The Flea-Infested Pet: How to Manage the Pet and Its Environment

Part 1 of this article—“The Flea-Infested Pet: Overview of Current Products” in the May/June 2017 issue—discussed important characteristics of today’s most commonly used flea control products. This follow-up article addresses key factors to consider in designing a flea control treatment program.

Individualization is the key: Although the products available today are an enormous improvement over those of bygone years, there is still no single product or protocol that is suitable for all situations. Instead, designing an effective protocol requires the assessment of many patient, client, and environmental factors, in addition to knowledge about features of the products and the product formats themselves. Table 1 provides an overview of available products.

Table 1 Overview of Flea Control Products

[ultimatetables 4 /]

Factors to Consider When Selecting a Product

What Format Will Work Best for the Patient?

Spot-on Products

Most products available today are topical spot-on preparations, which are easy to apply and do not require the owner to administer oral medications. However, these products have variable resistance to water immersion and bathing. In addition, some pets appear to be sensitive to the active ingredient or the vehicle itself and may develop dermatitis (ranging from mild scaling all the way to frank necrosis) at the site of application.¹

Oral Products

These products have the advantage of being completely waterproof, which makes them ideal for use in patients that swim or are bathed frequently. In addition, because they are not applied topically, they cannot rub off onto other animals, people, or furniture. They are also well suited for animals that may not tolerate application of spot-on formulations. However, almost all of them are chewable, flavored tablets. This flavoring may include ingredients such as beef, pork, or soy extracts, which may or may not be tolerated by food-allergic animals. Vomiting may occur with any of the oral medications.

Collars

Recently, a flea collar containing a combination of imidacloprid and flumethrin was released (Seresto, seresto.com). This collar is an easy, low-maintenance method of topical product application. Although the imidacloprid in the collar washes off, the collar replenishes it (this may take a toll on collar lifespan).² The extended duration of action makes the product convenient to use but may also increase the likelihood of a client forgetting to replace the collar frequently enough for optimal control. In addition, some patients (notably cats) will not tolerate wearing a collar or may develop dermatitis underneath the collar.

Is Water Resistance Likely to Be an Issue?

This may not be a relevant question for most cats, but many dogs swim or are bathed frequently. Oral agents (eg, spinosad, afoxolaner, fluralaner, sarolaner) are completely waterproof, as are topical agents that rely on systemic absorption and distribution (selamectin). Many topical agents may be removed by frequent bathing or water immersion or by bathing within 24 to 48 hours of application.^3,4 Agents that are fairly water resistant include indoxacarb, deltamethrin, topical fluralaner, and dinotefuran; fipronil is partially water resistant.^3,5 In my experience, imidacloprid has very poor resistance to water. The exception is the Seresto collar, in which the active ingredient still washes off but is replaced from the collar.

Is the Agent Effective on Immature Fleas?

Products that can kill or inhibit development of flea eggs or larvae prevent establishment of a self-perpetuating environmental population by fleas not killed by adulticides. Furthermore, the use of multimodal therapy may decrease the likelihood of the development of resistance. Some agents have inherent effects against immature stages, including spinosad (ovicidal), imidacloprid, selamectin, and indoxacarb (larvicidal).^4,6,7 Other products may incorporate insect growth regulators (IGRs), such as lufenuron (found in Sentinel [sentinelpet.com]), methoprene (found in Frontline Plus [frontline.com]), and pyriproxyfen (found in Advantage II [bayerdvm.com] and Vectra [vectrapet.com]).

Is the Agent Safe to Use On or Around Cats?

Pyrethroids (synthetic pyrethrins; examples include permethrin and cyphenothrin) are often incorporated into combination flea control products to provide efficacy against ticks. However, with few exceptions, most pyrethroids are extremely toxic to cats.⁸ Exceptions include natural pyrethrin, flumethrin, and etofenprox. A recent retrospective work by Malik et al reported several cats with pyrethroid toxicosis.⁹ In some cases, clients accidentally or knowingly treated cats with dog-only formulations. However, a few cases of toxicosis have occurred in cats that came into close contact with treated dogs soon after application. For this reason, it may be prudent to limit pyrethroid use (or use cat-friendly pyrethroids) if possible on dogs that live with cats or when using environmental treatments in homes with cats.

Does the Patient Have Known or Suspected Food Allergies?

All oral flea treatments available (except for Capstar) have some form of food-based flavoring. Comfortis (comfortis.com), Trifexis (trifexis.com), Sentinel Flavor Tabs, Bravecto (us.bravecto.com), and Simparica (simparica.com) contain pork protein; Sentinel Spectrum contains beef; and NexGard (nexgardfordogs.com) contains soy. Although individual food-allergic patients may be able to tolerate the small amount of food protein in these products, care should be taken to make sure that no other variables are changed when the product is instituted. It is prudent to avoid the use of any flavored product during a food allergy elimination diet. However, because Bravecto lasts for 3 months, this product can be given at the beginning of an elimination diet; this should provide flea control for the duration of the diet trial.

Is Tick Control Also Needed?

Some active ingredients are efficacious against ticks (eg, fipronil, pyrethroids, afoxolaner, fluralaner, sarolaner), whereas other products may be formulated to include agents (usually a pyrethroid) that kills ticks (Advantix [bayerdvm.com], Vectra 3D, and Activyl Tick Plus [us.activyl.com]).

Are There Any Relevant Medical Issues or Concomitant Medications?

Most flea control products in current use have good margins of safety. However, there are a few conditions under which certain products might be best avoided. Several oral flea control products should be used with caution in animals with preexisting seizure disorders (eg, spinosad, afoxolaner, sarolaner).^6,10,11 Oral fluralaner is normally well tolerated by dogs with seizure disorders, but there is some indication that topical fluralaner may be more problematic in these patients.⁵ Concomitant use of spinosad and extralabel doses of ivermectin has been associated with the development of seizures, ataxia, twitching, and other neurologic signs.⁶

Factors to Consider When Designing a Control Regimen

Is Specific Environmental Control Necessary?

Environmental flea control measures are not necessary in many circumstances if on-animal treatments are performed appropriately. Except in cases of very heavy environmental contamination, the regular application of adulticidal products (especially those using or incorporating products that also control against immature flea life stages) to all animals in the household provides good flea control in an acceptable period. In this case, the environmental flea burden is eliminated indirectly—fleas in the immature stages in the environment continue to develop, but the ensuing adults are killed before they can lay eggs or their eggs are rendered essentially infertile.

However, this may not be sufficient in cases of extremely heavy environmental infestation. Although on-animal treatments alone will eventually eliminate the flea population, it may take several months for the resident immature fleas to mature and be eliminated. In these cases, specific environmental control measures may help. Flea eggs are shed off of the animal and are most numerous where the animal rests. Therefore, frequent sweeping or vacuuming of the indoor environment and washing of the pet’s bedding helps decrease the number of eggs. Larvae are susceptible to desiccation, so they are typically found in cracks and crevices of floors or upholstery, or in relatively sheltered, moist areas, such as in carpets, in crawl spaces, or under shrubbery. Frequent vacuuming removes some of these larvae indoors.

In heavily contaminated environments, treatment of the premises with a product designed for environmental use may be of benefit. Examples include products containing IGR, such as methoprene or pyriproxyfen. Although these agents do not kill adult fleas, they should inhibit immature fleas from progressing to the adult stage. Some evidence suggests that indoor environmental treatment with borate dusts (Fleabusters RX, fleabusters.com) may have some larvicidal effects, although this is unlikely to be effective as a sole flea control agent.^12,13

Several agents have been advocated for use in the management of contaminated outdoor environments, including the application of entomopathogenic nematodes (which are supposed to kill flea larvae), pyrethroid sprays, or sprays containing the ultraviolet light–stable IGR pyriproxyfen. However, no literature supports the use of nematodes as a flea control agent. Pyriproxyfen-containing agents do inhibit flea development but have no adulticidal properties. Finally, because of the widespread prevalence of pyrethroid resistance, these products may also have limited efficacy.^14,15 Unfortunately, the best solution to minimize the effect of outdoor contamination is probably to limit access by pets and wildlife to “sheltered” areas that could support developing fleas. This may not always be feasible, which is one reason why aggressive on-pet treatment protocols remain the mainstay of effective therapy.

Are All the Animals in the Household Being Treated?

This would seem to be an easy question to answer, but the answer is not always so obvious. Clients may not volunteer the fact that they have (and are not treating) other animals, or they might think that some animals “don’t count” because they are not in direct contact with the treated pet. Many small pet mammals (such as ferrets and rabbits) may harbor fleas yet are often not considered during the development of flea control regimens.¹⁶ Pet dogs and cats that are allowed to roam freely will come into contact with flea-ridden animals and may become reinfested. Client education is very important in these circumstances. Owners must understand that almost any mammalian pet in the immediate environment can serve as a reservoir for fleas, regardless of whether the treated pet comes into direct contact with them, such as “outdoor-only” dogs and cats (including strays). Free-roaming pets should ideally be confined to a more controllable area or at the least should receive very aggressive flea control. Some flea-allergic animals are so sensitive that roaming must be entirely curtailed.

Another source of environmental contamination is wildlife. Numerous species of small wildlife (including raccoons, opossums, and skunks) are able to carry fleas and perpetuate their life cycle. Although most pets do not come into direct contact with wildlife, they may have access to areas where these wild animals also go, such as crawl spaces under houses, under shrubbery, or in outdoor sheds and garages. Ideally, both the wildlife and the pet should be excluded from these locations.

Conclusion

Despite the bewildering number of flea control choices available, a few quick questions about each patient can help narrow down the available choices to the 3 or 4 products best suited for your needs.