Roundworms
Roundworms (Toxocara Canis, Toxascaris leonine) are the most common intestinal parasites in dogs. They are especially common in puppies.
Adult roundworms live in the intestinal tracts of their hosts, consuming that host's food. The adult roundworm is round, white to light brown in color, and several inches long. These worms look a lot like spaghetti or angel hair pasta.
Adult dogs get roundworms from ingesting roundworm larvae, usually from contaminated soil or infected prey (such as a mouse or other small mammal).
Puppies are born with roundworms after contracting them from their mother's uterus during gestation. In addition, nursing puppies may ingest roundworm larvae in their mothers' milk.
Once ingested, larvae make their way to the dog's liver. While developing into adult worms, they travel to the lungs, are coughed up by the dog and then swallowed. The adult roundworms live in the dog's intestines. Their eggs are shed in the dog's stool and develop into larvae. The life-cycle is repeated when another host ingests the larvae.
Hookworms
Hookworms (Ancylostoma caninum, Ancylostoma braziliense) are another common type of intestinal parasites affecting dogs and puppies. The hookworm attaches itself to the intestinal mucosa of its host with its sharp teeth and sucks the host's blood for sustenance. Hookworms are significantly smaller than roundworms and not usually seen in stool or vomit.
Adult dogs get hookworms from contact with contaminated soil that contains hookworm larvae. The larvae burrow through the skin or paw pads when a dog is lying on the ground. Or, the dog can ingest the larvae after contact with contaminated soil, often when grooming. As with roundworms, nursing puppies may ingest hookworm larvae in their mothers' milk.
Many hookworm larvae develop into adult worms in the small intestine, but some travel to the lungs, are coughed up by the dog and then swallowed (similar to roundworms). The adult hookworms live and mate in the dog's small intestine. Their eggs are released into the environment via the dog's stool. The hookworm eggs hatch into larvae and live in the soil. The life-cycle is repeated.
Whipworms
Whipworms (Trichuris vulpis) are another common intestinal parasite in dogs. The whipworm lives in the large intestine, where it bites the tissue and embeds its head inside. Like the hookworm, the whipworm sucks the host's blood for sustenance. Whipworms are even smaller than roundworms and rarely seen in the stool. One end of the worm's body is wide while the rest tapers off to a narrow, whip-like head, hence the name "whipworm".
Dogs get whipworms from ingesting whipworm eggs that live in the soil. This typically happens through self-grooming. The whipworm eggs pass through the upper GI tract and hatch into larvae in the small intestine. Next, the larvae move down to the cecum or large intestine where they develop into adult whipworms. Their eggs show up in the dog's stool. Whipworm eggs can lay dormant in the soil for years until consumed by a new host. Then, the life-cycle is repeated.
Tapeworms
Tapeworms (Dipylidium caninum) are intestinal parasites that commonly affect dogs. They are long, flat (tape-like) worms that attach to the small intestine of their host. A tapeworm body is several inches long but consists of multiple segments that grow onto the head and neck of the worm. Each segment has its own reproductive tract.
Dogs get tapeworms from ingesting fleas. Flea larva hatch from eggs and consume surrounding flea dirt and debris. If present, they will also consume tapeworm eggs. The larval fleas develop into adults as the tapeworm eggs develop inside the fleas. Adult fleas jump on a host (usually a dog or cat) and cause the pet to itch. The host chews itself and consumes the adult flea, then the developing tapeworm is released into the host. The young tapeworm attaches to the small intestine and grows into segments.
The end segments are egg sacs which eventually detach and make their way out of the host's rectum into the environment. The tapeworm segment, which resembles a grain of rice or a sesame seed, breaks open and the eggs are released. If flea eggs are also present in the environment, the life cycle is repeated. Therefore, tapeworms are only passed from pet to pet by way of fleas.
There is another type of tapeworm that can affect pets: Taenia. This type of infection is less common and contracted after a pet consumes an intermediate host such as a rabbit or mouse. Fortunately, this type of tapeworm does not tend to have an adverse effect on the host. In addition, the same medication that kills Dipylidium caninum also kills Taenia.
