Flea allergy dermatitis: What's new? (Proceedings)


Flea allergy dermatitis (FAD) is a hypersensitivity disorder of animals that are sensitized to allergens in flea saliva.


Flea allergy dermatitis (FAD) is a hypersensitivity disorder of animals that are sensitized to allergens in flea saliva. This allergy can be a type I or immediate (ie occurs within 15-30 minutes,Ig E mediated) or a type IV or delayed (ie 24 to 48 minutes, haptens in flea saliva combine with dermal collagen to from a complete antigen) hypersensitivity reaction. In addition, a late phase IgE reaction with cutaneous basophil reaction (reported in dogs only). One flea bite every 10 to 14 days may be sufficient to keep an allergic reaction going.

Dogs and cats are the most common animal species seen in clinical practice with this allergy so these two species will be discussed. In order to gain a better understanding of this hypersensitivity disorder the history, clinical signs and treatment options for FAD will be discussed.


Flea allergy dermatitis most commonly develops in animals less than 3 years old but may occur at any age depending on flea exposure. One or more animals in the household may be affected. Most commonly animals have a history of seasonal pruritus but in warmer climates like Texas, the pruritus may be nonseasonal.

Clinical Signs

Clinical signs and diagnostic tests can be helpful for making a diagnosis of FAD in dogs and cats. The clinical signs in dogs vary slightly when compared to cats. Dogs tend to have skin lesions on the caudal third of the body (ie tailhead, rump, caudal thighs, and inguinal, abdominal and dorsal lumbar regions) whereas cats can have skin lesions in different areas of the body besides the caudal ⅓ (ie head, neck)

The skin lesions seen in dogs with FAD in companion animals are erythema, excoriations, crusts, superficial moist dermatitis ("hot spots"), alopecia, lichenification and hyperpigmentation. The skin lesions for feline FAD include: erythematous popular eruptions (military dermatitis), eosinophilic plaques, recurrent indolent ulcer, and bilaterally symmetrical alopecia.

The latter two skin lesions are seen with chronicity. The intensity of pruritus for FAD can vary from mild to intense (ie 10 out of 10 pruritus with 10 being the most severe).

Differential Diagnoses

Several differential diagnoses should be considered in FAD cases. These differential diagnoses include: atopy, food allergy, Sarcoptic or Notedric mange, allergic contact or irritant dermatitis, dermatophytosis, and pyoderma.


The diagnosis of FAD is based on the distribution pattern of the skin lesions and the presence of pruritus (usually seasonal but may be nonseasonal in the South). A positive flea antigen test can further substantiate that a flea allergy is present. It is important to remember that the positive skin tests can occur immediately (within 15 minutes) or delayed (24 hours). Therefore, the clinician should recheck flea allergy skin tests at 24 hours if the 15 minute reading is negative to make sure that a delayed hypersensitivity reaction is not present. The presence of fleas and/or flea dirt can be additional confirmation that fleas are present.


The most important part to flea treatment for the FAD patient is to control the fleas on the pet and in the environment The only way to be able to control the fleas is to have an understanding of the flea life cycle and to educate the clients about the flea life cycle.

Treatment for the environment

Indoor treatment-

All floor surfaces should be vacuumed and the vacuum bag should be disposed of after use. Vacuuming removes some eggs and flea feces and stimulates pre-emerged adults to hatch. Do not place moth balls or pieces of flea collar in the vacuum bag since these ingredients will become aerosolized and may be toxic to humans and animals. In addition to vacuuming, all bedding, rugs, etc that the pet comes in contact with should be washed. Steam cleaning can bee and hardwood and dispose of the bag. Resist the temptation to place moth balls or flea collars in the bag as human safety has not been evaluated. Steam cleaning is helpful but do not be overally confident about its efficacy.

Your options for treating the house are either to have the house professional exterminated for fleas or do a premise treatment. Regardless of which option the pet owner chooses, the entire house needs to be treated. The cracks, baseboards and areas where the animals spend the majority of time should be treated with a hand insecticide spray (follow label directions). Bayer has a multi-insect indoor and outdoor spray that appears to be very effective in treating fleas as well as other insects in the environment. If foggers are selected as a home treatment options, only one fogger should be used per room.

Foggers get the ceilings and walls and tops of furniture but they cannot treat underneath the furniture. Please follow label directions and take precautions for pet birds and fish when using this method of treatment.

Outdoor treatment-

Self treatment or professional treatment for the outdoors is also options for outdoor environmental treatment. Only shaded and protected outdoor areas need to be treated. Products approved for the outdoors and used according to label directions. Depending on the weather, treatment of the outdoors should be repeated every 30 days if self treatment is used. A professional exterminator may be more cost effective and require less frequent treatments (ie every 3 to 4 months). If a professional exterminator is used, the owner needs to make sure that the exterminator is treating specifically for fleas (both adult and pre-emerged adult). The minimum period of time that they should guarantee for at least 2 months. The exterminator should repeat the flea treatment for fleas if a flea is found during the guarantee period.

Treatment of the Pet

The FAD and all of the pets in the household should be treated for fleas. In the past, flea shampoos and flea dips were used. Many topical and oral medications have become recently available and are currently recommended by most veterinary dermatologists.

Some veterinary dermatologist will use prescription flea collars as a treatment option for the FAD pet. Prescription flea collars (ie Virbac brand) are better than the over the counter flea collars. Knock-out collar by Virbac has an insect growth regulator (pyriproxifen) that prevents flea eggs from being viable.

Flea sprays are available but not as readily used as other topical flea products. Pyrethrin or pyrethroid based, with an insect growth regulator (ie methoprene, pyriproxyfen) are very effective. Pyrethroid based sprays should NOT be used in CATS since they are toxic to cats. Examples of pyrethroid sprays would include: permethrin, allerthrin, fenvalearte, resmethrin, sumethrin. Side effects seen in cats are: vomiting, hypersalivation, muscle tremors, depression, seizures, anorexia, ataxia, and diarrhea. Follow bottle instructions for application rates. Read precautions about age limits and species limits as some products are not suitable for cats. Water based products may be helpful for pets that seem irritated by the application of flea sprays. Frequent application may be needed it the pet swims or is bathed frequently. An exception to this is the Frontline® spray which is an alcohol based spray with fiprinol. This drug gets into the sebaceous gland and gets re-released after swimming or bathing.

Lufenuron is a systemic chitin inhibitor that prevents the development of eggs and larvae by inhibiting chitin formation. Two products, Program and Sentinel, are commercially available. Since mammals do not have chitin, this product is very safe. Rare reports of vasculitis have been reported with lufenuron use in dogs.

Systemic oral adulticide products, Capstar® and Comfortis® , are also available for flea control. The active ingredient for both of these products differs. The active ingredient for Capstar® is nitenpyram which is a neonicotinoid. The active ingredient for Comfortis® is spinosad which targets nictotinic acetylcholine receptors. Both medications are an oral tablet that is to quickly kill adult fleas (usually within 30 minutes after administration). These product differs as to how long the product lasts (Capstar® lasts 24 hours whereas Comfortis® lasts 1 month). Capstar® is a non-chewable tablet whereas Comfortis® is a chewable medication. The flavoring may be a potential problem in food allergic animals. In addition, Comfortis ® needs to be given with a meal in order to be effective (food increases the bioavailability). Antedoctal reports suggest that some veterinarian's believe that Comfortis ® may not work the full 28 days and that a repeat dose at 14 days may be required for severely flea allergic patients.

Topical adulticides (Advantage® , Advantage Multi® , K9 Advantix® , Frontline® , Frontline Plus® and Promeris ® ) are popular flea control products in dogs and/or cats. One of the reasons for this popularity is the east of application. However, these products may be washed off with bathing. In the case of Advantage® , the studies were not conducted with medicated shampoo. Instead they were conducted with a mild shampoo. The Frontline® should not be washed off if the bath does not occur within 48 hours of application. Promeris® is waterproof but it is not recommended to bathe within several days of application.

Active ingredients for flea control vary with each topical product. Immidacloprid is the active ingredient for Advantage® products. Immidacloprid is known to affect the nictonyl receptors. Fiprinol is the active ingredient for Frontline® products which is product that affects GABA receptors. Metaflumizone is the active ingredient for flea control with Promeris® which is a sodium influx blocker. Regardless of the product, all of these products function as adulticides only and should be used in conjunction with a product that affects pre-adults. Frontline Plus® has methoprene whereas Frontline and Advantage do not. For better coverage of the flea cycle either Program® (lufenuron) or a Knock-out collar® (pyriproxifen, an insect growth regulator) should be used concurrently. NOTE: The formulation for the dog Promeris® contains amitraz whereas the cat formulation does not contain amitraz.

All of the topical flea control products have been associated with side effects. In the case of Advantage® , irritation with or without hair loss and caustic burns with skin sloughing have been seen. These side effects appear to be more common in purebred cats. Oiliness at the site of application and hair loss has been associated with Frontline® product usage in both dogs and cats. The side effects for Promeris® include: transitory hyperactivity, pruritus, head shaking, salivation, and lethargy. Since amitraz is present in the canine product and amitraz causes hyperglycemia due to alpha-2 adrenergic stimulation, Promeris® should not be used in diabetic animals.

Two additional flea products are available which treat adult fleas as well as immature stages of the flea cycle. These two products are Revolution® , Vectra 3D® (dogs only). Revolution contains selamectin which kills adult fleas and prevents the eggs from hatching for 1 month. Vetra 3D contains several active ingredients (2 adulticides= dinotefuran and permethrin and one IGR= pyriproxyfen). Selamectin is a synthetic avermectin which works by GABA receptors. Dinotefuran is an insect synaptic poison that mimics acetylcholine.

Side effects have also been associated with these two topical flea products. The side effects have been associated with Revolution usage only but appear to be uncommon. The following are the side effects reported with selamectin usage: transient alopecia with or without inflammation near the site of application, pruritus, urticaria, erythema, ataxia, fever and death (extremely rare).

Over the years, several other flea control products have been used but they have been found to be ineffective. These products are ivermectin, Brewer's yeast (this is actually used to help grow fleas in the laboratory),ultrasonic collars, oral organophosphates, and hyposensitization (allergy shots) without flea control.

Secondary complications from flea allergy dermatitis may need to be addressed. In the case or pruritus, anti-inflammatory doses of steroids have been effective. Antedoctal reports suggest that some dogs with FAD may benefit from administration of hydroxyzine to control the pruritus. Secondary pyodermas should be treated with topical medications (ie shampoos, lotions, ointments, etc) and/or oral antibiotics. A superficial pyoderma should be treated for a minimum of 3 weeks or 1 week beyond when the skin appears normal. Deep pyodermas should be treated for a minimum of 4 weeks or 2 weeks beyond normal.

Comments and Conclusions

Flea control for the pet and environment is essential for getting the flea allergy problem under control. All pets in the environment should be treated. The house and outside may need to be treated in order to get the FAD under control.

Anti-pruritic and antibiotics may need to be prescribed in order to control secondary complications from FAD. Some owners may be reluctant to do pet and environment control when the pruritus improves if steroids are used. Therefore, client education about the flea life cycle and how to treat the pet and environment is essential to controlling and treating this allergy.

Selected Readings

Carlotti DN, Jacobs DE. Therapy, control and prevention of flea allergy dermatitis in dogs and cats. Vet Dermatol. 2000;11:83-98.

Genchi C, Traldi G, Bianciardi P. Control of flea allergy dermatitis. Compend Cont Edu Pract Vet 2000; 22:12-14.

Medleau L, Clekis T, McArthur TR, et al. Evaluation of fipronil spot-on in the treatment of flea allergic dermatitis in dogs. J Small Anim Pract. 2003;44:71-75.

Medleau L, Hnilica KA, Lower K, et al. Effect of topical application of fipronil in cats with flea allergic dermatitis. J Am Vet Med Assoc. 2002;221:254-257.

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