Roundworms are a common parasite that affects cats. Learn how to prevent roundworms in cats, and how to recognize the symptoms so you can treat it quickly and effectively.
sad looking cat lying on blanket
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Roundworms are the most common intestinal parasite in kittens, but they can affect adult cats too. Though signs of roundworms in cats can include diarrhea, weight loss, and vomiting, many adult cats don’t display any symptoms. That’s why it’s so important to have your cat’s poop tested for roundworms every year during a yearly veterinarian visit.

What Are Roundworms? 

“Roundworms (also called ascarids) are long, brown, round worms that look like cooked spaghetti and commonly live in the intestines of cats,” says Jessica Nichols, DVM, who is the chief veterinary officer of Spay and Neuter Kansas City in Kansas City, Mo. “They are the most common intestinal parasite in kittens, and kittens are infected more often than adults. It’s reported that up to 50 percent of kittens will have a roundworm infection.” 

Nichols says that there are two main types of roundworms that affect cats. “Toxocara cati is the most common roundworm in cats and can only infect other cats,” she says. “Occasionally, cats can get infected with Toxascaris leonina from a dog.” And while humans can become infected with roundworms, cats can’t directly infect humans and humans can’t directly infect cats, Nichols says. 

How Do Cats Get Roundworms? 

According to Nichols, there are multiple ways cats can become infected with roundworms. Kittens, for example, often get it from their mother’s milk. “Even mother cats that have received a dewormer to kill the parasite can transmit roundworms to their kittens,” she says. “That’s because pregnancy can activate roundworms that were formerly dormant in the mom’s body. These newly activated worms are then transmitted to the kitten through the milk.” 

The other main ways in which cats can become infected are by eating roundworm eggs from the poop of an infected dog or cat and by consuming roundworm babies from the meat of an infected mouse or other small animal. 

What Are the Signs of Roundworm Infection in Cats? 

Adult roundworms live in the intestines of infected cats, and according to Nichols, some of the most common signs of their presence include diarrhea, weight loss, low energy, poor haircoat, failure to thrive (meaning the kittens don’t grow as they should), and sometimes vomiting. “Kittens will often have a potbelly appearance, and cats that are heavily infected will sometimes have dead worms in their poop or vomit,” she says. “Cats with a high number of worms can also suffer from anemia (meaning they don’t have enough red blood cells to carry the oxygen their body needs) and blocked intestines.” However, Nichols says that many cats—especially adults—won’t have any signs of roundworm infection, which is why an annual screening is so important. 

Diagnosing and Treating Roundworms in Cats

“Diagnosis is often done with a fecal float test, which involves using a microscope to look for roundworm eggs in a sample of the cat’s poop,” Nichols says. “This test can often be done the same day you visit your cat’s veterinarian, or the sample may be sent out to a laboratory for testing.” Because cats can have roundworms without showing any signs, she recommends using a fecal float test to screen all cats for the parasite once a year. 

Cats infected with roundworms are typically given a deworming medication by mouth. “This will immediately start killing the worms, and you may see dead worms in the cat’s poop or vomit,” Nichols says. “Cats with a high number of roundworms may need multiple doses to kill all of the worms.” As long as the condition is treated quickly, most cats recover well from a roundworm infection, though it can be fatal to severely affected kittens. Because roundworms are so common in kittens, veterinary experts recommend giving deworming drugs to all kittens as a precaution beginning at two weeks of age.

How to Prevent Roundworms in Cats

Many monthly heartworm preventative drugs also protect against roundworms. (Nichols notes that these drugs can also be used to treat infected cats as long as their worm numbers are low.) Your cat’s veterinarian will work with you to find the best roundworm treatment option for your pet. 

Nichols adds that it’s important to keep your cat’s environment clean by regularly emptying its litter box. And because cats can get roundworms by eating infected meat, the Companion Animal Parasite Council recommends keeping cats indoors so they’re less able to hunt and eat animals that may carry the parasite.