I have a pit Bull who had Parvo when she was 8 months old, she was lethargic and didn't look well at all. Took her to the vet, got her treated and after 4-5 days she was getting back to her old self. She lost a lot of weight though, probably 10-15 lbs.
Depending on the age of your dog, the older it is, the better shot your dog has to pull through. Just give your dog as much love as you can, to keep it's spirits up and let the medicine do it's job. Thats the best advice I can give you. I will tell you, your dog will never have a closer bond with you than the one you build nursing them back to health. It makes you love them so much more. (BTW, she is 5 years old now, and perfectly healthy)
Hope it works out for you guys, just pray and give your dog love!