What if Mars astronauts get sick?
A spacecraft really wouldn't be a great place to suffer from, say, salmonella poisoning - but new research indicates that microgravity and prolonged space flight could give unique advantages to germs.
Microgravity not only weakens the immune system in some ways, but also increases the virulence and antimicrobial resistance of some microorganisms, says infectious disease specialist Dr Leonard Mermel of Brown University and Rhode Island Hospital.
Meanwhile, without gravity, germs launched by coughs and sneezes no longer fall to the ground within a few feet, but continue to float around. This means they're more likely to be inhaled by astronauts, and can settle on a wider variety of surfaces.
"So you suppress the human immune response, and you enhance the ability of microbes to cause infection, and you put those together in a confined space where airborne particles can remain in the air for a protracted period of time," he says.
Unfortunately, the air on a spacecraft has to be recirculated, meaning astronauts can't use some hospital disinfectants and hand hygiene products because they could emit hazardous vapors.
But, says Mermel, there are measures that can be taken to reduce the risk. NASA's already implemented most of them, vaccinating astronauts for several diseases, including the flu, and screening for others, such as tuberculosis.
Food is selectively irradiated and astronauts have disinfecting wipes, surgical masks and respirators. They take off with multiple antibiotics on board.
However, Mermel suggests that vaccinations should be expanded to include germs like Meningococcus and Pneumoccocus, and pre-flight screening should be expanded too. Astronauts could be screened for all strains of staphyloccocus aureus, including some antibiotic-resistant forms, and stool could be screened and re-screened for salmonella.
Finding a way to somehow work HEPA air filtration into the energy budget would be a worthwhile goal if possible, he says.
One of the toughest calls NASA will need to make, says Mermel, is whether to irradiate more food for a longer trip. While this might seem like a good solution at first sight, some of the bacteria we eat ends up in our guts and has beneficial effects.
"We've evolved to have those microbes go into our gastrointestinal tracts, our immune system interacts with them and is stimulated by them and it's part of our homeostatic mechanism," he says.