Flea Treatments Old and New
World Small Animal Veterinary Association World Congress Proceedings, 2014
Andrew Hillier, BVSc, MANZCVS, DACVD
Placida, FL, USA

In the last 20 years we have made significant advances in our ability to control flea infestations and eliminate fleas in most circumstances. This is due to better knowledge of the flea life cycle, improved understanding of the role that wildlife and co-habitant animals play as reservoirs for flea infestations, and the plethora of products now available to treat adult and immature fleas on pets and in the environment.

Flea Biology

Although there are over 2000 species of fleas, the vast majority of flea infestations on pet dogs and cats are caused by Ctenocephalides felis felis. Infestations with C. felis are not limited to companion animals, but are also found on wildlife such as feral dogs and cats, coyotes, foxes, raccoons, opossums and rodents, which can act as environmental reservoirs for infestations of pets. We now know that while adult fleas are obligate parasites of the host, the vast majority of the life cycle is spent off the host in the environment.



Female adults start feeding within minutes of attaching to a dog or cat; the fleas mate within hours and eggs are produced within 24 hours. Eggs fall off the host with the highest concentration being in locations that pets spend most of their time (pet bedding, rugs, perches etc.). Eggs hatch within 2–10 days to larvae that burrow deep into carpet and under debris as they are sensitive to heat and desiccation. Within 1–3 weeks the larvae pupate - this life stage is very hardy and difficult to treat. Immature adults emerge from the pupa within 7 days in ideal circumstances or the pupa may survive for over 6 months.

Why Is Flea Control Important?

Heavy flea infestations may cause the host to become anemic as massive numbers of fleas engorge on blood meals. Large numbers of fleas may irritate the skin and cause flea-bite dermatitis, whereas some dogs develop flea allergy dermatitis, a hypersensitivity reaction that causes significant pruritus even when flea burdens may be low. Fleas also transmit a variety of diseases, including Rickettsia typhi, R. felis, Bartonella henselae, and Yersinia pestis and they may be intermediate hosts for tapeworms such as Dipylidium caninum and Hymenolepis nana and some filarids. Thus, even if fleas do not seem to be affecting companion animals directly, there are good medical reasons to institute flea control to eliminate all fleas.

Why Does Flea Control Fail?

Poor knowledge of the flea life cycle is a primary reason for failure of flea control as owners may not recognize that most life stages live in the environment (adult fleas on the pet are only the tip of the iceberg) and local wildlife and feral animals are a major source for reinfestation. There is a lot of poor information on the internet that is misleading, and poorly trained staff at pet stores who do not have comprehensive knowledge of the flea life cycle. Owners are also not always instructed correctly on how to apply flea control products (apply to the skin and not the hair coat for topicals, or should an oral medication be given with food) or they do not adhere to instructions. We also fail to treat all pets in the household or we incorrectly treat them only seasonally, believing that fleas are not present in colder months.

Flea control rarely fails because of resistance to flea control products. While some studies have shown resistance to older products (organophosphates, organochlorines etc.) may occur and have suggested some resistance to fipronil and permethrins, true resistance would appear to be very rare.

Flea Control From the Veterinary Practice

Veterinarians and veterinary practices should have the knowledge of the flea life cycle and flea reservoirs to be able to provide the best service to pet owners looking for comprehensive and effective flea control on their pets. The selection of which products to use is customized for each pet, home and environment; to be able to make the correct recommendations, everybody in the practice that interfaces with pet owners should have a good understanding of the key points. Do not allow pet owners to select products from a large display in the waiting room without having to seek advice. Training of staff is critical. The American Animal Hospital Association (AAHA) has an excellent booklet called "3 is Key" which works on the principle of assessment (of the circumstances), agreement (the owner must understand and agree) and action (actually implementing the flea control strategy). There are several good YouTube videos on training staff for their role in flea control and how to deal with common objections and myths from owners (see references for web links).

Key Points for Making the Best Recommendation

Flea control is individualized for each patient. Have a short questionnaire for owners to complete that will highlight the home environment and the pet and human lifestyles (see references for an AAHA Assessment Form).

Information that needs to be gathered includes:

 List of all pets in the household

 What is the indoor environment for pets (bedding, blankets, sleeping/resting areas, etc.)?

 What outdoor access do the pets have (where, wooded areas, under deck/porch, etc.)?

 Are there any visiting animals or does any pet visit a possibly infested home?

 What is the lifestyle of the pet/owner (sleeps with owner, children play with pet, frequent swimming or bathing)?

 Is the pet flea allergic?

 Is the patient food allergic?

 What can and will the owners be able to do long term?

 Are ticks, heartworm, biting insects, intestinal parasites also a problem?

Remember, the best flea control is the one that the owner can and will do on all pets correctly long term.

Guide for Instituting Flea Control


Flea allergy

See fleas, no FAD

Flea infestation

Affected animal




Other pets in household








Aggressive flea control (when a severe infestation exists or a pet had flea allergy) in the table is typically continued until flea control is achieved and then the pet is thereafter treated with routine/label dosing. Aggressive flea control sometimes requires off-label use of products and veterinarians should always abide by local regulations and restrictions that may apply.

Examples of aggressive flea control include:

 Monthly topicals applied every 2 or 3 weeks

 Daily oral administered every 2–3 days

 Alternating a monthly topical with a monthly oral with a 2-week interval between each

Flea Control Products

Flea control products differ by their method of application (topical, oral, injectable, or collar), and mode of action (adulticide, insect development inhibitor, or insect growth regulator [IGR]). Topicals may be favored if an adulticide/IGR combination is desired, if activity against biting insects is necessary, or if oral medications are undesirable (hypoallergenic food trial or known food allergic patient). Oral flea control may be preferable in patients who swim frequently, where medicated shampoos are dispensed, when close contact with other pets, owners or children occurs, etc. Collars with long-term efficacy against fleas and ticks may be better for owners who cannot remember to routinely administer monthly treatments.

The author recommends that in each veterinary practice, clinicians should have available a product for dogs and a product for cats to meet each of the following circumstances:

Route of administration








Fleas + ticks + biting insects


Fleas + heartworm





Fleas + ticks


Fleas + heartworm



Fleas + ticks


Mechanical Flea Control

Washing of beds, rugs, and sleeping areas, as well as vacuuming of areas where pets spend their time will help remove immature stages in the environment and the organic debris that they live on (i.e., biomass reduction). Additionally, if pets spend time outdoors, then fencing should be used to prevent access to wooded areas or wildlife habitats, as well as under decks or porches.

Flea Allergy Dermatitis

Flea allergy dermatitis (FAD) remains a very common cause of skin disease in pet dogs and cats. It is a Type I hypersensitivity, with the major allergen being Cte f 1, a flea salivary protein. The clinical signs are very characteristic in dogs with pruritus affecting the "pants area" (caudal dorsum, tail base, perineum, and caudal/medial thighs). The disease is more variable in cats, the "pants area" may be affected, while some cats demonstrate eosinophilic granuloma complex lesions, miliary dermatitis, or symmetric self-induced alopecia away from the typical "pants area." Many pets with FAD are also food allergic or have atopic dermatitis - the FAD is one aspect of their disease state that can and should be controlled. In patients with FAD from households with multiple pets or heavy infestations, it may take several months of aggressive flea control before the flea burden is lowered adequately. For these patients, temporary relief from the pruritus is necessary and may take the form of oclacitinib (0.4–0.6 mg/kg PO q 12 h for 2 weeks, then q 24 h) or prednisone/prednisolone (0.5–1 mg/kg PO q 24 h for 1 week, then q 48 h) for as long as is necessary to achieve flea control.


1.  "3 Is Key" booklet: www.aahanet.org/protected/3IsKey_BookletWeb_Secured.pdf (VIN editor: link could not be accessed as of 9/28/15; the updated link is www.aaha.org/public_documents/professional/resources/3iskey_bookletweb_secured.pdf)

2.  Role of each staff member: www.youtube.com/watch?v=cI6n3hqpAUQ

3.  Common objections and myths about flea control: www.youtube.com/watch?v=48anHZ6RIAU

4.  Home a pet lifestyle assessment form: www.aahanet.org/protected/Pet_lifestyle_ Assessment_Form.pdf (VIN editor: link could not be accessed as of 9/28/15; the updated link is www.aaha.org/public_documents/professional/resources/pet_lifestyle_assessment_form.pdf)

5.  Blagburn BL, Dryden MK. Biology, treatment, and control of flea and tick infestations. Vet Clin North Am Small Anim Pract. 2009;39:1173–1200.

6.  McDermott MJ, Weber E, Hunter S, et al. Identification, cloning, and characterization of a major cat flea salivary allergen (Cte f 1). Mol Immunol. 2000;37:361–375.

7.  Rust MK. Advances in the control of Ctenocephalides felis (cat flea) on cats and dogs. Trends Parasitol. 2005;21(5):232–236.


Speaker Information
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Andrew Hillier, BVSc, MANZCVS, DACVD
Placida, FL, USA

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