Introduction
Flea allergy dermatitis (FAD) or flea bite hypersensitivity is the most common small animal dermatological disease. Except for areas of low humidity or high elevations, this disease has a worldwide distribution.
The cat flea, Ctenocephalides felis felis, is the most common flea infesting dogs and cats in the United States.
Life Cycle of the Flea
The life cycle of the flea can range from 12 to 190+ days depending on environmental conditions and host factors. Eggs are laid on the host, 24-36 hours following the flea's first blood meal. One female flea can lay 1000 eggs within 30 days! Following emergence from the egg, a flea will go through 3 larval stages before forming a pupa. The pupal stage is the most resistant of all stages since the cocoon is highly tolerant of desiccation. An adult flea will emerge from its cocoon with proper environmental stimuli, such as carbon dioxide, warmth, physical pressure, and vibrations. A female flea will take a blood meal within minutes of contact with a host and will consume 15 times its body weight per day. Partially digested blood excreted on the host acts as nutrients for flea larvae, thus helping to reinforce their life cycle. Approximately 2000 eggs are produced per flea in one life cycle.
Pathogenesis of FAD
Flea saliva is introduced during blood meals. A number of inflammatory/antigenic components are released into the host, which provoke a number of immunological responses including immediate and delayed hypersensitivity reactions. Dogs with atopic dermatitis are predisposed to FAD.
Diagnosis
History
Pruritus may be seasonal or year-round
Licking, chewing, grooming excessively on the rear half of body, especially the tail-base area and ventral abdomen
Increased pruritus following introduction of a new pet, boarding, grooming etc.
Signalment
No sex or breed predilections
Development of disease may occur at any age
Physical Examination
Distribution of lesions dorsal lumbosacral region, tail base, caudal or medial thighs, umbilicus/umbilical fold (especially in male dogs), generalized
Lesion type papules or encrusted papules, crusting, scaling, excoriations, pyotraumatic dermatitis ("hot spots"), self-induced alopecia with dull, dry haircoat in overgroomed areas, hyperpigmentation, lichenification, fibropruritic nodules (rarely)
Secondary pyodermas are common
Presence of flea "dirt"
Evidence of Dipylidium caninum in feces
*Lack of fleas or flea feces is not uncommon, especially if the dog has been bathed
Diagnostic Tests
Blood loss anemia in puppies or heavy infestation
Peripheral eosinophilia noted in <20% of cases
Intradermal skin testing with flea allergen may reveal wheal formation with immediate and delayed hypersensitivity
Serum in vitro testing for flea-specific IgE has variable accuracy and does not identify animals with delayed hypersensitivity reactions
Histopathology is non-specific
Treatment
There are three objectives to treating FAD:
1. Complete flea eradication in the environment
2. Provide symptomatic relief to the patient
3. Treating and preventing infestations on the patient
1. Environmental Control
Wash all blankets, bedding, pet carriers, throw rugs
Vacuum all carpeted areas and remove furniture that can house pre-adult fleas
Prevent access to "flea zones" i.e., porches, garages, crawl spaces
Prevent contact with wildlife carriers i.e., raccoons, rats, squirrels, feral cats other neighborhood animals
Premise treatment with aerosols, exterminators if necessary
2. Symptomatic Relief
Treat secondary infections (bacteria and Malassezia)
Shampoo therapy*
Short-term oral anti-inflammatory doses of corticosteroids
Antihistamines and essential fatty acids are rarely effective
3. Treat and Prevent Flea Infestations
Treat all animals in the household
Tailored protocol to the individual
Ideal treatment is:
Safe, non-toxic, non-irritant
Quick kill
Long residual action
Active against multiple stages of the flea life cycle
IGR'S & IDI'S
Insect growth regulators (IGRs) are insect chemicals that control various aspects of insect metabolism, reproduction and organ development and maturation. However, the final maturation process and pupation of the larvae is dependent upon the absence of the hormones that were required for earlier development. Synthetic insect hormones therefore prevent pupation of flea larvae.
S-methoprene
An IGR that may be combined with topical insecticides
Ovicidal when female fleas are exposed on the pet, and larvicidal in the environment
Inactivated by sunlight therefore limited use outdoors
Broken down by flea larval esterases decreasing its longevity
Pyriproxyfen (Nylar®)
Pyriproxyfen is a traditional juvenoid IGR that is highly stable and efficacious
As an ovisterilant it remains 100% effective for 150 days after a single spray application; flea eggs are dead when laid
Effective even 3-4 months after pyriproxyfen-containing collars are removed from test animals
Insect development inhibitors (IDIs) inhibit the development of adult fleas by disrupting synthesis or development of chitin. Normal chitin development is essential for the survival and maturation of insect ova and larvae, however there is no mammalian toxicity since mammals do not produce chitin.
Lufenuron (Program®, Novartis)
Need to use in combination with adulticide in flea allergic animals
Virtually no acute or chronic mammalian toxicity recorded
Tablets or liquid is poorly absorbed unless it is administered along with a fat-containing meal
Other dermatologic uses:
Has not shown efficacy in preventing or treating dermatophytosis despite initial successful reports
Insecticides
Selamectin (Revolution®, Pfizer)
Broad-spectrum avermectin with systemic absorption
Distributed to sebaceous glands that re-establish concentrations on the skin post-bathing
Adulticide, larvicide and an IDI (ovicidal for fleas by preventing egg hatching)
Induces neuromuscular paralysis in susceptible parasites by increasing chloride permeability in glutamate-gated neuronal chloride channels
Safe for ivermectin-sensitive collies at the prescribed doses
Other dermatologic uses:
Canine nasal mite (Pneumonyssoides caninum)--q 2 weeks dosing for three treatments
Notoedres cati--one time therapy
Feline Cheyletiellosis--once monthly therapy for three treatments
Canine Cheyletiellosis--every other week for three treatments
Scabies--q 2 weeks for 3-4 treatments
Otodectes--1-4 applications q 1-4 weeks apart
Imidacloprid (Advantage®, Advantage Multi®, Bayer)
Flea adulticide and larvicide
Quick kill within 12-24 hours due to rapid surface distribution (translocation)
Chloronicotinyl compound that binds to Ach receptor site on post-synaptic nicotinic receptors
Minimal systemic absorption
Fipronil with s-Methoprene (Frontline Plus®, Merial)
GABA receptor antagonist working via chloride channel blockade
Broad spectrum insecticide
Minimal systemic absorption
Fipronil binds chemically to the hair/stratum corneum and is absorbed into the sebaceous glands and redistributed onto surface via translocation
Nitenpyram (Capstar®, Novartis)
Synthetic compound derived from a family of drugs called neonicotinoids
Acts as an agonist to insect-specific nicotinic acetylcholine receptors in the postsynaptic membranes
Does require a bite and blood ingestion by the flea
Rapid-kill (fleas fall off within 30 minutes) and lasts less than 24 hours as a systemic insecticide
Can be used daily for flea allergic animals
Very safe--excreted by kidneys virtually unchanged; broken down by UV rays in the environment
Useful in treating heavy infestation, animals in kennels, grooming and veterinary facilities
Newest Additions
Spinosad (Comfortis®, Eli Lilly)
First FDA-approved, chewable, beef-flavored (soy/pork-based) tablet that kills fleas
Protects for a full month
In the neonicotinoid family; activates nicotinic acetylcholine receptors (nAChRs)
Must be given with food
Starts killing fleas within 30 minutes
100% effective within 4 hours in a controlled laboratory study
Safe for dogs and puppies 14 weeks of age and older
Doesn't require separation or isolation of pets and avoids misapplications
Most common adverse reaction is vomiting
NOT LICENSED FOR CATS
Dinotefuran, Permethrin, and Pyriproxyfen (Vectra 3D®, Summit VetPharm)
Dinotefuran (4.95%; neonicotinoid adulticide), Pyriproxyfen (0.44%, juvenoid IGR) and Permethrin (36.08%, sodium ion channel blocker and insect repellent)
Kills fleas, larvae, and ova, as well as four species of ticks, and three species of mosquitoes
Dinotefuran is lipophilic and water resistant
Pyriproxyfen is photostable and prevents development of eggs and larvae
Permethrin kills fleas and repels insects
Kills 96% of fleas within 6 hours, up to 100% in 12 hours
Applied monthly to puppies as young as 7 weeks
DO NOT USE ON CATS (Feline product without permethrin available)
Metaflumizone + Amitraz (ProMeris®, Fort Dodge Animal Health)
A novel sodium channel blocker insecticide causes paralysis and death of fleas
Amitraz controls ticks
Following translocation on surface, full efficacy achieved against fleas and ticks in 24 hours
>95% control of fleas and >90% control of ticks 35 days after treatment
Monthly application recommended, but residual action against fleas up to 6 weeks, ticks up to 4 weeks
Maintains >95% efficacy at 4 weeks against fipronil-resistant flea strains
Product is lipophilic and water resistant
"Pleasant eucalyptus smell"
Feline product without amitraz available
Other dermatological uses:
Treatment against canine demodicosis at monthly or bi-weekly intervals resulted in >94% and >99% mite reduction after 3 months
Treatment against canine scabies resulted in 75% and 83% clinical resolution or zero mite counts after 56 days with monthly and bi-weekly treatment, respectively