Parasites that invade your cat or dog's intestinal tract


Roundworms, whipworms, hookworms, oh my!

Worms such as roundworms, whipworms, and hookworms are very common across the United States. They shed their infective eggs in the pet's stool and contaminate the environment. Some eggs can live in yards or fields for years. The eggs are ingested by another pet and the life cycle is completed when the worm grows into an adult in the intestine of the new host.

Puppies are frequently born with roundworms, and kittens can be infected via the mother’s milk or feces. Adult roundworms are ivory colored, four to six inches long, and round (not flat) in shape. These parasites can cause diarrhea, vomiting, weight loss, and coughing in these young patients. In most cases, the owner will not see the adult roundworms passed in the stool which is why it is important for the veterinarian to do a laboratory test to check for any parasites that might be present. You should bring a fresh stool sample (one produced that day) with you to your pets appointment because we check for parasite eggs with a microscope.

It is important to know that your pet can transmit roundworms to humans and in some cases cause serious disease. In a recent study from the Center for Disease Control (CDC), it was reported that almost 14 percent of all Americans are infected with Toxocara, the most common roundworm found in pets. Although most infected people have no symptoms, the parasite is capable of causing blindness (especially in children) and other systemic illness. The worm is transmitted through contact with the microscopic, highly environmentally resistant egg found in the animal's stool. The eggs have been shown to live in yards, playgrounds, and fields for up to 10 years.


Tapeworms are another very common intestinal parasite of dogs and cats. The transmission of this parasite is different because it needs to be spread by an intermediate host, most commonly a flea, but also mice, rats, or rabbits. The dog or cat eats the intermediate host containing the tapeworm egg, and the tapeworm develops into an adult in the intestine of the host. The intermediate host is necessary for a pet to acquire the parasite; if a pet eats an adult tapeworm or tapeworm segment, it will not cause tapeworms to grow in its intestine.

Adult tapeworms live in the digestive tracts of vertebrates and absorb food predigested by the host. Since the worms absorb the food, they have no need for a digestive tract or a mouth so they are made almost entirely of reproductive structures with a small "head" for attachment. The largest tapeworms can be 20 m or longer.

Symptoms vary widely depending on the species causing the infection but can include nausea, weakness, loss of appetite, abdominal pain, diarrhea, weight loss, malnutrition, seizures, fever, cystic masses or lumps, allergic reactions to the larvae, and bacterial infections.


Another parasite that lives in the intestine is a one-celled organisms called protozoa. Giardia and coccidia two common types of protozoa that can be transmitted directly from an animals to your pet, or transmitted through contaminated water.


In order to diagnose your pet with these parasites your veterinarian must find either the microscopic parasite or its eggs in the stool.

The only parasites that can be seen in the stool with the naked eye are roundworms and tapeworms. Roundworms are ivory colored, round (not flat) in shape, and about four to six inches long. Tapeworms are flat and ivory colored. The adult tapeworm is several feet long, but usually only tapeworm segments are visible that look like sesame seeds or rice.

Your pet could have either of these worms without the adult parasites ever being shed into the stool. If your pet's stool looks normal, it does not mean that your pet is not infected.

Treatment for parasites

There is no one drug that can kill all types of intestinal parasites that exist therefore your veterinarian needs to know what kind of parasite(s) infection is involved to prescribe the correct drug. Some monthly heartworm preventatives will also treat roundworms, hookworms, and whipworms.

If you think your pet is infected with a parasite, call or stop by our West Side Santa Cruz veterinary clinic today, we are here to help. Companion Animal Hospital is conveniently located on Mission Street in Santa Cruz.

If you think your pet is infected with a parasite, contact one of our westside Santa Cruz vets today.
Companion Animal Hospital, a Santa Cruz, CA veterinary office  • 2301 Mission Street • 831.425.1970

Get our app

Quickly schedule your next appointment, share your pet's pictures online and more.

Download App

Get Social

Laser Therapy

Reduce pain and help your pet heal faster with laser therapy right here in Santa Cruz!
Learn more