How many days does it take the parvo virus to run its course?

Your dog will not be cured without proper medical treatment. It's not like having a cold.

Parvo is a really tough one.
On average only about 50% of puppies survive the virus and that is WITH vet treatment. It's an almost guaranteed death without a vet.

Recovery varies between individual dogs, some take a few weeks, others a few months to fully recover.

Keeping up the fluids is the most important thing to do, you vet either will (or already has) given fluids under the skin as well as put the dog on an IV drip.

You need to make sure the living environment is also cleaned. Bleach is your best tool. You really should throw out all bedding he uses, toys, dishes, any shoes that have come in contact with the feces or urine. Your yard will harbor the virus for a long time, making any new or visiting animals susceptible to it. It's rare that once they get it, they will get it again, but it has been known to happen. Especially the way the virus is mutating.

How old is your dog? Did it get any of the vaccines, and have you sought out medical treatment?

The course parvo runs is getting sick to death.

The pup needs to see a vet if it hasn't already. Parvo is a puppy killer. These little guys can get parvo, even after their series shots have been completed.

This issue is not worth waiting around for an answer on here.. please go to the vet ASAP.