Flea allergy dermatitis is the most common cause of pruritus in both dogs and cats.
Symptoms can either be non-seasonal or seasonal, depending on the climate.
Addressing fleas is not only important for the well-being of the animal but also for
owners, as fleas can transmit zoonotic diseases. Diagnosis of flea allergy dermatitis is
usually based on clinical signs. Treatment may include palliative therapy with
antihistamines or steroids, but the best treatment option is preventing flea bites and
eliminating fleas from the household. Proper treatment of all animals in the
household as well as the environment will lead to resolution of clinical signs within
6-8 weeks.
Introduction
• Ctenocephalides felis felis: Most common flea for both dogs and cats
- Potentially carries pathogens: Bartonella henselae, Dipylidium caninum, and
Yersina Pestis
- Produce an average of 27 eggs/day
- Lay eggs within 24-36 hours
- Other flea species: C. canis, Pulex simulans, Echidnophaga gallinacea
(sticktight flea)
• Life Cycle
- Adult à eggs à larva à cocoon àpupa à hatch
- Average time to complete lifecycle = 3 weeks
Perfect conditions = 16 days
Can take months if conditions are not met
• Dermatological conditions
Flea infestation: skin disease with mild to moderate pruritus caused by biting
of the flea
Flea allergy dermatitis (FAD) (flea bite hypersensitivity): Allergic reaction to
flea saliva
Type 1, type 4, and basophil hypersensitivities
Salivary enzymes contain proteolytic enzymes, histamine-like
compounds, anti-coagulants, haptens and antigens
Clinical Signs
• Intense Pruritus
• Lesions: erythema, alopecia, papules, pustules, excoriations, crusts, and moist
dermatitis. Hyperpigmentation and lichenification may develop in more chronic
lesions.
• Distribution
- Dogs: Caudal-dorsal distribution
Base of tail, posterior/lateral aspect of rear legs and ventral abdomen
- Cats: Often neck and face
Common cause of miliary dermatitis and eosinophilic plaques
Can also see similar distribution as the dog
- Secondary infections are common.
Diagnosis
• Clinical signs
- In dogs, a diagnosis is mainly based on distribution of lesions; however,
often dogs that have FAD also have concurrent food and/or environmental
allergies which may complicate the diagnosis. Therefore; ensuring proper
flea control is crucial to rule out flea allergic dermatitis before working up
other causes of allergies.
- In cats, distribution is more difficult to rely upon for diagnosis and response
to treatment may be more helpful
• Fleas and flea excrement (flea dirt)
Majority of FAD patients will not have fleas or flea dirt
Using a wet paper towel and collecting excrement can help determine if it is
truly flea feces. Flea excrement is mainly digested blood and the “dirt”
should dissolve with water and cause a reddish hue on the paper towel
• Intradermal testing (IDT) and serological testing can aid in diagnosis of FAD
- IDT is highly specific but not very sensitive
If positive, then can help support your diagnosis of FAD
- Immunotherapy is unreliable.
Treatments
• Symptomatic and palliative therapy
- Short term glucocorticoids
- Antihistamines: generally not effective
• Approach to flea control
- Treat each animal in the house
- Treat the home environment to eliminate the environmental reservoir
• Adulticides
- Eliminates fleas present on animal but does not prevent re-infestation
- Speed of kill: Depending on the product, may take minutes to 48 hours
Dependent on concentration which declines over time
Speed at which new fleas are killed is important for FAD
• Important to use products that kill before eggs are laid
- Repellency
Two forms
• Fleas deterred by vapor phase: Affect is unclear in animals and
should not be used for sole purpose
- DEET (N,N,diethyl-m-toluamide)
- Citrus oil
• Fleas repelled by physical contact
- Permethrin.
• Insect Growth Regulators: Disrupt developmental process
- Juvenile Hormone Analogues: mimics hormone and prevents progression
through juvenile stages Methoprene: UV light sensitive: Not for use outside
Pyriproxifen: Stable in UV light
- Insect Development Inhibitors: Inhibit chitin synthesis
Disrupt formation of cuticle, mouthparts and other chitinous structures
Ex. Lufenuron.
Adulticides
• Afoxalaner
• Dinotefuron
• Etofenprox
• Fipronil: Toxic to rabbits
• Flumethrin
• Imidacloprid
• Indoxacarb
• Nitenpyram
• Selamectin
• Spinetoram
• Spinosad: Do not use in conjunction with ivermectin. Caution in neurological
patients
• Fluralaner.
Adulticides and Repellants
• Cyphenorthrin
• Deltamethrin
• Permethrin: Toxic to cats
• Pyrethrin
Repellants
• Amitraz
Insect Growth Regulators
• Lufenuron
• Pyriproxifen
• S-methoprene
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