If your dog is constantly vomiting, has diarrhea, is losing weight, and generally doesn't look well, it may have roundworms. Or maybe you notice that your puppy has a pot-bellied appearance. Roundworms in dogs are a common intestinal parasite that affects all ages and breeds. In this blog post, we will discuss the causes, symptoms, and treatment of roundworm infection in dogs.

What are roundworms in dogs?

Roundworms, or ascarids, are large, elongated, non-segmented nematodes. The most common roundworm in dogs is Toxocara canis. Roundworms in dogs have a typical spaghetti-like appearance and are up to a foot long. Both adult roundworms and larvae can be found in a dog's intestine.

roundworms in dogs

How do dogs become infected with roundworms?

The eggs of the roundworm (Toxocara) are carried in the feces of its definitive host. The larval stages develop inside the egg once it enters the environment. If a definitive host ingests an infected larval egg, the larvae will move through their intestinal wall, liver and then to the lungs. They may be coughed up and swallowed, maturing into adult worms within the small intestine.

Dogs become infected with roundworms by either ingestion of infective eggs or ingestion of hosts that harbour larvae within their tissues. Puppies can also become infected via the transfer through the placenta in the third trimester of gestation and via the mother's milk.

What are the symptoms of roundworms in dogs?

Adult dogs can be asymptomatic whereas puppies are most likely to show symptoms of roundworms. Possible clinical symptoms of roundworms in dogs include:

  • Vomiting and/or diarrhea
  • Weight loss
  • Failure to thrive
  • Poor haircoat
  • Pot-bellied appearance

If you notice any of these symptoms in your dog, it's important to take them to your veterinarian for an examination and fecal testing.

How are roundworms in dogs diagnosed?

Roundworms in dogs are diagnosed through a fecal exam and analysis. Your veterinarian will ask you to collect a fresh stool sample and they will examine it under the microscope for the presence of roundworm eggs.

fecal test for roundworms in dogs

How are roundworms in dogs treated?

The good news is that roundworms in dogs are very treatable. Your veterinarian will prescribe a dewormer medication that will kill the roundworms. For puppies, they may need to be treated more than once. It's also important to clean up any stool that contains roundworm eggs to help prevent the spread of infection. Infected dogs can be treated every 2-3 weeks.

As most monthly flea/tick/worm preventatives prescribed by your veterinarian will also help protect your dog against roundworms, it's important to keep up with their monthly preventative as prescribed.

What are some preventive measures for roundworms in dogs?

In addition to monthly preventatives, there are some other preventive measures you can take to help protect your dog against roundworms.

  • Keep your yard clean of feces and dispose of them properly
  • Avoid letting your dog eat any dead animals
  • Don't let your dog roam free in areas where other dogs defecate
  • Remove and dispose of feces promptly

Since transmission can occur via the placenta and lactation, administering selamectin (Revolution®) to the pregnant or lactating mother can reduce transmission to her puppies.

The current recommendations for treating and preventing puppies from developing roundworms are to deworm them at 2, 4, 6, and 8 weeks of age; Then monthly until they are 6 months of age.

FAQs about roundworm infections in dogs

Can roundworms be transmitted to humans?

Humans can be infected with roundworms. Human infection can occur due to ingestion of infective eggs from a contaminated environment or ingestion of improperly washed fruits and vegetables for example. Roundworm eggs can often be found in contaminated environments such as parks, sandboxes, playgrounds and gardens. There are two main diseases associated with Toxocara spp. (roundworm) infection in people: visceral larva migrans (VLM) and ocular larva migrans (OLM).

What are some of the long-term effects of roundworm infection in dogs?

If roundworms are not treated, they can cause several problems for your dog including:
- Intestinal blockages
- Harm to the liver and other organs
- Anemia
- Death (In severe cases such as puppies with a very heavy roundworm burden)

How can I prevent my dog from getting roundworms?

The best way to prevent your dog from getting roundworms is to have them on monthly heartworm, flea, and tick preventative as prescribed by your veterinarian. In addition, you should have them tested and dewormed as recommended by your veterinarian. You should also practice good hygiene such as washing your hands after handling your dog or their feces and disposing of their feces properly.

Do roundworms in dogs cause coughing?

Roundworms can cause a cough in dogs when they migrate to the lungs as part of their normal life cycle. If your dog is coughing, it's important to take them to your veterinarian for an examination and testing.

What are the risk factors for roundworms in dogs?

Risk factors for roundworm infections in dogs include eating other dogs or animals' feces (coprophagy), eating soil and other earth matter, and off-leash activities.

Are roundworms in dogs contagious?

Roundworms are contagious and can be spread from dog to dog. They can also be transmitted to humans. It's important to practice good hygiene such as washing your hands after handling your dog or their feces and disposing of their feces properly. You should also have your dog on monthly heartworm, flea, and tick preventative as prescribed by your veterinarian. In addition, you should have a routine fecal test performed at your dog's annual check-up visit.

Can a dog still have a roundworm infection even though non are visible in the stool?

Yes, a dog can still have roundworms even if they are not visible in the stool. When the intestinal tract is overloaded and there is nowhere for them to go, roundworms appear in the stool. This is why it's important to have your dog on monthly heartworm, flea, and tick preventative as prescribed by your veterinarian. In addition, you should have a routine fecal test performed at your dog's annual check-up visit.


Roundworms in dogs are a common intestinal parasite that can cause a variety of problems including weight loss, poor hair coat, vomiting and diarrhea. In uncommon circumstances, roundworms can be transmitted to humans, so it's important to practice good hygiene and preventative measures. Monthly heartworm/flea/tick preventatives as prescribed by your veterinarian are the best way to protect your dog (and yourself!) from roundworms.

If you have any questions or concerns, please don't hesitate to reach out to your veterinarian. They are always happy to help!