"To date, 47 out of 89 (53%) astronauts on short Space Shuttle flights and 14 out of 23 (61%) on longer ISS missions herpesviruses in their saliva or urine samples," said senior study author Satish K. Mehta of the Johnson Space Center. "These frequencies – as well as the amount – of virus excretion are significantly higher than in pre-, post-flight, or matched healthy controls."
Viruses are successfully reactivated during excretion.
Both short and long-range spaceflight missions expose astronauts to weightlessness, cosmic rays, and extreme G-forces during takeoff and reentry. In addition, the confinement in tight spaces, the social separation of family and friends and a changed sleep cycle, the researchers said.
Aerospace creates a stressful environment for astronauts and awakens sleeping viruses.
Four of the eight human herpesviruses have been detected, including oral and genital herpes, chickenpox and shingles. Since the herpesviruses settle in nerve and immune cells, they have never really disappeared, so they can "wake up". But fortunately for the astronauts, the reactivation of the viruses does not necessarily mean that the symptoms will return.
"" Only six astronauts developed any symptoms due to viral reactivation, "Mehta said." All were insignificant. " But the implication of infecting others when the astronauts return to Earth is very real, especially those with compromised immune systems or newborns.
Signs of infectious chickenpox and shingles were still present for up to 30 days after the astronauts returned always visible in bodily fluids.
Researchers are also looking at future space missions that will bring them on long-term voyages to the Moon and Mars through space. "It could take up to three years to travel to Mars.
"The extent, frequency and duration of virus clearance increase with the length of space flight," Mehta said. "The ideal countermeasure is vaccination for astronauts – but so far this is only available for chickenpox."
Studies with other herpesvirus vaccines are not very promising, so researchers are focusing on developing targeted treatment regimens for those who suffer from viral reactivation.
"This research has tremendous clinical relevance for patients on Earth, and our space-developed technologies have already been used to rapidly detect saliva in clinics and hospitals around the world," Mehta said. 
What happens to the immune system in space?
"Cancer is a big risk for astronauts during very long space flight missions due to radiation exposure," said Richard Simpson, senior study author and associate professor of nutrition science at the University of Arizona, in a statement. "[NK-cells] are also very important in killing virally infected cells, so if you're in the space station, it's a very sterile environment – you probably will not get the flu or a rhinovirus or any other community infection – but the infections The ones that are a problem are the viruses that are already in your body, mostly viruses that cause shingles, mononucleosis or cold sores, for example, they stay in your body for the rest of your life and reactivate them when you're stressed. "
During the Study The scientists examined blood samples from eight astronauts who were at the space station and compared them to healthy people who did not experience space flight. The astronaut blood samples were taken before, during and after the space flight.
Compared with healthy controls and pre-flight training, astronaut NK cell function was compromised during and after space flight. On day 90 of their stay on the space station, the number of NK cell activities against leukemia cells in culture dishes was reduced by 50% among crew members.
Astronauts entering space for the first time had an even greater effect compared to those who had previously completed missions.
"I do not believe so "There is some doubt that NK cell function will decrease in the space environment when analyzed in a cell culture system," Simpson said.
But what led to that? As in the new study, researchers in this study believe it could be stress-induced. The first-time astronauts were also younger than the space pilots and found their first experience tiring, which could increase their cellular response.
The study does not suggest that astronauts are more susceptible to cancer. Future studies can say something about this question.
"The next question is how to mitigate these effects, how do we prevent the immune system from weakening during space travel?" Simpson said. "To do that, you first have to find out what causes the decline: Is it stress? Is it microgravity? Is it radiation? Is it a wealth of things? If we figure that out, we can try to find ways to target it directly
Johnson Space Center researchers are working on possible countermeasures including athletic, nutritional, and pharmacological measures to keep space astronauts healthy. These could all increase the immune response.