Regarding the feasibility of Earth microbes affecting aliens, how much of our own immunity stems from our evolving new defenses against internal invaders, and how much of it is affected by the bacteria and viruses themselves evolving? In other words, which is more likely to harm us - a pathogen that maybe people in another part of the world have an immunity to and so is benign for them, but that we have never been exposed to - or a pathogen that we already have, but has mutated in some way to not be vulnerable to some aspect of our immunity or a particular medication? In the case of the movie, this would affect the feasibility in that it would seem more likely for aliens to be affected by not having encountered something than by it having overcome a specific immunal defense.
Frequently, the most aggressive pathogens are those that only recently crossed over from animal hosts to humans. In evolutionary terms, it is better for a parasite not to kill off its host too quickly, this way, the infection is more likely to spread.
All the same, since diseases are themselves very picky about their hosts species, it’d be very unlikely the worst we have would even bother them. Never mind in all likely hood that aliens would even be Carbon based or HAVE blood cells or anything similar enough to DNA that they could even be affected.
Microbes on earth have evolved to thrive by interacting in some way with humans. It’s hard to imagine that they would be able to interact with some alien species if it was very different from us.
Some bacteria are pretty tolerant of a wide range of growing conditions - anything wettish, warmish and with some kind of food in it might serve as a culture medium - so this would somewhat increase the possibility of aliens being affected by them. Of course there would probably be plenty of cases where the chemistry just wasn’t right and the bacteria would starve or be poisoned by the alien environment.
And if Panspermia has any truth to it, that would make it still more likely, and possibly viruses too in that case.
I used to work for a company that did explosives and munitions tests for the government. We had a test series once where we used a high speed round projectile to impact a rock. I wasn’t made aware of the specifics, but I seem to recall that they were doing it to see if any microbes would survive, a lunar and/or Mars impact. Unless the microbes were adapted to both extreme heat and cold, they wouldn’t be able to survive entry into our atmosphere.
I know that’s not the question you had, but thought you’d be interested in hearing it, at least.
What were the results?
AFAIK, both the book and the movie had the Martians layed low by common decay-causing bacteria, not specialized pathogens. The Martians had no immunilogical defense at all, or at least not against Terran microbes. The plausibility of that has been debated in previous threads, but I don’t think questions of parasite/host evolution come into it.
Wells doesn’t say exactly what kind of bacteria got the martians, and seems to say it wasn’t just one, but I agree that it seems it was mostly simple rot and decay that brought the martians down. At just about the end of the main story he says:
(emphasis added)
A little later he talks about the decay-causing bacteria again, but again seems to imply multiple types of bacteria:
So while he does twice talk about putrefactive bacteria, he also mentions disease causing bacteria.
Not that this is a scientific cite or anything, just thought I’d throw out what Wells wrote, since it apparently inspired the OP.
http://www.straightdope.com/columns/050722.html
the master speaks