Roundworms are one of the most common intestinal worms in puppies. The main species, Toxocara canis, passes from a mother dog to her puppies before birth and through her milk, so many puppies are infected from birth, which is why puppies are dewormed from 2 weeks of age.1,2 Adult roundworms are long, pale worms several inches in length that can be vomited or passed in the stool.2 Roundworms are easy to treat and prevent, and they matter for families too, because the eggs can infect people.3,1 This guide covers how dogs get roundworms, the signs, treatment, the deworming schedule for puppies and how to protect your family.
See a vet promptly if your puppy:
- Has a pot belly, poor growth or a dull coat2,4
- Is vomiting or passing worms, or has diarrhea2,4
- Is coughing or not eating well4
Large numbers of roundworms can cause life-threatening problems in puppies, so a puppy that is vomiting repeatedly, has a swollen, painful belly or seems weak needs urgent care.4
What the Research Shows
- Born with them. Some studies show virtually all puppies are born infected, and more than 30% of US dogs under 6 months old shed roundworm eggs.1
- Huge egg output. A single adult female roundworm can lay up to 85,000 eggs a day.1
- Eggs last for years. Eggs need 2 to 4 weeks in the soil to become infective and can then remain infective for years.1
- A risk to people. About 5.1% of people in the US aged 6 and older have antibodies to Toxocara, according to national survey data.5
- Eye damage in children. In one year, US eye doctors reported 68 new cases of eye infection from roundworm larvae; the median age was 8.5, and most patients with data had some vision loss.6
What Are Roundworms?
Dog roundworms (ascarids) live in the small intestine. Toxocara canis adults are cream-colored and 10 to 15 cm (4 to 6 inches) long; Toxascaris leonina is a less common species.2,1 In puppies, larvae travel through the liver and lungs before settling in the gut, which is why young puppies can cough.1,4,2 In adult dogs, many larvae instead lie dormant in the tissues and can reactivate during pregnancy to infect the puppies.1,2
How Do Dogs Get Roundworms?
Signs of Roundworms in Dogs
- A pot-bellied appearance in puppies2,4
- Poor growth and a dull coat2,4
- Vomiting or diarrhea, sometimes with whole, long, pale worms in the stool or vomit2,4
- Coughing in young puppies4
Adult dogs often have no signs at all.2
Treatment and Deworming Schedule
Roundworms are diagnosed with a stool test or by seeing the worms, and treated with a dewormer from your vet. Several drug types work, but many kill only adult worms, so doses are repeated to catch worms that mature later.2 The Companion Animal Parasite Council recommends deworming puppies at 2, 4, 6 and 8 weeks of age, treating the nursing mother at the same time, and then starting a monthly preventive that also covers roundworms.1 Stool tests are recommended at least four times in the first year and at least twice a year for adults.7
Because larvae can lie dormant in the mother's tissues, deworming a pregnant dog doesn't always stop puppies being infected; your vet can advise on a plan for breeding dogs.1,2
How to Prevent Roundworms
Can Humans Get Roundworms From Dogs?
Yes. People can be infected by swallowing roundworm eggs from soil or unwashed hands; it doesn't spread from person to person.3 Most infected people have no symptoms, but larvae can migrate through the body or into the eye, where they can cause vision loss, usually in one eye.3,6 Young children who play in or eat dirt are most at risk.3,1 Regular deworming, picking up feces and hand washing are the best protection.
See worms in dogs and hookworms in dogs.
Frequently Asked Questions
What do roundworms look like in dog poop?
Long, pale, cream-colored round worms, usually 4 to 6 inches long.
How do puppies get roundworms?
Mostly from their mother, before birth or through her milk. They can also swallow eggs from the environment.
Can I see roundworms in my dog's vomit?
Yes, puppies sometimes vomit whole roundworms. See your vet for deworming.
How long does it take to get rid of roundworms?
Treatment kills adult worms quickly, but repeat doses are needed over several weeks to catch worms that mature later.
Can humans get roundworms from dogs?
Yes, by swallowing eggs from contaminated soil. Children are most at risk, and the eyes can be affected.
How long do roundworm eggs survive in the yard?
They can stay infective in soil for years, so picking up feces promptly matters.
Do adult dogs get roundworms?
Yes, though they often have no signs. A monthly preventive and regular stool tests protect them.
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Sources and further reading
This article was rewritten and fact-checked on October 16, 2026 against current veterinary references and specialist guidelines:
- Companion Animal Parasite Council. Ascarid (Toxocara canis, Toxascaris leonina) guideline. CAPC.
- Merck Veterinary Manual. Roundworms in small animals.
- Centers for Disease Control and Prevention. About toxocariasis. CDC, 2024.
- Weir M, Llera R, Panning A, Ward E. Roundworm infection in dogs. VCA Animal Hospitals, 2025.
- Farmer A, Beltran T, Choi YS. Prevalence of Toxocara species infection in the U.S.: results from the National Health and Nutrition Examination Survey, 2011–2014. PLoS Neglected Tropical Diseases, 2017.
- Centers for Disease Control and Prevention. Ocular toxocariasis: United States, 2009–2010. MMWR, 2011.
- Companion Animal Parasite Council. General guidelines for dogs and cats. CAPC.
About this article
Last updated : rewritten and expanded using Companion Animal Parasite Council guidelines, CDC, national survey data, the Merck Veterinary Manual and VCA.
This page is for general information and is not a substitute for an exam by your veterinarian.
