Roundworms in Cats: Symptoms, Treatment & Zoonotic Risk

Roundworms are long, spaghetti-like intestinal parasites that live in a cat's digestive tract. The most important feline roundworm is Toxocara cati. These worms feed in the intestines and produce eggs that pass in stool, where they can contaminate litter boxes, soil, bedding, and other surfaces.

Roundworms are especially common in kittens. Nursing kittens can become infected through their mother's milk, and cats of any age can pick up infection by swallowing eggs from contaminated environments or by eating infected prey such as rodents. Some cats show no obvious signs at all, while others develop digestive upset, poor weight gain, or a swollen belly.

This parasite also matters because it is zoonotic. That means people can become infected after accidentally ingesting infective eggs from the environment. Children are at higher risk because of hand-to-mouth behavior and play in soil or sand. The good news is that roundworms are usually very treatable, and prevention steps can meaningfully lower risk for both pets and people.

Cats usually get roundworms in one of three ways. First, they may swallow infective eggs from contaminated litter, soil, paws, fur, food bowls, or other surfaces. Second, they may eat a prey animal, such as a rodent, that is carrying larval stages. Third, kittens can become infected while nursing from an infected mother.

After a cat swallows eggs or larvae, the parasite develops through a life cycle that can include migration through the body before returning to the intestines. That is one reason repeat deworming is often needed. A single dose may remove adult worms in the gut but not every immature stage.

Risk tends to be higher in kittens, outdoor cats, cats that hunt, cats from crowded environments, and homes with inconsistent litter-box sanitation. Indoor cats are not fully protected. Eggs can be brought inside on shoes, hands, carriers, or by newly adopted pets.

Your vet usually diagnoses roundworms by examining a stool sample with a fecal flotation test. This test looks for the parasite's characteristic eggs under a microscope. If your cat has diarrhea, produces only a small sample, or is early in the infection, your vet may recommend repeat testing because eggs are not always found on the first sample.

Sometimes pet parents notice adult worms in vomit or stool before testing is done. That can be a strong clue, but your vet still may want a fecal exam to confirm the parasite type and check for other intestinal parasites at the same time.

In some clinics or reference labs, fecal PCR testing may be used to detect parasite DNA, including infections that are not yet shedding many eggs. Diagnosis matters because not every dewormer treats every parasite, and the follow-up plan may differ for kittens, adult cats, multi-pet homes, or cats with ongoing digestive signs.

Prevention starts with routine parasite control and regular stool testing. Your vet may recommend fecal screening at wellness visits and more frequent checks for kittens, outdoor cats, hunters, or newly adopted cats. Many monthly parasite preventives for cats also help control roundworms, which can reduce reinfection risk over time.

Clean the litter box promptly, ideally daily, and wash hands well after handling stool, litter, or contaminated surfaces. Roundworm eggs need time in the environment before they become infective, so quick stool removal helps. Keep litter boxes, bedding, and food areas clean, and avoid feeding raw prey or allowing hunting when possible.

For households, zoonotic prevention matters too. Children should avoid playing in potentially contaminated soil or sand and should wash hands after touching cats or litter areas. If one pet is diagnosed, ask your vet whether other pets need testing or treatment. Consistent prevention is usually easier, safer, and less disruptive than repeated reinfection cycles.