Parasite Control

Effective control and prevention of both external and internal parasites is essential to promote the health of the cat, promote public safety, and to preserve the bond between pets and people. While prevention and treatment of parasites in the family dog is important, the health of the family cat should not be overlooked in this regard.

Evaluating Risk

A customized parasite control program should be created for every cat, regardless of indoor or outdoor status. Recognizing that geographic, seasonal, and lifestyle factors affect the risk of infection with parasites, a clinic prevention program should be adapted to suit the needs of individual patients within the geographic region. In some regions of Canada, the risk of parasite infection may be seasonally driven, but in dense environments such as apartment buildings and multi-pet households, year-round spread of parasites needs to be considered. It is an incorrect assumption that an indoor cat is not at risk for parasitic infection. Indoor cats are at risk of parasites transmitted on clothing, furniture, footwear, and potted plants. Additionally, the transmission of parasites from outdoor pets to the indoor cat should be considered. Indoor and outdoor cats that hunt and consume rodents and/or rabbits are at risk of tapeworm infection. Consumption of invertebrate gastropods such as snails increases the risk of lungworm infection in many geographical locations.

A clinic’s parasite prevention wellness protocol should be based on:

  • The age of the cat.
  • The life cycle and prepatent period for the parasite in question.
  • The environmental and geographic prevalence of the parasite(s).
  • The individual cat’s relative risk of exposure (including travel, boarding, showing).
  • The household number and types of pets.
  • The mechanism of action of the chosen product, including the duration of action and targeted parasite life stages.

In addition, client factors that may increase an individual’s susceptibility should be evaluated (see Zoonotic Diseases).

External Parasites


Depending on the individual’s lifestyle and geographic region, a cat may be at risk for flea infestation. High-risk scenarios include access to the outdoors, living with other pets that go outdoors, or living in pet-dense environments such as apartment buildings. In these cases, the use of a year-round, monthly veterinary flea control product is strongly recommended. Indoor cats living in a stable population are not free of risk.

Veterinarians play an important role in educating clients about the flea life cycle in cats and dogs and the appropriate use of recommended products. Risks associated with using retail topical products, including powders, sprays, spot-ons, and flea collars, must be discussed due to the high incidence of pyrethrin/permethrin toxicosis. A minimum 3-month treatment period is recommended for managing existing flea infestations due to the nature of the flea life cycle. Treatment with parasiticides effective against Dipylidium caninum, a tapeworm requiring fleas as an intermediate host, are an essential component of treatment protocols for flea infestations.

Diagnosis of fleas in cats can be challenging. The fastidious grooming of cats often results in the absence of flea dirt or fleas despite combing to look for evidence of infection. Thus, when fleas and/or flea allergy dermatitis are suspected, treatment should be initiated regardless of whether fleas or flea dirt are seen. An appropriate, licensed topical product should be used according to the manufacturer’s recommendations.


In Canada, tick distribution varies with geographic area and tick species. Climate change is resulting in ticks being found in regions previously unaffected by these parasites in increasing numbers. Cats seem to have a decreased susceptibility to tick-borne diseases but can still transport ticks to other pets and to humans in the household. Clients should be informed about the need for regular examination to detect ticks, and how to remove ticks. Additionally, because many retail and veterinary prescribed tick products used for dogs contain ingredients that are toxic and potentially life threatening for cats, it is critical to educate the client about the risks involved with using these canine products on cats. Instead, the many feline-safe, commercial veterinary products now available to protect cats from ticks should be recommended.

Lice and Mites

Kittens and newly adopted cats should be evaluated for infection with ear mites (Otodectes cynotis). Patients presenting with pruritus, scaling, excoriation, and hair loss should also be evaluated for feline lice (Felicola subrostratus), mites (Cheyletiella spp., Notoedres cati and others), and demodicosis (Demodex cati or D. gatoi). Appropriate diagnostic tests include skin scrapings, flea combings, hair trichograms, acetate tape preparations, and fecal examinations. Appropriate therapy should be based on the availability of approved products, available published data, and the specific diagnosis. In-contact cats and dogs should be evaluated for contagion risk and treated appropriately.

Internal Parasites

Laboratory Testing for Internal Parasites

Fecal testing is recommended as a part of every preventive healthcare examination for the purpose of monitoring compliance with monthly preventive medication as well as for the diagnosis of some internal parasites not treated by broad-spectrum preventatives. In kittens, testing can be coordinated with vaccine administration so that 2 to 4 tests are run during the first year of life.

Fecal centrifugation flotation techniques with either zinc sulphate or modified Sheather’s sugar solution (rather than fecal flotation by sedimentation) are considered the most reliable in-house screening tests for most intestinal parasites (especially nematodes). The ideal sample size is 1 gram (a cube measuring 1/2 inch on each side) of fresh formed feces (or 2 grams if feces are soft). However, the sensitivity of these tests may be low, and external laboratories should be consulted for further guidance and techniques that may produce improved recovery rates. Some commercial laboratories now offer ELISA-based fecal testing for common intestinal parasites. The sensitivity of testing is perceived to be best when both flotation and ELISA testing is utilized.

Fecal wet mount techniques are also useful, especially for detecting organisms such as Giardia and Tritrichomonas. A small (about the size of a rice grain), freshly passed or collected fecal sample is required. Baermann fecal testing is recommended for cats with outdoor access in areas at risk of lungworm, including Aelurostrongylus species, and for any cat presenting with cough or other clinical signs suggestive of lower airway inflammation.

Nematode Infections

Roundworm infections (Toxocara cati, Toxascaris leonina) are common in cats and kittens. Infection can occur by ingestion of contaminated food and water or infected paratenic hosts. Transmammary infection does occur, but transplacental infection has not been reported. The reported prepatent period for T. cati is 8 weeks but may be as short as 3 weeks depending on the mode of infection (e.g., ingestion of an egg or paratenic host, or transmammary infection). Similarly, the reported prepatent period for T. leonina varies but is generally accepted to be 7 to 10 weeks.

Hookworm infections (Ancylostoma spp.) are uncommon in cats. Infection occurs via ingestion of contaminated food or water, consumption of a paratenic host, or transdermal larval migration. Transmammary infection has not been reported in cats. The prepatent period ranges from 19 to 28 days. Toxascaris leonina and A. braziliense (rare in Canada) can also infect dogs, which is an important consideration in multi-pet households.

Whipworm infections (Trichuris felis) rarely occur in cats in North America. Eucoleus (Capillaria) aerophila should be considered when eggs with bipolar plugs are identified by fecal examination.

Prevalence data for different Canadian geographical areas can be found in the Canadian Guidelines for the Treatment of Parasites in Dogs and Cats.

Cestode Infections

While tapeworm infection is often diagnosed by finding tapeworm segments in the cat’s perineal area, on feces, or on bedding, this evidence is not always available. Therefore, the possibility of tapeworm infection must be based on the patient’s individual risk factors. At each preventive healthcare visit, the cat should be assessed for fleas and the client questioned about the cat’s hunting habits. Not all products have broad-spectrum activity against all tapeworm species, so it is important to identify which species is implicated. For example, fenbendazole will not eliminate tapeworm infection (Dipylidium caninum) secondary to flea ingestion.

Only affected individuals (not in-contact animals) need to be treated because cestodes require an intermediate host for transmission. Note should be made if exposure to common intermediate hosts (e.g., fleas in the household or access to rodents) exists as this increases the possibility of infection in other pets in the household. Repeated treatments for tapeworm infection should not be necessary in cases where the source of infection has been successfully eliminated. When repeat exposure occurs, such as in cats consuming rodents, a regular deworming plan for Taenia taeniaeformis is recommended. Similarly, if fleas are not successfully controlled, repeated therapy will be needed for D. caninum. All kittens should receive at least 1 deworming with a product effective against tapeworms during their initial deworming series. Adult cats should receive periodic treatment based on risk factors.


Kittens less than 6 months of age

Kittens are a vulnerable age group for internal parasites. All kittens should receive an anthelmintic at 2, 4, 6 and 8 weeks of age, to ensure prompt removal of Toxocara spp. acquired from the queen, followed by monthly treatments until 6 months of age. Alternatively, when kittens are first brought home, they should receive an anthelmintic that is adulticidal for a minimum of 3 treatments spaced 2 weeks apart. Initial deworming frequency is reduced if a product with adulticidal and larvicidal activity is used. Following this initial deworming, kittens should be treated with a broad-spectrum parasiticide monthly until 6 months of age. Nursing queens should be treated at the same time as their kittens to prevent patent infections. All kittens should receive at least 1 deworming treatment that includes a product effective against tapeworms.

Cats over 6 months of age

At 6 months of age, start a year-round or seasonal protocol administering a broad-spectrum parasiticide based on the cat’s risk for external and internal parasites. Heartworm prevention should be recommended for cats in endemic areas, and for cats that travel to endemic areas. Due to the high false negative rate for detecting parasites via routine in-house fecal examinations, deworming 2-4 times per year is recommended by various expert groups, if the cat is not receiving regular, monthly treatment.

Intestinal Protozoal Infections

Heartworm Disease in Cats

The cat is a partially adapted host for the heartworm parasite Dirofilaria immitis and is considered to be more resistant to infection with adult heartworm than the dog. Current research data indicate that 3 to 10 adult worms will develop in approximately 75% of cats experimentally infected with 100 3rd stage larvae (L3). This is in comparison to 60 adult worms in 100% of experimentally infected dogs.

However, cats can develop significant pulmonary disease in response to immature heartworms; adult worms are not required for pathologic changes and clinical signs. Wherever the heartworm host mosquito species are found, the risk of mosquito bite is the same for dogs and cats. While some mosquito species do demonstrate a preference for dogs, the most common mosquito species in urban centres, Culex spp., feeds on both cats and dogs without preference. Additionally, cats do not need to go outside to be exposed to infected mosquito hosts.

As a partially adapted host, where zero to minimal adult heartworms develop, diagnosis of heartworm infection in the cat is difficult. Infected cats may exhibit only transient clinical signs (e.g., vomiting or coughing) or die of infection without a diagnosis. It is therefore recommended that cats living in, (or travelling to) endemic areas should receive appropriate monthly preventives against heartworm beginning within 1 month of first mosquito exposure and continuing until 1 month after the last exposure to mosquitoes. Due to the low risk of adult worm development and the higher incidence of unisex infections (often male), testing before administration of prophylaxis is not required.

Testing cats for exposure (antibody) to heartworm or infection with adult (antigen) heartworm should be considered in endemic areas and where patients are exhibiting signs suggestive of feline heartworm infection, although interpretation of results is often difficult, and infection may be missed. Imaging (radiology, ultrasound) may provide additional diagnostic information.


  • Susan Little, DVM, DABVP (Feline Practice) Bytown Cat Hospital, Ottawa, Ontario
  • Diane McKelvey, DVM, DABVP (Feline Practice) Aberdeen Veterinary Hospital, Kamloops, British Columbia
  • Elizabeth O’Brien, DVM, DABVP (Feline Practice) The Cat Clinic, Hamilton, Ontario
  • Elizabeth Ruelle, DVM, DABVP (Feline Practice) Wild Rose Cat Clinic of Calgary, Calgary, Alberta
  • Kelly St. Denis, MSC, DVM, DABVP (Feline Practice) The Charing Cross Cat Clinic, Brantford, Ontario
  • Margie Scherk, DVM, DABVP (Feline Practice) catsINK, Vancouver, British Columbia

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