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Intestinal Parasites in Cats

ON THIS PAGE: Also visit our Dog Intestinal Parasites page.


Intestinal parasite control is a mainstay of effective cat preventive care. And testing for internal parasites is a cornerstone of our routine wellness exams. If infected with parasites, your cat has treatment and preventative options available at our sister practices. But what are intestinal parasites in cats?

Prevalent intestinal parasites in cats are worms and protozoans (microscopic, non-worm parasites). The more common internal parasites are hookworms, roundworms, and tapeworms. Non-worm parasites common to cats are coccidia, giardia, and toxoplasma.

If parasitic infections are left untreated, problems can arise in the health of your cat, including digestive complications, anemia, and immune deficiency. Kittens, more than adult cats, are particularly vulnerable because of their weaker immune responses. Here is what you need to know to help your cat be parasite free.

Intestinal Worms That Infect Cats

As their name indicates, intestinal worms infest and live inside a feline’s intestinal tract. Most cats—95 percent—are born already infected with intestinal worms, which they “inherit” from their mothers. An entire litter of kittens may acquire worm larvae through their mother’s milk if she is infected. When adult cats have worms, it may be that they have carried the parasites for their entire lives.

Cause and Symptoms

Moreover, adult cats may gain new parasites, especially if they have fleas or if they hunt rodents that themselves have worm larvae within their tissues. Yet, there is a more common source of intestinal worm infection in cats, young or old. Worm eggs can survive for some time in the waste, or waste-contaminated soil, of other (infected) cats. Healthy cats can pick up those eggs simply by making contact with the waste or soil.

Kittens are especially vulnerable to intestinal parasites, not only because worms can pass from their mothers, but also because of kittens’ still-developing immune systems. Therefore, intestinal worms can pose a serious health risk to young cats. They pose less of a threat to life in adult cats. Typically, adults whose health is already compromised are more likely to develop severe worm infections and symptoms.

There are a few species of intestinal worms that are common to cats: hookworm, roundworm, and tapeworm. Although a bit different in size and shape, there are some symptoms that one or all species may exhibit when they infect a cat.

  • Lethargy
  • Poor coat
  • Loss of weight
  • Extended abdomen
  • Vomiting
  • Diarrhea
  • Bloody stool
  • Worms, or worm fragments, in the stool or around the anus
  • (Many cats display no symptoms at all)

It’s important to note, however, that many cats are asymptomatic for intestinal parasites. That means a cat can spread a worm infection that the owner isn’t even aware of. Regular exams by your veterinarian are vital.

Diagnosis and Treatment

Your veterinarian can diagnose intestinal worms by examining a stool sample from your cat. If you notice any of the above symptoms in your cat, schedule an appointment with your vet and collect a fresh stool sample just before your visit. Take the sample with you to your cat’s exam.

This exam is a good annual health practice even if your cat doesn’t display symptoms. Every cat should be checked often for parasites. Cat owners should also clean the litter box every day to help prevent the spread of intestinal parasites.

If your cat’s doctor finds evidence of worms, he or she will prescribe a deworming medication. The dosage will depend on your cat’s weight. Follow the vet’s recommendations for administering the dewormer, in addition to any suggestions that will help your cat avoid a re-infestation. After several weeks, your vet will want to examine a new stool sample to ensure the infection is clear.

Routine deworming may be necessary in the case of cats who frequent the outdoors or who socialize often with other cats. We also recommend regular deworming for kittens during their early vaccination regimen. This is because kittens are very susceptible to worms and have not yet developed strong immune systems.

In addition, since dewormers kill only adult worms and not worm larvae, routine deworming periodically can help keep worm infestations from occurring in the case of high-risk felines. Talk to your veterinarian about your cat’s environment and lifestyle so he or she can offer recommendations suited to your individual needs.

Below, you’ll find a little more about each of the three most common intestinal worms in cats.


Hookworms grow in length to about one-half to one inch. They are white or pale yellow. The Ancylostoma braziliense and Ancylostoma tubaeforme species of hookworm are very common in cats, as well as a species that often infects dogs, Ancylostoma caninum.

Cause. Cats can contract hookworm infection from making contact with, or eating, infected animals or their waste. Kittens can acquire worms from their mothers through the uterus or milk. Cats can even contract hookworms via their grooming habits when they lick their paws after walking on contaminated soil or surfaces. Another way cats can get hookworms is through the skin, mainly through the feet.

Symptoms. Hookworms can burrow through the skin which may result in irritation and secondary infection. Because they attach themselves to the internal lining of the small intestines and feed on blood, hookworms can cause anemia. At the same time, many cats may show no signs of hookworm infection. To summarize, symptoms of hookworm infection can include:

  • Skin infection
  • Loss of weight
  • Poor coat
  • Bloody stool
  • Diarrhea, which may also contain blood
  • Anemia
  • (No symptoms at all)

Treatment and Prevention. Your veterinarian will examine a stool sample from your cat during a routine wellness exam or if symptoms cause you to suspect a parasite infection. This is the best method of hookworm diagnosis. If the vet discovers a hookworm infection, he or she will administer a deworming medication over some time to clear your cat of the parasites. The vet may also prescribe a preventative if your cat is at high-risk for worms.


Roundworms are the most common of the three intestinal worms discussed on this page. Unfortunately, almost all cats are either born with roundworms or acquire them soon after birth. A serious roundworm infection, with its symptoms, is called ascariasis.

Toxocara cati and Toxacaris learning are the two common species of roundworm found in cats. Roundworms grow up to 2 or 3 inches in length and resemble short strands of cooked spaghetti. Rather than attach themselves to the intestinal lining to feed on blood, they roam freely within the intestinal tract and eat food remnants. 

Cause. Transmission of roundworms happens most often when a cat ingests worm eggs or larvae that are 1) passed through the waste of infected animals, or 2) found in the cat’s prey, such as birds, rats, and roaches. Dormant roundworm larvae can activate after several years and grow into adults. Pregnant cats can pass the parasites to their unborn kittens, or later through nursing.

Symptoms. When kittens contract roundworms, they can suffer poor development and their growth can even be stunted. These parasites can cause lethargy, excessive gas, weight loss, diarrhea, and vomiting. Since the worms often form themselves into balls, they can cause intestinal blockage. A pot belly is another common symptom of roundworm infection.

  • Lethargy
  • Gas
  • Poor growth
  • Bloated abdomen
  • Loss of weight
  • Diarrhea
  • Vomiting
  • (No symptoms at all)

You may notice no symptoms at all in cats with roundworms. However, you may see worm eggs or larvae in an infected cat’s waste or around the anus. Since humans can contract roundworms (but rarely develop symptoms) it is important to protect, not only your cat but your entire household from these parasites.

Treatment and Prevention. Routine wellness exams, which include examination of a stool sample, by your veterinarian are the best way to diagnose roundworm infection in your cat. This is especially the case since infected cats may not display symptoms. If your vet finds roundworms, he or she can administer a dewormer to eradicate them.

As a preventive measure, the doctor may also recommend that your cat be treated with a dewormer regularly, particularly if your cat frequents the outdoors. You can also help protect the whole family by keeping the litter box clean and preventing rodent and bug infestations in the home.


There are a few species of tapeworms that infect cats. These are not directly passed from pet to pet, but require an infected flea, bird, rodent, or another intermediate host to transfer tapeworms to a cat. Dipylidium caninum (typically hosted by fleas), Taenia pisiformis (by birds and rodents) Echinococcus granulosus, and multilocularis (by sheep and humans).

Tapeworms reside in the small intestines and attach themselves to the interior wall. They grow in small segments that chain together and look like grains of rice when they break away from the larger chain. Segments (also called proglottids) may contain tapeworm eggs.

Cause. Typically, cats acquire the tapeworms by eating (intentionally or otherwise) the intermediate host. Echinococcus is zoonotic, which means humans can acquire these species of tapeworms and pass them to cats. Outdoor cats who hunt and eat prey typically acquire Taenia worms. Since the usual host of Dipylidium is the flea, pet owners can help prevent the spread of this species of tapeworm through flea prevention. 

Symptoms. While adult cats may suffer few symptoms of tapeworm infection, kittens can suffer stunted growth, an upset digestive tract, and intestinal blockage if a large number of worms accumulate. Other symptoms of tapeworms are poor coat, abdominal bloating, diarrhea, and vomiting if worms have moved into the stomach.

  • Loss of weight
  • Poor growth
  • Poor coat
  • Bloating
  • Digestive upset
  • Diarrhea
  • Vomiting, which may include worm segments
  • (No symptoms at all)

Worm segments may also be seen around an infected cat’s rectum or in its waste. On the other hand, cats with a tapeworm infection may display no symptoms.

Treatment and Prevention. Oral or injectable deworming medications can eliminate tapeworms from your cat. These are prescribed and administered by your veterinarian after he or she diagnoses a tapeworm infection. Your vet will also prescribe flea prevention for your cat, to control the spread of parasites that are hosted by fleas.

Non-Worm Parasites That Infect Cats

Intestinal parasites are not limited to worms. Microscopic single-cell organisms, or protozoa, can also infect cats as parasitic problem-makers. They reside mainly in the intestinal tracts of both adult cats and their kittens.

The common method of contracting these parasites is ingesting contaminated fur, food, or feces via grooming or eating prey. The sharing of litter boxes with other cats, or failing to keep litter boxes clean, can cause infections to spread even more.

Three species of protozoa are common in all cats, but their infections may not cause symptoms of the disease. If symptoms—large or small—appear, they typically occur in kittens or cats with weakened immune systems, such as from FeLV or FIV. The common non-worm parasites are CoccidiaGiardia, and Toxoplasma.

Kittens especially can suffer from Giardia and Coccidia, as these can cause severe digestive issues in the young. General symptoms include:

  • Only partial digestion of food
  • Loss of appetite and/or weight
  • Dehydration
  • Diarrhea
  • Vomiting
  • Blood and/or mucus in the stool
  • Inflammation around the anus
  • (No symptoms at all)

As with all intestinal parasites, many cats show no symptoms. But if you do notice any of these symptoms in your cat, call your veterinarian to make an appointment. The vet can make the appropriate diagnosis to reveal which parasite is the cause and recommend the correct treatment. Oral medications or vaccines can help eliminate or prevent (respectively) these protozoal parasites.


Coccidia in cats (Isospora felis and Isospora rivolta) can spread to kittens from their mothers. Additionally, cats may eat the contaminated droppings of mice, rats, rabbits, or other animals. Coccidia, in the form of cysts laying on the ground or within prey, may also be consumed when feeding. Infection by this parasite is called coccidiosis.

Coccidiosis is most commonly indicated by loss of appetite, dehydration, diarrhea, and vomiting. These symptoms typically occur in kittens and adult cats with immune deficiencies, while other cats may display no symptoms at all.

Only a veterinarian can diagnose Coccidia infection by examining a stool sample, as the required testing is very comprehensive. If diagnosed, the vet will prescribe an anti-parasitic and, if necessary, recommend extended treatment.


Giardia (duodenalis) attach themselves to the interior of the small intestines. Humans can contract them from their pets, and vice versa. An infection can cause diarrhea and vomiting in owners and their cats. The infection is called giardiasis.

Giardia, in cyst form, is acquired by cats when they consume prey or the waste of other infected animals. In addition to the symptoms listed above, cats may also develop fever and eliminate stool that is green and/or very wet.

A parasitic infection of Giardia is both difficult to diagnose and difficult to fully eradicate. Your vet will examine a stool sample and, if present, will prescribe an antibiotic or a specialized dewormer that kills Giardia. Additional treatment may be needed to address other symptoms. To help prevent Giardia infections, ensure a clean environment in your home and proper hygiene for your cat, including a clean litter box.


While the protozoa can proliferate among cats, symptoms of Toxoplasma (gondii) infection are more likely to occur in cats with compromised immune systems. If Toxoplasma moves into the lungs or liver, a cat may develop pneumonia or jaundice, as the case may be.

Cats acquire Toxoplasma by ingesting the cystic form of the parasites within raw meat, such as by eating prey. Symptoms of Toxoplasma infection include loss of appetite, lethargy, and fever. If inflammation occurs, your veterinarian can treat it with steroids, in addition to antibiotics to defeat the infection itself.

Humans can be infected with Toxoplasma. This infection can occur via contact with an infected cat, specifically by coming into contact with contaminated stool from the litter box, fur, etc. However, this is not the most common source of infection in people. Humans are much more likely to contract toxoplasmosis via handling fresh, raw meat, or by coming into contact with contaminated soil during gardening, etc.

Infected humans rarely show symptoms. However, pregnant women and people with immune deficiencies are particularly at risk of developing toxoplasmosis, the disease caused by Toxoplasma. The parasites are also dangerous to an unborn human fetus if the mother is infected while pregnant.

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