ANIMAL CLINIC of West Plains, Inc.

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The Flea Control Battle

How you and your clients can win the flea control battle

Why do fleas sometimes persist in an environment even when you think you and your client are doing everything right? The answer likely lies in gaining and sharing a firm understanding of how flea control products work.

March 1, 2009
By: Michael W. Dryden, DVM, MS, PhD
VETERINARY MEDICINE SUPPLEMENT

Many veterinarians and technicians have told me that today's veterinarian-recommended flea control products may not be controlling some flea infestations as well as in the past. Practitioners have asked whether resistance could be a cause. Although resistance is theoretically possible, no data have substantiated resistance in cat fleas as a cause of modern product failures. It is more likely that product failures result from factors other than resistance, such as ecological fluctuations and natural disasters, client compliance issues, lack of client education, lack of understanding of product performance attributes, naturally occurring differences in flea susceptibility, and changing perceptions because of product introductions.

Whatever the cause, flea control problems are occurring, and veterinarians must provide their patients with relief from flea infestations. In this article, I present information concerning the client education and compliance factors often responsible for persistent flea infestations and suggest ways to help you identify these factors and eradicate flea control problems.

OBTAIN A COMPLETE HISTORY AND CONDUCT A THOROUGH EXAMINATION

Flea control starts with a thorough history and a physical examination to look for fleas, flea feces, tapeworm segments, and evidence of pruritus or dermatitis. These findings will assist in determining the severity of the infestation, allow for assessment of clinical disease associated with the flea infestation, and assist in designing an overall control program.

SET REALISTIC EXPECTATIONS

Few pet owners thoroughly understand how flea products work. They may have false perceptions about the speed of kill, residual activity, and repellency, as well as how flea infestations are controlled. As a result, clients may come to the clinic, sometimes quite unhappy, saying that a certain product we sold or recommended is not working. Given a lack of knowledge of flea biology and of how flea products work, our clients may have product performance expectations that cannot be met.

So the first step in battling fleas may simply be setting proper client expectations. Select the best flea product to meet the client's and pet's needs; advise pet owners about additional control measures, if needed; explain and demonstrate correct product administration; and, most critical, tell clients what to expect once a pet leaves our practice and goes back to its flea-infested home.

UNDERSTAND AND COMMUNICATE THREE GOALS

It is important to understand the goals of a flea control program.¹

• Relieve the pet's discomfort by killing fleas on the pet, which are biting and feeding.

• Eliminate the infestation on the home premises since somewhere in the home or shaded areas of the yard flea eggs, larvae, and pupae are continuing to develop into adult fleas that re-infest pets. This aspect of flea control is likely the most difficult.

• Prevent future flea infestations.

Goal # 1 Get rid of existing fleas on the pet

To achieve the first goal of flea control, proper administration of a flea product is essential for the rapid and prolonged residual ability to kill fleas. We attempt to explain and demonstrate the correct administration technique to pet owners, and remember that it varies by product. Also we inform owners that the entire dose needs to be given to the pet and that veterinarian-recommended products will kill all fleas on the pet, but it may take four hours, or even as long as 36 hours, before all the existing fleas are dead. This does not mean that the product will "repel" new fleas as many pet owners believe.

Goal # 2 Eliminate fleas on the premises

Many flea control products not only kill the fleas on a dog or cat but also provide prolonged residual activity, often killing fleas for up to one month. In addition, some products provide prolonged activity against flea reproduction, either by killing the eggs or preventing eggs from developing or being laid.

We must impress upon pet owners that it often takes several weeks, or even 2 or 3 months, to eliminate a flea infestation because all flea infestations in dogs and cats originate from flea-infested premises, and it takes time to eradicate the immature stages living in the carpet or in the outdoor environment.^2-4

Review the flea cycle. The home or yard of any pet can became infested. Briefly, fleas lay eggs from which larvae hatch. These larvae spin cocoons in which they develop into pupae and later emerge as fleas. This cycle can take as little as two or three weeks, or as long as several months.

This information can be provided by the veterinarian, veterinary technician, or a highly trained staff member. Also, ask any of our staff and we can provide you with educational materials that are often provided by the product manufacturers.

Treat all pets for at least three months. Clients should know that the flea species that infests cats, Ctenocephalides felis, is the same species that infests dogs.^2,3 If you as a pet owner do not understand this basic aspect of flea biology, it can directly lead to flea control failures because you may not understand the need to treat every potential flea host in and around the home. Thus, in multiple-pet households, every dog, cat and any non-traditional warm-blooded pet in the home must be treated every month for at least three or four months to successfully eliminate all fleas within the environment. In addition, any domestic rabbits, ferrets, or hedgehogs kept as pets can also be cat flea hosts.

Every dog and cat must be treated because once newly emerged fleas jump onto the pet, the fleas will feed and mate, and female fleas will begin laying eggs within 24 hours.⁵ Since each female flea produces 40 to 50 eggs a day, within a few days hundreds and potentially thousands of eggs will be deposited into the home or yard.⁵ If a single monthly dose is missed on a single pet, flea control is likely to fail because of the flea eggs dropping off the untreated pet and continuing to develop and emerge within the home and environment. So we cannot treat only the scratching dog(s); we must also treat the cat(s) and other household pets that may falsely appear to be flea-free.

Figure 1. The opossum is an important urban wildlife host for Ctenocephalides felis in North America.

Other sources of new infestations. It is a myth that fleas infesting dogs and cats jump off to lay their eggs in cracks and crevices. Flea eggs are laid in the animal's hair, and then the eggs roll and drop off into the carpet, furniture, patio or onto the ground outdoors.⁵ Thus, it is the flea-infested pet that distributes the eggs, not the environment. In fact, think of a flea-infested pet as a living saltshaker. These white flea eggs are deposited in every place the pet has access to, and the largest number of eggs are deposited in places where pets spend most of their time, especially their bedding. So areas in and around the home such as on the owner's bed, next to the couch, on throw rugs or pet bedding, and outdoors under porches and bushes and in crawlspaces often have more severe infestations.

Figure 2. The mongoose is an important wildlife host for Ctenocephalides felis in Hawaii.

Not only is a flea-infested pet a flea egg distributor, wildlife such as opossums (Figure 1), raccoons, foxes, coyotes, and mongooses (in tropical locations) (Figure 2), all also commonly carry cat fleas, and, of course, so do stray dogs and cats.^2,3 As these animals move through the neighborhood and yards, flea eggs continually drop off. This distribution is particularly problematic in shaded, protected habitats where eggs and larvae are likely to survive and develop into adult fleas, such as under bushes, shrubs, and porches and in crawlspaces of homes and other buildings.

Within a few days, these flea eggs will develop into larvae. In a week or two, these larvae spin a cocoon and develop into pupae. In a few more weeks, the pupae develop into fleas that emerge from the cocoons and jump onto pets and, occasionally, people.

Figure 3. Flea pupae in carpet.

Dogs and cats rarely acquire fleas because fleas jumped from another dog or cat. The fleas that are biting pets and people in the home came from pupae, which came from larvae, which came from eggs laid by female fleas about three to eight weeks earlier. By the time the pet owner first notices fleas on a pet, immature stages have already been developing in the home or outdoors for about one or two months. So pet owners that see fleas on their dogs or cats should then be aware that flea eggs, larvae, pupae, and emerging fleas are in their carpet, homes or outdoor environment (Figure 3).

The residual effects. Once a flea product has been correctly administered to all pets within a household, what will happen after the client and pets go home? Pet owners must understand that in their homes or in shaded areas of their yards, immature stages of fleas are developing and fleas will be emerging continuously to re-infest the pets, as stated above.

Flea products labeled for monthly administration should have sufficient residual activity to kill most emerging fleas that jump onto a treated pet, and some products will even kill flea eggs. Currently, we do not sell or promote any flea control products that can actually "repel" fleas. It must be noted that you will continue to see fleas on your pet(s) until the infestation is eliminated within the home environment, and even then, it will be possible to see fleas on your pet(s) if they travel outside of their home environment. These products are meant to eliminate the infestation by killing fleas before they can lay eggs, and, with some products, by killing any eggs the fleas might produce.^4,6

Proper administration of flea products to all dogs, cats, and exotic household pets once every 30 days means no fleas reproducing and no eggs dropping into the environment. Therefore, within two to five days, eggs that were previously deposited have developed into larvae, and within one or two weeks, the larvae have developed into pupae, and two to six weeks later those pupae have become adult fleas. As those fleas emerge and jump onto treated pets where they come into contact with the flea product which then kills them. Thus, within three to eight weeks, or occasionally longer, all the fleas should be gone. If fleas cannot reproduce, they will go extinct in the home and yard. But if you as a pet owner misses treating even one pet, or skips a single monthly treatment, or administers the product incorrectly, fleas will survive and lay eggs and the infestation will continue.

Even if every flea-infested pet in a house is treated correctly, the premises in the home or shaded, protected areas in the yard will still be infested for several weeks with immature flea life stages and emerging fleas. These fleas continue to develop and jump onto treated pets. Existing flea products do not repel fleas effectively and do not kill fleas instantly. It often takes several hours, maybe even a day or two, after these fleas have jumped onto treated pets for the fleas to be killed by the residual insecticide.⁷ So expect to see some fleas on your pets for at least three to eight weeks and, occasionally, even longer. The period following treatment of pets until the infestation is completely eliminated is called the development window.⁴

Do I need to treat the premises? Several new insecticides and insect growth regulators have been shown to be effective in eliminating flea infestations under the most difficult climatic conditions. Field studies conducted between 1996 and 2001 in Tampa, FL., demonstrated that fipronil, imidacloprid, lufenuron (plus pyrethrin spray or nitenpyram tablets), and selamectin were 95% to 100% effective in eliminating established flea populations without treating the premises.^8-11 For example, during one of these field studies in Tampa, FL., a single application of imidacloprid was 95.3% and 97.4% effective in reducing flea populations on pets at seven and 28 days, respectively.⁹ In that same study, a single application of fipronil was 97.5% and 97% effective in reducing flea populations on pets at the same time points. Even though fleas continued to emerge, the products dramatically reduced flea numbers on pets. After three monthly applications of either imidacloprid or fipronil, flea burdens on pets were reduced by 99.5% and 96.5%, respectively.⁹ Such studies indicate that while the products were highly effective, fleas were still present in low numbers on many treated pets for several weeks after product applications.

However, data averaged from several homes and pets using geometric means to evaluate product efficacy can occasionally mask potential outliers. Understanding the limitations of study data analysis is important because while most products with residual activity work well most of the time, problems with perceptions of flea control failure occur. In a typical scenario, a pet is treated appropriately and flea numbers initially decrease but then rebound three or four weeks after initial treatment.

As good as the modern veterinarian-recommended flea control products are, direct environmental control may still be needed with severe flea infestations because the pet owner may not want to wait three to eight weeks until the problem is resolved. Measures to reduce the premises infestation include washing pet bedding, vacuuming carpets, washing area rugs, using flea light traps, and applying insecticides to the indoor and outdoor areas. These insecticides might include pump sprays, directed aerosols, total release aerosols (commonly referred to as bombs), or the services of a professional pest management specialist.

Goal # 3 Prevent new infestations with lifelong flea control

Now that the infestation is eradicated, pet owners should continue to treat their pets. Numerous animals, such as feral dogs and cats and wildlife, move throughout the neighborhood and yards carrying fleas. These flea-infested animals are continually depositing flea eggs in the outdoor environment, which can start the problem all over again. So it is essential to keep pets on lifelong flea control either seasonally (e.g. spring, summer and fall) or year-round. Then, when fleas that have developed from the eggs deposited by feral dogs or cats or wildlife jump onto a treated pet, the fleas will either be killed or their eggs destroyed. Thus, future flea infestations of beloved family members will be prevented.

SUMMARY

Effective flea control starts with effective client communication. Clients need to be educated on the objectives of a flea control program, taught how to properly administer a product, and given a detailed explanation of what to expect once a flea product is administered and the pet is back in the infested premises. If we set realistic client expectations through education, we can meet them, but if we allow clients to set their own expectations, we will rarely be successful.

Editors' note: Dr. Dryden is a consultant and speaker for Pfizer Animal Health, Novartis Animal Health, Bayer Animal Health, Merial, and Lilly.

Michael W. Dryden, DVM, MS, PhD
Department of Diagnostic Medicine and Pathobiology
College of Veterinary Medicine
Kansas State University
Manhattan, KS 66506

REFERENCES

1. Dryden MW. Flea control issues. NAVC Clinician's Brief 2008;January(suppl):2-4.

2. Rust MK, Dryden MW. The biology, ecology and management of the cat flea. Annu Rev Entomol 1997;42:451-473.

3. Dryden M. Biology of fleas of dogs and cats. Compend` Contin Educ Pract Vet 1993;15:569-579.

4. 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.

5. Dryden MW. Host association, on-host longevity and egg production of Ctenocephalides felis felis. Vet Parasitol 1989;34(1-2):117-122.

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

7. Dryden MW, Smith V, Payne PA, et al. Comparative speed of kill of selamectin, imidacloprid, and fipronil–(S)-methoprene spot-on formulations against fleas on cats. Vet Ther 2005;6(3):228-236.

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

9. 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.

10. 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.

11. 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, in Proceedings. Am Assoc Vet Parasitol Annu Mtg, 2001; P34.