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