One of Earth's Most Common STIs Gets Reactivated in Space

Viruses love zero gravity.

In 2018, Jeff Bezos predicted that off-world habitats would one day house trillions of people. What he failed to account for was the fact that that those trillions of people would bring their herpes infections with them. Unfortunately, according to the results of a study released in February in Frontiers in Microbiology, herpes seems to really thrive in space.

In the paper, the authors report that a surprisingly high percentage of astronauts who spent time on either the International Space Station or on a shorter space shuttle mission had reactivated herpes viruses in their urine and saliva samples. Overall, 53 percent of astronauts from shuttle flights (47 out of 89) and 61 percent of astronauts from ISS missions (14 out of 23) had at least one kind of herpes in their bodily fluids.

Those numbers didn’t just refer to HSV-1, the virus that usually causes oral herpes. They also included Epstein-Barr virus, which causes mono; varicella-zoster virus, which causes chickenpox; and cytomegalovirus, a virus closely related to herpes.

Astronaut Mark Lee in space.
Space can be stressful — so stressful that it can contribute to a new herpes outbreak. 

It’s important to know that these astronauts didn’t actually get herpes or any of these viruses in space. They’re easy to come by on Earth: By the World Health Organization’s estimate, 3.7 billion people have HSV-1, for instance. Once someone is infected with a virus like herpes, it stays in the body for life. Then, now and again, it can cause flare-ups when it reactivates and either becomes contagious again or causes physical sores.

Unfortunately, prolonged time in space seems to be one of the conditions that activates these viruses, at least partially because space takes a heavy toll on the immune system.

Zero-gravity conditions seem to be particularly taxing on the immune system. In December, a study on the spleens of 45 pioneering space mice showed that 30 days hurtling around in low Earth orbit had severely depleted their B lymphocytes, which are cells that are crucial to helping the body target and fight infection. As that study’s lead author Fabrice Bertile, Ph.D., previously told Inverse, the weightlessness of space seems to affect other animals — including humans — in a similar way.

“Impairment of the immune system therefore appears [to be] a common feature of the response to weightlessness in all organisms,” Bertile said.

space flight space shuttle
Emotional components, like spending extended time in tight quarters with only a few people could deplete the immune system even more. 

Fortunately, it was rare for the astronauts in this study to have actual symptoms of these diseases. Only six had actual herpes breakouts in space, but the astronauts generally had increased levels of viral shedding, explains co-author Satish K Mehta, Ph.D. This means that the viruses that once lay dormant in their systems started to reactivate and work their way into fluids where they might be passed from one person to another.

“These frequencies - as well as the quantity - of viral shedding are markedly higher than in samples from before or after flight, or from matched healthy controls,” Mehta said.

Mehta argues that viral activation is not just due to weightlessness taking a toll on the immune system. The emotional aspects of being in space take an additional toll. In the paper, the authors note that social isolation, confinement, sleep deprivation, circadian rhythm disruption, and anxiety are all elevated in space and can increase the production of stress-related hormones.

“During spaceflight there is a rise in secretion of stress hormones like cortisol and adrenaline, which are known to suppress the immune system,’ Mehta explains. “In keeping with this, we find that astronaut’s immune cells - particularly those that normally suppress and eliminate viruses - become less effective during spaceflight and sometimes for up to 60 days after.”

For the “trillions” of people looking to escape to a far-flung planet, this may not be good news — especially if they’ve been struggling with one of these common infections on Earth. However, as the authors suggest, the worst part of the experience may be the actual flight, not the actual colonization of a new world. In the paper, they write that “partial gravity environments e.g. on Mars, might be sufficient to curtail serious viral reactivation.”

In other words, there’s hope that once we get to Mars, we may be able to mitigate the impacts that zero gravity seems to have on the immune system — even if we don’t tackle the stresses that come from leaving Earth for a new, distant home. Mehta and his co-authors recommend that, for some viruses, an additional array of vaccines could provide extra immune protection. That might work for chickenpox, but since we’ve made no progress on a herpes vaccine, it remains to be seen what other interventions can stop viruses from resurfacing in space.

Until then it’s probably not worth kissing your fellow passengers aboard the Starhopper. That is, not until you’ve spent some time recuperating in your new, partial-gravity home.

Abstract

Latent herpes virus reactivation has been demonstrated in astronauts during shuttle (10–16 days) and International Space Station (≥180 days) flights. Following reactivation, viruses are shed in the body fluids of astronauts. Typically, shedding of viral DNA is asymptomatic in astronauts regardless of mission duration; however, in some cases, live/infectious virus was recovered by tissue culture that was associated with atopic-dermatitis or skin lesions during and after spaceflight. Hypothalamic-pituitary-adrenal (HPA) and sympathetic-adrenal-medullary (SAM) axes activation during spaceflight occurs as indicated by increased levels of stress hormones including cortisol, dehydroepiandrosterone, epinephrine, and norepinephrine. These changes, along with a decreased cell mediated immunity, contribute to the reactivation of latent herpes viruses in astronauts. Currently, 47/89 (53%) astronauts from shuttle-flights and 14/23 (61%) astronauts from ISS missions shed one or more herpes viruses in saliva/urine samples. Astronauts shed Epstein–Barr virus (EBV), varicella-zoster virus (VZV), and herpes-simplex-1 (HSV-1) in saliva and cytomegalovirus (CMV) in urine. Larger quantities and increased frequencies for these viruses were found during spaceflight as compared to before or after flight samples and their matched healthy controls. The shedding did not abate during the longer ISS missions, but rather increased in frequency and amplitude. These findings coincided with the immune system dysregulation observed in astronauts from shuttle and ISS missions. VZV shedding increased from 41% in space shuttle to 65% in ISS missions, EBV increased 82 to 96%, and CMV increased 47 to 61%. In addition, VZV/CMV shed ≤30 days after ISS in contrast to shuttle where VZV/CMV shed up to 5 and 3 days after flight respectively. Continued shedding of infectious-virus post-flight may pose a potential risk for crew who may encounter newborn infants, sero-negative adults or any immunocompromised individuals on Earth. Therefore, developing spaceflight countermeasures to prevent viral reactivation is essential. Our spaceflight-developed technologies for saliva collection/rapid viral detection have been extended to include clinical applications including zoster patients, chicken pox, post-herpetic neuralgia, multiple sclerosis, and various neurological disorders. These protocols are employed in various clinics and hospitals including the CDC and Columbia University in New York, as well as overseas in Switzerland and Israel.

Media via Marc Van Norden, Wikimedia Commons , Pixabay