Viruses are bundles of DNA or RNA, buttoned up in a protein overcoat. They do nothing for themselves. To reproduce, they exploit the manufacturing capabilities of the more complex cellular structures they gain entry to. All the cells get out of it is an early death, causing disease to the organism of which they were a part. A virus, who for understandable reasons prefers to remain anonymous, explains:
Beneath my protein coat, nucleic acid’s all I’ve got.
I haven’t got a nucleus, cell wall
Or Golgi apparatus. I can do without that lot;
In fact, I don’t need very much at all.
I drift around with all my mates: we’ve dropped out and we’re free,
We hitch-hike on the slightest puff of air,
Sub-microscopic hippies, yeah, it’s how we like to be.
There’s no way you can tell that we are there.
But when we get inside a cell and commandeer its works,
We make our presence felt – it can’t ignore us.
We’ve got this hip philosophy that working’s just for jerks,
So, once inside, we make the cell work for us.
Forced labour? No, it’s nature, man; and this seems clear enough:
God made that cell for viruses to breed in.
It’s not our fault if, when we’re done, the cell will die – that’s tough.
In evolution’s terms, man, we’re succeedin’!
You say we cause disease in you. Hey, man, don’t give me grief!
At least it isn’t me whose end is nigh:
Your cells will let you down, your earthly span of life is brief.
But we are not alive, so cannot die . . .