They’re not living organisms, so what are they? What created them; where did they come from? Why do they infect hosts? Bacterial infections make sense; bacteria use a host’s body to survive and propagate. Viruses aren’t alive, though, so why do they need to infect people at all?
And why do they all affect the body so differently? Why can you only catch some viruses (I.e. chickenpox) once, but you can catch others (Covid, flu) multiple times? Why do some (HPV, EBV) appear to cause cancers and autoimmune disorders while others don’t?
For as far as we’ve come in medicine, it seems like we don’t understand much at all about viruses, or their longterm implications.
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Viruses aren’t alive on the catch that they cannot reproduce autonomously; they require the cells of a living thing to reproduce.
In quite a few ways they resemble a living thing; their origins are presumably extremely similar to those of living cells, they are at least as diverse as living things, and the law of natural selection still applies to them. Natural selection, which applies to *anything* that can reproduce itself (not just living things), is the answer to all your questions.
you can look at the success of an organism by how successful it is at propagating it’s genome; that’s survival of the fittest, an animal with good genes survives and breeds and their genes live on in their offspring.
A virus is a genome without a body; they’re genes, and they seek to propagate themselves by making more copies of those genes. The ones that find new ways to infect and copy themselves are the ones that continue to spread. They do so by hijacking the cellular machinery of living cells and rewrite the code of the cell to become a virus factory
Viruses also evolve. The copy system isn’t perfect, it makes mistakes sometimes, each mistake is a novel **mutation**. The mutations that make the viral gene better at spreading go on to have more success, and so the virus changes over time.
not all viruses change at the same rate, viruses like the flu change a lot, have a lot of different flu mutations that are all slightly different, and they continue to change rapidly, so these new versions are able to infect people even fi they had previously had a different version
ones that don’t change much are easier to stop with vaccines, and if we get a very large percent of people vaccinated then that virus no longer can spread among the population
Imagine you had an IKEA instruction manual. It tells you to get some paper, some ink, and 2 staples and make a copy of the manual. It also tells you to stick it in a box and leave the copy on your neighbor’s porch.
Is there a purpose to doing this? No. But there are now two version of it anyway. Is it alive? Still no, but it didn’t need to be. It got in your home somehow and used you to make a second copy which is about to infect your neighbor. Similarly, viruses give instructions to your cells to make copies. There are some safeguards against this, but in general, you just churn out new versions that infect others, repeating the process.
Why we have different effects of viruses very simply boils down to (1) how they get into your house (cell), (2) how they tell you to make copies, and (3) how they stop the cops from busting your illegal IKEA instruction manual production ring.
1. Viruses are dumb, but they can recognize certain things. Covid, for instance, has patterns on it that match up to something called the ACE-2 receptor. This is a pretty common receptor, but there is a lot of it in the nose and lungs (where are most of your symptoms?). This starts a series of steps that results in the replication material getting inside.
2. Once it is inside, the virus has to get your body to make copies. Some viruses (ie: Herpes/HIV) are long term because part of their instruction manual told the previous host to make some machinery that busts open your DNA and inserts the virus. Others are more short-term and simply tell your cells to make a bunch of copies really quickly.
3. One of the most important parts of viruses is how they stop your immune system. Your cells tend to occasionally display what they are currently working on, analogous to a window into the house. Your immune system has a black-list of certain compounds and will straight up burn the house down if you aren’t working on something it approves of. Certain viruses, like influenza, are able to mutate though. While your immune system is looking for the red IKEA catalog, the flu has 1000’s of variations of the catalog. While you are immune to any red IKEA catalog versions, you have to learn that the blue I-KEA catalog is just as bad.
>They’re not living organisms, so what are they?
They’re infectious packets of genetic information.
>What created them; where did they come from?
The same questions can be posed for living creatures, and presumably the same answers will suffice, once we figure out what thos answers are.
>Why do they infect hosts?
Because infecting a host doesn’t require volition or intention, just chemistry.
>Bacterial infections make sense; bacteria use a host’s body to survive and propagate. Viruses aren’t alive, though, so why do they need to infect people at all?
Bacteria are animate matter, living organisms, and viruses are inanimate matter, but made up of the same kinds of organic molecules. Bacteria don’t “need to” do things, though they are autonomous (not self-determining, conscious, but volitional,) they just do them because the molecular chemistry of biology causes them to do those things. All organisms and creatures, with one exception, are the same: biological robots programmed by natural selection, lacking intent or purpose apart from doing whatever it is they do. That one singular and unique exception, of course, is human beings.
>And why do they all affect the body so differently? Why can you only catch some viruses (I.e. chickenpox) once, but you can catch others (Covid, flu) multiple times?
Often it is not the virus itself which makes the difference, but the way our immune systems respond to the presence of the virus replicating.
As for some distinctive difference between infections (or vaccines) that confer lifelong immunity and those that don’t, the particulars are not yet known categorically. But there is reason to believe it is an adaptive trait on the part of our immune system. Being so sensitive to more common virus types that we gain lasting immunity from an infection (or vaccine) might very easily result in an autoimmune disorder, where our immune system is so hyper-vigilant that it ends up getting triggered excessively or even “attacking” our own cells or other molecular components.
>Why do some (HPV, EBV) appear to cause cancers and autoimmune disorders while others don’t?
As with the previous question, it comes down to particulars and details of those specific viruses and the specific immune responses we have to them.
> For as far as we’ve come in medicine, it seems like we don’t understand much at all about viruses, or their longterm implications.
No more so than any other aspect of medicine, but of course it can seem that way for less problematic illnesses. When it comes to medicine, once we know how to deal with an issue, it is easy to believe, often incorrectly, that this means we understand it.
Fun fact to haunt your nightmares: nearly half of all the genes in our DNA may have come from viruses that accidentally got incorporated in our germline at some point or other in our biological past. It is even quite possible that one particular such formerly viral gene, called ARC, which is involved in encapsulating proteins that are used for intracellular mechanisms between the neurons in our brains, might be responsible for resulting in the existence of human consciousness, as it is necessary for neurological processes like memory and self-awareness.
>They’re not living organisms, so what are they?
They’re viruses. That fact that they aren’t alive is why we have an entirely separate category for them that is not connected to living organisms.
>What created them. where did they come from?
We’re not 100% sure but there are a few possibilities. It could be that they emerged from same process that created life (Self-replicating molecules that got more complex), or possibly they emerged from early organisms as bits of DNA or RNA that “escaped” the organisms, or they may have been early cellular organisms themselves that over time lost the ability to reproduce on their own and lost other functions as well.
>Why do they infect hosts? Bacterial infections make sense; bacteria use a host’s body to survive and propagate. Viruses aren’t alive, though, so why do they need to infect people
Because that’s just how their biology works. They bind to specific cells because there are proteins on them that fit into “locks” that our cells use for other things. They don’t have a purpose or a goal. There is no “why.” They don’t “need” to do anything, it just happens because that’s how chemistry works. Just like how if you put a log in a fire, the log will burn. The fire doesn’t set the log on fire because it “wants to,” that’s just the only thing it can do because that’s how chemistry works.
Also, you’ve got bacteria and viruses backwards. Bacteria are living organisms that can reproduce and metabolize energy on their own. With a few exceptions, they don’t need humans or other living organisms at all. Viruses on the other hand cannot reproduce on their own. The only way for a virus to replicate and spread is to infect a living organism
>And why do they all affect the body so differently? Why can you only catch some viruses (I.e. chickenpox) once, but you can catch others (Covid, flu) multiple times? Why do some (HPV, EBV) appear to cause cancers and autoimmune disorders while others don’t?
This is too complex to answer in eli5, but the short of it is that viruses are very different from each other and our immune systems are very complex, so how the two interact can be very in various situations.
>For as far as we’ve come in medicine, it seems like we don’t understand much at all about viruses, or their longterm implications.
Well this is just wrong and I don’t know what basis you have for saying this. Obviously we don’t know everything there is to know about viruses and we’re learning more every day, but that’s true for literally everything. We know just as much about viruses as we do about any other field of medicine, and there are plenty of fields of medicine that we know far *less* about.
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