Overview of Worms

Worms—roundworms, hookworms, tapeworms, whipworms, and heartworms—are parasites that can live inside your dog or cat, causing anemia (low levels of red blood cells), lethargy, poor appetite, and even death.

Pet owners should ask their veterinarians which parasites to watch for and take preventative measures against because worms have various geographical distributions (e.g., heartworm is more common among cats in warmer climates). Medications are commonly used to prevent worm infections.


Roundworm infection (Toxocara species) is transmitted through ingestion of eggs in an infected rodent, infected soil, or milk from an infected mother. The eggs hatch into larvae in the stomach, and the larvae travel to the small intestine where they mature into adults. The adults lay eggs, which pass out of the pet in feces. The worms can also be transmitted from mother to puppies or kittens in utero.

If humans ingest roundworm eggs, the eggs can cause infection. It is important to wash hands after handling dog feces. Children should not be allowed to play on soil where dogs defecate.

Symptoms typically include the following:

  • Bloated belly
  • Blood or mucus in the stool
  • Diarrhea
  • Lethargy
  • Loss of appetite
  • Vomiting

Severe infection can create intestinal obstruction and cause death in puppies and kittens.

Roundworm is diagnosed by examining the feces for the presence of eggs.

Several oral medications are available for the treatment of roundworms. Treatment generally requires more than a single dose.

Pet owners should discuss the options with their veterinarian and ask whether monthly preventative medication (e.g., Sentinel, Heartgard Plus) is necessary.


Hookworms (Ancylostoma) are the most common canine intestinal parasite in the United States, infecting nearly 20% of all dogs. Hookworms attach to a dog's intestinal lining with hook-like teeth.

Hookworm infection is transmitted by ingesting the infective larvae (which usually live in soil) or by the larvae attaching to and burrowing through the dog's skin. Once inside the dog's body, larvae travel to the small intestine, mature, mate, and lay eggs. The eggs pass into the soil through the dog's feces. Hookworm can also be transmitted through a nursing mother's milk.

Since hookworms can penetrate skin tissue, it is possible for people to pick up the larvae when walking barefoot on infected soil. Children should not be allowed to play in areas where dogs defecate.

Symptoms of hookworm infection include the following:

  • Anemia (severe cases)
  • Diarrhea
  • Diminished strength and vitality

The worms feed on the host's blood. Puppies can develop life-threatening anemia from blood loss even before eggs are detectable in the feces.

Hookworm disease is diagnosed by examining the feces for eggs.

Several oral medications are available for the treatment of hookworms and several preventative monthly medications are also available. Pet owners should discuss the options with their veterinarian.

Publication Review By: the Editorial Staff at HealthCommunities.com

Published: 01 Aug 2001

Last Modified: 26 Feb 2015