In preparation for continued human
spaceflight missions farther into space to the Moon and Mars, NASA continues to
investigate how the human immune system reacts in spaceflight. Certain viruses,
such as the Varicella Zoster Virus (VZV) that causes chickenpox in childhood or shingles in
adults, are not fully eliminated from one’s body. The immune system controls
them and maintains the virus in a “dormant” state in the spinal cord nerve
cells of the body. These viruses can intermittently “awaken,” or reactivate,
starting to grow and multiply. Most times this happens, the person experiences no
symptoms or overt illness; however, it is more commonly seen in elderly people
and in people whose immune systems are compromised that the reactivation does
cause disease. It is believed that stressful life situations causes the viral
NASA research published in Frontiers
in Microbiology extends
previous NASA research that these latent virus strains can reactivate in people
who spend time in space. This reactivation is typically “subclinical” in
astronauts, meaning they are not truly sick and do not exhibit symptoms.
However, the presence of the active viruses is a good indicator that those
astronauts are experiencing reduced immunity during a space mission.
NASA is using a process Dr. Satish K. Mehta of KBR Wyle at NASA’s Johnson
Space Center developed for rapid viral detection systems and is beginning to
test immune boosters, or countermeasures, for astronauts for future deep space
missions—work that could also benefit patients with decreased immunity on
Dormant viruses can reactivate in anyone, not just astronauts
“NASA astronauts endure weeks, or
even months, of constant microgravity and radiation—not to mention the increased G forces of take-off and
re-entry,” said senior author Dr. Mehta. “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, Mehta and his
colleagues analyze saliva, blood and urine samples collected from astronauts
before, during and after spaceflight.
“During spaceflight, there is a rise in the secretion of stress
hormones like cortisol and adrenaline, which are known to change the immune
system,” Mehta said. “In keeping with this, we find that astronauts’ immune cells—particularly those
that normally suppress and eliminate viruses—become less effective during
spaceflight, and sometimes for up to 60 days after they return home to Earth.”
The observable presence of the reactivated virus, or viral
shedding, as seen in the astronauts has typically been asymptomatic. “Only six
of all astronauts with viral reactivation developed any symptoms,” Mehta said.
“All symptoms were minor.”
Overall, four of the eight known human herpes viruses—including
the variety responsible for chickenpox and shingles (VZV)—were detected in
astronauts during their stay in space. Herpes viruses often remain dormant in
nerve or immune cells throughout a lifetime.
As NASA has plans to go forward to the Moon and beyond,
international space immunologists and virologists are characterizing this
phenomenon using the space station as a microgravity testbed, as well as here
on Earth in isolated conditions. Understanding how these viruses behave in
astronauts on the International Space Station will allow researchers to develop
countermeasures that will be needed for long-duration missions.
“The ideal countermeasure is vaccination for astronauts—but, so
far, this is available only against one variety of the eight herpes viruses, VZV,” Mehta said.
NASA’s present focus is to develop targeted treatment regimens
for individuals experiencing virus reactivation.
Mehta reiterates that this research has tremendous clinical
relevance for patients on Earth, too. Already, spaceflight-developed processes
for rapid viral detection in saliva have been employed in clinics and hospitals
around the world.
NASA Johnson Space Center
A colored, computer-generated depiction of an Epstein-Barr virus particle.