Herpes viruses reactivate in more than half of crew aboard Space Shuttle and International Space Station missions, according to NASA research published in Frontiers in Microbiology. While only a small proportion develop symptoms, virus reactivation rates increase with spaceflight duration and could present a significant health risk on missions to Mars and beyond.
[...] "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," says senior author Dr. Satish K. Mehta of KBR Wyle at the Johnson Space Center. "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 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."