With the US, Japan and China all actively talking about permanent settlements on the Moon and Mars, not to mention the prolonged stays of astronauts on the International Space Station, attention is being focused on a well-known but little understood fact: the human immune system actually degrades in weightlessness.

The human immune system, which [is] as complex as the central nervous system, includes an arsenal of responses to invading bacteria, viruses and other pathogens – ranging from first responders such as neutrophils and microphages to more sophisticated T-cells and B-cells that act on a molecular level. Although research into the workings of these infection-fighters during space missions remains limited – because of technical problems with collecting samples in space, very limited crew time and, more recently, deep funding cuts – [many] key infection-fighting molecules appear to be less available to people in space.

Not only are people more susceptible to sickness inducing microbes in zero gravity, but it also appears that some microbes, such as salmonella, become significantly more virulent in weightlessness.