• Roundworms are parasites that live in the intestines of dogs and cats.
  • Roundworm infections can be transmitted from animals to humans.
  • Depending on the type of roundworm, pets can be infected by their mother during pregnancy or nursing, by eating roundworm eggs in the environment, or by eating infected rodents or birds.
  • Signs in pets include a pot-bellied look, failure to gain weight, dull coat, vomiting, and/or diarrhea.
  • Roundworm infections are diagnosed by finding microscopic eggs during a veterinary fecal exam or by finding worms in vomit or feces.
  • Several antiparasite medications can treat roundworm infections.
  • Regular fecal exams and monthly preventive medications are recommended to keep pets free of roundworms and other internal parasites.

What Are Roundworms?

Roundworms are extremely common parasites that spend their adult lives in the intestines of puppies, kittens, dogs, and cats. There are several species of roundworms. Some can grow to about seven inches in length and cause severe illness, especially in younger pets.

How Do Pets Become Infected With Roundworms?

Mother dogs can pass roundworms on to developing puppies in the uterus or through milk when the puppies are nursing. Kittens do not become infected while in the uterus, but they can become infected when nursing.

Adult roundworms live in the intestines, where they reproduce by laying eggs. An infected dog or cat sheds roundworm eggs into the environment when it passes feces. Once the eggs are in soil, the worms develop to the infective stage within the egg. Other pets can become infected by eating the eggs from contaminated soil, which often happens when pets groom themselves, sniff or lick the ground, or eat grass and other things outside. Pets can also be infected when they eat infected prey, such as birds and rodents.

Once roundworm eggs are eaten, they hatch in the digestive tract. In most cases, the worms then migrate through the liver and lungs. Once in the lungs, the young worms are coughed up and swallowed, eventually making their way to the small intestine, where they mature into adults and reproduce.

What Are the Signs of a Roundworm Infection?

Puppies and kittens are usually the most severely affected and often look pot-bellied. Other signs include:

  • Coughing
  • Dull, thin coat
  • Vomiting
  • Diarrhea
  • Failure to gain weight

Can People Get Roundworms From Their Pets?

Yes. Roundworms are considered zoonotic parasites, meaning that they can be transmitted from animals to humans. Children are most at risk for infection. They usually become infected from eating contaminated soil, which is often found at playgrounds frequented by pets.

In humans, roundworms are a significant cause of several types of larva migrans, an illness caused by migration of young worms through body organs such as the liver, lungs, and nervous system. Young worms may also travel to the eye, where they can cause blindness.

If there are children in your household, make sure your pets are tested and treated for any roundworm infection. Keep your pets on a monthly preventive that also controls roundworms. Make sure children wash their hands after handling pets or frequenting playgrounds. Keep sandboxes covered when not in use to discourage neighborhood cats from using them as litterboxes.

How Are Roundworm Infections Diagnosed?

Your veterinarian can diagnose a roundworm infection by finding microscopic roundworm eggs on a fecal exam. Unfortunately, some owners discover that their pet is infected when live roundworms are expelled in vomit or feces.

How Is an Infection Treated?

Veterinarians routinely treat young pets with an antiparasite medication several times, until they can be placed on a monthly heartworm preventive that also controls roundworms and other internal parasites. Roundworm infections are very common in puppies and kittens, but eggs aren’t always apparent in fecal material from infected pets. Your veterinarian may therefore recommend deworming your puppy or kitten even if a fecal test does not confirm a roundworm infection.

Many antiparasite medications only kill the adult worms in the intestines, not the migrating younger worms or eggs. Therefore, if your pet is infected with roundworms, your veterinarian may recommend two to three rounds of treatment to clear the infection. Generally, fecal samples are rechecked after treatment to make sure the infection has been resolved.

How Can I Protect My Pet From Roundworm Infections?

Because roundworm eggs can remain infective in the environment for months to years, pet feces should be removed and disposed of immediately.

When walking your dog, keep him or her on a leash to help reduce exposure to areas that may have been contaminated by other dogs. This will also minimize the chance of your dog eating infected rodents and birds. If possible, cats should be kept indoors to prevent them from hunting infected prey. However, even indoor animals can catch infected mice. Sharing litterboxes and outdoor bathroom areas can spread roundworms among pets, so any new pets should be tested for roundworms and other internal parasites before being introduced to your other pets.

Always consult your veterinarian about the best ways to protect your pet—and your family—against internal parasites. A monthly preventive that includes medication for roundworms is a good start for year-round protection from parasites. Since it’s easy to forget a monthly treatment, periodic fecal exams are still recommended to ensure your pet is parasite-free.