Cats get worms by swallowing parasite eggs or larvae from their environment, from prey animals, or from insects like fleas and mosquitoes. Some kittens are even born with worms, picking up larvae through their mother’s milk. The specific route depends on the type of worm, but outdoor access, hunting, and flea exposure are the biggest risk factors across the board.
Roundworms: The Most Common Culprit
Roundworms are the intestinal parasite cats encounter most frequently. Cats pick them up by swallowing microscopic eggs from contaminated soil, grass, or surfaces. A cat that walks through a yard where infected animals have defecated, then grooms its paws, can easily ingest enough eggs to start an infection. Hunting is another major route: rodents, birds, and lizards can carry roundworm larvae in their tissues, and a cat that eats one of these prey animals swallows the larvae along with its meal.
Roundworm eggs are remarkably tough. They can survive in soil for months or even years, which means a patch of ground contaminated by a stray cat or wildlife remains infectious long after the original droppings have disappeared. This persistence is one reason roundworms are so widespread, particularly in cats that spend any time outdoors.
How Kittens Get Worms Before They Even Go Outside
Kittens are uniquely vulnerable because they can acquire roundworms through their mother’s milk. When an infected queen nurses her litter, dormant larvae reactivate and pass into the milk, infecting kittens within days of birth. Research on vertical transmission has shown this happens most readily when the mother picks up a new infection during late pregnancy rather than from a long-standing chronic infection.
Notably, roundworms in cats don’t appear to cross the placenta the way they can in dogs. No larvae have been found in kittens examined immediately after birth, confirming that nursing, not the womb, is the transmission point. This is why veterinary guidelines recommend deworming kittens early and treating nursing mothers, since the infection can take hold well before a kitten ever touches the ground.
Tapeworms and the Flea Connection
Tapeworms reach cats through an unexpected middleman: the flea. Flea larvae living in carpet, bedding, or soil swallow tapeworm eggs from the environment. As the flea matures, the tapeworm develops inside it into a stage that can infect a mammal. When a cat bites or swallows an adult flea during grooming, it ingests the tapeworm along with it. This is the primary way cats get the most common tapeworm species.
You’ll often notice a tapeworm infection before any other symptoms appear, because the worm sheds visible segments. These flat, quarter-inch pieces break off from the end of the worm and pass in the feces or cling to the fur around your cat’s tail. When fresh, they look like small grains of rice that stretch and contract. Once dry, they shrink to resemble sesame seeds. If you see these near your cat’s litter box or bedding, fleas are almost certainly involved, even if you haven’t spotted a single one on your cat.
Cats can also pick up a different type of tapeworm by eating rodents that carry larval cysts. This is more common in cats that hunt regularly.
Hookworms: Skin Contact and Ingestion
Hookworms have an unusual ability that sets them apart from other intestinal parasites: their larvae can burrow directly through skin. A cat walking or lying on contaminated soil can become infected without swallowing anything. The larvae penetrate the paw pads or belly skin, migrate through the body, and eventually settle in the intestines. Cats can also get hookworms the conventional way, by ingesting larvae from soil or grooming contaminated fur.
Hookworms feed on blood from the intestinal wall, so infections tend to be more damaging than roundworms in terms of physical impact. Mild cases cause diarrhea and weight loss. Severe infections, especially in kittens or debilitated cats, can cause anemia from ongoing blood loss.
Lungworms: Snails, Slugs, and Prey
Lungworms follow a more complex path to reach your cat. The parasite’s life cycle requires an intermediate host, specifically snails or slugs, where the larvae develop into an infectious stage. Cats rarely eat snails directly, though. Instead, they typically get lungworms by eating a “transport host” like a rodent, lizard, bird, or frog that previously ate an infected snail.
There’s also a less obvious route. Infected snails release larvae into their mucus trails, and larvae can escape into water when snails die and decompose. A cat drinking from a puddle or licking a surface where a snail has crawled could potentially pick up the parasite. Lungworm infections cause coughing rather than the digestive symptoms associated with intestinal worms, which can make them harder to recognize.
Heartworms: Mosquitoes Are the Only Source
Unlike intestinal worms, heartworms can only reach a cat through a mosquito bite. Mosquitoes pick up microscopic heartworm larvae when they feed on an infected dog (dogs are the primary reservoir for this parasite). The larvae develop inside the mosquito over a couple of weeks, then pass into the next animal the mosquito feeds on. For a cat to get heartworm, a mosquito species must feed on both dogs and cats, which many common species do.
Heartworm in cats is less common than in dogs, but it’s more dangerous in some ways because there’s no safe, reliable treatment once a cat is infected. Even a small number of worms can cause serious lung inflammation. Prevention is the main strategy, which is why broad-spectrum parasite preventives that cover heartworm are recommended even for cats with limited outdoor exposure.
Can Indoor Cats Get Worms?
Yes, though their risk is lower. Mosquitoes get indoors easily, making heartworm a realistic threat for any cat. Fleas can hitch a ride on human clothing or on other pets in the household, introducing tapeworm risk. If you track soil into your home on shoes, you could theoretically bring in roundworm or hookworm eggs. Indoor cats that catch the occasional mouse or insect that wanders inside face additional exposure.
The American Animal Hospital Association and the American Association of Feline Practitioners jointly recommend routine use of broad-spectrum parasite prevention for the majority of pet cats regardless of lifestyle. The logic is straightforward: the vectors that carry these parasites (fleas, mosquitoes, contaminated soil) are difficult to exclude completely from any home environment.
Signs Your Cat May Have Worms
Worm infections often produce vague, overlapping symptoms. A dull coat, vomiting, diarrhea, mucus or blood in the stool, decreased appetite, and weight loss are all common across different worm types. Kittens with heavy roundworm burdens frequently develop a characteristic potbellied appearance while the rest of their body stays thin. Pale gums can signal anemia from hookworms.
Some infections produce no obvious symptoms at all, especially in adult cats with light worm burdens. The cat’s immune system keeps the parasite population in check, but the cat still sheds eggs into the environment. This matters because several feline worms can infect humans. Roundworm eggs in soil can cause a condition called larva migrans if swallowed, and hookworm larvae can penetrate bare skin, causing an itchy, creeping rash. Children who play in sandboxes or gardens contaminated with cat feces are particularly at risk. Activities like gardening without gloves, going barefoot in areas where cats defecate, or cleaning a litter box without hand washing afterward all create opportunities for these parasites to cross from cats to people.
Why Some Cats Are More Susceptible
A study of over 100 cats in Nepal found intestinal parasites in 95.3% of the cats sampled, with feral cats reaching a 100% infection rate and household cats at 94.4%. Adult cats had higher prevalence than young cats (98.6% versus 88.6%), likely reflecting more cumulative exposure over time. Males were infected more often than females across both age groups, possibly because male cats tend to roam more widely.
The strongest risk factors were living exclusively outdoors, having no deworming history, and relying on hunting for food. These findings come from a region where parasite control is less routine than in many Western countries, but the underlying biology applies everywhere. Cats with outdoor access, cats that hunt, and cats that have never been dewormed carry the highest parasite burdens. Even in places with better veterinary access, cats that miss regular prevention are at significantly greater risk than those on a consistent deworming or preventive schedule.