Roundworm Infection in Cats

What are roundworms?

Roundworms (also known as nematodes or ascarids) are parasites that live freely in the intestine, feeding on partially digested intestinal contents. Their name comes from their tubular or “round” shape. Roundworms are one of the most common gastrointestinal worms found in cats and can also be transmitted to people.

How do cats get roundworms?

A cat is infected when it ingests roundworm eggs in the environment. These eggs may come from the feces of infected cats or from the tissues of an accidental (intermediate) host, such as an earthworm, cockroach, rodent, or bird.

The eggs hatch in the cat’s gastrointestinal tract, and immature worms (larvae) migrate through the muscles, liver, and lungs. After several weeks, the larvae return to the intestine to mature into adults. When the adult worms begin to reproduce, eggs pass into the cat’s stool, completing the parasite’s life cycle.

During their migration, some roundworm larvae may become enclosed in a cyst in the tissue of the host’s body. If a female cat is infected shortly before giving birth, roundworm larvae may enter the mother’s mammary glands and be passed to the kittens through the milk (trans-mammary infection) during nursing. Kittens can pass eggs in their stool by the time they are approximately six weeks old.

Are roundworms dangerous to my cat?

Roundworms are most dangerous to kittens but can harm adult cats as well, and the most common consequence of roundworms is stunted growth. Roundworms eat partially digested food in the intestinal tract, so if they are present in large numbers, they rob the growing kitten of vital nutrients and can even cause an intestinal blockage. Large numbers of migrating worms can also cause lung inflammation and coughing.

What are the clinical signs of roundworm infection?

Adult cats may have no signs of roundworms or they may have mild signs, such as coughing, soft stool, and vomiting. However, large numbers of roundworms may cause life-threatening problems in kittens and debilitated or older cats.

In kittens, common clinical signs include a pot-bellied appearance, abdominal discomfort, depressed appetite, dull coat, vomiting, diarrhea, poor growth, and seizures (rare). Kittens with small numbers of worms may have no obvious clinical signs of infection. You may notice adult roundworms in your kitten or cat’s stool or vomit.

How is a roundworm infection diagnosed?

To diagnose roundworm infection, a small amount of the cat’s stool is examined under a microscope (fecal flotation). 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 seen in the cat’s stool or vomit. 

Your veterinarian may also run a routine PCR screen on your cat’s feces that detects small amounts of parasite DNA to identify roundworm and other parasite infections even before the worms start to shed eggs.

What is the treatment for a roundworm infection?

Treatment is simple and effective. There are many safe and effective deworming medications available to kill adult roundworms in the intestine, such as pyrantel (Nemex®, Strongid®) or fenbendazole (Panacur®). These treatments kill only the adult worms and do not affect migrating or encysting larvae, so at least two or three treatments are needed, typically at two- to three-week intervals.

Ideally, kittens are dewormed at each booster vaccine appointment. Nursing cats should be treated at the same time as their kittens. Most flea and heartworm preventives also kill roundworms (e.g., Revolution® Plus, Advantage® Multi, Profender®, Nexgard COMBO®, and Milbemax®). Your veterinarian will advise you on the best treatment and prevention plan for your pet.

What is the prognosis for a cat diagnosed with a roundworm infection?

The prognosis for a roundworm infection is good if appropriate medication is given promptly. However, in some instances, extremely debilitated kittens may die.

How can I prevent a roundworm infection in my cat?

Prevention of roundworm infection should include the following measures:

• Deworm breeding female cats before pregnancy and again in late pregnancy to reduce the risk of environmental contamination or transmission from the mother to her kittens.
• Deworm kittens routinely, starting at about two to three weeks of age. Your veterinarian will recommend the most appropriate deworming schedule.
• Deworm your adult cat whenever you see roundworms. Work with your veterinarian to determine a regular deworming plan specific to your cat. Cats that have outdoor access or hunt mice indoors should also have a fecal examination several times a year.
• Use a heartworm preventive that is effective against roundworms to stop the shedding of eggs into the environment. Talk to your veterinarian about the best options for your cat.
• Control the population of insects and rodents, as they are sources of roundworm infection for cats.
• Scoop your cat’s litter box daily and clean it, and any contaminated surfaces, with a bleach solution (one cup of chlorine bleach in one gallon of water). Rinse the litter box thoroughly to remove all bleach since it is toxic to cats. The bleach solution makes the eggs easier to rinse away but does not kill the eggs.
• Properly dispose of pet feces, especially from yards and playgrounds. Roundworm eggs may remain viable in the environment for long periods.

Are roundworms dangerous to people?

Roundworms can be a health risk for humans. The most common source of human infection is soil contaminated with cat or dog feces. 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 if they are infected.

Humans are like any other accidental host. If a person swallows infectious eggs, the larvae can invade the tissues and become encysted in various organs. If a young child ingests a large number of eggs, clinical disease may become apparent. Very rarely, liver problems may result from roundworm larval migration. Even less commonly, the larvae can migrate into the eye and cause blindness.

In suitable environments, the eggs may remain infectious 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 (like playgrounds or sandboxes). Strict hygiene is especially important for children. Do not allow children to play in potentially contaminated environments. Be mindful of the risk posed by public parks and uncovered sandboxes. Roundworm eggs may be present even if feces are not visible.