Spaceflight and Pathogens

This from the linked EurekAlert article:

Spaceflight not only altered bacterial gene expression but also increased the ability of these organisms to cause disease, or virulence, and did so in novel ways. Compared to identical bacteria that remained on earth, the space-traveling Salmonella, a leading cause of food-borne illness, had changed expression of 167 genes. In addition, bacteria that were flown in space were almost three times as likely to cause disease when compared with control bacteria grown on the ground.

For reasons not yet understood space flight appears to make some pathogens more infectious. Is it because of changes only in the pathogens or a combination of both pathogenic changes and immunological changes in humans? What is the link between a space environment and the result? Studies will occur intended to provide answers. The problem could impair longer flight missions. It's an interesting development.