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Pet Owner Version

Gastrointestinal Parasites of Cats


Andrew S. Peregrine

, BVMS, PhD, DVM, DEVPC, DACVM-Parasitology, Department of Pathobiology, Ontario Veterinary College, University of Guelph

Reviewed/Revised Aug 2018 | Modified Oct 2022
Topic Resources

Many parasites can infect the digestive system of cats ( see Table: Gastrointestinal Parasites of Cats Gastrointestinal Parasites of Cats Gastrointestinal Parasites of Cats ). The most common ones are described below.



The large roundworms known as ascarids are common in cats, especially in kittens. The most important species is Toxocara cati, as it is both very common and will infect people. Toxascaris leonina also infects cats, but is typically much less common and does not infect people.

Infections with Toxocara cati are most likely to be acquired by ingestion of eggs passed in the feces of infected animals and by eating prey such as mice that carry the parasites. Sometimes, parasites can be passed to kittens through the mother’s milk. Adult parasites can then be found in the small intestine of kittens as early as 3 to 4 weeks of age. In kittens that have eaten infective eggs, hatched larvae penetrate the intestinal wall, travel to the lungs via the bloodstream, are coughed up, swallowed, and mature to egg-producing adults in the small intestine. However, larvae (an immature stage of the parasite) can sometimes also live within other organs of affected animals and people. Adult cats generally have some resistance to infection. However, around the time when they give birth, immunity to infection may be suppressed and significant numbers of eggs may be present in feces.

Infections are often not associated with any signs. The first indication of infection in young animals can be lack of growth and loss of condition. Infected cats can have a dull coat and often are “potbellied.” Worms may be vomited or passed in the feces. In the early stages, migrating larvae occasionally cause pneumonia, which can be associated with coughing. Diarrhea with mucus may be evident. Infection is diagnosed by microscopic detection of eggs in feces.

Several drugs are effective for treatment of roundworm infections in cats. Certain preventive programs for heartworm infection also control intestinal roundworm infections. Ideally, treatment for kittens should be started at 3 to 4 weeks of age, repeated at 2-week intervals until 3 months of age, and then continued monthly until 6 months of age. Your veterinarian will prescribe the most appropriate medication for your cat.

Because people, especially children, can become infected with roundworms, it is important to practice good hygiene (e.g., prompt removal of feces and washing of hands) in potentially contaminated areas or around affected cats.


Several types of hookworms can cause gastrointestinal disease in cats. Ancylostoma tubaeforme is the most likely to cause illness and is found globally. Ancylostoma braziliense is found in central and South America, southeast US, and Africa. Ancylostoma ceylanicum is found throughout Asia, the Middle East, and parts of South America. Uncinaria stenocephala is found globally in temperate and subarctic climates (including Canada and the northern US), but infections with this species are rare. Cats can become infected by ingesting the larvae in the environment (passed in the feces of an infected animal), by eating infected rodents, or by larval penetration of the skin. Infection is more common in kittens. When larvae mature to adults, they live in the small intestine.

Most infected cats show no signs. Anemia occasionally occurs and is the result of bloodsucking by the worms in the small intestine. Feces may become loose and have a tarry consistency. Loss of appetite, weight loss, and weakness occasionally develop in longterm disease. A diagnosis can often be made from the microscopic identification of hookworm eggs in fresh feces from infected cats.

A number of drugs and drug combinations are approved for treatment of hookworm infections. In addition, some heartworm medications also control certain species of hookworms. Deworming programs for roundworms in cats will usually also control hookworm infections.


Several types of tapeworms—properly known as cestodes—may infect cats. Adult tapeworms are segmented worms found in the intestines. They rarely cause serious disease. The common tapeworm of cats, Dipylidium, is acquired from eating fleas. Much less frequently, cats with access to infected house (or outdoor) mice and rats can acquire other types of tapeworm infections from these sources. In parts of the Middle East, southern Europe, and northern Africa, tapeworms can also be acquired by eating reptiles. Signs of tapeworm infection vary and can include a failure to digest and absorb food normally (unthriftiness), malaise, variable appetite, poor hair coat, and mild diarrhea. Often, there are no signs. Very rarely, seizures are seen. Diagnosis is based on finding tapeworm segments or eggs in the feces.

Control of tapeworms requires both treatment and prevention. Flea control is critical for tapeworm control, even for indoor cats. In addition to being exposed to fleas, cats that roam freely may also become reinfected by eating dead or prey animals. Confined animals can be reinfected by fleas. An accurate diagnosis will enable your veterinarian to provide effective advice on treating the infection and preventing reinfection. Several drugs are available for the treatment of tapeworms in cats.


Flukes (also called trematodes) are a class of parasites that can infect cats. They have a complex life cycle that can involve multiple intermediate hosts. There are several types of intestinal, liver, and pancreatic flukes that can infect cats ( see Table: Types of Flukes that Infect Cats Types of Flukes that Infect Cats Types of Flukes that Infect Cats ); however, infection of cats is uncommon in the US.


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