It seems space travel has a very unexpected side effect – herpes.
NASA scientists discovered that dormant herpes viruses lurking inside more than half of astronauts aboard the International Space Station (ISS) and Space Shuttle "resurrected" after time spent in space. The results have been published in Frontiers in Microbiology.
Fortunately, very few went on to develop symptoms. However, the study authors warn, virus reactivation rates appear to increase as time goes on – an observation that could pose a major challenge to missions to Mars and further into deep space.
Herpes has spent thousands of years co-evolving with humanity, improving its chances of survival by existing alongside its human host. This means following initial infection, the virus lives in a latent or dormant state, only rearing its head during times of stress and illness.
As a result, the vast majority of the time, people infected with the herpes virus don't have any symptoms. Indeed, herpes is so good at keeping itself hidden that eight herpes viruses have managed to parasitize the human race with global infection rates of 70 to 95 percent.
But space travel, it seems, is one of those moments of stress that causes the virus to reactivate. Immuno-suppressing stress hormones like cortisol and adrenaline surge during spaceflight, prompting dormant viruses like herpes to resurface.
"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," senior author Satish K. Mehta, of KBR Wyle at the Johnson Space Center, said in a statement.
"This physical challenge is compounded by more familiar stressors like social separation, confinement, and an altered sleep-wake cycle."
Mehta and colleagues compared samples of saliva, blood, and urine taken from astronauts before, during, and after space missions. They found that 53 percent (47 out of 89) of the crew aboard short space shuttle flights lasting between 10 and 16 days shed herpes viruses in their samples. The same was true for 61 percent (14 out of 23) of those involved in ISS missions lasting 180 days or more. However, only six displayed any actual symptoms.
Four of the eight herpes viruses known to routinely infect humans were identified – HSV (responsible for oral and genital herpes), VZV (responsible for chickenpox and shingles), and CMV and EBV (each responsible for different strains of mono). What's more, infectious VZV and CMV strains continued to shed for 30 days after the astronauts' return, potentially threatening those on Earth who are either immunocompromised or uninfected with the virus.
"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 explained.
"The magnitude, frequency, and duration of viral shedding all increase with length of spaceflight," he added, which could prove problematic for any mission to Mars.
Mehta proposes vaccines as an "ideal countermeasure" to the viruses' reactivation, though right now that would only be an option for the VZV strain.
It's not just herpes that poses a dilemma. The same could be true for any dormant virus. Plus it highlights a general immune compromisation or weakness that affects people involved in space travel. Let alone anyone who may be involved in extra-Earth colonization in the future.
"Reactivation of latent viruses is a powerful biomarker of immune status for astronauts deployed to space," the study authors conclude.
"Additionally, more than one virus generally reactivates at a time, potentially compounding the physiological ramifications of uncontrolled viral reactivation to not only rashes, but also severe target organ failures, and permanent vision and hearing loss."
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