With so many probes heading for Mars and other planets, the question of whether they could bring back new diseases has become important. SARS, Mad Cow Disease and HIV are only three of the diseases that have crossed the species barrier, so infectious pathogens from Martian rock samples probably could too.
Leslie Mullen writes in Astrobiology Magazine that the International Committee Against Martian Sample Return is worried about this. Not all pathogens cross the species barrier?our dogs and cats get diseases that don’t affect us. Chicken and sheep farmers are untouched by diseases that wipe out their flocks and herds. A Martian microbe could enter the human body, but be harmless because it’s incompatible with human physiology.