We all know the common symptoms like high temperature, chills, runny nose, etc, but it’s my understanding that those are the reaction your immune system has to fight off the virus. So what does the virus itself do? As in, what danger, if left unchecked in our bodies, would it pose?
A virus injects its genetic material (eg dna) into a cell, tricking it into making more viruses. Typically the problem is resources being sapped, but some viruses also kill the cell on the way out
I can’t speak to what the flu does in particular, but all viruses actually burrow into your body’s cells and command the cells to stop doing their normal things and start devoting all calories and resources to manufacturing viruses. So the cells can’t do their normal jobs.
Neurons need to send signals, or you can’t think and move. Kidney cells need to filter your blood or you’ll get poisoned. If any major group of cells stops working, it is going to kill you eventually.
Viruses might also incorporate their own DNA into your chromosomes, which can potentially turn normal cells cancerous. They might cause a genetic defect that your future children could inherit. Or even make you sterile.
Some viruses just get into your DNA and do nothing but take up space in your genetic code. Just junk. It makes it take longer for cells to divide. There are two little virus fragments that together take up 30% of the human genome. Just wasting data storage space in our genes with millions of identical copies of the virus DNA.
The virus injects itself into your cells and hijacks their reproductive machinery to copy itself. The virus presents its own genetic material to cellular organelles that produce folding proteins based on genetic blueprints. These foreign proteins form virus copies.
Once the cell becomes stuffed with virus copies it bursts and dies, spreading the virus. Left unchecked, a virus destroys large swaths of whatever tissues in which the virus can reproduce.