Regardless of where you acquired your little bundle of fur from, he or she could very likely have worms. Many pups have worms as there are a number of ways they can get them. They can get them from the mother while still nursing, from eating rodents, from fleas, from mosquitoes (heart worm) and from other animals. Some worms cause pups (and other animals with worms) to have a "pot belly" appearance, however some worms, like tapeworm, cause them to appear skinny. Pups may cough up worms and you may see them in their poop.
A few other indicators of worms may be pale mucus membranes like the soft, moist, normally pink skin around the eye and the gums, may look very pale pink or even white in severe cases. Eyes may appear droopy and your pup may even lack energy. This is because there are so many worms they cause the pup to become anemic, meaning there isn't enough blood cells in the body. Some intestinal worms actually feed on blood. Your pup may actually eat more food when infested with tapeworm and never gain any weight. Tapeworm steals nutrients from the system as it stays attached to the intestinal wall. You may also see what looks like grains of rice on the back end of your dog, which actually are part of the worms. However, not all worms are in the intestine. Heart worms are located in the heart as indicated by the name. You may notice your dog lacks energy or coughs after exercise, this is because the worms are in the chambers of the heart and it is hard on the heart to pump blood through with a large population of worms clogging the openings.A few other indicators may be diarrhea, scooting their rump on the floor, sometimes even licking their rump excessivly, and vomiting.
There are also many ways a vet can diagnose if your puppy has worms. Fecal tests are done to detect intestinal worms by using a sample of your pup's poop. However, these sometimes don't show the ova (worm eggs) because they may not be constantly shedding them, but are fairly accurate for most species of worm. For heart worm you must either have a vet do a filter test or a "snap" test, and will require a blood sample.You'll want to get your pup checked for intestinal worms and, if old enough, a heart worm test. Heart worm is less common in pups and takes weeks to actually show up on a test. After he appears clean of these, you can start your pup on Heartgaurd plus which deworms for a few types of worm and makes sure your pup doesn't get heart worm. So talk to your vet and get your pup checked out as soon as you get him so he can be as healthy as he can be.