Cats with worms often show a dull coat, vomiting, diarrhea, and changes in appetite. In many cases, though, infected cats look perfectly healthy, and the only clue is something you spot in their stool or stuck to the fur around their rear end. The specific symptoms depend on which type of worm is involved and how heavy the infection is.
General Signs of Intestinal Worms
Most intestinal worms produce a similar set of symptoms that can be easy to miss or chalk up to something else. The classic signs include a dull, rough-looking coat, vomiting, diarrhea (sometimes with mucus or blood), loss of appetite, and pale gums. Some cats develop a visibly swollen, rounded belly, especially kittens with heavy infections.
The tricky part is that these symptoms overlap with dozens of other conditions, from food sensitivities to kidney problems. A cat that’s vomiting once a week or slowly losing weight might have worms, or might not. That’s why a stool test is the only reliable way to confirm an infection.
Roundworms
Roundworms are the most common intestinal parasite in cats. Adult roundworms live in the intestines and look like pale, spaghetti-like strands several inches long. You might see them in your cat’s vomit or stool during a heavy infection. Most adult cats with roundworms show mild symptoms or none at all. When signs do appear, they typically include vomiting, diarrhea, constipation, or reduced appetite.
Tapeworms
Tapeworm infections rarely cause serious illness in cats, but they’re the type owners most often discover on their own. The adult worm sheds small segments called proglottids, each about the size of a grain of rice. You may notice these crawling near your cat’s anus or on the surface of a fresh bowel movement. Once they dry out, they look like small, hard, yellowish grains stuck to the fur around your cat’s rear.
Cats pick up the most common tapeworm species by swallowing infected fleas during grooming. So if you’re finding rice-like segments, your cat likely has a flea problem too. Beyond the visible segments, tapeworms occasionally cause mild digestive upset or weight loss, but many cats show no other symptoms.
Hookworms
Hookworms are small parasites that attach to the intestinal lining and feed on blood. Because of this, the hallmark sign is anemia: pale gums, weakness, and lethargy. You may also see dark, tarry stool (a sign of blood being digested) along with diarrhea and weight loss. Hookworm infections can be especially dangerous in kittens, where even a moderate number of worms can cause life-threatening blood loss.
Lungworms
Unlike intestinal parasites, lungworms settle in the airways and lung tissue. Symptoms range from a moderate, persistent cough with slightly faster breathing to severe respiratory distress with labored breathing. Some cats show no visible signs at all. Because lungworm infections are relatively uncommon, they’re often diagnosed only after a round of antibiotics for a suspected respiratory infection fails to help. The coughing and wheezing can look identical to feline asthma, which makes lungworm easy to overlook.
Heartworms
Heartworm is transmitted by mosquitoes and affects the lungs and blood vessels rather than the gut. In cats, immature heartworms trigger intense inflammation in the small arteries of the lungs, damaging both the airways and the tiny air sacs where oxygen exchange happens. This condition is known as heartworm-associated respiratory disease.
The most common signs include intermittent vomiting (sometimes with blood), rapid or difficult breathing, coughing, gagging, loss of appetite, lethargy, and weight loss. These symptoms are frequently mistaken for asthma or other bronchial diseases. Unlike in dogs, there is no simple, reliable treatment for heartworm in cats, which makes prevention especially important.
Why Kittens Are Hit Harder
Kittens can pick up roundworms from their mother’s milk, so some are already infected before they ever go outside. A kitten’s small body can’t tolerate the same parasite load an adult cat might barely notice. Heavy infections cause the classic potbellied look: a round, distended abdomen on an otherwise thin body. Kittens may also fail to gain weight on schedule, develop persistent diarrhea, or become lethargic. In severe cases, a large mass of roundworms can actually block the intestine.
What You Might See in Stool or Vomit
Some worm infections are visible to the naked eye, and knowing what to look for can help you act quickly. Roundworms appear as pale, smooth, spaghetti-like strands, sometimes still moving. Tapeworm segments look like flat, white or yellowish grains of rice, roughly 2 millimeters long. You may spot them wriggling near your cat’s anus, on fresh stool, or dried and stuck to bedding.
Hookworms and lungworms are too small to see without a microscope, so the absence of visible worms in your cat’s stool doesn’t rule out an infection.
How Vets Confirm an Infection
A stool sample is the standard diagnostic tool. The most accurate method is centrifugal fecal flotation, which spins a stool sample to separate parasite eggs based on their density. This technique is consistently more sensitive than simpler methods. For parasites that don’t shed eggs reliably, such as heartworm, vets may use antigen detection tests or PCR testing on blood samples. The Companion Animal Parasite Council recommends routine fecal screening, since many infected cats look completely healthy.
Risk to Humans in the Household
Some feline worms, particularly roundworms, can infect people. Humans typically pick up roundworm eggs from contaminated soil or surfaces, not from direct contact with a cat. Most people who are exposed never develop symptoms. When illness does occur, it takes two main forms. Visceral toxocariasis causes fever, cough, wheezing, abdominal pain, and an enlarged liver as larvae migrate through internal organs. Ocular toxocariasis affects the eye, usually just one, and can cause redness, seeing spots or flashes of light, and in serious cases, vision loss. Children are at higher risk because they’re more likely to put contaminated hands or objects in their mouths. Prompt deworming of your cat and regular litter box cleaning significantly reduce this risk.