Most of us have viruses sleeping inside us, and spaceflight wakes them up

One more thing to worry about in space.

Human spaceflight seems all the more remarkable when you consider the fact that our bodies didn’t evolve for space. We suffer in major ways as a result of microgravity and living in confined quarters hundreds of miles above the surface of the planet. Even our our immune systems take a hit, leaving us more susceptible to infection and disease as we spend more time in space.

A new study published last month in Frontiers in Microbiology reports that herpes viruses lying dormant inside the body become reactivated in more than half of all astronauts sent into space, potentially exacerbating what is already a high-risk environment. While we’ve yet to run into any kind of worrisome situation resulting from this phenomenon, those concerns loom larger as we set our sights on longer duration missions in orbit and seek to send astronauts back to the moon and on to Mars.

“NASA scientists have been studying the effects of spaceflight on the immune system for over 20 years,” says Satish Mehta, a scientist at the agency’s Johnson Space Center and the senior author of the new study. “It is believed that stressful life situations cause the lowered immunity, which causes viral reactivating.” And there are obviously very few situations that induce more stress on the human body than living and working in space.

Dormant viruses are not new phenomena. Herpes viruses are often never fully eradicated from the body, and are instead subdued by the immune system. The herpes virus that causes chickenpox and shingles (VZV), for example, remains in our spinal cord cells for life. The ones that cause mononucleosis (CMV and EBV) can actually end up renting out space within our own immune cells during childhood.

(Before you freak out that we’re talking about herpes, remember one thing: you probably have herpes of some sort, even if you’re an astronaut. And that’s okay!)

But stress can compromise the immune system. Mehta and his team believe that microgravity, cosmic radiation, and the extreme G forces experienced during launch (among other factors like confined life in a spacecraft and disruptions in circadian rhythms) encourage an increase in hormones like cortisol and adrenaline, which suppress the immune system. The factors that keep dormant viruses at bay are weakened, sometimes for up to 60 days after spaceflight.

We constantly shed viral cells from our body through fluids like urine and saliva, and higher rates showing up in bodily fluids indicate a virus is active. For this particular study, Mehta and his team studied blood, urine, and saliva samples of astronauts who had completed space shuttle missions (between 10 and 16 days in space) and stays on the International Space Station (typically over 180 days in space).

They found that four of the eight herpes viruses known to infect humans reactivated and resurfaced as a result of spaceflight. Specifically, 53 percent of astronauts who underwent space shuttle missions and 61 percent of astronauts who had gone on long stays on the ISS were shedding herpes viruses at much higher rates through their saliva and urine. The four herpes viruses detected include the three aforementioned types, in addition to the HSV type that causes oral and genital herpes.

Viral shedding indicates a reactivation of the virus, but it certainly doesn’t indicate sickness. In fact, the research team found that only six of the 112 astronauts who participated in the study experienced symptoms related to their viruses, and those symptoms were quite minor.

Nevertheless, there’s no question the new findings raise some concerns. Everyone’s body works differently, and minor symptoms in one person could be serious symptoms in another. “During deep space exploration missions, crew members would be constrained to a smaller area for a longer period of time with little or no ability to return to Earth quickly,” says Mehta. “The factors that negatively affect immunity will all be elevated. NASA is focused on understanding how these viruses behave and developing countermeasures to protect astronauts on longer duration missions farther into space.”

That’s much easier said than done, of course. When it comes to these herpes viruses, the ideal countermeasure, says Mehta, is vaccination, but so far this is only available against the VZV variety. Herpes vaccines have never shown much success. Mehta says previous studies have discussed other options like nutritional supplements and better medications, but none of these interventions is beyond the concept phase.

Moreover, the study underscores just how precarious the immune system is in space. Just last fall, it was revealed that superbugs had somehow managed to colonize the ISS. While these pathogens don’t really pose a risk that we don’t already see in hospitals, at least hospitals are equipped to help patients fight off infections. When you’re sick in space, you have to make do with what you already have.

While we’re pouring more resources into studying human immunity in space, we’re limited by the fact that there just aren’t that many astronauts to study. There is, however, one environment on Earth that we could use as a testing ground: Antarctica, where humans who spend the winter for research purposes have experienced depressed immunities, along with herpes virus reactivation. “In Antarctica, crews also experience isolation, stress, an extreme environment, and circadian rhythm misalignment in the form of 24-hour darkness,” says Mehta. These conditions are remarkably similar to spaceflight, and it may be prudent to study people stationed in Antarctica to get a better grasp on viral infections for future astronauts spending months or years in space.

After all, it’s going to be hard to sell tickets for a six-month space ride to Mars if there’s an acute fear of grappling with shingles the entire way over.