Gastrointestinal Parasites in Dogs and Cats

By Miguel E. Cordova, DVM

Gastrointestinal (GI) parasites include any parasites that live in the stomach or intestines of a host. A variety of GI parasites affect dogs and cats. They range from roundworms and tapeworms, which are visible with the naked eye, to microscopic organisms like coccidia and Giardia. Regardless of their size, GI parasites can cause serious illness and sometimes even death in pets. Some parasites are zoonotic, which means humans can become infected. The following are the most common GI parasites in pets:

Roundworms: Roundworms are visible with the naked eye and resemble small pieces of spaghetti. 

Hookworms: These worms attach to the intestinal wall and suck blood and other nutrients from their hosts. Hookworms can cause severe blood loss and diarrhea in infected pets. 

Tapeworms: Tapeworms are long, flat worms that are actually made up of numerous segments; each segment contains tapeworm eggs. 

Giardia: Giardia organisms are single-celled parasites that live in the intestines. Fecal-contaminated water, food, or soil can be sources of infection. 

Coccidia: Coccidia are microscopic GI parasites. They can cause severe diarrhea in some infected pets. 

Whipworms: Whipworms live in the large intestines of dogs and shed eggs into the environment. Female whipworms can produce over 2000 eggs daily, and environmental contamination can persist for years. 

How Do Pets Become Infected With Gastrointestinal Parasites?

In most cases, eggs or infective stages of GI parasites are shed in the host’s fecal material. Once parasites are in the environment, other pets can be exposed through direct contact with feces or exposure to soil, water, or plants that have been contaminated with feces. Some GI parasites can remain in the environment for months to years.

Tapeworms are slightly different in that they can be transmitted by fleas. The immature stage of the tapeworm lives inside the flea. When a pet grooms a flea off of its hair, it eats the flea (and the tapeworm). The tapeworm then hatches inside the pet and continues its life cycle.

What Are the Clinical Signs of Gastrointestinal Parasites? 

Diarrhea, vomiting, and weight loss can be among the clinical signs of GI parasite infection. However, many infected pets don’t show any clinical signs at all. The best way to tell if your pet is infected is to have him or her tested for parasites. 

What Is Deworming?

Deworming involves administering (or in some cases, applying) medication to treat and control infections with GI parasites. Because puppies and kittens are commonly infected with GI parasites, many veterinarians routinely deworm these young patients several times. Fecal testing can detect GI parasites in most cases, but parasites are not detectable all the time. Even if testing does not confirm parasites, your veterinarian may recommend deworming as a precaution. This is not harmful to your pet. 

Deworming medications come in a variety of formulations, including pills, chewable tablets, topical spot-on products that are applied to the skin between the shoulder blades, and liquid medications given by mouth. Your veterinarian can recommend the most appropriate deworming medications for your pet.

  • Animal Health Center @ Weston is “The Gentle Practice You Can Rely On”. Dr. Miguel E. Cordova and his staff are committed to caring for your precious pets. The practice is located at 2701 Executive Park Drive, Suite 1. For more information or to schedule an appointment, contact 954-385-8389 or