My Cat Has Intestinal Parasites – How Long After Deworming Are The Worms Gone?

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  • Your cat is curled up asleep in the sweetest little ball on your bed. As you walk past, you notice tiny little rice grains in the bed around her back end – Does she have worms?! As pet owners, we often don’t worry about our cats having worms until we see them with our own eyes, but worms are a fairly common problem in our household pets.

    There are several types of intestinal worms in cats that are commonly seen by your vet: hookworms, such as Ancylostoma species; roundworms, such as Toxocara cati and Toxascaris leonina; and tapeworms, such as Dipylidium caninum and Taenia taeniaeformis. It is important for your vet to identify the type of worm your cat has so that they can choose the most effective dewormer. 

    What types of intestinal worms are found in cats?


    This Cat-World article talks about different types of worms in cats.


    Hookworms get their name from the mouth-like parts that attach to the intestines of their host. They are transmitted via a mother cat’s milk to her kittens, as well as via larval penetration through the feet and skin when a cat walks through contaminated areas. Hookworms feed on blood and can lead to anemia (a low number of red blood cells). Since this worm feeds on blood, common symptoms include diarrhea and dark, tarry feces. They can also cause ulcers on paw pads if migrating through the skin. 


    There are two common species of roundworms found in cats – Toxcara cati and Toxascaris leonina. According to the Companion Animal Parasite Council (CAPC), T. cati is the roundworm most frequently seen with more than 25% of cats testing positive in recent studies. T. cati is passed to the cat by ingesting larva from the soil or from mother to kittens in late pregnancy. It can also be transmitted to cats when they consume an infected rodent. These worms do not attach to the intestinal wall but feed on nutrients consumed by the cat. This intestinal worm does NOT infect dogs; they are infected by a dog-specific species of roundworm. 

    Roundworms are not often seen in the stool or in the litterbox and may only be diagnosed via fecal sample when eggs are seen under the microscope. These worms typically cause more problems in kittens or immunocompromised than in healthy adult cats. Common symptoms seen with a roundworm infection include: 

    • Poor growth
    • Dull hair coat
    • Pot-bellied appearance
    • Vomiting
    • Severe infestations can lead to intestinal obstruction


    The most common tapeworm species, Dipylidium caninum, infects cats when they ingest an infected flea; they are not spread directly from cat to cat. The worm attaches to the cat’s small intestine and then drops egg sacs off the end of its tail. While tapeworms can grow quite long, owners often only see the segments when they are passed in the stool or on the hair around the rectum. They often appear small and flat, similar to rice grains or sesame seeds. 

    Tapeworms do not often cause significant symptoms but are unsightly when passed out of the cat’s anus onto the fur or the owner’s bedding. In severe cases, they can occasionally cause intestinal obstruction. 

    How do dewormers work? 


    Most dewormers work by targeting the worm’s nervous system and freezing or paralyzing it. The resulting paralysis of the worm causes it to lose its attachment to the host’s (in this case, your cat) intestines. Most dewormers take 1-3 weeks to take effect, but will start working within a few hours.

    The tapeworm dewormer, praziquantel, works a bit differently. It dissolves the worm’s skin and then is removed by the host’s immune system. Praziquantel is NOT found in most routine deworming products. This is why your cat may have a tapeworm infection despite yearly or twice-yearly “routine” deworming with products like pyrantel. 

    Will my cat still have worms after deworming? 

    my cat still have worms after deworming

    A dewormed cat can still have worms, even if you gave them an appropriate dewormer. It does not mean that the dewormer was ineffective. It often just means that it didn’t get ALL the worms. 

    There are a few reasons your cat may still have worms. Sometimes it is due to reinfection; for example, if your cat ingested another infected flea, then it could easily be reinfected with tapeworms. Since tapeworms are spread by fleas, it is important to treat for both tapeworms and fleas.

    The other important thing to remember about most dewormers is that they only affect worms in the intestinal tract, not those in other parts of the body. So if a worm has migrated to lung or mammary tissue, those are much harder to get rid of. You may need additional rounds of dewormer as worms migrate through the body. This is especially important for cats that go outside or hunt prey animals frequently.

    Do you need to deworm a cat again? 

    Some vets will recommend rechecking a fecal sample from your cat to ensure that the parasites are cleared. This involves getting a very small sample of stool; they look at the sample under the microscope for the presence of various worm eggs. This test helps them determine if another dose of dewormer is needed. 

    If your cat has been treated for tapeworms, keep in mind you will need to start a flea preventative program immediately as well. Even if your cat is treated for the tapeworms, they can immediately reinfect themselves as long as infected fleas are still present in the environment. Your vet may start flea prevention at the same time as the initial tapeworm treatment, recheck a fecal sample in a few weeks, and treat again if needed. 

    How can I stop my cat from being reinfected once they no longer have worms? 

    Dewormed Your Cat

    Use parasite treatments as prescribed by your vet

    Year-round prevention is the best way to keep your cat healthy and worm-free. While there are a lot of over-the-counter deworming products, it is best to consult with your veterinarian before starting any parasite preventative. They will be able to tailor preventative care to specifically to your cat’s needs and lifestyle. For example, a cat that lives outdoors and frequently hunts small prey animals may be more at risk than the indoor-only cat. Very young cats and immunocompromised cats are also more at risk for developing severe symptoms. 

    The Companion Animal Parasite Council has general deworming and testing guidelines for both kittens and adult cats: 

    • 4 times per year in kittens until 1 year old
    • 2 times per year in adults (depending on risk assessment) 

    Practice good hygiene and overall home cleanliness

    Good hygiene, feces removal, and overall home cleanliness are some of the most important steps you can take to protect your cat. For example, it is estimated that 90% of fleas are found in the environment (house, carpet) and 10% are actually on the pet. Since tapeworms are spread via infected fleas, home cleanliness becomes vital to controlling the spread of the worms and preventing reinfection. 

    Some worm eggs and larvae can live in the environment even in the harshest of conditions. If infected feces are left in the yard, they can get into the soil and are hard to get rid of. Removing feces immediately from infected animals helps minimize this environmental contamination. 

    Refer to this Cat-World to properly clean your house.


    Is it okay to use dewormers as a preventative treatment? 

    Parasite control is an important part of your cat’s year-round preventative care. Typically your veterinarian will recommend annual (or twice a year depending on risks) fecal testing to help identify and treat any active intestinal parasite infections. There are a variety of oral and topical deworming products available for cats. It is very important to choose a product specifically for cats, as some dog products can be toxic. Always consult with your veterinarian about what fits your cat’s needs best.

    Are there any side effects of deworming treatments?

    Deworming products are typically very safe when used appropriately. While uncommon, some side effects include vomiting, diarrhea, and some loss of appetite. You may also see itching or hair loss at the site if topical treatment is used. Symptoms often occur in the first 24 hours after administering the dewormer. Always check in with your vet if your cat is not feeling well and you have recently given them a deworming product. 



    • Dr. Sarah Graves has been a veterinarian for almost 10 years and graduated from one of the leading veterinarian schools in the world: the Royal Veterinary College at the University of London.