You need to get him to the vet as soon as possible. Any time a dog's been on the road, they almost assuredly eaten out of garbage cans & trash, etc. Rotten meat goes with the territory, when the dogs hungry enough, and along with the rotten meat comes WORMS.
Get him to the vet for a full check-up.
Thanks for rescuing the little guy. My thoughts are with you. I applaud your willingness to help our fellow K9 pal.
I so agree it was wonderful of you to rescue this poor dog. If he is neutered, he must have belonged to someone or possibly come out of a Shelter or Rescue. I agree you should have him checked out and take a fresh stool sample to the Vet to check for parasites. God only knows how many dogs I've picked up over the years. If you have pets of your own, I suggest you keep them separate from this dog just in case he is ill with something. My guess is he is sleeping due to exhaustion and probably happy to be in a home. Who knows what he has been eating or long it has been since he ate. Assuming his plumbing is working, he will defecate when he needs to or after he starts eating a good food.
Have you checked the local Shelter, newspaper ads, etc to see if anyone is listing a lost dog? If you are in an area where they have Craigslist, you might check their Pets Lost and Found section over the past couple of weeks at least. A lot of people post there now.
Good luck and thanks for the kind heart.
I second all that...
Plus -you can get the vet to check if he's microchipped. If he's a genuine "lost dog" his owners will be over the moon to have him back again. And with a microchip he could be just hours away from home.