What to Know About Roundworms in Cats

Reviewed by Amy Flowers, DVM on December 26, 2021

Roundworms are the most common parasites that infect cats. Cat and kitten roundworms live in the intestines, using up ingested nutrients and making your pet weak. This weakness can make your kitten with worms susceptible to viral and bacterial infections and other diseases. Additionally, there is a small risk of you or your family being affected by your cat's roundworms.

There are many species of roundworms, and two of them cause disease in cats — Toxicaris leonina and Toxocara cati. These worms are 3 to 5 inches long and live in your cat's intestine, consuming the food eaten by your cat.

Almost all cats get infested with these parasites at some time in life, usually when they are kittens. Other worms that can affect cats include hookworms, heartworms, whipworms, and tapeworms.

Your young kitten with roundworms is most likely to have Toxocara cati because it is transmitted by breast milk, among other ways. Toxicaris leonina is transferred by ingestion of the eggs or larva.

Adult female roundworms living in a cat's intestines release eggs that are passed out in the cat's feces into the environment. These eggs develop into infectious larva.

An infected pregnant cat can pass on the infection through the placenta to her kittens during pregnancy. Kittens can get infected through the breastmilk of an infected cat. Kittens can also get infected by ingesting the roundworm eggs. Eating rodents that have consumed the larva can also infect your cat.

Although kittens are most likely to get roundworms, cats are susceptible at all ages. Cats of any age can get the parasites by ingesting the eggs from soil or larva-infested rodents.

Your kitten with roundworms may have a poor appetite, diarrhea alternating with constipation, and weight loss. Growth will be reduced as well, and their coat will appear dull. Vomiting is common, and you may see worms in the vomit. These worms are usually large and alive.

If the worms are large in number, they migrate and may reach the lungs. Your cat will develop a cough. A large number of worms migrating to the lungs can cause a frothy discharge from the nose, pneumonia, fluid collection (edema) of the lungs, breathing difficulty, and even death.

A large load of worms can make your cat look potbellied. Sometimes, you may see living, adult worms in your cat's feces.

Roundworm infection can cause severe disease in your cat. Sometimes, these worms can cause severe anemia (a reduction in red blood cells, causing a reduced capacity to transport oxygen). Kittens with worms may also develop:

  • Thickening of the intestines
  • Swelling of the duodenum (the first part of the intestines)
  • Blockage of the intestine, preventing passage and digestion of food
  • Blockage of the bile duct, which carries bile from the liver
  • Blockage of the pancreatic duct, which carries digestive juices from the pancreas
  • Bursting of the intestines, a life-threatening situation

If your young cat seems to be weak and not gaining weight, you should take them to your veterinarian. Roundworms are diagnosed by examining the feces for eggs of the worms. A test that detects specific roundworm protein antigen in the feces is also available.

Many drugs are effective in the treatment of roundworms in cats. The most commonly used are:

  • Pyrantel
  • Fenbendazole
  • Emodepside
  • Ivermectin
  • Moxidectin

Since kittens are very prone to roundworm infection, they should be treated every two weeks between ages three and nine weeks of age. Beyond age 9 weeks, this preventive treatment should be given monthly.

Giving a course of treatment to your cat when she is pregnant will protect kittens from getting infected. Roundworm treatment of cats treats the existing infection, but cats can get infected again.

Parasites are common in cats. Keeping your cat parasite-free is important for their good health. To prevent parasite infection:

  • Clean the litter box daily and remove the feces
  • Use an effective disinfectant
  • Avoid overcrowding of pets
  • Avoid diets based on raw meats, which may have larva
  • Don't allow your cat to hunt rodents

Rarely, yes. 

Humans can get infected by putting unwashed fingers into the mouth, eating vegetables grown at farms using animal dung as fertilizer, or eating raw vegetables contaminated by eggs or larva. Infected cats cannot directly cause infection in humans.

Toxocara cati larva cannot develop into adulthood in humans. Instead, they migrate to various parts of the body and cause disease. The organs most affected are the liver, lungs, and brain. Such disease is called visceral larva migrans.

If the larva reach the eyes, they cause ocular larva migrans. In humans, ocular larva migrans is a frequent cause of blindness in some parts of the world. One-sided blindness in children who are ages 5 to 10 is most common.

Children are especially prone to getting such infections. Children often play in the soil of gardens and playgrounds contaminated with animal feces, and they have low standards of hygiene, making infection more likely.

Safety measures:

  • Do not allow children to play in areas where cats are passing feces. 
  • When cleaning your cat's feces and litter box, wear gloves for your safety.
  • Regular preventative treatment of domestic companion animals also protects against human disease.

Show Sources


Cornell College of Veterinary Medicine: "Gastrointestinal Parasites of Cats."

Parasites and Vectors: "Pet roundworms and hookworms: A continuing need for global worming."

Pets and Parasites: "Roundworms."

Winders W. Statpearls, "Toxocara canis," Statpearls Publishing, 2021.

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