New Delhi, June 22 : Researchers have said that space travel might alter gene expression in white blood cells (WBC) and weaken the immune system, making astronauts more susceptible to infections while in space, a new study showed on Thursday. For instance, astronauts on board the International Space Station (ISS) commonly suffer from skin rashes, as well as respiratory and non-respiratory diseases. Astronauts are also known to shed more live virus particles, like Epstein-Barr virus, varicella-zoster responsible for shingles, herpes-simplex-1 responsible for sores, and cytomegalovirus, according to the study published in the online journal Frontiers in Immunology. "Here we show that the expression of many genes related to immune functions rapidly decreases when astronauts reach space, while the opposite happens when they return to Earth after six months aboard the ISS," said Dr Odette Laneuville, an associate professor at the University of Ottawa, Canada. The research was funded by the Canadian Space Agency. A cohort of 14 astronauts, including three women and 11 men, who resided on the International Space Station between 2015 and 2019, were examined for gene expression in leukocytes (white blood cells) by researchers. About 15,410 genes were found to be differentially expressed in leukocytes. Among these genes, the researchers identified two clusters, with 247 and 29 genes, respectively, which changed their expression in tandem along the studied timeline, according to the study. Genes in the first cluster were turned down when they reached space and back up when they returned to Earth, whereas genes in the second did the opposite. Both clusters were mostly made up of genes that code for proteins, but their primary function was related to immunity in the first cluster and cellular structures and functions in the second. The researchers said that these results suggest that when someone travels to space, these changes in gene expression cause a rapid decrease in the strength of their immune system. "A weaker immunity increases the risk of infectious diseases, limiting astronauts' ability to perform their demanding missions in space. If an infection or an immune-related condition was to evolve to a severe state requiring medical care, astronauts while in space would have limited access to care, medication, or evacuation," said Dr Guy Trudel, a rehabilitation physician and researcher at The Ottawa Hospital and professor at the University of Ottawa. Moreover, the data showed that most genes in either cluster returned to their pre-flight level of expression within one year after return to Earth, and typically much sooner -- on average, after a few weeks. According to researchers, these results suggest that returning astronauts run an elevated risk of infection for at least one month after landing back on Earth. /IANS