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Dogs can come into contact with internal parasites at any point in their lives, including before they are born. These parasites—which are often different types of worms—can cause problems once they find their way into your dog’s gastrointestinal (GI) tract. Depending on the parasite, your dog may experience symptoms, but this isn’t always the case. Deworming dogs is a key part of preventative measures as well as treating parasites if your dog has them.

Since dogs of any age are at risk, your veterinarian will recommend a deworming treatment plan, which will include routine testing and treatment. This medication will help eliminate any current parasites as well as prevent your dog from getting parasites in the future.

How Are Worms Transmitted in Dogs?

Puppies can be born with parasites like worms. Typically, a breeder will check the mother for worms, which could be dormant in her system. As hormones are released during pregnancy, Dr. Amy Attas, VMD says it’s possible for worms to be transferred to the puppies. “Parasites can transfer via blood in utero and also through nursing.”

She explains that dogs are ideal carriers of parasites, as they are often in places where parasites thrive. Some dogs eat grass or other things, like poop, that can contain parasites. That increases the chances of pets picking up worms through their mouths. Dogs also tend to investigate with their noses where other animals have defecated, so if other animals have parasites, they can be transmitted that way as well.

Pembroke Welsh Corgi eating grass in the park.
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If another animal’s poop contain parasites, the eggs of these worms can mature inside the affected dog. If both male and female worms are present in your dog’s GI tract, the female worms will lay eggs. As a result, if left untreated, the problem can spread.

Treatment to deworm a puppy usually starts when they are very young, even before they go home with a new owner. Ask your vet when to start giving your puppy a heartworm preventative.

Types of Worms in Dogs

There are a variety of different worm species that can affect dogs, and depending on the type, can cause different issues your dog. The worms that commonly affect dogs are roundworms, hookworms, and whipworms—which veterinarians collectively call “long worms”—as well as tapeworms and heartworm, the disease caused by heartworms.

Long Worms in Dogs

If your dog passes roundworms, hookworms, or whipworms in their poop, Dr. Attas says it can look like a piece of white thread, a skinny spaghetti noodle. While it can be alarming to see long worms alive and moving, it’s not always the case that dogs will shed these worms in their stool. “Oftentimes, people are completely unaware that their pets have parasites,” Dr. Attas explains. “Worms could be living very happily inside a dog’s GI tract.”

If your dog is symptomatic, they may experience vomiting, diarrhea, abdominal pain, lethargy, and weight loss. Hookworms and whipworms can suck blood, too, which may result in your dog becoming anemic.

Tapeworms in Dogs

A dog may swallow an external parasite like a flea, which can be carrying tapeworm eggs. When that happens, tapeworms can pass from the parasite to the dog. Tapeworms can be found in feces or around the dog’s rectum and can look like a little kernel of rice in a dog’s poop.

“They will cause discomfort and an itchy rectal area because the worms are moving around,” Dr. Attas says. “If your dog has had fleas, they should be dewormed for tapeworm.”

Heartworm in Dogs

Heartworms are the most preventable parasite in dogs, and are transmitted by mosquitos. “Heartworms are completely different types of parasites because they reside in the heart and blood vessels, not in the gastrointestinal tract,” says Dr. Jerry Klein, AKC Chief Veterinary Officer.

Signs that your dog may have heartworm include coughing, weakened pulse, and exercise intolerance. Unlike the diagnosis of other worms (which requires fecal analysis), the diagnosis of heartworms requires a blood test. Some dogs may even require an ultrasound or echocardiogram. Without proper treatment, heartworm can lead to heart failure, lung disease, and even death.

Make sure you schedule a visit and talk to your vet about the best product for heartworm prevention in dogs. Some breeds might be sensitive to certain heartworm medications, so that your vet can help you choose the safest options for your dog.

Worm Burden

Aside from the type of worm present, another concern is the “worm burden,” or how many worms are actually inside a dog’s GI tract. Puppies that are not dewormed routinely can develop dull coats and experience stunted growth.

Since worms are competing with the host animal for nutrition, dogs with high numbers of worms, especially puppies, can suffer from malnutrition, Dr. Attas explains. “With excessive worm burden, dogs can get sick and die.”

What to Do if You Think Your Dog Has Worms

If your dog has soft poop, diarrhea, or the poop’s appearance changes, it’s a good idea to make an appointment with your vet. Bring in a fecal sample to check for evidence of parasites. Dr. Attas also recommends having your dog’s stool checked when you take them for their annual physical examination.

Collecting a Fecal Sample from Your Dog

The night before your vet visit, your vet will ask you to collect a fresh stool sample. Dr. Attas recommends using a plastic spoon and a plastic container, which your vet will often provide, for best results. The container can be stored in the fridge overnight.

You might be able to get a fresher sample the day of your visit, but it’s good to have a backup just in case. “If your dog has diarrhea, the same method of scooping with a plastic spoon and getting as much as you can into a plastic container will give us a sample with a sufficient amount of feces,” she says.

saint Bernard dog is pooping in field
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Since these parasites can cause disease in people, it’s critical to take extra care with washing your hands after picking up your dog’s poop. If your dog has diarrhea and it gets on their coat, it’s a good idea to bathe your dog while wearing gloves.

Testing for Worms in Dogs

The vet will examine the fecal sample under a microscope. Once the sample is mixed with a solution, any parasite eggs will float to the top. The use of a special stain makes it easier to see the eggs through a microscopic examination.

“The eggs of different parasites have different appearances so we can actually pinpoint what worms are present without seeing the worm,” Dr. Attas says. Sometimes the test can come back with a false negative. This can happen if the worms aren’t laying eggs at that time. We would call that fecal specimen negative but in fact, there still could be parasites present,” Dr. Attas says. “That’s why we recommend repeat deworming.”

Treatment for Deworming Dogs

For puppies, deworming typically begins when your pet is two weeks old, and continues every two weeks until they’re weaned. The timing depends on which product the vet is using and what the label recommends. Some medications have a weight limit, so a puppy may receive their first dose at closer to three weeks old.

For adult dogs, Dr. Attas says that deworming is recommended when worms are present or when there’s a high index of suspicion that worms are present. “They’re very safe drugs, except if you’re a worm.”

If your dog has abnormal stool and testing comes back negative, your vet might administer a dose of deworming medicine to treat any worms that aren’t showing up on the fecal test. “Fortunately, the readily available prescription medications for deworming kill all of the different types of long worms, and some kill tapeworms as well,” she adds.

Which Deworming Treatments Work Best?

There are many deworming treatments available that are safe and effective for dogs. Oral deworming medication can come in pill, powder, or liquid options. For puppies, your vet might recommend a liquid dewormer. Dr. Attas notes that it’s often much easier to give the exact dose you need for the weight of the puppy through liquid dewormers.

Pills can be cut in half or in quarters, but it’s harder to get the right dosage as your puppy gains a pound or two. Some dogs may feel unwell or experience decreased appetite in response to an oral dewormer, but these possible medication side effects are very rare.

German Shorthaired Pointer dog with bowl indoors
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In addition, there are topical deworming treatments that get absorbed through the skin. Topical dewormers target the worm and likely won’t cause negative side effects for your dog. Some dogs, however, may experience a skin reaction that leads to itchiness and discomfort. If this happens, you can try washing the product off to provide some relief.

“Worms are something we want to get rid of to make sure that puppies and dogs stay healthy,” Dr. Attas says. “It’s an easy problem to fix with conscientious owners and good veterinary care.”

Related article: Dog Diarrhea: Signs, Symptoms, and Treatments
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