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Worms in Dogs and Cats: Everything You Need to Know

Worms in dogs or cats can be a startling discovery. See the veterinarian right away to give your pet the best chance of effective treatment and recovery.

worms in dogs
Worms in dogs and cats: An unpleasant experience for everyone involved. Photo: SneakyElbow

We can all agree that worms in dogs and cats — or wriggling in their poop or vomit — ranks pretty low on the list of awesome things about keeping pets.

That’s why your veterinarian asks you to bring in a stool (fecal) sample at least once a year to check for parasites (worms).

Try this on for size: It’s estimated that over 30% of pets are walking around with undiagnosed worms.

Did you know that some of the most dangerous worms are never even seen by the naked eye? They are microscopic. That’s why that all-important stool sample should be checked as part of a complete checkup.

Anyone who’s ever had phone duty in a small animal practice is familiar with the horrified voice on the other end:

  • “My dog just vomited these worms that look like spaghetti.”
  • “There’s little white things around my cat’s anus.”
  • “I see white things in my dog’s poop. I’m freaking out!”
  • “Oh my God, they’re moving!”
  • “She just licked my face and I saw worms yesterday. Does that mean my dog can give me worms?”

I’ll answer these questions and more in this article.

Worms in Dogs and Cats: Terminology

“Worms” — this is actually a common misnomer for gastrointestinal (GI) parasites.

That’s because all GI worms are parasites but not all GI parasites are worms.

There are truly only 6 GI parasites common in the dog and/or cat, the first 4 of which are, well, worms.

The 6 Major GI Parasites of Dogs and Cats

Roundworms are visible to the human eye and look like spaghetti. Photo: Pongsak Tawansaeng


These worms occur in dogs (Toxocara canis) and cats (Toxocara cati) and are super-obvious spaghetti-looking worms that are highly visible to the naked eye. They are also called ascarids.

Your pet might vomit up a big pile of them or pass a pocketful of them in poop. To top off the yuck factor, they are often moving!

Puppies and kittens routinely get these worms from their mothers. Adult dogs and cats get them from infected feces. And dogs can certainly get them from eating poop.

Rarely, roundworms can infect people. Kids are more at risk because they might be playing in sand or soil with infected fecal matter.

Roundworm infections in people can be very serious. The worm can migrate to the eyes, lungs and other organs. Washing hands and cleaning up all pet excrement safeguards against this rare zoonotic disease.

In adult dog tapeworms like this one, segments break off from the “parent.” Photo: CDC’s Division of Parasitic Diseases


Tapeworms (Dipylidium caninum) are little flat worms that you can see in poop, but they’re not as disgusting as roundworms, in my opinion.

To use yet another food analogy, they look like rice — or, for the more discerning palate, orzo.

A tapeworm is a long, flat, off-white worm, but they are segmented. Often, you find only pieces of a tapeworm that look like rice grains in feces or taking up real estate around your pet’s anus, dried up on the fur.

Once in a while, you get to see a long, living tapeworm doing its slinky dance and pulsating out in little segments.

Tapeworms are generally contracted when your dog or cat eats a flea while grooming. The tapeworm eggs are inside the flea but can’t come to full maturity until eaten by a mammal.

Dog hookworms, attached to the intestinal mucosa. Photo: CDC’s Public Health Image Library


Hookworms (Ancylostoma caninum) are very small parasites that infect the small intestine of dogs and sometimes cats.

They attach to the lining of the gut and suck blood, causing mild to severe GI signs.

These parasites also migrate through the lung, but coughing is fairly rare. The majority of damage is typically done in the intestines.

Dogs and cats contract hooks from infected feces in soil.

Hookworms live in the soil and can infect humans by entering the skin, causing a parasitic skin disease called cutaneous larva migrans. This is most common in warmer climates, where people walk on infected soil or beaches with bare feet.

The hookworm does not enter the GI tract of humans.

Whipworms taken from a 6.5-year-old Labrador Retriever. Photo: Okstate Parasit D-lab


Whipworms (Trichuris vulpis) are tiny worms that mainly infect dogs but can also be seen in the cat.

Humans have their own species of whipworm and do not contract dog whipworms except in the rarest circumstance. Dogs and cats contract whips by swallowing whipworm eggs in soil or directly from infected feces.

Whipworms live in the cecum and large intestine of dogs, where they attach to the inner lining and can cause severe damage.

Giardia at 6,000x magnification. Photo: Doc. RNDr. Josef Reischig, CSc.


Giardia is a type of protozoan parasite that attaches to cells in the small intestines of many species (dogs, cats and humans), which leads to maldigestion, malabsorption and diarrhea.

Pet-to-human transmission of giardia is quite rare. People are usually affected after drinking infected water, not from their pet.

Giardia is not easily seen on a regular fecal exam. If it is suspected, we can run a more specialized stool check with centrifugation. A reliable ELISA test is now available as well. Any of these tests require a small amount of fresh stool.

Coccidia from a cat, who was underweight and had diarrhea. Photo: Joel Mills


Coccidia (Isospora) are microscopic intracellular parasites.

We can find immature coccidia (oocyst) microscopically on a fecal exam.

Coccidia can cause young animals and immunocompromised individuals to have diarrhea, sometimes severe. The oocysts can be difficult to eradicate in the environment, particularly in a large kennel, shelter or boarding facility.

Unchecked parasites in dogs and cats can do untold damage to their organs. Photo: Chiemsee2016

“Deworming” Dogs and Cats

People talk about “worming” or “deworming” a pet.

This means giving the pet medication to eradicate parasites in the GI tract.

To deworm correctly, we need to identify the parasite and choose the appropriate “wormer” or medication. This class of drug is properly known as an “anthelmintic” or “antiparasitic.”

You may have heard that puppies and kittens frequently get “dewormed” as part of pediatric care. This is because certain worms can be passed in utero or while nursing.

Parasites can make a puppy or kitty very sick, so many breeders or vets will begin to give a safe dewormer to them starting at 2 weeks of age or so. It’s still highly recommended to have several stool samples checked on young animals.

Symptoms of GI Parasites

GI parasites can have few to no symptoms early on or cause a pet to be gravely ill if left untreated.

Common symptoms are:

  • Diarrhea
  • Vomiting
  • Nausea
  • Loss of appetite
  • Weight loss
  • Gas
  • Abdominal pain
  • Pot-bellied appearance in young animals
  • Foul-smelling poop
  • GI blood loss leading to anemia
  • Damage to the GI tract causing a malabsorption or low protein syndrome (hypoproteinemia)
  • Cough (some stages of parasites migrate through the lungs before hitting their final destination in the gut)
  • Unthrifty appearance

Diagnosing “Worms” in Dogs and Cats

Although some worms in dogs and cats can be identified visually (roundworms and tapeworms), a stool specimen is required to diagnose GI parasites correctly and thoroughly.

Let’s start with the all-important fecal sample — the bag of poop you bring to your vet for the annual physical:

  • A small amount is all you need to bring. Think sample size — no super-sizing of the poop sample, please.
  • You may be asked to scoop the poop at other times too and bring us a small sample, particularly when your pet is having diarrhea.

In a routine stool sample, we float the poop in a solution that allows the parasite eggs to float to the top. Then we mount a drop of the sample on a slide and look for the eggs under a microscope.

We can identify parasites by the shape of their eggs. With the parasite identified, we can prescribe the proper drug and “deworm” the pet. There are other, more esoteric tests we can run on poop if we suspect uncommon parasites or pathogens.

By flotation or centrifugation in a special solution, parasitic eggs, larvae or protozoal cysts in the fecal sample will be separated from the feces.

We then analyze this sediment under the microscope and identify parasites by the shape and character of the eggs or cysts.

Learn more about deworming puppies in this video:

YouTube player

How We Treat Worms in Dogs and Cats

Treatment involves identifying the worms or parasites and using the right medication to get rid of the pests.

There is no true “all-around” dewormer, and a one-time treatment is usually insufficient to get rid of a parasitic infection.

  • The majority of dewormers are oral medications: pills, powders, pastes or liquid.
  • Some topical dewormers are now available and very effective when used correctly. These are applied similar to a flea/tick topical treatment.

Because the life cycle of parasites are very different, it’s important to correctly identify the worms infecting your dogs or cats. This will dictate how many times to treat the pet, at what intervals and what follow-up, if any, should be done in the environment.

Most wormers begin to act immediately:

  • You may actually see worms pass in the poop after the administration of a wormer.
  • Some pets can be transiently sick after worming if they have a very high worm burden (lots of parasites). This is usually self-limiting, and diarrhea often resolves quickly or a diminished appetite returns within a day.

While the adult or final stages of a parasite are often treated with the first dose of a wormer, remember: These parasites have a life cycle. Eggs or larvae may take weeks or months to develop, so most wormers must be given more than once.

Once the parasite is identified, your vet will know at what intervals your pet should be wormed.

Depending on your pet’s lifestyle, health status, routine care and breeding status, most vets recommend a stool sample be analyzed at least once a year. If evidence of parasites is found, the proper wormer is dispensed and given on a schedule.

Treating GI Parasites With Over-the-Counter (OTC) Products

There are safe and effective deworming products that you can buy yourself, such as fenbendazole, a dewormer that used to be available only through a veterinarian.

It’s important, however, to know what parasite you’re treating, how your pet got them, how many times to give the medication and what to do to prevent re-infection.

Fenbendazole, for example, is effective against tapeworms, roundworms, hookworms and whipworms, but dosing should be carefully formulated for the animal’s weight, and the follow-up care is essential.

On the package of one generic fenbendazole product called safe-guard®, for instance, the company claims its product, if administered for 3 consecutive days, is completely effective for up to 6 months. This is misleading.

Fenbendazole is generally not considered to be effective as a one-time treatment:

  • Roundworms and hookworms should be re-treated within a few weeks.
  • Whipworms should be re-treated in several months.
  • And tapeworms? The one-time treatment fenbendazole is effective, but if you don’t get rid of the fleas that most likely caused the tapeworm infection, your pet will probably get tapeworms again. Then you’ll think the medication failed when actually the lack of flea treatment is the cause of the re-infection.

If you buy an OTC wormer, please call your vet to get specific instructions to make sure you’re using the proper product.

Under-dosing or not repeating the dose at the proper interval can lead to your pet always living with a low level of parasites.

Kittens and puppies can get roundworms if their mothers are infected with them. Photo: Pexels

Untreated GI Parasites

Most of our pets who get regular preventive care have a stool sample analyzed annually and are on heartworm preventive are unlikely to develop a case of severe parasitism.

If your dog or cat does have diarrhea or weight loss because of a GI parasite, you will (hopefully) seek veterinary help, and they will be treated promptly. The GI tract will recover quickly, and no permanent damage will be done.

Stray animals or “backyard” dogs and cats who never get any veterinary care can become very sick from worms if they’re never treated. Parasites living in the intestinal tract for months to years can destroy the body’s ability to absorb food and nutrients.

  • Worms in dogs and cats can mean anemia from so much blood loss due to a heavy worm burden.
  • These pets may experience a failure to thrive, become emaciated, lose their appetite and can die of complications related to GI parasites.

Many years ago, when I was just starting as a veterinarian, a man brought in an emaciated hunting dog and said the dog had no energy and had just stopped eating completely. I immediately assumed the dog was very old and must be in kidney or multi-organ failure or cancer. Poor thing.

I said something like, “Boy, you must have had him for a very long time. He looks like he’s having a hard time.”

The man said, “He ’s only 4 years old. He should be in his prime.”

My boss took me aside. “Has this dog ever been to a vet before?”

“I don’t think so,” I said.

“Check for whipworms.”

Sure enough, my country doc was right: The dog was severely infected with whipworms, had lost a lot of blood in the GI tract and was on death’s door from parasites, not from a geriatric disease.

The hunter was willing to treat him. With IV fluids, supportive care and proper deworming, he did OK.

Contrary to what some people think, worms can still occur in dogs or cats who don’t spend a lot of time outside. Photo: howliekat

Additional Worming

Most monthly heartworm medications can treat some of the most common GI worms in dogs and cats.

Occasionally, in the case of a high worm burden or continual re-infection, the once-a-month treatment is not enough, and your vet will dispense additional medication.

Breeding dogs may be wormed on a more regular schedule or before being bred. Puppies and kittens may be wormed every 2 weeks until they reach a certain age, depending on the breeder and the vet.

If your pet is experiencing GI symptoms or diarrhea that doesn’t clear up on its own, bring in a stool sample to be analyzed.

Empiric Deworming

Empiric deworming means you give your pet a safe deworming medication if you suspect intestinal parasites (worms), even if your vet hasn’t found actual evidence of the worms in a stool sample.

The most common reasons to do this are:

  • There is a history of recurrent worms found in a pet or a household.
  • You can’t supply the vet with a reliable stool sample.
  • If a pet has recurrent or intractable diarrhea but multiple stool samples don’t reveal any parasites, it’s perfectly acceptable to give a broad-spectrum wormer to treat worms that cannot be found.

Say a dog or cat has intractable diarrhea, is not responding to diet trials and various medications, and has negative stool samples. In these cases, it’s not only acceptable but recommended to empirically deworm the pet. We suspect worms but can’t find them.

We also suggest deworming puppies, kittens, stray animals and pets who spend a great amount of time outdoors roaming.

People often ask why I couldn’t find worms in their dogs or cats. The simplest answer is that parasites are sneaky pests that don’t show up in all samples. Parasites don’t like:

  • Old poop (rock poop)
  • Frozen poop (poopsicles)
  • Icky poop (watery poop)

Vets must pay attention to the shelf life and quality of your pet’s poop. Some parasites shed intermittently, so your vet might ask you to collect stool samples 3 days in a row.

A Note on Maggots (Not a GI Parasite of Pets)

Some folks see maggots in poop and think they’re coming from inside the pet.

But maggots are found in poop after it has been deposited on the ground or in a trash can.

Maggots top tapeworms on the gross-out scale, in my opinion. People might confuse maggots and tapeworms, but they look very different:

  • They are larger than tapes, and there are usually a lot of them.
  • Also, maggots hatch on top of the poop from fly larvae in hot weather.
  • They are never apparent when your dog poops.

If you ever find maggots on your cat or dog, see your vet right away. Your vet will most likely find a wound or sore or matted fur that’s been colonized by fly eggs — and maggots have developed.

Your pet will need professional wound care and antibiotics.

Keep your pets worm-free and parasite-free by having their vet run a fecal analysis. Photo: Free-Photos

Why Vets Use Stool Samples

We get better treatment results and can give a person guidelines on how to avoid re-infection if we can identify parasites in a stool sample.

Some people don’t want to empirically deworm their pet for the following reasons:

Unnecessary Medication

Some folks just don’t want to give a medicine if they don’t think there is a good reason to do so.

Some people are very holistic and distrust many medications. I often hear, “I don’t want to give that poison to my pet.”

If a dog or cat shows no evidence of GI problems or if the person thinks they have a low exposure to contracting intestinal parasites, such as the lap dog or the cat who goes outside on a limited basis, they just don’t want to give deworming medication on spec.


Good prescription dewormers can be a bit pricey, particularly for a large dog or in the case of multi-pet households.

Insufficient Treatment

We have a higher success rate if we identify the parasite.

There are different dewormers for different parasites, some being less expensive than others.

Parasites also have different life cycles, requiring dewormers be given at different intervals to kill all the stages of the parasite.

Lastly, some worms can be transferred from pet to pet, so better to know what you’re dealing with before going home with a bag full of medicine for each critter.

So the next time your vet asks you to bring in a stool sample, do it! If you left it on the kitchen table, go back and get it. (This is also a good idea before someone else opens it.) If you get home and find the stool sample in your purse, bring it back to the vet to get analyzed.

Worms in dogs or cats can be a serious issue, and a little poop analyzing goes a long way to ensure your pet is in good health.


  • Bowman, Dwight, PhD. Georgis’ Parasitology for Veterinarians, 10th ed. Saunders. 2013.
  • Burke, Anna. “Whipworms in Dogs.” American Kennel Club. June 7, 2017.
  • “Gastrointestinal Parasites in Dogs.” VetFolio.
  • Zajac, Anne et al. Veterinary Clinical Parasitology, 8th ed. Wiley-Blackwell. 2012.
vet-cross60pThis pet health content was written by a veterinarian, Dr. Debora Lichtenberg, VMD. It was last reviewed Dec. 11, 2018.

If you have questions or concerns, call your vet, who is best equipped to ensure the health and well-being of your pet. This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. See additional information.