Roundworms in Dogs

Medically Reviewed by Amy Flowers, DVM on November 09, 2022
4 min read

Roundworms, also known as ascaridsor nematodes, are common parasites that live inside your dog’s intestines. They feed on partly digested food.

Most dogs get them at one time or another. Roundworms are more common in puppies.

Dogs get two main roundworm species: Toxocara canis and Toxascaris leonina. Toxocara canis is worse, and people can get it, too. They’re usually white or light brown and can be up to a few inches long. (They look like spaghetti.)

Some dogs don’t show symptoms, but many do. Here’s what to look for:

  • Potbelly
  • Weakness
  • Diarrhea
  • Vomiting
  • Belly pain
  • Dull coat
  • Weight loss
  • Malnourishment

If your dog has roundworms, you may notice them in poop or vomit. If you see something that looks like rice, it might be a different parasite called a tapeworm.

Roundworms are common. Puppies have the highest risk of getting them and becoming sick.

Your dog may get them from:

  • Their mother. If your puppy’s mother is infected with roundworms, they may pass them before it’s born. Or they may get them by drinking their milk. This can happen even if your puppy’s mother had roundworms in the past. Dormant (“encysted”) roundworm larvae still in their body can get reactivated in pregnancy and passed on to their puppies.
  • The environment. Your pup can get roundworms if they eat roundworm eggs that come from another animal’s poop, or if they eat mice or other small animals that are infected. A puppy can even get roundworms by sniffing another dog's poop.

This is how the cycle continues: After your dog swallows the eggs, they hatch and turn into larvae. The larvae then spread through your dog’s liver and up to their windpipe. Next, the dog coughs and then swallows the larvae. That’s how they get into the dog’s intestine, where they can grow into adult worms. Then they lay their own eggs, which continues the cycle.

If you see signs of roundworms, take your dog to the vet. They’ll look at a sample of your dog’s poop under a microscope to see if there are any roundworm eggs in it.

Many deworming drugs are safe and effective. They include fenbendazole, milbemycin, moxidectin, piperazine, and pyrantel.

Your vet will give your dog one to three doses at first, which will kill the adult worms. Your dog will get follow-up doses to kill any new worms that weren’t fully developed when the first doses were given.

Even after your dog is treated, they should get regular fecal exams. For puppies, that’s two to four times a year. For dogs 1 year or older, it’s one to two times a year.

Roundworms spread easily. One roundworm can produce up to 85,000 eggs a day.

Because they’re so common in puppies, many vets deworm pups when they’re 2 or 3 weeks old just to be safe.

If they have untreated roundworms, puppies are at risk of weakness, weight loss, and stunted growth from malnutrition. But you can do a lot of things to ward them off.

  • Deworm your puppy every few weeks when they’re young. The best time to start is before they’re 3 weeks old. Keep things clean, including the areas where they eat, sleep, and play. Throw away poop properly. Clean up after them in your yard and in the park. Don’t let your dog use a playground or sandbox as a litter box.
  • Keep your dog away from small, wild animals. They can carry roundworms. Consider keeping the dog on a leash or in a fenced yard.
  • Give your dog medication to prevent heartworms. Many have ingredients that also treat and control roundworms.
  • Talk to your doctor about deworming your dog every so often if they’re at high risk of an infection.
  • If your dog is pregnant, ask your vet about deworming to lower the chance that roundworms will be passed to their puppies.


Roundworms can cause significant problems in people. If you have contact with dog poop or soil that’s contaminated, you may get an infection. That can lead to eye, lung, heart, liver, and neurological problems.

Children have a higher risk and may get infected by accidentally eating eggs that are in soil or dog poop. These eggs can hatch into larvae that get encysted in various organs and lead to serious illness.

Pick up after your dogs in yards or other outdoor areas. Keep kids away from areas where dogs have used the bathroom. Be sure they wash their hands regularly.