I’ve read somewhere that it wold be impossible but i dont clearly remember why.
So whats the straight dope on this?, i know it may be to dependent in the hipothetical alien biology (and maybe more of a great debate than a GQ, if so i hope a kind mod would fix without previously banning me or something .
)
Frodo
Frodo, lay off that pipeweed!
It all depends on the alien biology. This question has no factual answer.
It wouldn’t be impossible, just highly unlikely. There was a thread on this a couple months ago, and the general concensus was that there was a remote possibility such biological agents could be dangerous to Earth life, but the likelihood was small.
I wouldn’t say impossible. I doubt it could get a cold or the flu or anything, but there are MANY bacteria on earth, I imagin if some chemical reactions are sufficient for life we have some bacteria somewhere working on them. I don’t think an alien would get human diseases, but I bet you could find SOME bacteria somewhere that would find a home in the alien’s biology. a deep sea vent bacteria, a lithovore, a chemovore. there are alot of possible biologies, but we have alot of bacteria.
I go with what Qadgop the Mercotan
, Q.E.D., and owlofcreamcheese said, but I’ll also add that the chances of a virus (or alien equivalent) crossing planets is pretty much zero. Viruses use the cellular machinery of their host–in order for them to come out right, we’d have to have the same (or very similar) cellular machinery as the aliens, and the chances of that are very, very, very, very, very (etc) slim.
Unfortunately, viruses sound scarier, so sci-fi always loves to make the alien pathogen a virus rather than a bacterium…
Well, viruses are harder to detect, and MUCH harder to deal with.
Just based on the tiny amount of knowledge at hand, I’d say you or I have about as much chance of being infected with Denebian Flesh-Melt Fever…
…as we would of being infected with Dutch Elm Disease.
Cellular biology is just too different, even among species on THIS planet. Hell, I live with cats, and there are any number of diseases they can get that I can’t, and vice versa. What are the chances that the folks on Alpha Centauri could catch a cold?
Its unlikely unless life on other planets evolves in an extremely similar manner to that on earth.
Bacterium and Viruses that infect humans have been evolving with us for millions of years and they are geared specifically to attack our form of biology.
A virus that harms aliens is not programmed to harm humans, it hasn’t evolved to do so. Its never been in an enviroment where it has needed to adapt in that fashion.
Why is everyone concentrating on viruses when the OP asks for germs generally?
I agree the chances of being infected with an alien virus is pretty remote. The chances of an lien species having DNA, much less anything we would recognise as virus, is so remote as to be ludicrous.
However other alien microbes of the bacterial/fungal type are far more likely prospect. The evolution of lifeforms that excrete exozymes and simply abosrb any nutrients around them is pretty much garaunteed it’s such an efficient, adaptable and
elegant design.
So then we have to figure out what these things can digest.
Given that any alien lifeform will probbaly be carbon based we can assume that any long-chain hydrocarbons will be on the eating list just as they are on Earth. Beyond that it’s hard to say. Things like sugars and proteins are more likely to be shared between unrelated groups than something ascomplex as DNA/RNA. It’s odds on that any alien microbe will be able to digest at least some of the componenets of the human body. Mabe not efficiently, but as well as some microbes can digest syntehtic polymers. So they could pose a risk.
Then we have to ask whether our immune system could effectively deal with them. I’d say unlikely. Our immune systems are geared towards terrestrial lifeforms. It locks in largely on recognised sugars and proteins. Anything that isn’t a ‘recognised’ sugar or a protein tends to be largely ignored by the immune system and instead is detoxified by the liver or excreted in the kidneys. That’s how most drugs retain effectiveness. Aspirin may be a complex molecule, but it doesn’t cause an immune reaction. Alien bugs aren’t likely to have any recognisable antigens, even if they are composed of something analogous to carbohydrates and protein.
So we have an alien bug with, for arguments sake, a poly-cyclopropane/chlorinated hydrocarbon shell instead of a carbohydrate/lipopolysaccharide shell and producing ‘enzymes’ composed not of organic amino acids, but of organic phosphoric acids. There’s nothing there for our immune systems to recognise. The creature’s surface coating is going to be immunologically ‘inert’ or at best provoke a very minor immune response. The damaging exozymes that are melting us from the inside out are also probably immunologically inert. Even if they aren’t, I don’t think we have anything in our arsenal to denature phopsphoric acid proteins.
But even if they do provoke an immune response and they do get denatured, what sort of physiological effect will be produced by having fragments of phosphoric acids floating around in our bloodstreams? The same is true of the microbes cell walls. So we can kill the microbes. They then lyse and release PCBs and cyclopropanes into our systems. That ain’t good.
This is of course all guesswork. But it does show some of the problems associated with compleyely alien bugs. They will most likely be able to use us as a food supply. Our immune systems are not geared to fight them, and may not be able to deal with them at all. The secondary metabolites of these creatures may well be dangerous to us simply by chance.
So yeah, on the balance of probabilities some alien microbes will be able to infect us. Odds are they will have a hard time digesting us and become annoying tinea/thrush type infections. Worst case they can digest us with relative ease and produce even moderately toxic secondary metabolites.
The biggest factors will be that any alien organism will probably have evolved to cope with temperatures and gas mixtures very different to anything found in the human body. But that isn’t garaunteed. Opportunistic Earth microbes like Clostridium tetani also evolved with very differebt gas mixtures, but they still kill people. They also have the capacity to operate at very wide range of temperatures.
That is only true of viruses. Things like C. tetani or C. botulium are not true pathogens and haven’t evolved as such. They just can’t tell the difference between the inside of your leg, a can of tuna and a peat bog.
It is almost inevitable that alien micobes will be the same. The only question is whether they can digest human bodies sufficiently well to provide the energy and nutrients needed to multiply.
If they can then we may have a probelm, because the human immune system ha a hard time dealing with bacterial infections, and they are dependant upon easily identified foreign proteins. Imagine if there were no proteins or anything else that the body readily recognised as an invader.
You could argue it either way. Unfortunately, having an experimental sample size of exactly zero, it’s tough to come to an ironclad conclusion.
Unknown. Insufficient data. Call back when we actually have extraterrestrials to diddle with.
Thanks for all the replies!.
So we can reach the conclusion that is at least theoretically possible but not likely, and order of magintude more probable than (for example) an alien-human hybrid?
Thanks.
Frodo
Oh boy, is this wrong on so many levels. Our immune system is NOT “geared toward terrestrial lifeforms”. The cells are actually geared toward nothing and everything. Every antibody, and every T cell is geared toward random shapes, and though this point is currently hotly contested in the field, probably are able to recognize anything that is “non-self”. Thus enabling them to pretty much respond to anything that doesn’t belong, alien or terrestrial. If an antibody (or T cell) happens upon something that it fits, it proliferates (in the case of antibody, it is the specific B cell that is proliferating) and exerts a response.
Back to the original question. An alien virus may have a hard time, especially if it is not, as pointed out, DNA or RNA comprised. They have to get into a cell, and take over the cell’s machinery (and in the case of retroviruses, actually insert themselves into the genome). Since they rely on host machinery, an alien virus would have to rely on similar architecture (enzymes and such) But, bacteria bring everything they need with them in terms of enzymes, if they had the right nutrition and biological precursors such as amino acids, which are fairly universal (and I’m assuming extracellular bacteria, so I don’t have to deal with receptor mediated endocytotic events) may be able to infect humans.
This too is conjecture but based on the way the immune system actually works.
Hey Blake:
This latter point is false. Clostridia possess both two-component and quorum sensing systems that switch on virulence genes upon entry to the human body. These bacteria most definitely can “tell the difference between the inside of your leg, a can of tuna and a peat bog.”
Also, as kflanaga has pointed out, our immune systems are not “geared toward terrestrial lifeforms.” A number of systems, including immunoglobulin somatic hypermutation, ensure that our immune systems can recognize any number of strange structures we have never encountered before.
One other thing:
What? What makes a piece of DNA or RNA more complex than a protein?
Hey kflanaga:
What does “fairly universal” mean? Furthermore, what makes amino acids “fairly universal?”
-Apoptosis
Uh, Teflon? Silicones? Arsenic?
Speaking of being wrong in so many ways.
Yes T shells are geared towards random shapes. But as I pointed out, there is a limit to what those shapes can be. They must essentially be of terrestrial organic origin, and in fact must be within very specific classes of terrestrial organic origin. No T cell reacts with complex molecules such as tattoo ink, plastic surgical implants or titanium hip joints. The molecular structure is just too far removed for them to react to. As a result those object stay in the body forever in contact with the blood stream without ever provoking an immune response. Any alien microbe with those or other molecules as their primary cell bodies are going to provoke zero response.
A protein can function simply by simply existing. An enzyme combined with its substrate will do its job independent of any other chemicals. DNA, in order to be effective, needs a range of associated enzyme systems for transcription. I didn’t mean that DNA was chemically more complex, although it arguably is. I meant that in order to fill the role that it does in terrestrial lifeforms it requires the evolution of a whole range of other systems. It’s less likely to have evolved physically and operationally identically twice, and that’s what would be required for an alien virus to be able to integrate. In contrast a protein produced via any string of reactions is going to be just as digestible. It doesn’t need to be produced from DNA transcription. It doesn’t even need to contain all the same amino acids. It will still be a food source.
Have you got a refernce for that? I am at least a decade out of date, but last I heard the virulence genes were also activated in response to any stress in high nutrient environents. They evolved to enable competition with other microbes, not to kil people.
However if Clostridium spp. is a poor example I will susbtiute Legionella or Aspergillus, which can’t tell the difference between your lung and a pond. The point is that there are huge numbers of opportunistic pathogens out their that will attack animals. They don’t need to evolve as pathogens to be able to act as pathogens.
Well, flame me if you must, but I still think it’s highly unlikely that any alien microlife will cause so much as a sneeze, much less giant piranha-maggots bursting out of your chest or whatever…
Hey Blake:
Most definitely. Legionella is a very interesting example. It evolved as a parasite of freshwater amoebae. Strangely enough, charateristics that promote amoebae infection also allow Legionella to invade human alveolar macrophages. However, I believe that saying Legionella “can’t tell the difference between your lung and a pond” is an oversimplification. I would be very surprised to find that the 2D gel profiles of Legionella growing in amoebae and Legionella growing in macrophages are identical. I have been unable to find any references supporting or refuting this.
As for Clostridium spp., simply do a PubMed search for “Clostridium” and “two-component system.” For example, the VirSR pathway of C. perfringens controls the expression of the cholesterol-dependent cytolysin, perfringolysin O. Bacteria do not possess cholesterol. I think you can see where I’m going with this.
Ah, I see. I would be very interested to hear your argument that DNA is chemically more complex than proteins, considering the former is made up of 4 subunits, while the latter are made up of at least 20. DNA is found in less-than-a-handful of conformations, while proteins can be found in more conformations than you can imagine.
I have no idea what this means. Are you suggesting it’s more likely that extra-terrestrial organisms have evolved nucleic acid-independent methods of constructing proteins than it is that they have evolved nucleic acids themselves?
I still think the only answer to this question is this: “Probably not impossible, but really- who the hell knows?” Not surprisingly, this is the answer most posters have given.
-Apoptosis
Actually I don’t. The saponins commonly found in plants act as potent antimicrobials. They also act largely by affecting cholesterol, in this case directly rather than by disprupting cholesterol action. The fact that bacteria don’t possess cholesterol tells us nothing at all because other microbes do possess cholesterols and interfering with them is a very effective way of producing an antimicrobial. Just not an antibacterial.
The fact that the virulence gene affects cholesterol production fits very neatly with what I said previously: that it is designed to promote competition with other microbes in nutrient rich environments. Unless you have a reference for a lack of effect of Clostridium on cholesterol-dependant systems in fungi and protozoa then we’ve really gone nowhere. The system will still work very well assisting the bacterium in competing with other microbes and is far more likely to have evolved as such rather than as an aid to pathogenicity.
I said say it was arguable. 
Although DNA is simpler in terms of the available monomers the monomers themselves are more complex. It’s a bit like arguing that a tuba is more complex than a dry stone wall. The wall might have millions of different shapes of stones as the subunits, while a trumpet can have as few as 10 individual subunits. But each subunit in the tuba is individually more complex and more complex to make.
It’s an argument, and a rather irrelevant one.
Not more likely than evolving nucleic acids, but more likely than evolving functionally identical DNA that a terrestrial virus could exploit.
errata
"The fact that the virulence gene affects cholesterol production " should of course reead “The fact that the virulence gene affects cholesterol action”.