Spaceflight reactivates herpes virus in astronauts

A NASA-led study suggests the stress of spaceflight seems to trigger various types of herpes to reactivate in astronauts.

  • The study examined saliva, blood and urine obtained from astronauts who went on short- and long-term space missions.
  • The results showed that virus reactivation rates in these astronauts were much higher than controls.
  • Spaceflight seems to weaken the immune system, enabling these once-dormant viruses to reactivate and potentially cause serious health problems.

The stress of executing space missions could cause dormant viruses to reactivate within astronauts, suggests a new study led by NASA.

The study, published in the journal Frontiers in Microbiology on February 7, analyzed samples of saliva, blood, and urine obtained from astronauts before, during, and after 10- to 16-day space flights and long-term missions aboard the International Space Station.

"To date, 47 out of 89 (53 percent) astronauts on short space shuttle flights, and 14 out of 23 (61 percent) on longer ISS missions shed herpes viruses in their saliva or urine samples," said lead study author Dr. Satish K. Mehta at Johnson Space Center. "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."

Shedding occurs when herpes successfully reproduces and leaves the host cell, whereby it could potentially infect another person. The process can occur without any noticeable symptoms. This — combined with the fact that the herpes simplex virus cleverly conceals itself in the central nervous system where the immune system can't eradicate it — helps explain why about two-thirds of people worldwide have some form of herpes.

"Only six astronauts developed any symptoms due to viral reactivation," Mehta said. "All were minor."

​Cosmic stress

Astronauts face a unique set of stressors in space that seem to hinder the immune system's ability to keep viruses dormant. The study shows that space missions seemed to reactivate at least four types of the herpes virus within astronauts. Alarmingly, these reactivation rates increased as astronauts spent more time in space.

"NASA astronauts endure weeks or even months exposed to microgravity and cosmic radiation — not to mention the extreme G forces of take-off and re-entry," Mehta said. "This physical challenge is compounded by more familiar stressors like social separation, confinement, and an altered sleep-wake cycle.

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

What's more, the researchers wrote that more than one virus generally activates at a time, potentially compounding the risks the viruses pose, including "not only rashes, but also severe target organ failures, and permanent vision and hearing loss."

It's a major concern for space agencies looking to send astronauts on long-term missions to Mars.

"Ultimately, the information gleaned from these space studies will shape the way we prepare for and design exploration-class missions, beyond the moon and mars, where reactivation of latent viruses could result in increased risk for wide-ranging adverse medical events."

​Herpes and the general public

As with astronauts, stress can cause herpes outbreaks and shedding among everyday people.

"Daily stress is enough to be a trigger," Connecticut-based dermatologist Mona Gohara, MD, told Health.

Although researchers are searching for a cure, none currently exists for the eight strains of herpes virus, which include chicken pox and shingles, in addition to what's commonly called oral (HSV-1) and genital (HSV-2) herpes.

"Herpes lives in your system dormant forever. It's kind of like a sleeping bear: When you get stressed out, the bear is mustered out of hibernation," Gohara said.

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  • The finding builds on the hygiene hypothesis, first proposed in 1989.

Are modern societies trying too hard to be clean, at the detriment to public health? Scientists discovered that a microorganism living in dirt can actually be good for us, potentially helping the body to fight off stress. Harnessing its powers can lead to a "stress vaccine".

Researchers at the University of Colorado Boulder found that the fatty 10(Z)-hexadecenoic acid from the soil-residing bacterium Mycobacterium vaccae aids immune cells in blocking pathways that increase inflammation and the ability to combat stress.

The study's senior author and Integrative Physiology Professor Christopher Lowry described this fat as "one of the main ingredients" in the "special sauce" that causes the beneficial effects of the bacterium.

The finding goes hand in hand with the "hygiene hypothesis," initially proposed in 1989 by the British scientist David Strachan. He maintained that our generally sterile modern world prevents children from being exposed to certain microorganisms, resulting in compromised immune systems and greater incidences of asthma and allergies.

Contemporary research fine-tuned the hypothesis, finding that not interacting with so-called "old friends" or helpful microbes in the soil and the environment, rather than the ones that cause illnesses, is what's detrimental. In particular, our mental health could be at stake.

"The idea is that as humans have moved away from farms and an agricultural or hunter-gatherer existence into cities, we have lost contact with organisms that served to regulate our immune system and suppress inappropriate inflammation," explained Lowry. "That has put us at higher risk for inflammatory disease and stress-related psychiatric disorders."

University of Colorado Boulder

Christopher Lowry

This is not the first study on the subject from Lowry, who published previous work showing the connection between being exposed to healthy bacteria and mental health. He found that being raised with animals and dust in a rural environment helps children develop more stress-proof immune systems. Such kids were also likely to be less at risk for mental illnesses than people living in the city without pets.

Lowry's other work also pointed out that the soil-based bacterium Mycobacterium vaccae acts like an antidepressant when injected into rodents. It alters their behavior and has lasting anti-inflammatory effects on the brain, according to the press release from the University of Colorado Boulder. Prolonged inflammation can lead to such stress-related disorders as PTSD.

The new study from Lowry and his team identified why that worked by pinpointing the specific fatty acid responsible. They showed that when the 10(Z)-hexadecenoic acid gets into cells, it works like a lock, attaching itself to the peroxisome proliferator-activated receptor (PPAR). This allows it to block a number of key pathways responsible for inflammation. Pre-treating the cells with the acid (or lipid) made them withstand inflammation better.

Lowry thinks this understanding can lead to creating a "stress vaccine" that can be given to people in high-stress jobs, like first responders or soldiers. The vaccine can prevent the psychological effects of stress.

What's more, this friendly bacterium is not the only potentially helpful organism we can find in soil.

"This is just one strain of one species of one type of bacterium that is found in the soil but there are millions of other strains in soils," said Lowry. "We are just beginning to see the tip of the iceberg in terms of identifying the mechanisms through which they have evolved to keep us healthy. It should inspire awe in all of us."

Check out the study published in the journal Psychopharmacology.