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

In this guide, “worms” refers to the broad category of parasites. Note: Interceptor Plus (milbemycin oxime/praziquantel) prevents heartworm disease and treats/controls specific intestinal worms (hookworm, roundworm, whipworm, and tapeworm).

Worms are common parasites 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 cause your dog to get very sick. Certain kinds of worms in dogs can also cause sickness in people.

Recognizing the signs of worms in dogs and getting timely treatment, usually a parasiticide like Interceptor Plus (milbemycin oxime/praziquantel), can help reduce the risk of complications associated with parasite infestations and reduce the spread of worms to other pets.

What Are Worms in Dogs?

Worms in dogs are parasites that typically live in the intestines. They can spread through contaminated soil, feces, fleas, or infected animals. In the United States, roundworms, whipworms, and hookworms are the most common worms seen. Some worms, such as heartworms, can also live in the heart and lungs.

Worms are very common, especially in puppies or dogs who often spend time around other dogs at places such as dog parks, grooming or boarding facilities, or doggy day care. In fact, a study found that about 1 in 5 dogs at off-leash parks had intestinal parasites. Most parks had at least one infected dog.

Some dogs can have few to no symptoms, but worms can also cause serious illness and, in some cases, spread to people.

Types of Worms in Dogs

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

Roundworms

Large roundworms, also known as ascarids, are common in dogs, especially young puppies, and live inside the digestive tract. The most significant roundworm species, Toxocara canis, can also be passed from animals to people (zoonotic).

Hookworms

Hookworms are intestinal worms that get their name from their hooklike mouths. They attach to the small intestine and feed on blood, which can cause anemia. Dogs can get them several ways, including from their mother’s milk and contact with contaminated soil.

Whipworms

Adult whipworms in dogs attach themselves to the inside of a dog’s large intestine. They spread when dogs ingest eggs from contaminated soil or feces.

Tapeworms

Tapeworms (otherwise known as cestodes) are another type of intestinal worm. Dogs get infected with tapeworm by eating fleas or infected prey animals. Dipylidium caninum is the tapeworm that most often affects dogs and cats.

Giardia

Giardia is not a worm but a microscopic protozoan parasite that infects the small intestine. Giardia causes symptoms similar to those of intestinal worms in dogs and spreads when dogs ingest the protozoa from contaminated environments. It can also spread to people.

Heartworm

Heartworms in dogs are spread by an infected mosquito bite. Heartworms affect a dog’s heart and lungs, not the gastrointestinal tract. 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?

Dogs can get worms in several common ways, depending on the type of parasite:

• Swallowing worm eggs found in the environment (most common)
• From their mother
• Through the skin
• Eating infected animals or fleas
• From mosquito bites

This chart explains how the worms spread and which worms spread that way:

How Can You Tell if Your Dog 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.

Symptoms of worms in dogs are:

• Worms in dog poop or vomit
• Diarrhea
• Weight loss
• Muscle wasting, especially in puppies
• Blood in the stool (fresh red blood or black digested blood)
• Weakness
• Vomiting
• Change in appetite
• Lethargy
• Inflammation (swelling) of the rectum/anus
• Worms found around the rectum
• Scooting their bottom on the ground
• Slower growth rates in puppies
• Pot-bellied appearance or swollen abdomen
• Coughing
• Pneumonia
• Anemia
• Exercise intolerance
• Intestinal blockage

When To Call Your Vet

Contact your veterinarian as soon as possible if you:

• See worms in your dog’s stool
• Notice symptoms
• Think your dog may have been exposed to worms

While most worm infections aren’t emergencies, prompt treatment helps avoid more serious illness.

If you find a worm, bring it—and a fresh stool sample—to your vet to help confirm the diagnosis and guide treatment.

How Do Vets Diagnose Dog Worms?

Finding microscopic intestinal worm eggs in the stool is the most common way to diagnose worms in dogs. Because different worms need different treatments, veterinarians will often test the dog’s stool first to identify the specific worm type.

Heartworms are most commonly diagnosed with a blood test, but sometimes with an X-ray of the chest or an ultrasound of the heart.

Treating Worms in Dogs

Worms in dogs can be treated with deworming medications prescribed by a veterinarian. These medicines kill or paralyze worms so your dog can pass them safely in their stool.

Your vet may use:

• Oral medications (chews, tablets, or liquids)
• Topical treatments on the skin
• Injections (less common)

For example, Interceptor Plus is a monthly chew that protects dogs and puppies age 6 weeks and older against all five major worms*, including tapeworms. It kills and controls hookworms, roundworms, whipworms, and tapeworms. Plus, it prevents heartworm disease.

Many infections require multiple doses of deworming medication to fully eliminate immature stages of the parasite, so it’s important to complete the full treatment as directed.

Your veterinarian may also recommend monthly parasite protection and cleaning your dog’s environment to help minimize worms from causing reinfection.

Most intestinal worm infections resolve quickly with proper treatment, although some parasites, such as heartworms, require more complex and prolonged therapy. Always follow your veterinarian’s guidance for safe and effective care.

How To Help Protect Against Worms in Dogs

Worms in dogs can be prevented with monthly parasite protection and good hygiene habits, especially in places where dogs gather.

Use Monthly Parasite Protection

Some deworming medications like Interceptor Plus can be given monthly to help protect against intestinal worms and prevent heartworms, though which worms will vary by product.

Many prescription flea and tick medications also prevent heartworm disease and treat and control common intestinal worms, though again exactly which worms will vary by product. Credelio Quattro/Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, and pyrantel chewable tablets), for example, is a chewable tablet for dogs that covers seven types of parasites*: fleas, ticks, heartworm disease, roundworms, hookworms, tapeworms, and New World screwworm larvae infestations.

Practice Good Hygiene

Staying clean and using proper hygiene can help as well, especially in places where there are many pets, such as dog parks and boarding facilities. 

• Avoid contaminated areas where possible. This includes areas with visible dog feces or where many dogs frequently go to the bathroom.
• Use extra caution in shared dog spaces. After coming back from areas where dogs congregate, washing your pup’s paws with dog shampoo and water, using a wipe, or even giving them a full bath can help prevent your dog from getting worms. 

• Clean up your dog’s stool right away. Worms spread through infected feces, which can contaminate soil and infect other dogs.