Dermatitis in dogs: treating flea allergy dermatitis with fipronil

Flea allergy dermatitis (FAD) is the most common allergic disease in veterinary practice. It may appear at any age, although it is more frequent in dogs 3–5 years old. Some breeds, such as Labrador, Pekinese, Chow Chow, Fox Terrier and Setter, are more susceptible to FAD.

Animals with atopy caused by certain environmental allergens are also more prone to FAD, as reported in a study conduced at the Faculty of Veterinary Medicine, University of Zaragoza.¹

Clinical signs of flea allergy dermatitis

Flea allergy dermatitis is a reaction seen in dogs that have become sensitised due to a previous bite. There is a hypothesis that dogs continuously exposed to fleas may develop an immunological tolerance, but intermittent exposure is more likely to cause hypersensitivity, as suggested in a study published in Veterinary Immunology and Immunopathology.²

Essentially, the dog reacts to allergens found in the flea’s saliva. Flea saliva does indeed have irritant and allergenic characteristics. In dogs, the most antigenic protein fractions are responsible for this hypersensitivity reaction.

As a result, patients have signs characteristic of pruritic papular dermatitis, including:

• Pruritus of varying intensity
• Localised or generalised erythema
• Secondary lesions (alopecia, abrasions, papules, flakes and scabs) due to the patient scratching, biting or licking the affected area.

Lesions are usually concentrated in the lumbosacral region, the base of the tail and the caudomedial muscles, according to a study published in Veterinary Dermatology.³ Chronic cases may also course with hyperpigmentation, lichenification and hyperkeratosis.

Flea allergy dermatitis in dogs: treatment

The treatment of flea allergy dermatitis involves eliminating exposure to the antigen: fleas. So the focus must be on their control. A study at the University of Georgia⁴ analysed the efficacy of fipronil in treating flea allergy dermatitis in dogs.

The researchers treated 31 dogs with flea allergy dermatitis with three monthly applications of a 10% fipronil solution. They performed a flea count, analysed the level of pruritus and assessed any skin lesions at each visit.

After 90 days, flea counts had decreased by 98% and there was less or no pruritus in 84% of the subjects. The skin lesions also improved significantly, so the researchers concluded that “the application of a 10% fipronil solution is effective in reducing the frequency and severity of signs of flea allergy dermatitis in dogs”.

However, the application of an anti-flea product is not always sufficient and corticosteroids are sometimes required to improve or even quickly resolve the clinical signs. Prednisone or prednisolone can be given orally for 5 to 10 days. If the animal experiences adverse effects, first-generation antihistamines can be used.

Hyposensitisation therapy is currently being studied, which involves injecting ever-increasing doses of flea extracts, although there are still no conclusive results to confirm its efficacy.

1.    Navarro, L. & Verde, M. T. (2002) La dermatitis alérgica a la picadura de pulga: estudio de factores epidemiológicos en el área urbana de Zaragoza. Rev. AVEPA; 22(4): 311-317.

2.    Halliwell, R. E. & Longino, S. J. (1985) IgE and IgG antibodies to flea antigen in differing dog populations. Vet Immunol Immunopathol; 8(3): 215-223.

3.    Bruet, V. et. al. (2012) Characterization of pruritus in canine atopic dermatitis, flea bite hypersensitivity and flea infestation and its role in diagnosis. Vet Dermatol; 23(6): 487-493.

4.     Medleau, L. et. al. (2003) Evaluation of fipronil spot-on in the treatment of flea allergic dermatitis in dogs. J Small Anim Pract; 44(2): 71-75.