When a puppy is dewormed, the dog is usually given an oral medication around 2 to 3 weeks after birth; it's common for the deworming to take more than one dose, and worms may be noticeable in the puppy's stool. Puppies must be dewormed to ensure they are healthy and do not pass on any worms to other dogs.
Dogs are susceptible to several different kinds of worms, including heartworms, roundworms and hookworms. Especially in puppies, the most common type of worms live in the intestinal tract, and owners may notice their dogs being lethargic or not gaining weight as they should. A vet visit to check for worms and get the proper treatments usually clears things up quickly.