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Veterinarian Technician March 2011 (Vol 32, No 3)

Educating Clients About Fleas

by Sandra Rhodes, RAHT

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    More than 2000 species of fleas are recognized worldwide, including Ctenocepha­lides felis (the cat flea) and Ctenocephalides canis (the dog flea).1 In North America, the most common ectoparasite of dogs and cats is C. felis.1,2 Cat fleas are not host specific; they have been found to infest more than 50 different species of avian and mammalian hosts throughout the world, including cats, dogs, raccoons, and opossums.1,3 Infestation can result in skin trauma because of scratching by the pet. In addition, the pet may develop anemia (due to blood loss) or flea allergy dermatitis (FAD)—a skin condition caused by hypersensitivity to flea saliva.4–6 Fleas can also serve as vectors for Rickettsia typhi, Bartonella henselae, and Mycoplasma haemofelis and as hosts for Dipylidium caninum (BOX 1).2,7

    BOX 1. Diseases and Parasites Transmitted by Cat Flea

    Cat fleas are vectors for disease transmission and hosts for parasites. For example, cat fleas can transmit diseases such as hemobartonellosis, which is caused by Mycoplasma haemofelis,7 or cat-scratch disease, which is caused by Bartonella henselae.2 Cat fleas also serve as the intermediate host for Dipylidium caninum (the canine tapeworm).1,2,5 When flea larvae ingest tapeworm eggs, cysticercoids (i.e., tapeworm larvae) develop in the body of the flea, which in turn may be ingested by a dog or cat during grooming.1

    Typhus, which is caused by infection with Rickettsia typhi or Rickettsia felis, can be transmitted by cat fleas to humans and small mammals.6 The disease is more prevalent along the southeastern, southwestern, and Gulf coasts of the United States.1,2

    Because fleas are not always visible on a pet, infestation may not be apparent to the owner, especially if the pet is not scratching itself excessively or exhibiting skin conditions such as FAD. Technicians should understand the flea life cycle, recognize the clinical signs of infestation, and educate owners about treatment options and preventives. The remainder of this article pertains only to the cat flea.

    Characteristics and Life Cycle

    Flea eggs

    FIGURE 1. Flea eggs.

    (©2009, The Companion Animal Parasite Council [CAPC], www.capcvet.org)

    The cat flea is a wingless insect with a hard exoskeleton, a laterally flattened body, and an enlarged third pair of legs that allows it to jump between hosts.4,5 Adult fleas are about 1/8 inch (3.2 mm) in length and are medium-brown to black. Flea eggs, which are white, smooth, and oval, are slightly larger than 1/64 inch (0.5 mm) in length1,4 (FIGURE 1).

    Flea larvae are only 3/16 inch (4.7 mm) in length and resemble worms4 (FIGURE 2). They have short, hair-like bristles and a brownish head.

    Flea eggs, larvae, and pupae (FIGURE 3) can be found off the host3 on surfaces such as bedding, carpet, or grass; however, fleas in the adult stage spend most of their life on the host.4 Adult fleas require a host to feed. They pierce the skin of the host with their mouthparts and suck the host’s blood. Al­though cat fleas prefer dogs or cats as hosts, they will move to a different host species, such as humans, if the preferred host is unavailable.5

    Flea larvae

    FIGURE 2. Flea larvae are maggot-like with chewing mouthparts and small hairs.

    (©2009, The Companion Animal Parasite Council [CAPC], www.capcvet.org)

    Cocoons of flea pupae

    FIGURE 3. The cocoons of flea pupae are like soft, moist silk and become coated with debris from the environment.

    (©2009, The Companion Animal Parasite Council [CAPC], www.capcvet.org)

    On the host, female fleas feed and mate, laying up to 50 eggs per day.8,9 The eggs fall off the host and land on surfaces such as carpet or bedding. Under optimum conditions (room temperature) the eggs hatch in 2 days,4 producing larvae that feed on the feces of adult fleas, on skin cells, and on organic matter in the environment. Larvae avoid direct light and burrow into carpet, bedding, cracks in the floor, grass, or decaying organic matter. They are susceptible to heat and desiccation.1 A relative humidity of at least 50% is required for successful development of larvae; exposure to a relative humidity below 50% is lethal at this stage.6The duration of the larval stage varies according to temperature and environment (i.e., location and time of year) but is approximately 2 weeks, after which the larvae spin a cocoon and pupate.4,5 Pupae develop into adult fleas, but at cool temperatures, they can remain dormant in the cocoon for up to 12 months.4 Warm temperatures, body heat, or activities such as walking or vacuuming stimulate them to emerge. The adult fleas seek a suitable host and begin feeding as soon as they find one. Flea populations increase during spring and summer, but fleas are found year-round in North America. Environmental temperatures <37.4°F (3°C) for several days can kill all stages of fleas.1,6 Adult fleas survive winter in northern temperate climates by living on hosts, including wild or domestic mammals. Eggs laid on the nesting site of a host survive and develop into adults if the site is protected from the cold. Pets housed indoors offer the ideal breeding ground for fleas during colder months.

    Clinical Signs Associated With Flea Infestation

    Except for scratching, animals without FAD may exhibit few clinical signs of flea infestation, although severely infested hosts—particularly young animals—can develop anemia.6 Combing the entire pet with a flea comb is the recommended method for identifying fleas and flea dirt. Examination of the pet’s ventral abdomen and inner leg regions may reveal adult fleas moving or jumping along the skin surface as well as the presence of flea dirt (i.e., feces), which resembles sprinkled pepper.6 When specks of flea feces are placed on a wet paper towel, they dissolve and turn red.2

    Animals with FAD often have intense pruritus, leading to excessive scratching, skin infections, and alopecia.4,6 Clinical signs associated with FAD vary depending on factors such as presence of concurrent skin disease or degree of hypersensitivity. FAD should be differentiated from other dermatologic conditions, such as atopy, food allergy dermatitis, or mange.1 If FAD is diagnosed, it should be treated concurrently with the flea infestation because additional flea bites contribute to more itching and self-trauma, which prevent the skin from healing.

    Treatment of Flea Infestation

    Pets that are infested with fleas may be treated with products that are administered topically, orally, or by injection (TABLE 1) .4

    When a flea control regimen is recommended, technicians should determine whether clients are using any over-the-counter flea products and whether any of these products have been effective. Technicians should review administration instructions with the owner and instruct the owner to care­fully read the label before administering the product, noting any cautions or contraindications. It is important to remind clients that many products that are formulated to treat fleas on dogs should never be used on cats or other species. Also, many products are administered according to the pet’s weight; therefore, it is important to weigh pets routinely.


    All veterinary staff should make owners aware that all flea control products are species specific; therefore, canine flea shampoos, sprays, collars, or topical or oral medications should never be used on/in cats.

    The products prescribed may contain insect growth regulators (IGRs), insect development inhibitors (IDIs), or insecticides.4 IGRs interrupt larval development by mimicking the juvenile growth hormone produced by fleas, thereby inhibiting maturation of flea eggs and larvae into adult fleas.10 IGRs are available as topical treatments applied directly to the pet’s skin every month.4 Some of the topical formulations can withstand bathing; however, the owner should check the product label for specific instructions.4 IDIs prevent larvae from hatching from eggs.4,10 For example, the IDI lufenuron can be administered monthly to dogs or cats as a tablet or to cats as a food additive to suppress flea populations; it can also be administered to cats as an injection every 6 months.4

    Some products combine an IGR with an insecticide to kill adult fleas, eggs, and larvae.6 Some also kill pupae (e.g., Vectra for Dogs and Puppies [Summit VetPharm] contains dinotefuran and pyriproxyfen). Topical formulations, such as those containing the insecticides fipronil, imidacloprid, nitenpyram, selamectin, or spinosad, are applied directly to the pet’s skin to kill adult fleas. These compounds have a wider margin of safety than products containing cholinesterase inhibitors such as carbamates or organophosphates, which can pose health risks to pets, especially cats and young animals.4,6,10 However, in households with infants, young children, or pregnant women, human health professionals should be consulted before insecticides are used.

    Environmental Management

    In addition to treating the pet, it is important that the owner implement indoor and outdoor control measures to effectively control fleas.

    Indoor Control

    After treatment of the pet is initiated, the owner should take steps to control fleas in the indoor environment. Flea populations are most dense in areas where pets sleep.6 Therefore, bedding and throw rugs should be washed in hot, soapy water. Human and pet bedding should be laundered once a week.

    Floors, carpets, and upholstered furniture should be thoroughly vacuumed daily.4 The owner should also vacuum along baseboards and other crevices.4 The upholstery in vehicles that have been used to transport flea-in­fested pets should be vacuumed. Vacu­uming helps to remove not only adult fleas, eggs, and larvae but also pupae, which are resistant to many products.3,4 A study11 revealed that vacuuming kills 96% of adult fleas and 100% of fleas in the pupal and larval stages. Used vacuum bags should be promptly disposed of in a sealed garbage bag.

    Some insecticides (e.g., Advantage, Bayer; Revolution, Pfizer) can behave like an IGR/IDI by inhibiting adult and larval populations when a treated pet has contact with carpeting or bedding3; IDIs (Program, Novartis) applied to a pet can control infestation over time—without the benefit of adulticidal activity—by preventing larvae from hatching.

    If the flea problem does not re­solve or if the infestation becomes severe, the pet owner should be advised to contact the veterinarian.

    Outdoor Control

    Outdoor flea populations are most prevalent in coastal areas and locations with moderate daytime temperatures and fairly high humidity.4 Outdoor control measuresinvolve removing organic debris (e.g., fallen leaves, wood piles), watering the lawn regularly to drown flea larvae and adult fleas, and trimming low-hanging vegetation to allow sunlight penetration, all of which can inhibit larvae development.4,6 The owner should also spray an IGR–insecticide combination product in shaded or protected areas frequented by pets, such as crawl spaces, sheltered animal enclosures, or doghouses.4 It is usually not necessary for the owner to treat the entire lawn because flea larvae generally cannot survive in areas with heavy foot traffic or direct exposure to sunlight.4

    Spraying insecticide outdoors may be unnecessary if the owner does not detect a significant number of adult fleas. To confirm outdoor flea infestation, the owner should walk through pet resting areas while wearing white socks pulled up to the knees. If fleas are present, they will jump onto the socks and be clearly visible.4

    Because use of some flea control products outdoors may affect other species, such as butterflies, bees, and aquatic invertebrates,12 the owner should read the cautions on all products and carefully follow the application instructions on the label regarding the amount of product to use and the method of application.


    Flea infestation of pets is a common problem that can transmit disease and cause mild to severe discomfort because of itching and FAD. Treatment of the indoor and outdoor environment, in conjunction with treatment of the pet, is an important element of flea control.

    Technicians should educate owners about the flea life cycle, the clinical signs associated with infestation, and the available preventives and flea control products, including the indications and contraindications.

    Downloadable PDF

    1. Fleas and flea allergy dermatitis. In: Kahn CM, ed. The Merck Veterinary Manual. 9th ed. Whitehouse Station, NJ: Merck & Company; 2005:710-715.

    2. Companion Animal Parasite Council. Ectoparasites: Flea Guidelines. Accessed October 2010 at www.capcvet.org.

    3. Bowman DD. Georgis’ Parasitology for Veterinarians. 8th ed. St. Louis: Saunders Elsevier Science; 2003:40-45.

    4. University of California Statewide Integrated Pest Man­agement Program. Pests of Homes, Structures, People, and Pets. Accessed October 2010 at www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7419.html.

    5. Sloss MW, Kemp RL, Zajac AM. Veterinary Clinical Par­asitology. Ames: Iowa State University Press; 1994:134.

    6. Fleas and flea allergy dermatitis. In: Kahn CM, Line S, eds. The Merck Veterinary Man­ual. 10th ed. Whitehouse Station, NJ: Merck & Company; 2010:803-808.

    7. Lappin MR, Brunt J, Riley A, et al. Mycoplasma haemo­felis and Mycoplasma haemominutum DNA in blood of cats and their fleas. Proc 21st ACVIM 2003:929-930.

    8. Dryden MW. Understanding Persistent and Recurrent Flea Problems. Accessed December 2010 at www.vet.ksu.edu/depts/dmp/personnel/faculty/pdf/Persistent.Recurrent.Flea.Problems.pdf.

    9. Holzmer S, Hair JA, Dryden MW, et al. Efficacy of a topically applied formulation of metaflumizone on cats against the adult cat flea, flea egg production and hatch, and adult flea emergence. Vet Parasitol 2007;150(3):219-224.

    10. Sousa CA. Fleas, Flea Allergy, and Flea Control: A Review. Accessed October 2010 at dermatology.cdlib.org/DOJvol3num2/fleas/fleas.html.

    11. Hink WF, Needham GR. Vacuuming is lethal to all postembryonic life stages of the cat flea, Cteno­cephalides felis. Entomol Exp Appl 2007;125(2):221-222.

    12. Pesticide Information Profile: Fenoxycarb. Accessed October 2010 at pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/fenoxycarb-ext.html.

    References »

    NEXT: Preventing Canine Tick-borne Diseases

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    Did you know... Dogs remain the most popular pet in America, as 36.5% of all households own a dog, compared with 30.4% owning cats. But cats are still the most common pet (74.1 million), compared with 70 million dogs. Cat owners are more likely to own multiple cats—2.1 per household—compared with dog owners, who average 1.6 dogs per household.Read More

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