Intestinal Parasites

General Information

What You Need to Know about Intestinal Parasites (worms) and Your Pet!

Warding off Intestinal Parasites

 Learn more about intestinal parasites in our Pet Care Libraries and the Companion Animal Parasite Council.

Intestinal Parasites


Coccidia are single-celled organisms that infect the intestine of dogs and cats. They are microscopic parasites detectable on routine fecal tests in the same way that worms are, but coccidia are not worms and are not susceptible to most deworming medications. Coccidia infection causes a watery diarrhea that is sometimes bloody; it can be a life-threatening problem, especially to a young or small pet.


Giardia is a single-celled parasite that lives in your dog’s intestine. It infects older dogs but more frequently infects puppies. Dogs become infected when they swallow Giardia that may be present in water or other substances that have been soiled with feces. Many dogs infected with Giardia do not get any disease. Giardiasis, the disease caused by Giardia infection, usually results in diarrhea. Having Giardiasis a long time can cause weight loss and generally poor condition. 


Hookworms are intestinal parasites that live in the digestive system of your dog or cat. The hookworm attaches to the lining of the intestinal wall. Its eggs are ejected into the digestive tract and pass into the environment through your pet’s feces. Hookworms suck blood and therefore cause internal blood loss. They are a serious threat to pets, especially young puppies and kittens. In older animals the blood loss may be more chronic, and the pet may have diarrhea and show weight loss. Learn more about Hookworms in our Pet Care Libraries and the Companion Animal Parasite Council.


Roundworms are the most common of the parasitic worms found inside a dog or cat. Almost all dogs become infected with them at some time in their lives, usually as puppies. Roundworms may be contracted in different ways, making them easy to spread and hard to control. Adult roundworms live in the intestines. Many pets do not have signs of infection; however, with major roundworm infections, your pet may show weight loss, dull hair, and a potbellied appearance. 


Tapeworms are long, flat worms that attach themselves to your dog’s or cat’s intestines. A tapeworm body consists of multiple parts, or segments, each with its own reproductive organs. Tapeworm infections are usually diagnosed by finding segments—which appear as small white worms that may look like grains of rice or seeds—on the rear end of your pet or in your pet’s feces. There are several different species, of tapeworms that can infect your pet. Pets usually are not sick and do not lose weight from the worms. 


Whipworms reside in the cecum, which is inside your dog’s body where the small intestine and large intestine meet. Dogs become infected with whipworms by swallowing infective whipworm eggs in soil or other substances that may contain dog feces. Dogs that are infected with a few whipworms may not have any signs of infection. More severe infections can cause bloody diarrhea. If an infected dog is not treated, then severe whipworm infection can cause serious disease and even death. 

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