According to a new NASA study, the longer astronauts spend long in space, the more likely they will be to reactivate viruses such as herpes, chickenpox and shingles. The reason may be the same for viral reactivation on Earth: stress.
Samples of blood, urine and saliva were collected from astronauts before, during and after the short space shuttle flights and long-term missions of the International Space Station. Herpes viruses have been reactivated in more than half of the astronauts. The study published last week in the journal Frontiers in Microbiology.
"To date, 47 out of 53 astronauts (53%) have made short space shuttle flights and 14 out of 23 (61%) have participated in longer ISS missions. Herpes viruses in their saliva or urine samples, "said Satish K. Mehta, lead author of the study, at Johnson Space Center. "These frequencies – as well as the amount – of viral shedding are significantly higher than in samples taken before or after the flight, or in matched healthy controls."
Excretion occurs when a virus is reactivated successfully.
During short and long-term space flight missions, astronauts are exposed to zero gravity, cosmic radiation, and extreme G forces during take-off and reentry. Added to this are the confinement in small spaces, the social separation of family and friends and an altered sleep cycle, the researchers said.
Spaceflight creates a stressful environment for astronauts, awakening dormant viruses.
Four of eight human herpes viruses have been detected, including oral and genital herpes, chicken pox and shingles. Because herpes viruses get into nerve cells and immune cells, they have never really disappeared, so they can "wake up".
But fortunately for astronauts, reactivation of viruses does not necessarily mean that symptoms return.
"Only six astronauts have developed symptoms due to viral reactivation," said Mehta. "All were minors."
But the implication of infecting others when astronauts return to Earth is very real, especially for those with compromised immune systems or for newborns.
Signs of chicken pox and infectious shingles were still present in body fluids up to 30 days after the return of the astronauts.
Researchers are also considering future space missions, which will lead them to the Moon and Mars in the long term, in deep space. A round-trip mission on Mars could take up to three years.
"The magnitude, frequency, and duration of viral shedding all increase with the duration of spaceflight," said Mehta. "The ideal countermeasure is the vaccination of astronauts – but this option is only available up to now against chicken pox."
Since trials of other herpesvirus vaccines are not promising, the researchers focused on developing targeted treatment regimens for those suffering the consequences of viral reactivation.
"This research is also of considerable clinical relevance to patients on Earth. Already, our technologies developed by spaceflight for the rapid detection of viruses in saliva have been used in clinics and hospitals around the world, "said Mehta.
What happens to immune systems in the space
Some of the effects of extended spaceflights are well known, such as the loss of muscles and bones. Astronauts struggle against this situation by exercising more while they are stationed.
In January, researchers examined the impact of long-term space flight on the cells of the astronaut's immune system. Specifically, they studied the effects of six months of spaceflight on a type of white blood cell that kills cancer cells in the body called natural killer cells. These NK cells also prevent viruses from reactivating.
"Cancer represents a significant risk to astronauts during very long spaceflight missions due to radiation exposure," said Richard Simpson, lead author of the study and associate professor of radiation sciences. Nutrition at the University of Arizona, in a statement. "[NK-cells] are also very important for killing cells infected with the virus. When you're in the space station, the environment is very sterile – you probably will not get the flu, a rhinovirus or a community-type infection – but the problematic infections are the viruses already in your system . body. These are mostly viruses that cause things like shingles, mononucleosis or cold sores; they stay in your body for the rest of your life and reactivate when you're stressed. "
During the study, scientists studied blood samples from eight astronauts who spent time on the space station and compared them to healthy people who did not experience spaceflight. Blood samples from astronauts were taken before, during and after spaceflight.
Compared to healthy controls and pre-flight condition, astronaut NK cell function was altered during and after spaceflight. On day 90 of their stay at the space station, samples of NK cell activity against leukemic cells in dishes in culture were reduced by 50% in crew members.
The effect was even more pronounced for first-time space-faring astronauts compared to those who had previously performed missions.
"I do not think there is any doubt that the function of NK cells decreases in the environment of spaceflights when it is analyzed in a cell culture system," he said. said Simpson.
But what caused that? As in the new study, researchers in this study believe that this could be stress-induced. The first-time astronauts were also younger than the space flight veterans and found their first experience more stressful, which could exacerbate their cellular response.
The study does not imply that astronauts are more susceptible to cancer. On this question, future studies can say.
"The next question would be: how can we mitigate these effects? How to prevent the immune system from degrading when traveling in space? Simpson said. "To do this, you must first understand what causes the decline: is it stress? Is it microgravity? Is it a radiation? Is it a plethora of things? Once we understand this, we can try to find ways to directly target and mitigate these factors. "
Researchers at the Johnson Space Center are working on possible countermeasures, including exercise, nutrition, and pharmacology, to preserve astronauts' health in the space. All this could stimulate the immune response.