Flea Allergy Dermatitis
• Other names: FAD, flea bite hypersensitivity, flea allergy, flea bite dermatitis
• Cause: Allergic reaction to flea saliva. Flea saliva contains histamine-like compounds that irritate the skin in most animals. A dog or cat with an allergy to flea saliva will have an exaggerated, disproportionate response. The allergic reaction may be immediate or delayed. Depending on individual sensitivity, one flea bite may be enough to cause severe flea allergy dermatitis.
• Species: dogs and cats
• Signs:
- compulsive biting, scratching, licking, and chewing ("corncob nibbling")
- Animals appear restless and uncomfortable
- Animals may be sensitive to touch, particularly along the flanks, lower back, caudal abdomen, neck, and ears
- Fur may be broken, brittle, greasy, and/or stained brown from licking.
- Dogs often display a classic "Christmas tree" pattern of dermatitis over the dorsum and tail base; alopecia and skin lesions may also occur in the caudal aspect of the thighs, lower abdomen, inguinal region, and cranial forelegs.
- Cats typically present with a crusted, miliary dermatitis over the dorsum ("racing stripe" dermatitis) and around the head and neck. Sometimes they will present instead with alopecia in the inguinal region with or without inflammation or with eosinophilic plaques or other forms of eosinophilic granuloma complex.
- fleas and flea dirt may or may not be present (for some patients, simply one bite can be enough to cause an allergic reaction; additionally these patients tend to over groom themselves and may remove all traces of fleas if the burden is light)
- incidence varies with climatic conditions; may be seasonal or year-round
- may be seen at any age, but usually first develops between 3-6 years old.
• Diagnosis: History and exam; skin scrapings and skin cytology may be done to rule-out mange, bacterial, or fungal infections. To complicate matters, animals can have multiple concurrent problems contributing to their clinical signs (ex. FAD and mange; or FAD and seasonal or food allergies)
• Treatment: No cure is available; this condition is only managed.
- Quality flea control for all animals in the environment is the only effective means of therapy. Everything else is only for patient comfort while the fleas are being brought under control. (Some areas are seeing resistance to different flea control products. Consult a local veterinarian for what works best in your area).
- Depending on your local climate, flea control may be needed year-round or only seasonally. If your pet is primarily indoors, it will likely need treatment year-round regardless of the outdoor climate. Consult your local vet for their recommendations.
- Antihistamines may help relieve pruritis while fleas are being controlled.
- Corticosteroids for inflammation while fleas are being controlled.
- Antibiotics or antifungals to treat secondary skin infections.
- Prescription shampoos can be used to help treat secondary skin infections and restore skin health in amenable animals.
- Avoid flea dips, powders, collars, etc. (except the new Seresto collars) They use older paraciticides that are much less effective and more toxic than the newer spot-ons, oral preventatives, and Seresto collars.
- Avoid pyrethrin/pyrethroid flea products, particularly in cats -- adverse reactions include depression, hypersalivation, muscle tremors, vomiting, ataxia, dyspnea, and anorexia.
- Avoid organophosphate products, especially in cats, young animals, and sick/debilitated animals -- adverse reactions include hypersalivation, lacrimation, urination, defecation, vomiting, diarrhea, miosis, fever, muscle tremors, seizures, coma, and death
- Avoid carbamate products
- Selemectin is contraindicated in heartworm-positive dogs.
- Vacuuming (and immediately disposing of the canister contents or bag) and washing the pets' bedding with detergent and hot water can help decrease the burden of flea eggs and larva in the environment.
• Prevention: Strictly adhering to a veterinarian-recommended flea control protocol.
Sources:
• "Flea Bite Hypersensitivity and Flea Control." Blackwell's Five-Minute Veterinary Consult: Canine and Feline, 4th ed. (Pg. 512-513) Larry P. Tilley and Francis W.K. Smith, Jr.
• Flea Allergy
https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/flea-allergy
• Flea Allergy Dermatitis https://www.merckvetmanual.com/integumentary-system/fleas-and-flea-allergy-dermatitis/flea-allergy-dermatitis
• Flea Allergy Dermatitis http://www.skinvetclinic.com/fleaallergydermatitis.html
• Scratching the Surface of Allergies in Dogs
https://todaysveterinarynurse.com/articles/scratching-the-surface-of-allergies-in-dogs/
• Flea Allergy Dermatitis: What Your Clients Need to Know https://todaysveterinarynurse.com/articles/flea-allergy-dermatitis-what-your-clients-need-to-know/