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Know the Facts of FAD (Flea Allergy Dermatitis)

Know the Facts of FAD (Flea Allergy Dermatitis)

By Colleen Mendelsohn, DVM

It may seem baffling to you that veterinarians will emphasize and re–emphasize flea bite prevention for pets when neither you nor the owners have ever noted the presence of fleas or “flea dirt”. It is sometimes difficult to convince pet owners to consider flea bite allergy as the primary trigger for their dog’s itching and hairloss on the rump or tail when owners insist that, “My pet doesn’t have fleas!”  

Flea allergy dermatitis (FAD) results from a true hypersensitivity to flea salivary allergen, not from heavy flea infestations. If a client lives in a geographical area in which fleas are common or in home environments, apartments or condos that are flea infested and their pet is flea allergic, they are at increased risk of exhibiting clinical signs of FAD. Flea allergic signs develop because of exposure to flea salivary allergen that is transmitted into the skin via the flea bite. 

Fleas must take a blood meal, and while they are engorging on the blood of the pet, they are transmitting their saliva and the allergen directly into the pet. A single bite is generally not enough to initiate a flea bite hypersensitivity reaction; however, the length of time that a flea feeds and the number of fleas feeding will directly correlate with the amount of allergen to which the pet will be exposed. 

Numerous fleas taking a blood meal (and dying) can be enough to start a reaction, despite a flea infestation never being established. In fact, infrequent or intermittent flea bites can perpetuate severe symptoms. Additionally, FAD animals spend so much time chewing and grooming, they often remove fleas before you or the pet owner get the opportunity to see them. 

There are numerous issues that owners and pet professionals need to consider in dealing with fleas and the problems that they create for flea allergic pets.

Problem Scenarios with Topical Treatments

With recent advancements in flea/tick preventative methods, which include oral and collar forms, topical treatments still remain the most common but must be applied according to product application directions. Here are some possible scenarios which may inhibit the efficacy of topical treatments applied by pet owners:

• Incorrect perception: If a pet owner is still seeing fleas just days after application of a product; that is actually expected and is not a result of the product “failing”. Fleas are still hatching in the environment and are expected to be present. Even if live fleas are found on the pet, in most cases the flea product will prevent prolonged feeding times which will result in an inability to reproduce and establish infestations.

• Additional Pets Not Being Treated: If a pet owner has other pets in the household that are not being treated, those pets are providing healthy blood meals for those fleas to continue to flourish in the environment and controlling the FAD patient will be more difficult. 

• Bathing: If your clients are telling you that they are faithfully applying the topical flea bite prevention product but they still have signs attributed to flea bite allergy; it is time to examine how often the pets are being bathed. If a pet owner is applying topical therapy, depending on the shampoo, bathing will likely reduce the efficacy of the product. If the pet is being bathed more than monthly (which is absolutely necessary for almost all allergic patients) then consider recommending that they discuss with their veterinarian switching that pet to an oral product that is not affected by bathing.

• Repellents: Pyrethrins and Permethrins are not good options as a single treatment modality to prevent infestation—let alone treat FAD. However, they can be used if the pet owner knows in advance that their pet is going to be going into a potentially flea infested environment such as the dog park, walking in an area with a lot of feral cats, or even going to a grooming appointment or daycare.

• Product Doesn’t Last the Entire Month: Most flea products will have lessened efficacy as the next application–due time is approaching. This may mean that more fleas take blood meals (and then lay eggs) before they die. For FAD patients, this results in increased clinical signs, and because a flare of FAD can last weeks, it is hard to associate the worsening with the timing of product application. If this is a concern, pet owners should consider discussing using combination therapy for heightened flea bite prevention with their veterinarian.  

• Inappropriate Application Method: This is the most common problem with the topically applied products. Mistakes often made include: incorrect dosing, accidentally wiping it off after application with halter collars or other clothing, applying to a wet animal or immediately after a bath, or simply not applying to the skin and leaving the bulk of the product in the hair coat.  

Environmental Treatment Options

Environmental controls and measures aimed at controlling all stages of the flea life cycle are numerous. These can be very important as the majority of flea populations are the immature stages and live in your pet’s surroundings (unlike the adult that resides on the pet). Some options for client homes and facilities include: 

• Premise Spray Insecticides: These will be the most effective when combined with growth hormone regulators in order to kill both the adults as well as prevent juvenile forms (larvae) from maturing into adult fleas. These are available through professional exterminators as well as at hardware stores for self application.

• Predatory Nematodes: These are microscopic “worms” that prey on numerous insect pests that have a larval stage in the soil. These are available for self–application from hardware stores and nurseries. However, these nematodes are very sensitive and have limited efficacy in most situations.

• Borate Powders: These powders are safely applied to indoor carpets. They will result in an environment that will dehydrate fleas and other pests. These can be self–applied and professionally–applied. 

• Yard Maintenance: Keep vegetation near the home or kennel mowed or clipped, also remove leaves and other organic debris covering moist ground to allow the ground to dry.

• Stray and Wild Animals: Keep the area free of carrier hosts such as free–roaming cats and dogs, raccoons, squirrels and opossums.

Making the Pet Comfortable

The pruritus (itching) from a single flea bite hypersensitivity episode can take days to weeks to subside, even after the fleas are gone. Therefore some pets benefit from additional anti–inflammatory medications and owners should be encouraged to discuss this with their veterinarians. 

If infection is present, treatment with antibiotics is also necessary. Pruritus associated with infection is often underestimated and managing allergic skin disease generally requires a multi–modal approach. 

Treating the pet and environment for fleas, as well as managing the skin of the pet to control both inflammation from the allergic response as well as any secondary infection, is critical for the best management of the flea allergic patient. 

Dr. Mendelsohn is a 1997 graduate of UC Davis School of Veterinary Medicine and received Diplomate status with the American College of Veterinary Dermatology in 2004. After graduation from UC Davis, Dr. Mendelsohn completed an internship with the Animal Emergency Clinic and Animal Specialty Group in San Diego. She later practiced general medicine before starting her residency with the Animal Dermatology Clinic in 2000. Her love and appreciation of the human-animal bond is what drew Dr. Mendelsohn to this specialty. Another opportunity that Dr. Mendelsohn enjoys is the training of veterinary students, helping these students appreciate the hidden complexities of dermatologic disease.

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