Why do fleas sometimes persist in an environment even when you think you and your client are doing everything right?
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.
Flea control starts with a thorough history (Table 1) and a physical examination to look for fleas, flea feces, tapeworm segments, and evidence of pruritus or dermatitis. Your findings will assist you in determining the severity of the infestation, allow assessment of clinical disease associated with the flea infestation, and assist you in designing an overall control program.
Table 1: Getting a Good History: Flea Control Questions to Ask
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 us, 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 a 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 your practice and goes back to its flea-infested home.
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 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 reinfest pets. This aspect of flea control is likely the most difficult.
• Prevent future flea infestations.
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. Explain and demonstrate the correct administration technique to pet owners, and remember that it varies by product. Also 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.
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 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 outdoors.2-4
Review the flea cycle. Explain how the client's home or yard 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. Let clients know that 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 consider giving your clients educational materials that are often provided by product manufacturers.
Treat all dogs and cats 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 pet owners do not understand this basic aspect of flea biology, it can directly lead to flea control failures because they may not see the need to treat every potential flea host in the home. Thus, in multiple-pet households, every dog and cat in the home must be treated every month for at least three or four months to successfully eliminate all fleas in the environment. In addition, you need to ascertain whether your clients have domestic rabbits, ferrets, or hedgehogs as pets since these species can also be cat flea hosts.
Explain to owners that every dog and cat must be treated because once newly emerged fleas jump onto their 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 in the environment. So we cannot treat only the scratching dog; we must also treat the cat that may falsely appear to be flea-free.
Discuss other sources of new infestations. Inform pet owners that 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 or outdoors.5 Thus, it is the flea-infested pet that distributes the eggs. 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. So areas in and around the home such as on the 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 1. The opossum is an important urban wildlife host for Ctenocephalides felis in North America.
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), 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 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.
Figure 2. The mongoose is an important wildlife host for Ctenocephalides felis in Hawaii.
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.
Dogs and cats rarely acquire fleas because fleas jumped off 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 tell pet owners that if they see fleas on their dogs or cats, then flea eggs, larvae, pupae, and emerging fleas are in their carpet or outdoors (Figure 3).
Figure 3. Flea pupae in carpet.
Explain residual effects. Once a flea product has been correctly administered to all dogs and cats in 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 reinfest 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. Explain to the client how these products will 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 and cats every month 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, the flea product kills them. Thus, within three to eight weeks, or occasionally longer, all the fleas will be gone. If fleas cannot reproduce, they will go extinct in the home and yard. But if a pet owner misses treating one pet, 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 clients should expect to see some fleas on their 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, Fla., 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, Fla., 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. Data from one home clearly illustrate such a problem (see related sidebar titled "Focus on residual activity: Case study data reveal a clearer flea control picture" ).
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.
Now that the infestation is eradicated, pet owners should continue to treat their pets. Remind owners that numerous animals, such as feral dogs and cats and wildlife, move through 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 keep pets on lifelong flea control either seasonally (e.g. 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.
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
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