Washington: Space travel caused herpes viruses to reactivate in more than half of crew aboard Space Shuttle and International Space Station (ISS), according to a NASA study, a finding that could jeopardise mankind's future missions to Mars and beyond. While only a small proportion develop symptoms, virus reactivation rates increase with spaceflight duration and could present a significant health risk on future missions.

"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 Satish K Mehta at NASA's Johnson Space Center. "This physical challenge is compounded by more familiar stressors like social separation, confinement and an altered sleep-wake cycle," said Mehta. To study the physiological impact of spaceflight, researchers analyse saliva, blood and urine samples collected from astronauts before, during and after spaceflight.