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Compendium August 2011 (Vol 33, No 8)

Flea Control: Real Homes, Real Problems, Real Answers, Real Lessons: The What?

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


    This is the last 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.


    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: The What?

    Has this ever happened to you?

    Signalment: Sadie, a 5-year-old, spayed shih tzu.

    History: Sadie presented to a clinic in Tampa that was already working with the Flea Team. At the initial examination, one of the clinic technicians combed 35 fleas off the dog.  Sadie’s medical record showed that her owner, Mrs. Smith, had purchased a three-pack of Frontline Plus at the clinic just over 2 months ago, and Mrs. Smith was unhappy that the product had not worked.

    When the Flea Team arrived later on the day of Mrs. Smith’s visit, the veterinarian, Dr. Jim, told them, “I have the perfect case for your investigation. The owner purchased a three-dose pack of Frontline Plus 2 months ago, and the dog is still covered in fleas. It looks like a classic product failure.” Dr. Jim then called the owners’ home, and Mr. Smith answered the phone. Dr. Jim explained to Mr. Smith about the Flea Team study, that his dog was still covered in fleas, and that it looked like the Frontline his wife had purchased had failed to work properly. He was about to explain the process for the Flea Team to conduct its investigation when Mr. Smith interrupted him: “You mean the Frontline in the kitchen drawer that my wife never even opened?”

    Diagnosis: The owners had failed to treat their dog with the Frontline Plus they had purchased from Dr. Jim’s clinic.

    Conclusions and lessons learned: It is important to not jump to conclusions. Pet owners do not always adhere to the medication instructions given to them by their veterinarians. 


    It can be very difficult for veterinarians and clinic staff to solve many of the flea cases they are faced with because they do not, or cannot, have the information necessary to find the solution. But flea control cases are like any other diagnostic challenge, and clinics can develop diagnostic skills that can be used to respond to the flea problems of their clients.

    Basic prerequisites to become better diagnosticians of flea cases include an understanding of the following:

    • Flea biology
    • Where fleas come from
    • Animals that harbor C. felis
    • Where flea infestations develop outdoors
    • Where flea infestations develop indoors
    • People can transport fleas indoors
    • How flea products work and what to expect when they are used

    —Products do not effectively repel all fleas6,13–15
    —Products do not kill fleas instantly6

    • Pets can be infested with new fleas whenever they come in contact with a flea development site
    • During an active infestation, owners will see fleas on their pets
    • The same fleas seen on pets treated with a modern monthly adulticide were not on the pet yesterday and will not be on the pet tomorrow

    Questions to Ask Pet Owners

    • How many dogs and cats are in your home? Do you have other pets?
    • What products are you using?
    • Are all the dogs and cats being treated?
    • How are you applying the product?
    • How many hours do your pets spend outside? (Do not ask if the pet is an indoor or outdoor pet!)
    • Where does each pet rest inside?
    • Where does each pet go outside?
    • Do you see neighbors’ pets in the yard?
    • Do you see feral cats, opossums, or raccoons in the yard?
    • Do other pets visit your home, or do you take your pets to other homes?


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

    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. Flea and tick control in the 21st century, challenges and opportunities. Vet Dermatol 2009;20:435-440.

    14. Bossard RL, Dryden MW, Broce AB. Insecticide susceptibilities of cat fleas (Siphonaptera: Pulicidae) from several regions of the United States. J Med Entomol 2002;39:742-746.

    15. McCoy C, Broce, AB, Dryden MW. Flea blood feeding patterns in cats treated with oral nitenpyram and the topical insecticides imidacloprid, fipronil and selamectin. Vet Parasitol 2008;156(3-4):293-301.

    References »

    NEXT: WSAVA Nutritional Assessment Guidelines


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