Treating roundworms in cats is straightforward: a deworming medication kills the adult worms, and a follow-up dose two to three weeks later catches any that matured in the meantime. Most cats recover quickly with no lasting effects. The key is completing the full course, because a single dose won’t eliminate the entire infection.
How Cats Get Roundworms
The most common feline roundworm is Toxocara cati. Cats pick it up in three main ways. The first is swallowing microscopic eggs from contaminated soil, grass, or surfaces. These eggs are shed in the feces of infected animals and take one to four weeks in the environment to become infectious. Once swallowed, the eggs hatch in the gut and the larvae burrow through the intestinal wall to continue their lifecycle.
The second route is through prey. Mice, birds, and other small animals can harbor roundworm larvae encysted in their tissues. When your cat eats an infected mouse, those larvae are released in the gut and develop into adult worms. This makes outdoor and hunting cats especially prone to reinfection.
The third route matters most for kittens. An infected mother cat can pass larvae to her kittens through her milk. This transmammary transmission means kittens can be infected from their very first days of life, which is why deworming protocols start so early.
Signs Your Cat Has Roundworms
Many adult cats with roundworms show no obvious symptoms at all, especially with light infections. When signs do appear, the most recognizable is a potbellied appearance, particularly in kittens. You may also notice vomiting (sometimes with visible worms), diarrhea, a dull coat, and poor weight gain despite a normal appetite. In heavy infections, kittens can become seriously malnourished.
Occasionally, you’ll see the worms themselves. Adult roundworms are white or cream-colored, several inches long, and look like spaghetti. They may show up in vomit or stool. Even if you don’t see worms, your vet can diagnose the infection through a fecal flotation test, which uses a salt or sugar solution to separate parasite eggs from the stool sample so they can be identified under a microscope.
How Deworming Medication Works
The standard treatment uses a deworming drug that paralyzes the adult worms in the intestine, causing them to release their grip on the gut wall and pass out in the stool. Pyrantel pamoate is one of the most widely used options, effective against both roundworms and hookworms. It’s available in liquid and tablet form and is generally well tolerated, even in young kittens.
Other active ingredients your vet may prescribe include milbemycin oxime and moxidectin, which belong to a different drug class and are often found in monthly preventive products that also protect against heartworm. Your vet will choose the right medication based on your cat’s age, weight, and whether other parasites are present.
Why a Second Dose Is Necessary
This is the part many owners miss. Most deworming medications only kill adult worms. Any larvae migrating through the body tissues at the time of treatment will survive, mature into adults over the following weeks, and reestablish the infection. The prepatent period for T. cati (the time from infection to egg-producing adults) is roughly eight weeks. That’s why a second dose is given 10 to 14 days after the first: it catches the next wave of worms before they can start producing eggs. Skipping the second dose is the most common reason a roundworm infection seems to “come back.”
Deworming Schedule for Kittens and Adults
Kittens need more aggressive treatment than adult cats because they’re so frequently infected through their mother’s milk. The Companion Animal Parasite Council recommends starting deworming at just two weeks of age, then repeating every two weeks until the kitten is at least eight weeks old. After that, most vets transition to a monthly preventive product that continues to protect against roundworms along with other parasites.
For adult cats, the standard approach is two doses spaced two to three weeks apart, followed by ongoing monthly prevention. Cats that hunt, go outdoors, or live in multi-cat households are at higher risk of reinfection and especially benefit from year-round preventive treatment. Even strictly indoor cats can be exposed through contaminated soil tracked in on shoes, so most veterinary guidelines recommend routine prevention regardless of lifestyle.
Side Effects of Deworming
Most cats tolerate deworming medication with no noticeable side effects. When reactions do occur, they’re typically mild: brief lethargy, a soft stool, or a single episode of vomiting. These usually resolve within a day or two.
Serious reactions are rare but can happen, particularly with certain drug classes. Macrocyclic lactones (the group that includes some monthly preventives) act on the nervous system of parasites, and in cases of overdose or sensitivity, they can affect the cat’s nervous system as well. Signs of toxicity include drooling, an uncoordinated or wobbly gait, dilated pupils, tremors, and in severe cases, seizures. These symptoms can appear anywhere from three hours to a few days after treatment. If you notice any of these, contact your vet immediately. Following the correct dose for your cat’s weight is the simplest way to avoid problems.
Cleaning Your Home During Treatment
Killing the worms inside your cat is only half the job. Roundworm eggs shed in feces are remarkably tough. Most household disinfectants, including bleach, do not kill them. What does work is heat. Boiling water poured over contaminated hard surfaces destroys eggs instantly. For litter boxes, daily scooping is essential because freshly deposited eggs take at least two to four weeks to become infectious. Removing feces before that window closes breaks the cycle of reinfection.
Wash any bedding your cat uses in the hottest water setting your machine allows. For hard floors, steam cleaning is more effective than mopping with chemical cleaners. If your cat has had accidents on carpet, a steam cleaner is your best option there too. Outdoors, eggs can persist in soil for years under the right conditions. Turning over contaminated soil and exposing it to direct sunlight and heat helps, but complete decontamination of outdoor areas is difficult.
Scoop the litter box at least once daily during and after treatment, wash your hands thoroughly afterward, and dispose of waste in a sealed bag. These steps protect both you and your cat from reinfection.
Roundworms Can Infect Humans
This is worth knowing, especially if young children share your home. Roundworm eggs from cat feces can infect people, causing a condition called toxocariasis. It takes two forms. Visceral toxocariasis occurs when larvae migrate through internal organs like the liver, causing fever, coughing, wheezing, abdominal pain, and liver enlargement. Ocular toxocariasis occurs when a larva reaches the eye, where it can cause inflammation, retinal damage, and vision loss, typically in just one eye.
Children are at highest risk because they’re more likely to play in soil and put their hands in their mouths. Prevention is simple: wash hands with soap and water after handling your cat or cleaning the litter box, keep children’s play areas free of animal waste, and maintain your cat on a regular deworming schedule so fewer eggs reach the environment in the first place. Prompt treatment of your cat is one of the most effective ways to protect your family.