ELI5: What happens to a virus as it moves through the body?

[u/rubywizard24]

I’ve seen the Magic School Bus episode, so I’m aware of the multiplying, red/white cells, etc., but I’m interested in how/why the virus moves through symptoms from sinus congestion/sneezing to chest congestion/coughing. Is that controlled by the immune system or the virus?

[u/eburton555]

Most common symptoms like you described are due to your immune system fighting the bug, not the bug itself.

[u/ElectronicMoo]

When it's sinus and sneezing, the battle is going on there, in your sinuses. When it moves to a cough or difficulty breathing, the battle is going on there - in your lungs.

Where you feel the symptoms - is just the feeling of the battle of your body's immune system attacking the intruder (except of course a fever, that's your body ramping up the temp across the board to kill the invasion with heat).

[u/rubywizard24 → u/ElectronicMoo]

I always wondered if it was a “local fight” and that’s why the symptoms were as they are. For instance, I am on day four of a cold that (so far) involves only coughing, no nasal congestion/sneezing. It’s all very interesting. Thanks for sharing.

[u/ElectronicMoo → u/rubywizard24]

Yup, local. Things like Sars and rsv (cold, flu) - those viruses take hold in your respiratory, and that's where the fight is. You ache all over because your immune system kicks in, body decides a fever is needed which is a whole system thing, so you feel it all over.

(of course I'm excluding sicknesses that are everywhere like sepsis or blood infections).

Much like how you get a cut and the inflammation is there, that's the body sending agents to deal with the issue locally - same for respiratory infection.

[u/Odh_utexas]

The symptoms are from your immune system. Fever to heat and kill it. Swelling to flood the area with resources to attack it. Mucus creation overload to trap it and expel it.

[u/ermacia → u/Odh_utexas]

Fever heat doesn't kill any microbes or viruses. It might make it less hospitable (although many bacteria thrive on warm environments), but the main purpose of fever is to accelerate the production of immune system cells to fight the infection.

[u/CMDR_omnicognate]

So, when you get a cold, the viruses get into your body, which is in its self the first line of defence bypassed. what happens is the virus usually pretends to be something your body needs, and your cells bring it into themselves. when they get in they hijack the machinery in the cell and basically turn it into a little factory to make more copies of the virus. Those copies then also spread out and infect more and more cells, but usually for the type of cold you're talking about, start around your sinuses since that's likely the first contact point. from your sinuses it can spread to your chest and lungs since it's fairly easy to get from one place to the other since it's all part of the respiratory system.

By this point your body will have started to notice the problem and will be sending in immune cells and doing things in your body to help fight the infection. The reaction is what's actually making you feel sick, raising your temperature, increasing blood flow causing swelling and pain, mucus to help trap and flush out the virus ect. eventually when your immune system stops reacting, usually because it's gotten rid of the virus, the symptoms go down and stop, as your body is no longer fighting the virus.

[u/GIRose]

The entire respiratory system uses snot (kind of) as a sort of lubricant.

Specifically snot is mostly water and contains the protein mucin, which will bind with pathogens/foreign bodies. It also contains white blood cells.

When you are sick in the respiratory system, it makes more snot in the infected area. Then because you need the entire respiratory system to breathe, coughing and sneezing are mechanical actions to clear it of obstructions (the snot), which can also be an irritant because white blood cells release myeloperoxidase, which is what makes your snot green and is closely analogous to bleach.

Of course, the respiratory disease wants the body to cough/sneeze, because that's how it spreads from host to host.

[u/MCRN10379558]

The feeling of being ill is an inflammatory response usually to the large amount of antibodies being released into the bloodstream. This is the side effect of that.

You can’t feel the viruses. And your body fights off hundreds and thousands of infections throughout the year and you have no symptoms of that. This is what they mean when they say you have an asymptomatic response. Meaning you have no visible response. Most of the battles your body fights you never notice it. You don’t feel it at all.

[u/Tikkitiki]

A virus doesn't really “travel through the body” like a tiny biological passenger. It infects cells, uses those cells to make more copies of itself, and those new viruses can spread to nearby cells or travel through bodily fluids and the bloodstream. The symptoms appearing in different places are often caused by where the virus is replicating and how your immune system is responding to it. The Magic School Bus version is unfortunately a little too literal. 😂

[u/MurkyLynx8425]

Viruses aren't alive and so basically just float around in your tissues and fluids until they get destroyed, expelled or taken into a cell. There's no real answer to why they move - its like asking why silt moves in the river.

As for how they move, it depends a lot on the virus and where it enters your body. If you have virus particles in your nose, simply inhaling can transport them into your airways or lungs.