Most of these live in the dog’s intestines. In the United States, the most common intestinal worms that dogs can contract are roundworms, hookworms, whipworms, and tapeworms. Heartworms, another type of internal parasitic worm, live in the dog’s heart and lungs, as well as the associated blood vessels.

Intestinal worms can be a serious problem in young puppies. Hookworms can cause anemia and roundworms can lead to poor growth and development. In adult dogs, however, intestinal parasites are only occasionally life-threatening.

Roundworms are extremely common parasites in dogs. Almost all dogs have roundworms at some point in their lives—most often in puppyhood. There are two main species of roundworms affecting dogs: Toxocara canis and Toxascaris leonine. Toxocara canis causes more serious disease and can be transmitted to humans.

Roundworms are the most common worms in dogs, especially puppies, and live freely within the intestinal tract. Humans can also be infected with roundworms, typically by ingesting the eggs from contaminated soil. Hookworms are a parasite that are about 1/2 inch to one inch long and attach to the lining of the small intestines feeding on blood.