Carson is still at the vet today, but he's doing much better. The vet doesn't know for sure what it is--he could run a test for Parvo, but the treatment (IV, antibiotic) would be the same regardless of what it is. He has some of the symptoms except no blood in the diarrhea and no fever. Anyway, he was barking today and whining to come home with me so I feel much better about things this evening than I did yesterday morning! Thanks so much for your prayers and concerns.