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Compendium June 2011 (Vol 33, No 6)

Flea Control: Real Homes, Real Problems, Real Answers, Real Lessons: Hitchhiker Fleas and the Indoor-Only Cats

by Michael W. Dryden, DVM, MS, PhD, Doug Carithers, DVM, EVP, Michael J. Murray, DVM, MS, DACVIM


    This is the third of a five-part series of cases that formed part of a field-study research project conducted by the Kansas State University Flea Team in 2009 in Tampa, Florida. BOX 1
    describes the criteria for inclusion and the methods used in this study.

    Veterinarians often hear pet owners say that they don’t need a flea control product for their indoor-only cat. In this case, you will learn how people can transport Ctenocephalides felis (the cat flea) into their homes to infest their indoor-only cats (or dogs). You will also get a close-up view of a flea development site in the furniture!


    Flea control has always been difficult. The advent of modern flea control products with excellent month-long activity against fleas and/or their eggs has had a tremendous impact on flea control; however, for some pet owners, flea control still seems problematic. Consequently, veterinary practices continue to get cases in which it appears that the flea control product they sold failed to work. 

    It is often not possible for the veterinary clinic to get to the root cause of all of these cases. Flea biology and its interaction with the environment and flea hosts are complex, and it is not feasible for veterinary staff to conduct in-home investigations. This series of cases illustrates real examples of challenging flea control situations in which owners continued to see fleas on treated pets. By understanding the results of these investigations, you and your staff can see how complicated flea infestations can become and why simply blaming product performance is not a solution.

    Essentials for Understanding Flea Biology and Flea Control

    Before examining this case, it is essential to understand the following facts about flea biology and flea control:

    • As an adult, Ctenocephalides felis felis, the cat flea, is an obligate parasite that is metabolically and reproductively bound to its host.1–3 This revelation dramatically changed approaches to managing fleas: by applying products to and on pets, owners and veterinarians attempt to control reproduction and “break the life cycle” rather than focusing on the environment.4–6
    • Once on a preferred host, cat fleas begin feeding within minutes and start breeding soon after. A female flea can begin laying eggs within 24 to 48 hours of jumping onto a host. In a few days, a female flea can lay 40 to 50 eggs/day.2
    • Flea eggs roll off the host, and larvae typically hatch in 3 to 5 days. The larval stage is the most sensitive. Flea larvae require flea feces for nutrition, protection from direct sunlight, temperatures in the range of 45°F to 90°F, and relative humidity in the range of 50% to 85%.7,8
    • Most larvae do not survive to become adult fleas. 
    • The rate of flea development depends on the temperature. Development from eggs to fleas can take less than 3 weeks at 85°F and can take 7 to 12 weeks at 65°F.7,8
    • New fleas develop and emerge where pets or other flea hosts spend most of their time because this is where the most eggs and feces are deposited, and larvae require flea feces for nutrition.  
    • Common hosts for C. felis include cats, dogs, opossums, raccoons, domestic rabbits, and hedgehogs.7,8 Squirrels and birds are not hosts for cat fleas.  
    • Feral cats, opossums, and raccoons move throughout neighborhoods. These “urban wildlife” hosts for the cat flea often seek shelter in covered, protected areas, and wherever they rest, they leave behind flea eggs and flea feces.  

    With some indoor flea infestations, the number of fleas emerging into the home increases substantially in the month after all pets are treated with a monthly flea control product.5,6 These are called redline homes, and in these cases, pet owners will see more fleas on their pets—and possibly themselves—than before treatment. When confronted with increasing numbers of fleas, pet owners inevitably conclude that the flea control product is not working at all. In fact, the fleas emerging into the home after the pets were treated came from eggs laid weeks before treatment. Those eggs will continue to develop into larvae, pupae, and adult fleas, and the pet owners will continue to see new fleas on their pets until all the adult fleas have emerged. Depending on the temperature, it can take 3 weeks to several months for the infestation to run its course.9–12

    Case Presentation: Hitchhiker Fleas and the Indoor-Only Cats

    Signalment: Three permanently indoor cats aged 3, 5, and 18 years.

    History: All three cats had fleas at the initial examination. Flea counts on the two younger cats declined after treatment with Frontline Plus, but flea counts on the older Persian cat continued to increase during the first 3 weeks after treatment (FIGURE 1A and FIGURE 1B). Flea traps were placed on a throw rug in the dining room and on a rug at the foot of a couch on which the older cat liked to lie. Flea trap counts spiked 1 week after the cats were treated and then abruptly declined to 1 or 0 for the remainder of the study. The source of fleas on the cats after day 7 was unknown and prompted further investigation (TABLE 1).

    Table 1. Questions Asked of the Owner



    How many hours a day does the pet spend outdoors? Where does it go: the backyard, shared courtyard, sidewalk, or dog parks?

    The cats never go outside.

    Do other pets visit your household, or does your pet visit another home?


    Where do your cats sleep or rest?

    The cats tend to spend their time in the main living area and like to lie on the throw rugs. The Persian  cat likes to lie on the sofa in the living room.

    Do you have an elevated porch, a crawl space, or another structure under which your pet, stray animals, or wildlife might go?


    Do you see feral cats, dogs, or wildlife in your yard or neighborhood?

    Yes: many opossums, raccoons, and cats in the yard.

    Examination of the pets: At an examination on study day 39, the Persian cat had two fleas. This cat had poor dentition, as expected for her age, and a bit of a rough haircoat.

    Cat on couch

    Figure 2. The Persian cat on the sofa in the living room. A flea trap is at the base of the couch.

    Examination of the premises: Inside, the home had all hardwood floors with a few throw rugs and was kept very clean. The white sofa in the living room, where the Persian cat liked to rest, had cat hair and flea dirt on a corner of a cushion (FIGURE 2 and FIGURE 3). More flea dirt was visible under the cushion. Outside, the home had an attached, screened lanai. Walking into the yard, the Flea Team immediately noticed two members of a “pack” of cats that frequented the yard (FIGURE 4). The yard had numerous shrubs and shady, protected areas ideal for flea development (FIGURE 5). The owner was working in the yard during the examination, and he later explained that he spent a lot of time in the yard.

    Cat in tree

    Figure 4. One of the “pack” of cats resting in a tree during a site visit.

    Diagnosis: Opossums, raccoons, and the outdoor cats were a source of flea eggs in the yard, where conditions were ideal for flea development. It was likely that fleas were jumping onto the owner and being carried into the home, where they found their preferred hosts, the cats. Because the flea trap counts declined to 1 or 0 after the first week of the study, another source of fleas in the home was suspected but could not be found.

    Follow-up examination: On its last visit to the home, the Flea Team brought a microscope attached to a laptop computer. Looking under the cushion of the sofa in the living room, where the owner had vacuumed several weeks before, they still observed flea dirt, a large number of flea egg casings, and shed larval skins (ectoskeletons; FIGURE 6). However, no evidence of any currently active (productive) infestation was observed.


    Figure 5. The shady backyard, frequented by opossums, raccoons, and several cats.

    Conclusions and lessons learned: The older Persian cat had the most fleas because her poor dentition and age made her an inefficient groomer. Because she spent much of her time lying on the sofa, she shed flea eggs and flea dirt (a crucial food source for flea larvae7,8) onto it and into the carpet. Flea larvae were able to develop in the darkness under the cushion and the high relative humidity inherent to Tampa. Vacuuming under the cushion likely contributed to the rapid decline in emerging fleas from the sofa but did not remove all flea eggs, as demonstrated by the large number of egg casings under the sofa cushion several weeks later.

    This case illustrates that permanently indoor cats can and do get fleas, often from their owners. As described in case 1, when something moves in front of the light source to which a flea has oriented, the flea immediately jumps onto that object.13 That instinct is a successful action for the species because, often, the flea jumps onto a suitable host on which it can feed and reproduce. Cat fleas jump onto people and bite people.7,8 When a person carries fleas into a home, the fleas eventually jump off the person and, if an indoor cat walks by, onto the cat, on which they will feed, reproduce, and remain until they are groomed off.2


    Click here to take a quiz and see what you have learned!

    In next month’s case, The "Deep Dive,” you will learn how complicated flea control cases can be.

    This information has been peer reviewed. It does not necessarily reflect the opinions of, nor constitute or imply endorsement or recommendation by, the Publisher or Editorial Board. The Publisher is not responsible for any data, opinions, or statements provided herein.

    © 2011 Merial Limited, Duluth, GA. All rights reserved. Sponsored by Merial.

    The study from which these cases were selected was funded by Merial Limited, Duluth, GA. Dr. Dryden is a professor at Kansas State University College of Veterinary Medicine, and he performs studies and consulting work for Merial Limited and other animal health companies. Dr. Carithers and Dr. Murray are employees of Merial Limited.


    1. Dryden MW. Evaluation of Certain Parameters in the Bionomics of Ctenocephalides felis felis (Bouché 1835) [master’s thesis]. West Lafayette, IN: Purdue University; 1988:115. 

    2. Dryden MW. Host association, on-host longevity and egg production of Ctenocephalides felis felis. Vet Parasitol 1989;34:117-122. 

    3. Dryden M, Gaafar S. Blood consumption by the cat flea, Ctenocephalides felis felis (Siphonaptera: Pulicidae). J Med Entomol 1991;28(3):394-400. 

    4. Dryden MW, Broce AB. Integrated flea control for the 21st century. Compend Contin Educ Pract Vet 2002;24(1 suppl):36-39. 

    5. Chin A, Lunn P, Dryden M. Persistent flea infestations in dogs and cats controlled with monthly topical applications of fipronil and methoprene. Aust Vet Pract 2005;35(3):89-96. 

    6. Dryden MW. How you and your clients can win the flea control battle. Vet Med 2009;Mar (suppl):17-26. 

    7. Dryden M, Rust M. The cat flea: biology, ecology and control. Vet Parasitol 1994;52:1-19. 

    8. Rust M, Dryden M. The biology, ecology and management of the cat flea. Ann Rev Entomol 1997;42:451-473. 

    9. Dryden MW, Perez HR, Ulitchny DM. Control of fleas on pets and in homes by use of imidacloprid or lufenuron and a pyrethrin spray. JAVMA 1999;215(1):36-39. 

    10. Dryden MW, Denenberg TM, Bunch S. Control of fleas on naturally infested dogs and cats and in private residences with topical spot applications of fipronil or imidacloprid. Vet Parasitol 2000;93(1): 69-75. 

    11. Dryden M, Denenberg TM, Bunch S, et al. Control of fleas on dogs and cats and in private residences with the combination of oral lufenuron and nitenpyram. Vet Ther 2001;2:208-214. 

    12. Dryden MW, Burkindine T, Lewis L, et al. Efficacy of selamectin in controlling natural flea infestations on pets and in private residences in comparison with imidacloprid and fipronil. Proc Am Assoc Vet Parasitol Annu Meet 2001:34. 

    13. Dryden MW, Broce AB. Development of a trap for collecting newly emerged Ctenocephalides felis (Siphonaptera: Pulicidae) in homes. J Med Entomol 1993;30(5):901-906.

    References »

    NEXT: How a Diplomate of the American College of Veterinary Nutrition Can Help Your Practice and Patients


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