Flea Allergy Dermatitis in Dogs


Overview of Canine Flea Allergy Dermatitis

Flea allergy dermatitis is the most common allergy in dogs and is caused by flea bites, specifically the saliva of the flea. It is a very itchy disease and predisposes to the development of secondary skin infections.

Oddly enough, most animals with flea allergy have very few fleas – because they are so itchy, they groom themselves excessively, eliminating any evidence of fleas. However, a couple of flea bites every two weeks are sufficient to make a flea allergic dog itchy all the time. Any animal can become allergic to fleas, although some dogs are more attractive to fleas than others.

Fleas are bloodsucking insects with a life span of 6 to 12 months. This life span is influenced by environmental conditions and can vary from two to three weeks up to a year. Optimal conditions include humidity of 75 to 85 percent and temperature of 65 to 80 degrees Fahrenheit. Humidity is more important than the temperature. The adult flea spends most of its life on the host, while the immature stages (eggs) are found in the environment.

What to Watch For

Signs of flea allergies in dogs include: 

  • Severe itching
  • Chewing and biting of the tail, rump, back legs and occasionally front legs
  • Oozing lesions (lick granuloma) from chewing
  • Hot spots on the hips or face, which is severe skin damage from scratching
  • Diagnosis of Flea Allergy Dermatitis in Dogs

    Flea allergy dermatitis is a common cause of itchiness and scratching in dogs, but other medical problems can lead to similar symptoms. Other disorders that must be excluded are:

  • Food allergy
  • Atopy
  • Trauma or other cause of local skin irritation
  • Sarcoptic mange
  • Cheyletiellosis (a mite infestation)
  • Otitis externa (ear infection)
  • Primary keratinization defects

    Some pets may have more than one medical problem. For example, scratching or biting due to flea irritation can cause a “hot spot” (acute moist dermatitis) and secondary bacterial skin infection (pyoderma) can follow.

    Diagnosis of flea allergy is made based on history, clinical signs and a positive response to flea control.

    Treatment of Flea Allergy Dermatitis in Dogs

    Treatment of flea allergy dermatitis in dogs involves three phases:

  • Prevention of flea bites. The most important part of treatment is preventing flea bites with aggressive flea control on your dog and in the environment.
  • Treatment of secondary skin infections. Antibiotics and antifungal drugs may be necessary to treat secondary skin infections triggered by the flea allergy.
  • Breaking the itch cycle. If your dog is intensely itchy, a short course of steroids may be necessary to break the itch cycle and make your dog more comfortable.
  • A newer therapy called Oclacitinib (Apoquel) has been very effective in control of itching in dogs with flea allergies.
  • Preventative Care

    Use an effective safe flea control product on your dog on a regular basis beginning one month before the flea season starts and continuing up until one month after the flea season ends.

    Use frequent vacuuming and carpet cleaning strategies to remove eggs and larvae from the dog’s indoor environment. Use a professional cleaning or exterminating service in difficult cases.

    See your veterinarian promptly if your dog develops acute skin lesions (acute moist dermatitis) as a result of biting or scratching at fleas. Frequent grooming of your dog with a “flea comb” may be helpful to remove fleas.

    In-depth Information 

    Veterinary care should include diagnostic tests and subsequent treatment recommendations.

    Diagnosis In-Depth of Flea Allergy Dermatitis in Dogs

    Diagnostic tests often are performed to confirm a diagnosis of flea allergy dermatitis and exclude other diseases that may cause similar symptoms. Tests may include:

  • A complete medical history including questions about itchiness, areas of involvement, prior history of skin problems, diet, response to therapy, and any concurrent medical conditions
  • A thorough physical examination, including examination of the skin
  • Fecal flotation tests to determine the presence of concurrent gastrointestinal parasites or identify tapeworms, which are transmitted via fleas
  • Skin scrapings examined under the microscope to detect mange mites (sarcoptes, cheyletiella, demodex). The sarcoptic mange mite can be very difficult to find and several skin scrapings may have to be collected.

    Your veterinarian may recommend additional diagnostic tests to exclude or diagnose other conditions. These tests insure optimal medical care and are selected on a case-by-case basis. Examples include:

  • A complete blood count (CBC or hemogram) to identify infection or inflammation and anemia, which can be seen in severe flea infestations. Occasionally, a high percentage of circulating eosinophils may be seen in the blood smear. This type of white blood cell may be found in increased numbers in some animals with parasitic infections.
  • Serum chemistry tests to evaluate the overall health of the dog and to evaluate the function of vital organs such as the liver and kidneys
  • Allergy tests such as the radioallergosorbent test (RAST) or the enzyme-linked immunosorbent assay (ELISA), although the accuracy and usefulness of these tests is variable
  • Intradermal allergy testing (skin testing) to identify the responsible allergens in allergic animals. Most flea allergic dogs will react to the flea antigen used in this test.
  • Microscopic examination of material collected from the external ear to check for mites or infectious organisms like bacteria or yeast.
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