Feline Roundworms or Toxocara Cati

Filed Under: Cats, Parasites

The feline roundworm or Toxocara cati is the most common parasite seen throughout the U.S. in cats. Roundworms are a spaghetti-type worm typically found in the intestines of infected felines. Roundworms are especially common in young kittens and their nursing mothers.

Symptoms of infection include diarrhea, stunted growth, an unthrifty coat, and the vomiting or elimination of worms themselves. The most characteristic symptom is a pot-bellied appearance. Less commonly you will see a pneumonia, intestinal obstruction, and even death. Pneumonia results from the third stage larva that migrates through the lungs.

Infection occurs by the spread of embryonated eggs in the stool and transmammary (via the mother’s milk). The kittens ingest the embryonated eggs from the milk and the hatched larvae penetrate the intestinal mucosa. From the intestines, the larva enters the liver and the bloodstream migrating to the lungs where they are coughed up and swallowed, thereby becoming mature adults. As adults, they again find themselves in the small intestine of their host. In older cats, the larva migrate to many body tissues where development may be arrested until mobilized by hormones present during pregnancy. Predatory cats (cats that hunt) may become infected by arrested infective larvae (larva that did not develop into adult worms) in the tissues of a mouse. The paratenic host (intermediate host, usually a mouse) prevents migration through the tissues of the carnivore (somatic migration) and development proceeds to maturity within the intestinal tract of the final host. Prenatal infection across the placenta does not occur with Toxocara cati. The entire life cycle (time from infection before sexually mature adult worms are present) takes 28 to 35 days.

Numerous products are effective against roundworms and include Feline Drontal®, produced by Bayer Animal Health, Pyrantel pamoate or Nemex®, manufactured by Pfizer. Several heartworm preventatives also prevent and treat roundworm infections and include Heartgard®, from Merial, and Revolution®, manufactured by Pfizer. Recently released Profender® by Bayer is the only topical feline dewormer for use in roundworm, hookworm, and tapeworm infections. Cases with concurrent pneumonia should be treated with antibiotics, antihistamines, and in some cases corticosteroids may be indicated.

Most, but not all cases of roundworms, can be picked up by a fecal examination by your veterinarian. Second-stage larvae may become encysted in the somatic tissues of the mother cat until parturition (the process of giving birth). It is widely assumed that hormonal changes in the mother will cause the roundworm infection to again become active and thereby cause infection in the kittens. For this reason Strategic deworming is advocated, although there may be no clinical signs of infection or appearance of eggs on a stool sample. Currently both the Companion Animal Parasite Council (CAPC; www.capcvet.org) and the Centers for Disease Control and Prevention (CDC; www.cdc.gov) recommend that deworming begin at two weeks of age and continued every two weeks through eight weeks of age. After eight weeks of age it is recommended to have each kitten on a heartworm preventative that will prevent the occurrence of roundworms as well as heartworms.

Feline Roundworm infections can be Zoonotic (capable of being transmitted to people). Visceral larva migrans (feline roundworm infection in people) can occur in people due to the ingestion of infective eggs with second-stage larva. This Zoonotic infection occurs most commonly in children 16 to 32 months of age because children at this age are more likely to ingest infective eggs by placing fingers in their mouths after handling kitten feces. The larvae can migrate to several tissues including the lungs, liver, brain, and the eyes. Blindness and enlargement of the liver or pneumonitis can result from this migration through the various organ systems. Routine hygiene by simply washing hands after handling kitten feces will prevent the occurrence of visceral larva migrans. Daily disposal of kitten feces and excluding cats from the area where small children play outside, especially sandboxes unless they are covered when not in use, will greatly reduce the possibility of Zoonotic infection. Excrement from litter boxes should never be used to fertilize a vegetable garden.


Dryden, Michael. “Total Parasite Control: Piecing the Puzzle Together”. Parasite Developments. Proceedings from the 2007 NAVC Conference and 2007 Western Veterinary Conference. Supplement to Veterinary Forum. Vol. 24, No. 3 (A). March 2007. p. 20.

Bowman, Dwight. “Gastrointestinal Parasites: A Broad Approach”. Parasite Developments. Proceedings from the 2007 NAVC Conference and 2007 Western Veterinary Conference. Supplement to Veterinary Forum. Vol. 24, No. 3 (A). March 2007. pp. 13-15.

Georgi, Jay. “Parasitology for Veterinarians.” Second Edition. W.B. Saunders Inc. 1974. p 267, 268 and 270.

Topics: roundworms

Symptoms: abdominal distention, diarrhea, stunted growth, vomiting

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