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There are many different types of worms that can cause health problems in dogs. Many worms in dogs are intestinal parasites that are found in a dog’s gut, but some worms infect other bodily systems or organs like the heart. 

Worms in dogs may cause mild symptoms, like diarrhea, or more serious symptoms, like blood loss or heart disease. 

If you suspect your dog has worms, fast treatment is necessary to keep her from becoming ill and to prevent the spread of infection. 

Types of Worms in Dogs

Depending upon where you live, the most common types of worms that infect dogs can be either intestinal worms, some of which migrate through multiple tissues before reaching the intestines, or heartworms (a type of filarial worm), which grows inside a dog’s heart.  

Some of the most common worms include:


Roundworms are intestinal worms that live inside a dog’s intestines. They are cylindrical in shape, often coiling up into a circle. Adult roundworms may be several inches long (1). They are very common in puppies. These intestinal parasites often cause symptoms such as diarrhea or vomiting.


Hookworms are small, intestinal worms, measuring about 0.5 to 1 inch in length (2). They live inside the intestines. Hookworms bite onto the inside of your dog’s intestines to suck blood. Because of this, they can cause a dark almost black-colored diarrhea, tiredness, and decreased activity in dogs. They can also cause severe anemia, which can result in death due to blood loss. 


Tapeworms are flat-bodied worms that vary greatly in size, depending upon the species. For instance, adult Echinococcus tapeworms are tiny, at only 1 to 7 millimeters, but the larval form can cause severe disease and death in people. Adult Taenia pisiformis, on the other hand, can reach up to a staggering 200 centimeters (about 8 feet) in length (3). 

Tapeworms attach to the inside of a dog’s intestines and absorb nutrients. It is uncommon for tapeworms to cause your dog to feel ill, but a tapeworm infection will take vital nutrients from her. Large numbers of tapeworms can also cause intestinal blockages.


Whipworms are shaped like a whip, with one end being very thin and one end being much thicker. They are about 1.5 to 3 inches in length (4). Whipworms live in the intestines, specifically the large intestine and cecum. They are relatively common in dogs. 

While light infections may not cause visible signs in dogs, additional signs will likely occur as the infection becomes more severe. Some dogs will experience chronic diarrhea that may have some blood in it. This can drain your dog of energy and cause weight loss (4).


Heartworms are very different from the other worms discussed above. They live in a dog’s blood vessels inside the lungs and the heart. These worms are round-bodied, measuring anywhere from 5-6 inches in length for males and 10-12 inches in length for females when fully grown (5). 

When a dog has heartworms, it can cause additional problems like heart disease, lung disease, or even kidney disease. If a dog becomes infected with heartworms, treatment can be dangerous and cause serious illness when the worms die. Heartworm preventives are essential for preventing heartworm disease.

How Do Dogs Get Roundworms?

mother and puppies

Practically every puppy is born with roundworms. That’s because dormant larvae in the mother’s bodily tissues can reactivate during pregnancy and transfer to her pups through the placenta. 

Adult dogs frequently get roundworms by eating small animals like birds or rodents, or by eating soil or other items contaminated by eggs from other infected dogs. Unlike tapeworm eggs, which are immediately infective when passed, roundworm eggs must mature for a couple of weeks in the environment to become infective.

Once the worm eggs are inside your dog, they hatch into worms and travel through the liver, lungs, and then into the intestines. These adult worms attach themselves to the lining of the intestines, feed on partially-digested food, and lay eggs to be passed out into your dog’s poop. 

Once roundworm eggs are in the environment, they can infect other dogs for years. Roundworm eggs can survive in soil long after the dog poop is gone. It’s hard to spot what areas outside are contaminated, since the eggs are far too small (microscopic, in fact) to be seen with the naked eye. 

How Do Dogs Get Hookworm?

In puppies, infection with hookworms can be life threatening due to a severe loss of blood. the hookworm larvae will pass through the lungs, causing coughing or an infection called pneumonia.

Hookworms most commonly infect dogs when they are puppies through their mother’s milk. Otherwise, dogs get infected with hookworms by eating small animals like rodents, or by eating contaminated soil or dog poop. your dog may get hookworms by walking through or sleeping in a contaminated environment—the worms can penetrate the skin, even the pads on her feet. 

How Do Dogs Get Tapeworms?

closeup of flea

Tapeworms require an intermediate host, such as fleas, rabbits, rodents, livestock, or wildlife, before they can infect your dog. Multiple types of tapeworms can affect dogs.

Fleas are the most common source of Dipylidium caninum tapeworm infections in dogs.  Your dog can become infected if he accidentally eats a flea that’s infected with tapeworm larvae. 

Dipylidium caninum sheds sacks of eggs, or segments, that may look like flat, white worms in dog poop. These tapeworm segments are about the size and appearance of a grain of rice. In addition to seeing these segments in a dog’s stool, many pet parents notice these egg sacks (that look like rice) in the fur underneath the tail or on the back of the legs. 

If your dog enjoys hunting or chasing small animals, such as rabbits and rodents, he could be at risk for contracting Echinococcus or Taenia tapeworm infections. Your dog can become infected after eating a small host carrying tapeworm eggs. 

Even if you do not see the egg sacks on your dog, she may still be infected with tapeworms.

How Do Dogs Get Whipworms?

Bloodhound sniffs ground

Dogs can get whipworms by eating infective eggs from the soil or feces. Even if the feces is no longer present, the worm eggs are hardy and can remain in the environment for years, waiting to infect other dogs. (Your dog can also easily get reinfected.) The eggs of whipworms are too small to be seen by the naked eye.

How Do Dogs Get Heartworm? 

Dogs get heartworm through infected mosquitoes. Over 70 species of mosquitoes can transmit heartworm to dogs (5). 

Once a mosquito bites your dog, little immature heartworms crawl into her skin where she was bitten. These immature worms, known as larvae, slowly make their way into the bloodstream and travel to the heart and lungs. Over time, they become full grown (reaching up to a foot (25 cm) in length), creating inflammation and clogging important blood vessels in the heart and lungs. 

How to Protect Your Dog from Worms

veterinarian exams dog

Protecting your dog from worms by regularly deworming them with a broad-spectrum dewormer is much safer and easier than treating your dog after he has been diagnosed with a worm infection and having to deal with the illness that could accompany that infection.

Give Your Dog Monthly Parasite Protection

To protect against worms in dogs, pet parents should ask their veterinarian about year-round, broad-spectrum parasite protection.

Some dewormers, including Interceptor® Plus (milbemycin oxime/praziquantel), kill roundworms, hookworms, tapeworms and whipworms. It even prevents heartworm disease and can be given to puppies as young as 6 weeks of age. Providing heartworm disease prevention at a young age is critical. 

Monthly flea control can also help protect your dog against flea tapeworm infections by killing fleas. Credelio® (lotilaner) is a small, chewable tablet that not only kills fleas and prevents and treats flea infestations, but also kills four types of ticks for a whole month.

See important safety information below for Interceptor® Plus and Credelio®.

Be sure to visit your veterinary clinic to discuss the right products for your pet. 

Schedule Regular Veterinary Visits

Each year, your dog should be tested for heartworm and intestinal worms during their veterinary appointment. 

Your veterinarian can evaluate your dog’s overall health and check your dog for ticks and fleas. Ticks and fleas need to be controlled by a monthly product—even in winter, as both Brown dog ticks and fleas can live indoors. Other species of ticks are active whenever outdoor temperatures are above freezing. If your veterinarian finds ticks or fleas on your dog, he or she can offer tips on how to best clean your living space.

Keep Your Dog and Home Clean

Other ways to protect against worms include picking up your dog’s poop right away, and making sure dog parks and walking routes are free of dog feces. Dogs can be infected by contaminated environments. The issue remains that infective eggs can live for years, long after the poop is gone.

Don’t allow your dogs in any outdoor environment unaccompanied, as they may snatch and eat questionable things off the ground. Try as you may, you won’t always be able to stop them from doing so, even when they’re on a leash.

Credelio Indications

Credelio kills adult fleas and is indicated for the treatment and prevention of flea infestations, treatment and control of tick infestations (lone star tick, American dog tick, black-legged tick, and brown dog tick) for one month in dogs and puppies 8 weeks and older and 4.4 pounds or greater.

Credelio Important Safety Information

Lotilaner is a member of the isoxazoline class of drugs.  This class has been associated with neurologic adverse reactions including tremors, incoordination, and seizures. Seizures have been reported in dogs receiving this class of drugs, even in dogs without a history of seizures. Use with caution in dogs with a history of seizures or neurologic disorders. The safe use of Credelio in breeding, pregnant or lactating dogs has not been evaluated. The most frequently reported adverse reactions are weight loss, elevated blood urea nitrogen, increased urination, and diarrhea.  For complete safety information, please see Credelio product label or ask your veterinarian.

Interceptor Plus Indications

Interceptor Plus prevents heartworm disease and treats and controls adult roundworm, hookworm, whipworm, and tapeworm infections in dogs and puppies 6 weeks or older and 2 pounds or greater.

Interceptor Plus Important Safety Information

Treatment with fewer than 6 monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. Prior to administration of Interceptor Plus, dogs should be tested for existing heartworm infections. The safety of Interceptor Plus has not been evaluated in dogs used for breeding or in lactating females. The following adverse reactions have been reported in dogs after administration of milbemycin oxime or praziquantel: vomiting, diarrhea, decreased activity, incoordination, weight loss, convulsions, weakness, and salivation. For complete safety information, please see Interceptor Plus product label or ask your veterinarian.

Disclaimer: The author received compensation from Elanco US Inc., the maker of Interceptor Plus and Credelio, for her services in writing this article. 


  1. Dog Owners: Roundworms. Pets & Parasites. Retrieved from: https://www.petsandparasites.org/dog-owners/roundworms/
  2. Hookworms for Dog. CAPC. Retrieved from: https://capcvet.org/guidelines/hookworms/
  3. Conboy, Gary. (2009). Cestodes of Dogs and Cats in North America. The Veterinary clinics of North America. Small animal practice. 39. 1075-90, vi. 10.1016/j.cvsm.2009.06.005. 
  4. Trichuris Vulpis for Dog. CAPC. Retrieved from: https://capcvet.org/guidelines/trichuris-vulpis/
  5. Heartworm for Dog. Retrieved from: https://capcvet.org/guidelines/heartworm/

Credelio and Interceptor are trademarks of Elanco or its affiliates. 

© 2020 Elanco.  PM-US-19-2128

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