Yes, but microbial-like or virus-like life can be very deadly and spread rapidly, as who can forget 2020?
Sure, given plenty of time to develop in a very similar host, before jumping to a new species (typically via the use of the original host as food), viruses and microbes can be extremely dangerous.
But it seems implausible that there are any sufficiently human-like hosts for such microbes currently alive on Mars, and even if there were, it would be unexpected if the first human explorers on that planet were to attempt to eat them.
OTOH, it could be that Martian life, if it exists at all, would be nothing like earth life, and maybe they and us would have no basis for biological interaction.
That seems far more likely to me. Humans can catch viruses from chickens, because humans and chickens are fundamentally almost identical at the biochemical level. Neither is likely to be as similar to Martian life as we are to each other.
And then also, not everyone thinks viruses even qualify as life, and who knows what kind of borderline life/not life may be found on Mars?
The life/not life dichotomy is a product of human imagination, and of our apparently innate desire to build dichotomies. However, our continuing inability to produce a clear definition of "life", that includes everything that we know is alive, and nothing that we know is not, strongly suggests that "life" is not a real attribute of real objects.
There's no such thing as "life". Or rather, there is a spectrum, whereon things at
this end are "life", and things at
that end are "not life", but there is nowhere we can point to that marks a non-arbitrary boundary between those two descriptors, and nowhere that even can be agreed upon as a candidate for an arbitrary boundary, without angering an entire field or discipline of natural philosophy.
Shit, we can't even get scientists to agree as to whether "life" is defined at the population level or that of the individual - many definitions of life include "the ability to reproduce", which sounds great from a population perspective, but which leads to individual level consequences that are truly insane, such as defining castration or hysterectomy as instantly fatal; And vasectomy as instantly
and reversibly fatal.
Personally, I will be satisfied that we have found "life" on Mars if we can demonstrate the existence on that planet of self-isolating cyclic chemistry, driven by an external energy source, and with the population level ability to reproduce, with or without the use of other locally available self-isolated chemistries.
But I can guarantee that whatever definition we use, someone will reject that definition; And that some people will say "sure, but it's not really
life" even if it hunts, kills and eats the first taikonauts.
