I've cured parvo in puppies about 8 times so far with grapefruit seed extract.
I dilute 5 drops in 1 ounce of water and give them a couple dropper fulls of the mixture every hour around the clock until they start to feel better, I then reduce to two hours and so on. I continue the treatment for a couple days.
Once there was two pups from a litter who were sick, my puppy and one another person was purchasing...I tried pursuing him to have me try cure him but he decided to bring it to the vet. 600$ later and a dead puppy, mine was thriving and back on its feet. It worked every time for me!