When my pup got parvo, it was brutal. Not only on him, but on my heart for him.
I kept him hydrated through IV hydration (ex-girlfriend is a nurse), and kept him with me 24/7 to monitor him through it.
That was 3 years ago, and he's doing very well! No ill effects at all.
It's a virus in the ground that dogs get by ingesting dirt particles. It's something that just happens I suppose.
We'll pray for your pup's speedy recovery.
Keep him hydrated, and he'll be fine.