A woman is about to throw a tennis ball for her dog
A woman is about to throw a tennis ball for her dog

Roundworms: What You Need to Know

Of all the intestinal parasites that affect dogs, roundworms are the most common. In fact, nearly all dogs will be infected with roundworms at some point throughout their lives.1 If left untreated, a roundworm infection can have a serious impact on your dog’s health. Learn how to protect your pets from all types of roundworms.

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A tangle of roundworms

What Are Roundworms?

Roundworms, also known as ascarids or nematodes, are intestinal parasites that can grow to be several inches long. Roundworm infection is very common in young puppies. Roundworms rob your dog of much-needed nutrients, which can cause malnourishment and other health issues.1 The two main roundworm species that affect dogs are Toxocara canis and Toxascaris leonine.

How Do Dogs Get Roundworms?

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There are several ways your dog could become infected by roundworms.2 Learning the different ways your dog may contract roundworms can help you take measures to protect them from infection.


  • In Utero or While Nursing. Infected mothers can pass roundworms to their puppies either in utero or through the mother’s milk while nursing. This is the most common mode of infection and the reason why roundworms are so common in young puppies.2


  • Contaminated Feces. Because infected dogs have contaminated feces, other dogs can contract roundworms by sniffing or licking the infected feces.


  • Self-Grooming. Roundworm eggs can attach themselves to your dog’s fur. If your dog swallows any of the eggs while licking himself, a roundworm infection can develop.


  • Accidental Transport Hosts. Roundworms can also be spread through paratenic hosts, or accidental transport hosts. This happens if a dog eats another animal that has been infected, such as an earthworm, cockroach, bird, or rodent.
A dog practicing self-grooming A dog practicing self-grooming

The Life Cycle of the Roundworm

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The life cycle of a roundworm is complex, but it’s important to understand each stage if you want to protect your dog from infection. It starts when a dog ingests roundworm eggs from a contaminated environment, usually through one of the methods listed above. The roundworm larvae, which hatch from the eggs, soon become active and migrate to the dog’s liver, lungs, and small intestine. The roundworms then mature and begin laying more eggs, which get passed back into the environment via the dog’s feces.2

Two dogs meeting each other Two dogs meeting each other

What Are the Risks of Roundworms in Dogs?

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Roundworms pose the biggest risk to young puppies. This is because the roundworms feed on the nutrients from what the puppy eats, robbing the puppy of much-needed nutrition. As a result, that dog may fail to gain weight or become malnourished. In severe cases, roundworms can even cause intestinal obstruction.

A happy golden retriever gives you a smile A happy golden retriever gives you a smile

What Are the Signs of Roundworms?

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It’s important to note that not all dogs will display signs if they have roundworms—it depends on the severity of the infection. Here are some signs to look out for if you believe your dog may have contracted a roundworm infection:1


  • Diarrhea
  • Vomiting
  • Weight loss
  • Dull coat
  • Potbellied appearance
  • Cough


If your dog is infected, you may also see roundworms in their feces or vomit. The roundworms will be white or light brown in color, and they can grow to be several inches long.1

A puppy rolls on its back and shows you its belly for pets A puppy rolls on its back and shows you its belly for pets

How Are Roundworms Diagnosed?

The only way to diagnose your dog with roundworm infection is to make an appointment with a licensed veterinarian. Your vet will perform a microscopic examination of your dog’s fecal sample. They may perform what’s called a “fecal float,” where the stool sample is mixed with a chemical solution. The solution will make the roundworm eggs rise to the top so they can be examined and properly identified.2

Are Roundworms Dangerous to People?

Dogs aren’t the only ones who are affected by roundworms—humans can become infected, too. If humans encounter contaminated soil or pet feces, they may accidentally ingest the roundworm eggs. Roundworm infection in humans can cause damage to the eyes, lungs, heart, and brain.3


To prevent roundworm infection in people, never allow children to play in areas where animals have passed feces. If you come in direct contact with soil that may be contaminated with animal feces, wash your hands immediately.1

How Are Roundworms Treated?

The only way to get rid of roundworms in your dog is to get a deworming medication from your vet. Because roundworm infection is so common in young puppies, the Companion Animal Parasite Council recommends that all dogs be checked for worms four times within their first year of life. Once they reach adulthood, dogs should be checked at least once a year.2

How Can You Reduce the Risk of Roundworm Exposure?

There are many things pet owners can do to reduce their dog’s risk of contracting roundworms. First, keep your dog’s environment clean by picking up their poop on a regular basis. (Be sure to wear gloves when doing so to protect yourself as well!)

If possible, you should also take measures to keep your dog from eating wild animals or bugs that may be contaminated. You can do this by closely monitoring your dog while outdoors.

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A woman is about to feed her puppy a Heartgard treat | HEARTGARD® Heartworm Protection

Use a Parasite Treatment

Finally, protect your dog consistently with a monthly, broad-spectrum parasite preventive. HEARTGARD Plus chews treat and control roundworms and hookworms as well as prevent heartworm disease. HEARTGARD Plus chews are safe for use in dogs as young as 6 weeks of age.