How do I cure this? I've had it forever.

Did you hand in the cure to save the child?

Yes ... Oooo crap So it's permanent now?

What is crap is that you get it even when it's one of your followers which get bitted, then you are stuck with the icon in the pipboy (far more annoying than the -10 hp) for the rest of the game.

It's the price to pay, for being a hero. You have an incurable status effect that mocks you in your Pip-boy for eternity.