roundworms in dogs and cats: signs, spread, and treatment

Roundworms are among the most common intestinal worms in dogs and cats. They look like pale, round strands of spaghetti and may show up in your pet’s stool or vomit. Finding worms can be upsetting, but it’s a common and treatable problem.

Pets can get roundworms by swallowing microscopic eggs from the environment, eating infected prey, or, in some cases, becoming infected through their mother. Puppies and kittens are especially likely to have roundworms, which is why they’re routinely dewormed on a schedule, even when a test hasn’t confirmed an infection.

Roundworms are usually diagnosed with a fecal test and treated with a veterinarian-directed dewormer. Because roundworms can also infect people, prompt stool cleanup and handwashing are important.

If you’ve seen something that looks like spaghetti in your pet’s poop or vomit, save a sample and book an exam with your Banfield veterinarian. They can help identify what you’re seeing, recommend testing, and determine whether your pet needs deworming. Get a pet parasite check

What do roundworms look like?

Roundworms appear pale white or light tan, round in cross-section rather than flat, and can reach up to about 6 inches long. Roundworms in cats tend to run smaller than those in dogs. When freshly passed, they may be curled up or even still moving. They can turn up in vomit just as easily as in stool.

It helps to know what roundworms aren't. Tapeworm segments look completely different: flat, small, and shaped like grains of rice rather than long strands. See our tapeworm guide for a side-by-side comparison

Many infections are found on a fecal test without a single visible worm, since the eggs themselves are microscopic. Not seeing anything unusual doesn't rule out roundworms.

What do roundworms look like?

Roundworms appear pale white or light tan, round in cross-section rather than flat, and can reach up to about 6 inches long.

Roundworms in cats tend to run smaller than those in dogs. When freshly passed, they may be curled up or even still moving.

They can turn up in vomit just as easily as in stool.

It helps to know what roundworms aren't. Tapeworm segments look completely different: flat, small, and shaped like grains of rice rather than long strands. See our tapeworm guide for a side-by-side comparison

Many infections are found on a fecal test without a single visible worm, since the eggs themselves are microscopic. Not seeing anything unusual doesn't rule out roundworms.

Eating infected prey

Pets can also become infected by eating prey, such as rodents, that carry roundworm larvae. This makes it a risk for cats and dogs that hunt and catch or eat small animals.

Infection from the mother

The maternal route differs between dogs and cats:

• Puppies: Can commonly become infected before birth and through their mother’s milk.
• Kittens: Don’t have the same prenatal route as puppies. They’re infected mainly through the environment and prey, with transmission through milk a more limited route.

Because young pets can become infected early, it’s standard veterinary practice to deworm all puppies and many kittens on a schedule, regardless of whether a fecal test has already detected roundworms.

What are the signs of roundworms?

Roundworm infections can cause digestive and growth-related signs, particularly in puppies and kittens. Some pets may have no obvious symptoms, especially if the infection is light.

Signs may include:

• a potbellied or swollen-looking abdomen, especially in a young pet
• poor growth or failure to gain weight as expected
• weight loss
• a dull coat
• diarrhea
• intermittent vomiting
• visible worms in stool or vomit

Seeing worms may be the first clue an owner notices. However, not seeing worms doesn’t mean your pet is parasite-free. Roundworm eggs are too small to see without a microscope, and routine fecal testing can detect infections that aren’t visibly obvious.

Healthy adult pets with light infections may show no signs at all. That’s one reason routine fecal testing is an important part of preventive care, including indoor pets.

How are roundworms diagnosed and treated?

Roundworms are diagnosed and treated by a veterinarian with fecal testing and a targeted medication that’s safe for your pet’s age and health.

How veterinarians diagnose roundworms

A fecal test can detect roundworm eggs in your pet’s stool. Your veterinary team may also consider your pet’s age, symptoms, deworming history, and whether you’ve seen worms in stool or vomit.

If you’ve found a worm, tell the team what it looked like, where you saw it, and when it happened. A clear photo or sample can help them assess what you found. Even if a fecal test is negative, seeing a worm is meaningful information that your veterinarian should know about.

Roundworms are treated with a veterinarian-directed deworming medication. Treatment usually involves more than one dose because a medication may kill some stages of the worms but not all the immature worms that are still developing.

Your veterinarian will recommend the medication and timing based on your pet’s age, health, and likely exposure. Follow the full schedule, even if your pet seems better after the first dose.

Some over-the-counter dewormers cover only certain parasites or life stages, and products can differ in dosing and safety. Check with your veterinary team before giving your pet a dewormer so they can choose one that’s appropriate.

Is it normal to see worms after deworming?

Yes, you may see roundworms in your pet’s stool for a few days after treatment as the worms are passed. This doesn’t automatically mean the medication failed.

However, if you continue seeing worms, your pet’s symptoms worsen, or you’re unsure whether the treatment schedule is complete, contact your veterinary team. They can advise whether another dose, a different treatment, or follow-up testing is needed.

What happens during a Banfield puppy or kitten visit?

Your Banfield veterinary team can help establish a schedule for fecal testing and deworming during your puppy’s or kitten’s first months.

The team considers your pet’s age, health, history, and risk of exposure when recommending next steps.

Repeated deworming and testing are important because one treatment may not reach every worm at every stage of development, and young pets can be exposed again. Your veterinarian will explain when to give any recommended doses and when to bring in another stool sample.

A heavy roundworm burden can cause serious illness in a very young pet, including an intestinal blockage. A puppy or kitten with a painful, bloated abdomen and repeated vomiting needs urgent veterinary care rather than a wait-and-see approach.

Optimum Wellness Plans^® for puppies and kittens include the fecal testing and deworming they need to get started parasite free. Explore OWPs 

How do I prevent roundworms?

Year-round broad-spectrum parasite prevention recommended by your veterinarian is an important part of keeping your pet parasite free. Many heartworm preventives also cover roundworms and hookworms, but coverage varies by product, so ask which parasites your pet’s specific medication covers.

Other ways to reduce exposure include:

  Pick up poop promptly. Clean up after your pet every day. Roundworm eggs need time in the environment to become infectious, so daily cleanup helps reduce contamination.

  Cover sandboxes. Keep children’s sandboxes covered when they aren’t in use, so pets can’t use them as a litter area.

  Discourage digging or eating dirt. Be especially careful in areas that may be contaminated with animal waste.

  Limit access to prey. Reduce hunting and opportunities to eat rodents or other small animals.

  Keep up with fecal testing. Ask your veterinary team how often your pet should have a stool test, even if they’re on preventive medication.

Indoor cats still need routine fecal testing. Living indoors can reduce some exposures, but it doesn’t eliminate the possibility of roundworms.

Never use a dog parasite-prevention product on a cat because some ingredients in dog products can be toxic to cats. Your veterinarian can help pick a product that’s safe and appropriate for each pet in your home.

Can people get roundworms from pets?

Roundworms can infect people, and young children face the highest risk, largely because they're the most likely to put contaminated hands or soil in their mouths.

Infections happen when people swallow roundworm eggs picked up from contaminated soil, sand, or unwashed hands. Freshly passed eggs aren't an immediate risk, since they need time in the environment before they become infectious, which is similar to pets.

In rare cases, migrating larvae can cause more serious complications in people. This is uncommon, but it's part of why prevention is worth it to protect your pets (and you). The CDC's page on toxocariasis covers the human infection in more detail.

Practical protections are straightforward: wash hands after handling pets, soil, or stool; clean up stool promptly; and keep sandboxes covered when not in use.