Latent herpes viruses such as herpes-simplex-1 (HSV-1), Epstein-Barr virus (EBV), varicella-zoster virus (VZV), and cytomegalovirus (CMV) reactivate in more than half of crew aboard Space Shuttle (10-16 days) and International Space Station (over 180 days) missions, according to a study published in the journal Frontiers in Microbiology.
The stress of spaceflight gives viruses a holiday from immune surveillance, putting future deep-space missions in jeopardy. Image credit: NASA.
“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,” said study senior author Dr. Satish K. Mehta, a researcher at KBR Wyle Laboratories Houston.
“This physical challenge is compounded by more familiar stressors like social separation, confinement and an altered sleep-wake cycle.”
To study the physiological impact of spaceflight, Dr. Mehta and his colleagues from GeoControl Systems, Inc., NASA’s Johnson Space Center and the University of Colorado Denver analyzed saliva, blood and urine samples collected from astronauts before, during and after spaceflight.
“During spaceflight there is a rise in secretion of stress hormones like cortisol and adrenaline, which are known to suppress the immune system,” they explained.
“In keeping with this, we find that astronaut’s immune cells become less effective during spaceflight and sometimes for up to 60 days after.”
In the midst of this stress-induced amnesty on viral killing, dormant viruses reactivate and resurface.
“To date, 47 out of 89 (53%) astronauts on short space shuttle flights, and 14 out of 23 (61%) on longer International Space Station missions shed herpes viruses in their saliva or urine samples,” Dr. Mehta said.
“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.”
Overall, four of the eight known human herpes viruses were detected. These include the varieties responsible for oral and genital herpes (HSV-1), chickenpox and shingles (VZV), as well as CMV and EBV, which are associated with causing different strains of mononucleosis.
“So far, this viral shedding is typically asymptomatic. Only six astronauts developed any symptoms due to viral reactivation. All were minor,” Dr. Mehta said.
“However, continued virus shedding post flight could endanger immunocompromised or uninfected contacts on Earth, like newborns.”
“Infectious VZV and CMV were shed in body fluids up to 30 days following return from the International Space Station.”
What’s more, as we prepare for human deep-space missions beyond the moon and Mars, the risk that herpes virus reactivation poses to astronauts and their contacts could become more crucial.
“The magnitude, frequency and duration of viral shedding all increase with length of spaceflight,” Dr. Mehta said.
“Developing countermeasures to viral reactivation is essential to the success of these deep-space missions.”
“The ideal countermeasure is vaccination for astronauts — but this is so far available only against VZV.”
“Trials of other herpes virus vaccines show little promise, so our present focus is on developing targeted treatment regimens for individuals suffering the consequences of viral reactivation.”
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Bridgette V. Rooney et al. Herpes Virus Reactivation in Astronauts During Spaceflight and Its Application on Earth. Front. Microbiol, published online February 7, 2019; doi: 10.3389/fmicb.2019.00016
