Exobiological Illnesses

The risk that Martian microbes exist, and could cause disease in humans, is considered to be very small. It is one of the aspects of planetary protection. Other vectors for illnesses might be viruses or prions.

Arguments As To Why There Are No Martian Diseases That Can Effect Humans

Disease organisms are parasites which have evolved along with their hosts. Animals have evolved elaborate defences which prevent foreign material from harming them, parasites have to have 'learned' how to defeat these defences.

There can be no diseases that will attack animals, plants or fungi on Mars because they would starve to death, simply because none of these things live on that planet. You would be more likely to catch Dutch Elm Disease than some Martian bug.

Martian bacteria (if it exists on the surface) would have evolved to survive: a near vacuum, very dry environment, high radiation, toxic chemicals (such as perchlorates), low gravity, and icy temperatures that go down to -125 C. Any creature which is happy with such conditions, is unlikely to out compete bacteria native to the warm, wet interior of a human body.

Further asteroid strikes on Mars kick up rocks into space. A few kilograms of these fall to Earth each year. Note that bacteria spores can last for a very long time in a hard vacuum. It has been shown that the heat of reentry is insufficient to sterilize cracks inside the rocks when they crash on Earth. So for billions of years, Earth has been receiving Martian bacteria (if any exist). If a plague didn't start from the Martian meteorite Allen Hills 86001, then it is hard to justify why the bacteria on Mars pose any threat.

Finally the Martian explorers are in a perfect quarantine while on the planet, and will be quarantined for an additional 6.5 months while flying home. This will give any harmful bacteria plenty of time to be found, in the astronomically unlikely chance that they exist.

People have suggested passing laws to prevent people from going to Mars because of this 'danger'. It would be much more sensible to pass laws making gardening illegal. It is known that disease organisms (including rabies, anthrax spores, and tetanus) can last for a long time in the subsoil.

People have suggested that elaborate safety precautions are taken to avoid this 'risk'. These include elaborate facilities carried to Mars from Earth, transporting teleoperated robots to Mars to be run by astronauts who stay inside their habitat, having the returning explorers go into a quarantine at an orbiting Lunar space station, and others. Some of these plans would cost hundreds of millions of dollars. Spending this money on Earth providing health care to people would actually help people's health.

Precautions

Precautions to manage this risk include the following:

• rules that limit direct and indirect human contact with the martian environment, particularly when relatively warm and wet conditions are present (e.g. "airlock procedures, sample transportation and handling, and in-situ resource utilization"). A specific example would be procedures specifying how and under what circumstances space suits will be decontaminated upon return to spacecraft/habitats.
• rules that limit where humans may travel, including use of robots to conduct initial evaluation of unexplored sites
• life support systems designed to prevent contamination of air and water supplies
• medical monitoring, including markers of immune system function
• monitoring of normal human microbiomes and free-living microbes inside spacecraft/habitats
• habitats designed to separate living areas from research facilities (e.g. lab facilities that meet biosafety level 2 standards)
• a facility for quarantine of someone who may have been infected with a martian microbe

A related risk is the possibility that microbes carried from earth could evolve to become more pathogenic in a different environment. There is also the possibility that the human immune system could weaken in the absence of the normal scope of interactions with earth microbes, leading to infections with normally benign microbes carried from earth.

If it is considered needed, then planetary protection measures could be implemented upon completion of a Mars exploration mission to ensure that any microbes carried by astronauts, equipment, or samples cannot be transferred to the Earth environment. For example, Apollo astronauts were quarantined for 21 days after returning.

Further Reading

National Research Council. 2002. Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface. Washington, DC: The National Academies Press. https://doi.org/10.17226/10360.