness, such as breast milk, saliva and vaginal secretions) is known as an exocrine fluid. These are fluids excreted by the body and are each the result of a kind of modified sweat gland. Perhaps, then, Ebola is “going to ground in the modified sweat glands,” he explained over the phone, commenting on the pattern of distribution of Ebola in the body.

Hunter added that he didn’t know why Ebola would be camping out in these areas, but that it was interesting that these were the fluids most affected.

Regardless, in light of reports of late complications in Ebola patients, this new research provides critical insight into the nature of Ebola virus infectivity in survivors, with the goal of informing public health campaigns and safe sex policies.

Leigh Cowart is a freelance journalist covering science, sex and sports. She is fully vaccinated for rabies.

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