Is parvovirus less severe if there is no blood in the vomit or stool?

I have a 16 week old french mastiff pup, that has the parvovirus. We took him in to the vet on Thursday and she put him on IV that day. He still gets up sometimes when we visit him, and it is already Sunday. However he seems very depressed. There has never been any blood in his vomit or stool, does this mean that his case of parvovirus is less severe? He only eats when forced, has not thrown up in over a day, and approaches his food and water as if he is thinking about it, but only to turn away. He seems quite frail and lost quite a bit of weight because of not eating.