How To Tell if Your Dog Has Worms: Symptoms, Treatment, and Prevention

Published May 30, 2024
A dog lays in the grass.

CBCK-Christine/iStock / Getty Images Plus via Getty Images

Intestinal parasites, or worms, are common in dogs. You may see them in your dog’s poop but it’s likely you would not even know they have worms, since many types are not visible with the naked eye.

These worms can also cause your dog to get very sick. Certain kinds of worms in dogs can also cause sickness in people.

If you see worms in your dog’s stool or think they could be affected, it’s always best to take your dog to the vet for a checkup.

Bring a fresh stool sample—and even a worm if you’ve seen one—to the vet’s office for analysis.

What Are Worms in Dogs?

Worms in dogs refers to your pet having a parasite, usually in their digestive system, also known as the gastrointestinal tract (GIT). The GIT is made up of the esophagus, stomach, and small and large intestines. Most kinds of worms in dogs live in the intestines. These worms also lay eggs and multiply.

In the United States, roundworms and hookworms are the most common worms seen.

Worms are a very common medical diagnosis made in dogs, especially puppies or dogs that often spend time around other dogs at places such as dog parks, grooming or boarding facilities, or doggy day care. In the United States, roundworms and hookworms are the most common worms seen.

While some dogs can have few to no symptoms when they have worms, the parasites can also cause very serious illness and can even be life-threatening.

Types of Worms in Dogs

While there are many different types of worms in dogs, the most common are:

  • Roundworms: Large roundworms, also known as ascarids, are common in dogs, especially young puppies. The most significant roundworm species, Toxocara canis, affects dogs and can also be passed from animals to people (zoonotic).

    • T. canis is also more common in puppies and can be spread to newborn pups from their mom during pregnancy. Toxascaris leonina is less common and more often seen in older dogs.

  • Hookworms: Many different types of hookworm cause disease in dogs. Ancylostoma caninum is the most common in tropical areas of the world, while A. braziliense infects dogs in the US Southeast and Gulf Coast states.

    • Uncinaria stenocephala causes hookworm infection in dogs in colder areas of the country, particularly near the Canadian border.

  • Tapeworms: Dogs get infected with tapeworms (otherwise known as cestodes) by eating fleas or infected prey animals. Dipylidium caninum is the tapeworm that most often affects dogs and cats.

    • Other kinds of tapeworms occur in dogs that spend more time outdoors and in rural areas.

  • Whipworms: Adult whipworms in dogs attach themselves to the inside of a dog’s large intestine.

    • Once their eggs are passed into the environment, they survive for a very long time in moist conditions.

  • Giardia: Giardia is an intestinal parasite caused by protozoa. Giardia causes symptoms similar to those of intestinal worms in dogs and is also zoonotic.

    • Giardia is the most common intestinal parasitic disease in the United States, according to the CDC, infecting up to 45% of dogs.

  • Heartworm: Heartworms in dogs are spread by an infected mosquito bite. Heartworm affects a dog’s heart and lungs, not the GIT. Heartworm disease is caused by Dirofilaria immitis, and these large worms can be longer than one foot and multiply inside a dog’s heart and lungs for several years.

How Do Dogs Get Worms?

There are a few ways that dogs get worms:

  • Transplacental infections occur in puppies before birth, with the infection passed through the placenta. Roundworms are an example of worms that cross the mother dog’s placenta to infect puppies.

  • Transmammary infection occurs when puppies drink infected milk. Hookworms are commonly ingested in colostrum (the mom’s first batch of milk) by newborn puppies.

  • Transdermal infection comes through the skin, which can occur with hookworms when the parasite enters the dog’s skin from infected soil.

  • Fecal-oral infection occurs when dogs encounter infected stool. Whipworms, hookworms, roundworms, and other parasites spread this way, and it is the most common way that dogs get worms.

  • Contact with infected soil.

  • Eating wild game, small mammals, or fleas with tapeworms.

  • Mosquito bites can spread heartworm disease to dogs.

How Can You Tell if Your Pup Has Worms?

Most often, you can tell if your dog has worms by seeing them in your dog’s feces. Worms can also be seen in the environment, in your dog’s vomit, or on their fur.

Other symptoms of worms in dogs are:

When To Call Your Vet

If you notice that your dog has worms in their stool, are concerned that they have been exposed to worms, or if they are having any symptoms, they should be examined by their veterinarian immediately.

If you see a worm, bring it to your vet’s office for identification to help create your dog’s treatment plan.

While most causes of worms in dogs are not an immediate medical emergency, it’s important to have them treated as soon as possible to avoid more severe symptoms or death.

If you see a worm, bring it to your vet’s office for identification to help create your dog’s treatment plan. Also bring a fresh stool sample for them to check for the presence of worms.

Finding microscopic intestinal worm eggs in the stool is the most common way to diagnose worms in dogs. Heartworms are diagnosed with a blood test, an X-ray of the chest, or an ultrasound of the heart.

How To Prevent Worms in Dogs

Most worms can be prevented in dogs with a variety of methods. Heartworm is prevented with a routine medication, often given orally, or put on the skin once a month, but it can also be given by injection at your vet’s office.

Most heartworm prevention, such as Heartgard Plus®, and flea and tick prevention medications, such as Simparica Trio™, also prevent the most common intestinal worms. Flea prevention, such as Bravecto®, is essential to prevent tapeworms in pets.

Worms can also be prevented by ensuring pregnant dogs are dewormed routinely and are given the right preventatives.

Staying clean and using proper hygiene can prevent intestinal worms in dogs, especially in places where there are many pets, such as dog parks and boarding facilities.

After coming back from these places, washing your pup’s paws with dog shampoo (such as DermAllay™) and water, using a wipe (like MalAcetic®), or even giving them a full bath can help prevent your dog from getting worms.


What Every Pet Owner Should Know About Roundworms & Hookworms. US Centers for Disease Control and Prevention. 2003.


Barri J. Morrison, DVM


Barri J. Morrison, DVM


Barri Morrison was born and raised and currently resides in Ft. Lauderdale, Florida. She went to University of Florida for her...

Help us make PetMD better

Was this article helpful?

Get Instant Vet Help Via Chat or Video. Connect with a Vet. Chewy Health