Can Cats Catch Roundworms From Dogs?

Roundworms, scientifically known as nematodes, are a diverse group of parasitic worms that live in the gastrointestinal tract of their hosts, which includes humans, cats and dogs. The most common species of roundworms to infest dogs is Toxocara canis, followed by Toxascaris leonina.

Tococara canis

Adult worms live in the intestine of the dog and feed off the intestinal contents. Female worms produce a large number of eggs, which are then excreted in the dog’s feces. Eggs can contaminate the environment and can be ingested by other dogs. Once in the gastrointestinal tract, the egg shell breaks down and the larvae emerge. They penetrate the intestinal wall and enter the bloodstream where they migrate to various tissues and organs. This process is called somatic migration. In puppies, the larvae often migrate from the bloodstream to the lungs. They then move up the trachea, are coughed up and swallowed, returning to the intestine. In the intestine, the larvae mature into adult worms. The adults attach to the intestinal walls and begin producing eggs, which are then excreted in the feces, repeating the cycle.

In adult dogs, especially  bitches, some larvae don’t complete the tracheal migration. Instead, they encyst in different tissues, entering a dormant state. This is likely a survival mechanism for the parasite, as encystment allows it to avoid the host’s immune response, environmental hazards and worse, dewormers.  If a bitch becomes pregnant, hormonal changes reactivate the encysted larvae which migrate to the mammary glands instead of the stomach. When the puppies nurse, larvae infect the puppies. Unfortunately, dewormers are only effective against adult worms in the stomach and do not kill encysted larvae or larvae in the mammary glands.

Toxocara leonina

T. leonina has a more direct life cycle than T. canis. Adult roundworms lay eggs, which pass out of the dog’s feces and develop into infective larvae in the environment. When another animal ingests these infective eggs, they hatch in the intestines and mature into adult worms, which then produce more eggs.

T. leonina does not undergo tissue migration, meaning that it doesn’t have transmammary transmission seen in T.canis.

Can dogs transmit roundworms to cats?

Dogs can indirectly transmit roundworms to cats. Toxascaris leonina is a generalist parasite, which means it has a broad host range, including dogs, cats, and other carnivorous mammals. It is the second most common type of roundworm to infest dogs. Research shows that T. leonina accounts for 2.9% of roundworm infections in dogs and 3.4% in cats.

Transmission doesn’t occur directly from dog to cat, but rather through contaminated dog feces in the environment.

  • Roundworm eggs are present in the feces of dogs infected with roundworm.
  • These eggs contaminate the environment and, after some time, develop into infective larvae within the eggshell.
  • A cat, while grooming or playing in a contaminated area, ingests the infective eggs.
  • Once inside the cat’s intestines, the eggs hatch into larvae.
  • The larvae mature into adult worms in the cat’s intestines, completing the cycle.

It’s also possible for a cat to become infected by eating a rodent that has ingested roundworm eggs and has larvae in its tissues.

Toxocara canis, which is primarily a roundworm of dogs, can also infect cats, though it is less common for cats to be infected with T. canis than it is for dogs. Cats are a dead-end host to T. canis, and the larvae do not usually progress into adult roundworms. Instead, the ingested eggs hatch into larvae in the cat’s intestine, and these larvae often migrate through the cat’s tissues. This migration is similar to what happens in accidental human hosts and can result in a condition known as visceral larva migrans.

What are the symptoms of roundworms in cats and dogs?

Most infected cats and dogs will be asymptomatic; however, pets with a heavy worm infection as well as puppies and kittens may display the following symptoms:

How do roundworms affect cats and dogs?

Kitten with a pot belly
Notice the pot belly on this stray kitten who most likely has a heavy roundworm infestation.
  • Gastrointestinal issues: Roundworms live within the lumen of the small intestine. The small intestine follows the stomach and is where most digestion and absorption of nutrients occur. Unlike hookworms which attach to the intestinal wall, roundworms live freely in the small intestine, where they feed on the host’s nutrients.
  • Stunted growth and malnutrition: A heavy roundworm infection, especially in puppies and kittens can lead to stunted growth due to the worms consuming a significant amount of nutrients.
  • Potbelly appearance: Infestations can lead to a bloated or ‘potbelly’ appearance, particularly in puppies and kittens, due to the accumulation of worms in the intestines.
  • Coughing and respiratory Issues: The lifecycle of the roundworm includes a phase where larvae migrate through the lungs. This can cause coughing and, in severe cases, pneumonia, especially in puppies.
  • Obstruction: A heavy infestation can cause an intestinal blockage due to the sheer number of worms. This is a life-threatening situation that requires emergency veterinary care.
  • Poor coat condition: An infected animal may have a dull and coarse-looking coat due to malnutrition caused by the worms consuming nutrients.


To prevent roundworm transmission between dogs and cats, it’s essential to regularly clean and remove feces from the environment and to maintain a regular deworming regime for both dogs and cats under the supervision of a veterinarian.

Bitches who are going to be mated should be wormed prior to becoming pregnant as well as regularly during pregnancy. Speak to your veterinarian about safe and effective dewormers. Puppies should be wormed from two weeks, and every two weeks until they are 12 weeks old. Again, it is important to seek veterinary advice on safe dewormers for young puppies.

Dogs and cats should have a fecal analysis as part of their annual check-up. This will help the veterinarian determine if the cat or dog has any intestinal parasite burden and if so, prescribe an effective dewormer.

Common dewormer treatments

There are a number of safe and effective dewormers for dogs and cats. It is important to speak to your veterinarian who can prescribe the most effective dewormer. The age of the animal, as well as the type of worms, will help the veterinarian determine the appropriate treatment.

You may notice the presence of roundworms in the dog’s feces after deworming, which is normal.

Roundworms in a puppy's feces

  • Fenbendazole: Roundworms, hookworms, whipworms, and certain tapeworms in dogs.
  • Pyrantel Pamoate: Roundworms and hookworms, and is often used in dogs, cats, and horses.
  • Ivermectin: Heartworms, roundworms, and other parasites in dogs and other animals. It should be used with caution in certain breeds of dogs, like Collies, due to sensitivity.
  • Praziquantel: Tapeworms and is used in both animals and humans.
  • Milbemycin Oxime: Heartworm preventative, and treats roundworm and hookworm infections in dogs.
  • Mebendazole: Roundworms, hookworms, whipworms, and certain tapeworms in humans, and is also used in veterinary medicine.
  • Selamectin: Applied topically and is used to prevent heartworm disease and to treat and control hookworm and roundworm infections in dogs and cats.
  • Moxidectin: Used in animals for the prevention and control of various parasitic worms including heartworms, roundworms, and hookworms.
  • Levamisole: Used in both veterinary and human medicine, primarily for parasitic worm infections.
  • Febantel: Often used in combination with other anthelmintics to treat roundworms, hookworms, and whipworms in dogs.

You may notice the presence of roundworms in the dog’s feces after deworming, which is normal.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio

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