a virus
Examples
Love is like a virus. It can happen to anybody at any time.
Ignorance is a virus. Once it starts spreading, it can only be cured by reason. For the sake of humanity, we must be that cure.
Language is a virus from outer space.
Only one form of contagion travels faster than a virus. And that's fear.
My big problem with corporate structure is this bizarre sense of loyalty you're supposed to feel -- towards what is basically a virus. It grows or dies, like any virus. And you use it for your own selfish ends.
A virus is not just DNA; a virus is also packaged up, covered over with a series of proteins in a nice, elegant, well-compacted form.