Download Incidence of Latent Virus Shedding During Space Flight

Incidence of Latent Virus Shedding During Space Flight
Satish K. Mehta1, Randall J. Cohrs2, Donald H. Gilden2, Steven K. Tyring3, C. Mark Ott4,
and Duane L. Pierson4
1
Enterprise Advisory Services, Incorporated, Houston, TX
2
University of Colorado Health Sciences, Denver, CO
3
University of Texas Health Science Center, Houston, TX
4
NASA Johnson Space Center, Houston, TX
Measurements of immune parameters of both cellular and innate immunity indicate alterations in immune
function in astronauts. Immune changes may be the response to stress associated with launch, flight, and
landing phases. Medical relevance of observed changes is not known. The reactivation of latent viruses has
been identified as an important in vivo indicator of clinically relevant immune changes. The polymerase
chain reaction (PCR) was used to detect the presence of specific viral DNA. Initial studies demonstrated
Epstein-Barr virus (EBV) reactivation during all 3 mission phases. EBV is shed in saliva following
reactivation from B-cells. Incidence of EBV in saliva was several fold higher than controls during all 3
mission phases. However, quantitative PCR revealed 10-fold higher levels of EBV DNA present in saliva
collected during flight than found in pre- and post flight specimens. To determine if other latent viruses
showed similar effects, cytomegalovirus (CMV), another herpes virus, shed in urine following reactivation
was studied. A very low incidence (<2%) of CMV in urine is found in healthy, low-stressed individuals.
However, 25-50 % of astronauts shed CMV in their urine before, during, or after flight. Our studies are
now focused on varicella-zoster virus (VZV), the etiological agent of both chicken-pox during childhood
and shingles later in life. We demonstrated reactivation of VZV and shedding of the virus during and after
spaceflight in saliva of astronauts with no sign of active infection or symptoms. The maximum shedding of
VZV occurred during the flight phase and diminishes rapidly during the first five days after landing. We
have utilized the PCR assay for VZV in a clinical study with shingles patients. Generally, shingles patients
shed much more VZV in saliva than astronauts. However, the VZV levels in astronauts overlap the lower
range of VZV numbers in shingles patients. The question of infectivity of shed virus was answered by
culturing saliva immediately after landing. Successful culturing of VZV on monolayer of human fetal lung
fibroblast cells and subsequent staining with VZV specific stain confirmed that the VZV that reactivate
during spaceflight was live and infectious.
We have concluded that latent viruses do reactivate before, during, and after spaceflight. This is consistent
with previous findings of diminished immunity; specifically cell mediated immune response, and
reactivation and shedding tend to increase with length of mission. Future plans will be focused on the
clinical risk posed by the reactivation of these viruses. Initial efforts will determine the effect of longer
missions on the International Space Station on the reactivation patterns of these viruses.