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Nobody wants to think about their dog having worms. Just the sight of the disgusting critters is enough to make you squirm. But unfortunately, worms are a common health risk for dogs. Puppies can even be exposed before they’re born. Part of being a responsible dog owner is keeping your dog healthy and parasite-free. If you understand the risks, symptoms, and treatment options for worms in dogs, you can better protect your dog and your family from infection.

What Are Worms, and How Are They Harmful?

When people talk about worms in dogs, they are referring to certain types of internal dog parasites. Most of these live in the dog’s intestines. In the United States, the most common intestinal worms that dogs can contract are roundworms, hookworms, whipworms, and tapeworms. Heartworms, another type of internal parasitic worm, live in the dog’s heart and lungs, as well as the associated blood vessels.

According to Dr. Jerry Klein, Chief Veterinary Officer for the AKC, dogs with internal parasites won’t live their best lives. “These worms are parasites to their host, meaning that they live in the dog (its host) and benefit by getting nutrients at the host’s expense, thereby denying the dog from thriving to its ultimate healthy state,” he says. “This is especially important and potentially dangerous in newly born and young puppies, but can affect dogs of all ages.”

Miniature American Shepherd puppy laying in the grass chewing on a treat.
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To increase the risk, some of these worms are zoonotic, which means they can pass from animals to humans. Dr. Klein warns that children are especially at risk of contracting parasitic worms because they may play barefoot in sand or dirt infected with feces having worm larvae. They may also accidentally ingest larvae that may be present on the fur or from the saliva of a dog infected with larvae. For protection, Dr. Klein suggests practicing good hygiene. “Use gloves, if possible, when handling your dog’s fecal waste, and always wash your hands thoroughly with soap and warm water. This type of hygiene with handwashing should be stressed to young children as well, as they often put their fingers in their mouths after touching their puppy,” he explains.

Types of Worms and How Dogs Get Them:


Roundworms are quite common in dogs, particularly in puppies. There are two main species of concern – Toxocara canis and Toxascaris leonina. T canis is the more frequently seen species, and it can lead to fatal infections in puppies. Plus, it’s the one that can transfer to people. T leonina is rarer and usually only seen in older dogs.

Both species of roundworms live freely in a dog’s intestines and don’t need an intermediary host, but can pass from dog to dog. An infected pregnant female can pass roundworms directly to her unborn puppies by the larvae that can pass through the placenta. Or, after she gives birth, she can transmit the worms again via the larvae through her milk to her nursing pups.

Dogs can also contract roundworms if they eat or step on worm eggs or larvae. “The worms’ eggs are deposited in the soil via the feces of infected dogs, where the eggs can survive for long periods of time, even in harsh climates,” Dr. Klein explains. “If a dog accidentally sniffs or licks the dirt or grass infected with these eggs, the dog can become infected. Rarely, if ever, the dog can become infected through close contact with larvae in soil and sand if the worm burrows through the skin of the dog’s paws.”

German Shepherd Dog getting its paw checked by the vet.
©V&P Photo Studio -


Hookworms, named for the bent fishhook appearance at their front end, attach to the wall of a dog’s small intestines. There are three species of concern in dogs including Ancylostoma caninum, Ancylostoma braziliense, and Uncinaria stenocephala. The blood-sucking feeding behavior of A caninum can lead to anemia in dogs, which is potentially deadly in puppies. Although hookworms can’t infect humans in the way they infect dogs, these parasites can burrow into a person’s skin and cause itching or more serious complications.

Dogs can pick up hookworms by eating larvae found in the environment, such as infected soil or feces. Or a dog could lick larvae off their paws after walking through a contaminated area. You can even inadvertently bring hookworm eggs into your home on the bottom of your shoes. Along with ingestion, the larvae can also penetrate a dog’s skin. And just as with roundworms, a mother dog can pass the parasites via larvae onto her puppies in her milk.


Trichuris vulpis, or whipworms, are found in a dog’s large intestine and colon where they attach to the intestinal wall. Mild infections usually have no signs, but if your dog has a heavy infestation, you will see problems such as diarrhea, bloody poop, weight loss, and anemia. Whipworms are known for not always showing positive on fecal exams, so if a problem persists, it’s often recommended to repeat a fecal exam in two to three weeks.

Thankfully, dog whipworms don’t transmit to humans. However, you should still practice good sanitation, like cleaning up immediately after your dog’s bathroom breaks because whipworm eggs are shed in an infected dog’s poop. And although they are susceptible to drying out, those eggs can survive in the environment for up to five years under the right conditions.


Unlike roundworms, hookworms, and whipworms, tapeworms have a life cycle that involves an intermediary host. The adult worms live in a dog’s small intestine, but the larvae live in another animal, such as a flea or rat. The most common tapeworm in dogs is Dipylidium caninum which shares its life cycle with fleas. Dogs will eat the fleas while grooming themselves or consuming flea-infested prey, although dogs can be infected with other tapeworm species if they ingest other types of infected animals. Though it rarely occurs, humans can also be infected with dog tapeworms if they accidentally ingest an infected flea.

Mild tapeworm infections might not have any signs, but usually, an infected dog will be unable to digest and absorb their food properly leading to a range of problems. Because you need to control the fleas to control the tapeworm, it’s important to take flea prevention seriously. Dr. Klein advises discussing a good flea preventative program with your veterinarian to ensure you have eliminated fleas from the environment (house, car, etc.) as well as your dog.

AleksandarNakic/Getty Images Plus


Last, but very much not least, are heartworms. These parasites cause heartworm disease which is a preventable yet potentially fatal infection that causes severe complications such as lung disease and heart failure. Like tapeworms, heartworms (Dirofilaria immitis) require an intermediary host, in this case, the mosquito. Mosquitos pick up heartworm larvae from the blood of an infected host when they feed. Then, when they move on to feed on another animal, they transport those larvae into the new host’s bloodstream. The larvae migrate to the tissue of the dog’s heart where they mature into adult worms which can grow up to 12 inches long. It’s extremely rare for humans to get infected with heartworms, and when they do, they usually show no symptoms.

Avoiding mosquitoes is practically impossible, particularly in warm weather. But although mosquitos aren’t a year-round pest across all of North America, heartworm disease has been reported throughout the United States and Canada. However, the U.S. Food & Drug Administration reports that it’s most common along the Gulf and Atlantic coasts of the United States from New Jersey to the Gulf of Mexico, as well as along the Mississippi River and its major tributaries.

Because of the severity of the disease and the long, potentially risky, and expensive treatment, the best approach to heartworms is prevention. That requires administering preventative medication. But be aware, that the preventatives don’t kill adult heartworms and can be dangerous for a dog that’s already infected. That’s why annual testing for heartworm infection, before administering medication, is necessary.

Symptoms of Dogs With Worms:

Depending on the type of worm affecting your dog and the severity of the infection, your dog can exhibit a range of symptoms. It’s important to take these signs seriously, particularly with puppies or dogs with weakened immune systems. Some signs of intestinal worms to watch for include:

  • Weight loss
  • Bloated pot-bellied abdomen
  • Abdominal pain
  • Poor muscle tone
  • Coughing and pneumonia
  • Dry, dull skin and coat
  • Soft poop or diarrhea
  • Blood in the poop (bright red or darker purple)
  • Lethargy
  • Dehydration
  • Anemia and nutritional deficiencies
  • Vomiting
  • Intestinal blockage

Heartworms can present differently as they reside in the heart rather than the digestive system. Watch for weight loss, exercise intolerance, coughing, weak pulse, decreased appetite, and a swollen abdomen. At later, more serious stages of the illness, your dog can exhibit labored breathing, pale gums, and dark-colored urine.

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Diagnosing Worms in Dogs

Most intestinal parasites are diagnosed based on examination of fresh poop from the dog. That means you need to collect a sample. Be careful and wash your hands thoroughly after collection. “You can collect a fecal sample as you would when picking up after your dog using a poop bag, securing it, and then taking it to your veterinarian within 24 hours,” Dr. Klein says. “Also, many veterinarians have plastic fecal collection containers that can be used for obtaining fecal collection.”

Tapeworm segments can sometimes be seen with the naked eye as appearing like segments of rice in the dog’s stool or around their anus. But for all intestinal parasites, your veterinarian will look at the stool under the microscope for worm eggs. And because your dog can be infected without showing any signs, it’s smart to take a sample of your dog’s poop for inspection at every annual vet exam.

Unlike intestinal parasites, heartworms are usually found using a blood test. But other tests, such as an echocardiogram or ultrasound, might be used to examine your dog’s heart. Treatment for heartworm is most successful if it begins early which is why the American Heartworm Society advises annual blood testing for your dog’s well-being.

Treating Worms in Dogs

Because worms are so common in puppies, deworming usually starts when pups are two weeks old and continues every two to three weeks until they have stopped nursing. Worms in dogs are treated using a deworming medication, known as an anthelmintic. Dr. Klein says that your veterinarian will determine which medication is appropriate for that type of parasite, based on the species and the weight at the time of the deworming. Depending on which worm is infecting your dog, you might give the medication once and then repeat it several weeks later, or you might need to give daily doses over a number of days. Finally, the anthelmintic might be in tablet, liquid, or powder form. Although there are over-the-counter treatments for some types of worms, Dr. Klein warns that it’s imperative to discuss any medication with your veterinarian prior to giving it to your dog and read the instructions carefully regarding age, weight, and dosing.

Chihuahua getting a check-up at the vet.
FatCamera/Getty Images Plus

Preventing Worms in Dogs

Prevention is the best course of action for worms in dogs. Especially because dogs can be infected without showing outward signs. Plus, you don’t want worms passed on to you or your family members. Dr. Klein advises getting your dog checked for parasites at least once a year and more often in puppies and dogs with chronic gastrointestinal issues. It’s also important to pick up your dog’s poop regularly and keep your dog’s environment clean as well as to prevent your dog from getting into hazards like dead wildlife or other animals’ feces. Taking these precautions and practicing flea and heartworm prevention will help keep your dog healthy and parasite-free.

This article is intended solely as general guidance, and does not constitute health or other professional advice. Individual situations and applicable laws vary by jurisdiction, and you are encouraged to obtain appropriate advice from qualified professionals in the applicable jurisdictions. We make no representations or warranties concerning any course of action taken by any person following or otherwise using the information offered or provided in this article, including any such information associated with and provided in connection with third-party products, and we will not be liable for any direct, indirect, consequential, special, exemplary or other damages that may result, including but not limited to economic loss, injury, illness or death.
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