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Vet and Cat
Regular heartworm treatments can prevent roundworm in at-risk cats.
Q. I have a chance to adopt a rescued Ragdoll kitten who got roundworms from her abandoned mother. The kitten was treated with Panacurin, but recently she tested positive for roundworms again. This is her second treatment.

After researching roundworms, I'm not sure if I would want to take the cat. Only the mature worms are killed when treated, because the eggs survive and mature. Also, the worms/eggs can stay dormant in the host, possibly being released later in life. This concerns me since my mom visits once in a while and brings her cat with her. I live in a small studio apartment and cannot separate them, and I would hate to spread the worms to her cat. Also there is the concern of passing the worms to humans.

A. About 90% of the kittens I see are infected with roundworms (also known as ascarids or by their scientific name, Toxocara cati). This is so common in kittens that most veterinarians treat all kittens throughout the first few months of life whether or not the fecal examinations demonstrate eggs.

Roundworm Life Cycle
Kittens get roundworm by ingesting stage 2 larvae, which can transmit through their mother's milk. Therefore, kittens are infected from birth. Cats can be infected later in life by eating mice and other small mammals.

The second stage larvae encysted in the tissues of cats cannot be eliminated by routine deworming. The good news is that this stage does not commonly become active in adults, so treating kittens and young cats to minimize egg shedding is usually enough to control it. I recommend three treatments on kittens at two- to three-week intervals, to complete an effective treatment regime. Because only the dewormers kill the adults, as larval stages mature you must continue the deworming process.

Cat Roundworm Transmission
Cats get roundworms by:

  • Eating something tainted with the parasite. A cat that has ingested the eggs or larval (stage 2) from an infected cat (or other small mammal) becomes infected.
  • More rarely, an older cat that sheds eggs (through feces) could transmit roundworms through the litterbox. Roundworm parasite eggs could likely spread through the house from a cat's paws. 
  • Most cats, such as your mom's, probably had the infection as kittens and have encysted larvae, now dormant, because this is so common. Transmission of a new infection to your mom's cat is unlikely.


  • Repeat three dewormings at three-week intervals and continue to have the feces checked over the next couple of months for evidence of the parasite.
  • If your cat catches mice, deworm her on a monthly basis by putting her on heartworm prevention, which will also protect her from roundworm.
  • Test your cat for feline leukemia virus (FeLV) now and in eight weeks, and feline immunodeficiency virus (FIV) after 6 months of age.

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