Flea Allergy Dermatitis in Dogs

By Tammy Hunter, DVM; Ernest Ward, DVM

I was told that my dog has flea allergy dermatitis, but I have never seen a flea on him. How can he have flea allergy dermatitis?

Flea allergy dermatitis (FAD) is a leading cause of allergic reactions in dogs. In an allergic reaction, the body’s immune system overreacts or is hypersensitive to a substance (called an antigen) that is normally harmless.

FAD is a common cause of itching in dogs. Adult fleas must bite a dog and obtain a blood meal in order to reproduce. Fleas typically do not remain on the dog except for the minutes to hours when they are feeding. This is why dog owners often do not see live fleas on their dog unless there is a severe flea infestation in their immediate environment. When fleas feed, they inject a small amount of saliva into the skin. It is the antigens or proteins in the saliva that cause an intensely itchy response to sensitive dogs.

"A single fleabite can cause itching for days."

Dogs with FAD do not have to be infested with fleas to be itchy. In fact, a single fleabite can cause itching for several days.

Are only certain dogs allergic to fleas?fad_triangle_dog_2018-01

FAD can develop at any age but most cases of FAD appear between age two and five in most dogs. It is important to note that dogs with other forms of allergies, such as inhaled allergies (e.g., pollens, molds, dust mites), tend to be highly sensitive to flea bites, and are therefore much more susceptible to FAD than dogs that do not have other allergic conditions.

How is flea allergy dermatitis diagnosed?

Clinical signs often give the first clue that your pet may suffer from FAD. Itching and hair loss in the region from the middle of the back to the tail base and down the rear legs (the flea triangle) is often associated with FAD.

Intradermal allergy tests (skin tests similar to those performed in humans) or specialized blood tests (IgE blood tests) can confirm flea allergy in your dog. The signs of FAD are often very classic and response to treatment occurs so quickly that formal allergy testing is only necessary in some cases.

What does treatment involve?

Since the injection of flea saliva causes the allergic response, it is important to prevent fleas from biting your dog. Strict flea control is essential. Even though you have not seen fleas on the dog, it is important to continue rigorous flea treatment and maintain environmental control. Most flea infestations occur in the warmer weather, but can occur year round (for more details, refer to our handout "Flea Control in Dogs"). Modern monthly oral and topical flea preventives are an essential part of good pet parenting for all dogs and cats. For a dog with FAD, flea prevention is the best form of treatment.

What about desensitization?

Desensitization (also referred to as hyposensitization), or administering allergy injections, involves injecting increasing doses of a diluted flea antigen over a prolonged period. In some cases, these allergy injections may be required for the pet's life. Desensitization, unfortunately is not considered to be very successful in treating flea allergy, and is rarely used.

It is important not to confuse desensitization therapy with corticosteroid or cortisone injections to relieve the symptoms of an acute FAD flare-up.

What about steroids or other drugs?

Corticosteroids (cortisone or steroids) are widely used to treat acute (sudden) episodes of particularly itchy FAD. They often bring about almost miraculous relief from the itching. However, there are significant potential side effects to steroid use (see handout "Steroid Treament - Effects in Dogs" for more information). Steroids can be safely used for short-term relief while flea control is being implemented. Combining corticosteroids with antihistamines and/or omega-fatty acid supplements is an ideal regimen for many patients. The goal is to use the lowest dosage of corticosteroids as possible, as infrequently as possible, preferably on an alternating- or every third-day basis. If your dog has developed a secondary bacterial skin infection because of the scratching, antibiotics may also be necessary.

"Corticosteroids are widely used to treat acute (sudden) episodes of particularly itchy FAD."

Fortunately, due to very effective newer technologically advanced flea control products, steroids are often not necessary in today’s treatment of FAD.

Your veterinarian will discuss the pros and cons of the various treatments for FAD with you during the examination, and will recommend the safest and most effective treatment plan for your pet's individual needs. Prevention is essential and relatively simple and inexpensive. Ask your veterinarian for the best flea preventive for your pet’s lifestyle and needs.


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