Intestinal Parasites

Ever wondered about the types of intestinal parasites your pets pick up? Or why we recommend yearly fecal testing to look for parasites? It is because your pet can pick up parasites fairly easily, and some of them cause severe illness, and/or can be transmitted to people!

Let's explore!


The most common intestinal parasite in puppies and kittens, it is often passed from the mother animal to its offspring while they are in the uteris, via milk ingestion, or through exposure to an infected animal's feces. Also, our pets can pick up this parasite if ingesting wild rodents, such as mice or rats, or from eating their intestines. This parasite has a round, long body, with a small curl at the end of its tail. We often relate it to cooked spaghetti, with the similar size and shape. It lives its life in the intestinal tract, releasing roundworm eggs with the animal's stool to continue the life cycle.

In small numbers, these parasites do not tend to cause any signs or symptoms in our pets. Infested dogs with roundworms are easily found on routine fecal exams. In large numbers of worms, these worms clog up intestines- much like clumps of hair clog up a drainpipe. Animals can develop signs and symptoms such as vomiting or diarrhea, intestinal pain and bloating, inappetance, and lethargy.

Oddly, this parasite can cause major issues with people as well, if animal feces is ingested inadvertently. (Yet another reason to wash your hands after handling pets, and definitely before eating or drinking). This worm can travel to the skin and/or eye of humans and cause damage. This parasite is the major reason why we deworm all puppies and kittens multiple times, and also adult animals monthly.


Our next most common intestinal parasite, mainly because animals most commonly obtain the parasite from eating fleas, or eating wild rodents. When a pet is itchy, they chew at the spot of itch. It is very common for animals with fleas to eat the flea during the itching process! Interesting that fleas can contain tapeworm eggs in their intestinal tract.

Many people have heard about people eating tapeworms in the Victorian era as a method of weight loss. Sounds crazy? Well, tapeworms eat our food in the intestinal tract, instead of our bodies using the nutrients. Much like pets with roundworms in small numbers, we may not see any symptoms with the pet. In larger numbers, we may see issues such as intestinal blockages, lethargy, inappetance, and anemia. Unfortunately, with this parasite, it is more difficult to find on fecal examination. It all has to do with the anatomy of the tapeworm. The body of the tapeworm has segments which break off into the feces of animals. Each segment can contain thousands of eggs, but only when the segment is opened will the eggs be seen. So, if there is no segment present in the feces, or the segment isn't opened- we many not see tapeworm eggs on the test.

If fleas are present, deworming is a good option for these pets, as a precaution. Good news, tapeworms usually don't cause any issues with humans, with one rare exception. Echinococcus is a tapeworm which can cause a cyst disease in the abdomen of humans. There was only one case of an animal in Ontario with this disease last year, none for a few years prior. We hope it continues to stay rare.


So called because they have narrowed tails, making them appear like a whip, these are less common intestinal parasites. They bury themselves in the large intestine of dogs, cats, and other animals, causing watery, bloody diarrhea, and weight loss. These parasites shed eggs in the stool, which become infective after sitting for 10-60 days. Remember to pick up any poop from your backyard often! This can slow to stop the life cycle and infective nature of these parasites to other animals.

With this parasite, since it sheds eggs on and off, there are times when it may not be found in the stool sample, even if the pet has the parasite. Good news, many of our heartworm preventions and broad spectrum deworming medications will also treat this parasite. Also good news, it isn't spread to people.


This one-celled parasite is spread from one animal to another via feces. In many animals, they won't cause any symptoms, but animals who have other health issues or high burdens, they can cause a severe watery diarrhea, dehydration and vomiting. It can be found on a fecal exam, but because if its size, can only been seen with a microscope.

Yes, this parasite can be spread to people via feces- wash your hands after handling your pet, and pick up their poop often to prevent spread.

Giardia (a.k.a. "Traveller's Diarrhea" or "Beaver Fever")

Another one-celled protozoan parasite, giardia is picked up from drinking from fecal contaminated water sources such as puddles, or from exposure to another dog or cat's feces. This parasite is easily spread to humans via ingesting contaminated water, or feces. It causes a watery diarrhea in animals and humans, and severe dehydration. Wash your hands after handling your pet to reduce your risk!

This parasite is often found on routine parasitic testing, though it is also shed into the feces on and off during an infection. Another parasite which necessitates picking up their feces as soon as it has been excreted, multiple baths to prevent re-infection through self-grooming, and multiple treatments.

Those are the most common intestinal parasites in dogs and cats. Now remember, wash your hands after handling your pet, and definitely before eating or drinking; pick up their feces regularly (daily is best); fecal test yearly; and don't forget to deworm your pet!

Dr. Kim Quinn

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South Windsor Animal Hospital

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