Most Common Parasites in Cats

What kinds of parasites do cats get?

Parasites in cats are varied and fall into two main types: external and internal. As the name implies, external parasites live on the hair and skin of cats and internal parasites live in the body and organs like, for example, the heart or intestines.


Parasites are defined as organisms that live inside or on another organism, called the host, and feed themselves off the host, causing it harm. Parasite prevention is key for a healthy cat, and a general understanding of potential health hazards helps protect your cat from several illnesses.



What are the most common external cat parasites?


Fleas are small insects that live on your cat’s skin, feeding on their blood and causing irritation. They are some of the most common parasites in cats and are considered one of the more serious groups of pests since they can transmit various diseases in addition to causing discomfort through biting, these include tapeworm and bacterial infections.

Flea infestations can affect any cat, but outdoor cats, cats living with pets that have outdoor access, and cats in multi-pet households are at greater risk of catching fleas. Cats are known to conceal their flea infestations, but the usual indicators of fleas are constant scratching, licking, or biting of the skin.

Thankfully, fleas can easily be treated once they are found. There are safe and convenient spot-on medicines you can get from your veterinarian, with indications on how to use them and how often. There are also flea collars available that can help too. And lastly, there are also medicines you can feed your cat and will kill fleas present on your pet.


These are eight-legged and egg-shaped arachnid parasites that range in size from 1mm to 1cm. They are more common in wildlife-rich locations, making it easier for cats to catch ticks. These parasites are active all year long, but spring and autumn are when pets are most likely to come across them. Ticks can cause Lyme disease and Mycoplasma, which can be passed on to cats and even people if they bite you.

Ticks are large enough to be noticed when running your hands over your cat when checking for bumps and irritation. A tick feels like a surface-level bump on their fur. They are usually found on the head, neck, ears, and legs.

There are several commercially available tick repellents. Ranging from over-the-counter remedies like spot-ons and collars to prescription treatments provided by your veterinarian. It is important to note you should never use flea and tick products designed for dogs on cats because they can be poisonous.


Mites are tiny spider-like parasites that live on a cat’s skin or in the ear canals. They can cause substantial irritation, skin diseases as well as bacterial infections. The most common mite found in cats is the ear mite, generally found in the ear canal but which can also live in other areas of the body. Other types of mites can cause scabies and trombiculosis.

The most common sign of mites in cats is constant scratching, head-shaking, licking or biting, all of which can lead to wounds, scabs, inflammation and hair loss.

The best way to prevent mites in your cat is with anti-parasite treatments, monitoring and regular grooming. If you notice signs of these parasites, it is best to have them examined by a vet who will determine the specific type involved and will provide the proper treatment.


What internal parasites afflict cats?

There are various types of internal parasites that make cats their hosts, including wormlike parasites known as roundworm, tapeworm, heartworm, and hookworm; and other protozoan parasitic species such as giardia, coccidia and toxoplasma.


Giardia duodenalis is a one-celled parasitic organism that attaches itself to the intestine and causes giardiasis, it is not a worm, bacteria or virus, it’s a protozoan parasite. Cats get infected by ingesting the parasite in its cyst stage that is found in the feces of other infected animals.

Cats with giardiasis may develop diarrhea, fatty stools, and gradual weight loss. Stool can be mushy or watery, have a green tint to them, and contain blood. Excess mucus is common in the stool. Diarrhea can be chronic or recurring. Cats affected may be less active and sometimes develop a fever.

If your cat is diagnosed with giardiasis, your vet will determine the course of action and prescribe the medications necessary to eliminate the parasite with supplemental treatment for dehydration and diarrhea if present. Environmental disinfection and good hygiene are the best ways to prevent giardiasis.


Isospora felis and Isospora rivolta are one-celled parasitic organisms that cause an infection called coccidiosis. Cats generally become infected by ingesting cysts found in cat feces, other animals (such as mice and flies) or soil where the cysts are present. The common species of coccidia that infects cats cannot infect humans.

Most cats infected by coccidia will not show clinical signs, but kittens and adult cats with lowered immune systems can suffer from severe watery diarrhea, dehydration, vomiting and decreased appetite. Coccidiosis can only be diagnosed by a very exhaustive examination of the stools.

If a cat is diagnosed with coccidiosis, the veterinarian will prescribe specific anti-parasitic medications to treat the infection. Other supplemental treatment may be needed but most cats will not need them.


Toxoplasma gondii is the single-celled parasite that causes toxoplasmosis, a quite common parasitic organism in cats that seldom develops into a disease. Most cats are infected by eating the Toxoplasma parasite in its cyst stage in raw meat (such as infected prey). Cats can transmit toxoplasmosis to humans, and while most healthy humans show little signs of disease, people with compromised immune systems and pregnant women are most at risk of developing the disease.

Signs of toxoplasmosis are most likely to present themselves in cats with weakened immune systems, like kittens or cats suffering from FeLV or FIV. Common symptoms are fever, lethargy, and appetite loss. Other clinical signs may develop depending on where the parasite is located, such as pneumonia if the parasite attaches itself to the lungs or jaundice if it is in the liver.

Antibiotics are normally used to treat toxoplasmosis, sometimes in tandem with steroids if inflammation is present. Your veterinarian will prescribe a treatment as soon as your cat is diagnosed, and it should continue for a few days


Roundworms, or ascarids, are a common parasite in cats. As the name implies, they’re large and round worms that live in the intestines and cause ascariasis. Kittens generally become infected with roundworms through nursing and can, along with adults, catch these parasites by eating the larvae found in the feces of infected animals or in prey that acts as egg hosts, such as birds, rodents and cockroaches. Humans can become infected with roundworms, but seldom develop the disease.

The most common signs of roundworms are diarrhea, lethargy, weight loss and some vomiting. In cats with few worms present, there may be no signs of infection, but you may notice them in the stool or vomit.

Since roundworm infection symptoms may not be visible, it is important to keep up to date on yearly wellness visits including stool analysis. Once diagnosed, treating ascariasis is relatively easy, with a few doses of specific dewormers needed to eliminate them. Since cats are always at risk of getting roundworms, periodic deworming should be performed as a preventative method, especially with outdoor cats. Keeping a clean litterbox and controlling insect and rodent infestations is also recommended.


These are flat, long, segmented parasites that attach to the walls of the small intestine. Cats are most commonly infected by the Dipylidium caninum species, but several types are known to infect pets. Cats only become infected after swallowing a flea that has been infected with the tapeworm, this generally happens through grooming or as a response to flea bites. Humans are highly unlikely to be infected by tapeworms.

Tapeworms are not known to cause many symptoms in cats, the most obvious sign of infection is the presence of worm segments -or proglottids- in the feces and around the anus; there may also be vomiting, including proglottids, if the worm has travelled to the stomach and ocassionally some weight loss.

Tapeworm treatment includes deworming medications either in oral or injection form. The best way to prevent tapeworm infection in cats is through flea control treatments, especially in cats with outdoor access.


Heartworms or Dirofilaria immitis, are protozoan parasites that live in the heart and surrounding blood vessels. Cats are generally more resistant to heartworm infection than dogs, however, infection may still happen. This disease is transmitted by infected mosquito bites, when eggs are injected into the pet; the larvae travel through the bloodstream for several months, finally settling in the heart and pulmonary arteries.

Heartworm infection may not show any symptoms in cats until its later stages. The most common visible signs are rapid breathing and coughing attacks, with some vomiting, loss of appetite and weight loss. Cats may infrequently faint, have seizures and have trouble walking. Sudden collapse and death are sometimes the first signs of heartworm disease in cats.

Unfortunately, there is no specific medication for treating heartworm disease in cats and the medication used on dogs isn’t safe for cats. The usual treatment in cats includes treating the symptoms stabilizing the animal, including hospitalization if the veterinarian considers it necessary. However, heartworm infection is easily preventable with regular administration of heartworm preventives available in different formulations. Remember to always consult your veterinarian first and have your cat tested for heartworm before administering this medication.


These parasites are small (1/8″) and very thin worms with hook-shaped mouthparts that help them attach to the walls of the intestines and feed on the host’s blood and tissue fluids. Cats are commonly infected by Ancylostoma tubaeforme and Ancylostoma braziliense but may be infected by the dog hookworm (Ancylostoma caninum).

Hookworm eggs can infect cats by either being ingested (commonly when grooming their paws), burrowing through the skin, or eating prey that has been infected. Kittens may also become infected via their mother’s milk. Humans can not be infected internally, but larvae can burrow into the skin and cause skin infection.

The most common signs of hookworm infection in cats are anemia, weight loss, diarrhea, poor haircoat and blood in the feces.

The best way to diagnose hookworms is through a stool analysis; and, once diagnosed by a veterinarian, treatment involves a few rounds of deworming. Regular use of parasite preventives is recommended for cats at risk, along with periodic deworming, daily litterbox cleaning and good hygiene.


We hope this article has proved informative! Please contact the team at Wellesley if you have any further questions or concerns about external and internal parasites in cats. We recommend you take the time to talk in detail with one of our licensed veterinarians. They will provide the best suggestions and strategies for your pet. For an appointment, please contact us at 416-966-1830 or click the button below.




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