Roundworm Infection in Cats

What are roundworms?

Roundworms are one of the most common intestinal parasites of the cat. They can be an important cause of illness, even death, in kittens. Almost all cats will become infected with roundworms at some point in their life, and most often as kittens. As their name implies, these are large-bodied round worms, averaging about 3-6 inches (8-15 cm) in length. They do not attach to the wall of the intestine, as some intestinal parasites do. Instead, they swim freely within the intestine.

The scientific name for the roundworm that infect cats is Toxocara cati. Another less common roundworm, Toxascaris leonina, can infect both dogs and cats. Roundworms are also known as ascarids and the disease they cause is called ascariasis.


What are the clinical signs of roundworm infection?

Roundworms are not particularly harmful to adult cats, but large numbers may cause life-threatening problems in kittens and debilitated older cats. In kittens, common clinical signs include a pot-bellied appearance, abdominal discomfort, depressed appetite, dull hair coat, vomiting and diarrhea, or poor growth.

"Large numbers of roundworms may cause life-threatening problems in kittens and debilitated older cats."

In both kittens and adult cats with small numbers of worms, there may be no clinical signs of infection. You may notice adult roundworms in your cat’s stool or in their vomit.


How do cats get roundworms?

Trans-mammary or milk-borne infection is the major route of roundworm transmission in kittens. The immature roundworms called larvae are present in the mother's mammary glands. The larvae pass to her kittens in her milk during nursing.

Both kittens and adult cats may become infected by swallowing eggs that contain infective roundworm larvae. These eggs may come from the feces of infected cats or from the tissues of paratenic hosts (an accidental host). In a paratenic host, the roundworm eggs do not mature into adults, but are just transported. If a cat eats the paratenic host, the roundworm is able to complete its life cycle. Common paratenic hosts for roundworms include earthworms, cockroaches, rodents, and birds.


During migration, some roundworm larvae may encyst (the larvae become enclosed in a cyst) in a dormant state in the host's body. In female cats, the larvae can come out of the cyst during pregnancy. These larvae can then be passed to the kittens across the placenta during pregnancy, or through the milk after birth.


How are roundworms diagnosed?


"The distinctive eggs are easily recognized under the microscope."

The distinctive eggs are easily recognized under the microscope. Roundworm eggs are usually plentiful but, in some cases, it may take more than one fecal examination to find them. Occasionally, adult roundworms can be found in the cat's stool or vomit.


What is the treatment for roundworms?

Fortunately, the treatment for roundworms is safe, simple, and relatively inexpensive. The dead and dying roundworms pass into the stool after administration of the anthelmintic or deworming medication. Since none of these treatments will kill the immature forms of the worm or the migrating larvae, at least two or three treatments are needed. Treatments are typically done at two to three week intervals. Ideally, kittens are dewormed with each visit for booster vaccinations. If your adult cat goes outdoors, you may wish to administer periodic doses of a dewormer. Nursing females should be treated at the same time as their litter of kittens.


What is the prognosis for a cat diagnosed with roundworms?



Can I prevent my cat from getting roundworms?

Prevention of roundworm infection should include the following measures:

  • Kittens should be dewormed as recommended by your veterinarian. The first deworming should be given at two to three weeks of age. Note that this is prior to the time most kittens are seen for first vaccines. It is entirely appropriate to present new kittens for an initial examination and deworming at two weeks of age.
  • Adult cats remain at risk for re-infection with roundworms throughout their lives. Whenever roundworms are seen, the cat should be dewormed immediately. Cats at high risk for infection with roundworms should be routinely dewormed. Cats that like to hunt mice or indoor/outdoor cats should have a fecal examination several times a year.
  • Contact your animal control officials when homeless animals are found.


Are roundworms a danger to my family or me?



As many as 10,000 cases of roundworm infection in humans have been reported in one year in the United States. Children are at an increased risk for health problems should they become infected. If the infective eggs of Toxocara canis are swallowed by people, the larvae can invade the tissues and become encysted in various organs. Humans act like any other paratenic or accidental host. If a young child ingests a large number of infected eggs, clinical disease may become apparent.

Very rarely, liver problems may result from roundworm larval migration (visceral larval migrans). Even less commonly, the larvae can migrate into the eye and cause blindness (ocular larval migrans). Modern monthly heartworm preventives also prevent roundworm infections and are highly recommend for all dogs and cats.

In suitable environments, the eggs may remain infective to humans and cats for years. It is important to wash your hands thoroughly after playing with your pet, or after being in areas where they may have defecated.



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