Alien Illnesses

If an alien comes to earth, which do you think is more likely to happen? Is the alien going to bring exotic illnesses to earth which promptly make huge numbers of people sick, or is the alien more likely to be the one who gets sick from one of our native lurgies? Or maybe both?

Not sure if it'll make for a discussion, but any feedback would be interesting.

Well, it'd probably be a bit of both, although I suspect it would only really become a problem were someone to sneeze in the alien's face or something.

Little Egypt wrote:

If an alien comes to earth, which do you think is more likely to happen? Is the alien going to bring exotic illnesses to earth which promptly make huge numbers of people sick, or is the alien more likely to be the one who gets sick from one of our native lurgies? Or maybe both?

Not sure if it'll make for a discussion, but any feedback would be interesting.

For diseases to spread, the two lifeforms, earthbound and alien, must share nutrients of pathways. Bacteria will want to make acquaintance immediately, but if alien life developed indipendently from ours, it may be, for example, that their aminoacids and sugars are specular images of the ones in the earth food chain - assuming that they use aminoacids or sugars at all and aren't, for example, a lifeform based on vanadium instead of carbon. So the bacteria would find them unpalatable or even poisonous (specular molecules can arrest metabolic pathways). For viruses, which are usually specific to a host or range of hosts, the aliens probably wouldn't register.

It depends on 'how much alien' these people are...

I'm with Unoriginal. Unless terrestrial life and the alien life are very similar, biochemically speaking, it's unlikely that any diseases will cross the gap. I mean, it's incredibly rare for a disease to cross from trees to humans - now realise that humans and trees are actually quite similar, compared to how different humans and aliens are going to be. Sooner or later our bacteria are going to figure out how to snack on their proteins, assuming they're carbon-based, but it's probably not going to be rapid[1].

On the other hand, allergies are a distinct possibility. A human landing on a new world who takes off his or her helmet and takes a lungful of the alien air is quite possibly going to go into anaphylactic shock as they're exposed to literally thousands of entirely novel proteins that their body has no idea how to deal with. Assuming the alien's immune system is at least comparable to ours, they may suffer something similar, or at least equivalent.

Practically speaking, it's unlikely most aliens are going to want to be exposed to human environments. Chances are, our atmosphere is going to be too hot, too cold, too wet, too dry, too dense, too thin, too corrosive[2] or lacking in necessary substances[3]. Plus, they're probably adapted for different levels of gravity, radiation, and thousands of other things.

[1] Or maybe not. It only took fifty-odd years for nylonase to evolve, after all.
[2] Oxygen is freaking deadly. Seriously.
[3] Methane breathers, for example, are unlikely to find our atmosphere palatable.

There's only so many illnesses that can jump from one mammalian species to another. If these are human aliens or rubber forehead aliens, then it's possible, but not necessarily likely. If these are starfish aliens, then us getting them sick or the reverse is probably not a concern.

What Kel said. Consider how few diseases are transmissible between humans and dogs. Despite both being in the class Mammalia, and having thousands of years of shared history, only a relatively small number of zoonoses can cross the species barrier. It's doubtful that any aliens would be biologically as close to us as, say, blue-green algae, or even horseshoe crabs, let alone dogs.

When you consider that the same basic source material has given us such biologically bizarre creatures as the cephalopods with their copper-based blood, the Antarctic icefish that function at below-freezing temperatures, and the extremophile bacteria that can live in boiling water or jet fuel, it's highly unlikely that aliens are going to be much like us, let alone enough so to be tasty to our bugs.

This is, of course, ignoring the "space seed" hypothesis and its science fictional variants. If some precursor race went around sprinkling potentially habitable worlds with microorganisms as a way of terraforming (alienforming?) them, then the same basic biochemistry might be widespread throughout the galaxy. Getting more elaborate, the precursors could have moved early hominids to other worlds (we're too closely related to everything else on Earth to be from elsewhere), giving us the legions of nose-and-forehead aliens, or if we really want to run with it, genetically engineered all those races/species ... though I really have to question their creativity, or maybe just that of the writers of SF series.

Actually, there's not much question about the creativity of most of those writers. When you look at the amount of variation in appearance among, say, the great apes ... hell, among our own species ... and the best they seem to be able to do is rarely more than stick-on antenna, forehead lumps, and pointy ears? A very large number of "aliens" look more like a northern European than the Inuit, Maasai, Han, or Lakota do.

But that's a whole other rant.

Hmm. In my own sci-fi, I make the aliens worry about cross-species contamination (specifically, exporting something deadly from Earth, which is a relatively isolated environment), but I try to justify it in-story because A) there have been problems with cross-species contamination before and B) given how close the aliens are to terrestrial life (similar biochemistries, respire a similar atmosphere at similar pressures due to similar gravities) they would have cause for concern, even if those concerns are unfounded.

The thing is, a lot of plots don't support aliens that are too biologically alien to us, simply because we couldn't interact with them (except by proxy) if our required environments were too different. So generally I have aliens worry about it and take precautions and thereby justify never talking about it further.

Late to the party, but I think (assuming that diseases can make the jump and all that) the alien would be more likely to catch something because our whole planet is full of diseases, whereas he would only be able to have a limited number on him when stepping off his spaceship. Am I making sense?

A little bit of both.

Island communities are usually the kind hardest hit by foreign disease because for generations, they've had immunities built up to bugs that existed solely within their own area.

People in a very isolated situation like ships, living in close with each other, are more likely to get sick from each other, and spread diseases from one person to another, but that's the only reason they're susceptible to external disease: If one goes down, most will go down. They still have whatever built-up immunities that they already had when they set out.

So the way I see it, if space aliens came from a system of colonies or some kind of Federation/coalition/whatever directly to here, Earth would be far worse off as far as disease went. Otherwise they're pretty much on the same playing field.

The real medical issue, I think, is one that isn't going to manifest itself until we've spent a generation or so casually leaving the atmosphere: developmental disorders brought on by growing up in space. Bone disorders, growth disorders, autoimmune disorders, even respiratory problems... a child born and raised on a ship would need a lifelong regimen of trace gasses, nutritional supplements and physical therapy to even survive planetside.