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M. W. Yroom

Flea allergy dermatitis

Flea allergy dermatitis (FAD) is the most common pruritic dermatosis in the cat.^1,2 A diagnosis of FAD cannot be eliminated by the absence of fleas or flea faeces because allergic cats can remove fleas from their coat by grooming. FAD should be suspected when self-induced, principally dorsolumbar, alopecia, miliary dermatitis or, morę rarely, eosinophilic plaąues or linear granulomas are present. Allergy testing has little diagnostic value. Treatment initially involves rigorous flea control for the affected cat, in-contact animals and the environment. When antipruritic treatment is necessary, the use of corticosteroids produces immediate improvement. Immunotherapy is, currently, of no benefit.

Aetiopathogenesis

Numerous studies on the immunopathogenesis of FAD have been published in the guinea-pig, man and the dog, but it is difficult to extrapolate these to the cat. Saliva from the flea Ctenocephalides felis felis contains numerous allergenic proteins, one of which, a high molecular weight protein, designated Cfel 1, could be a major allergen in the dog \ In the dog, FAD is due to an immediate type 1 hypersensitivity reaction with a late-phase reaction and a delayed cutaneous basophil hypersensitivity reaction. In the cat, the immunopathogenic mecha-nisms of FAD are still unknown. Some authors report only immediate intradermal reactions whereas others also mention delayed reactions^{4 5,6}.

Clinical features

FAD is seen in cats of every age, sex and breed ^{17 8 910}. It can be seasonal or non-seasonal depending on the geographical region. Signs are often the result of cutaneous self-trauma and generally involve the caudal half of the body (back and caudomedial thighs) (Figs 9 : 1,2). Pruritus is constant and sometimes even severe. The clinical picture is variable, involving symmetrical alopecia, broken hairs (Figs 9 : 3,4), scaling, papules, little crusts which feel miliary to the touch, or crusts of a true miliary dermatitis (Figs 9 : 5-7). Morę rarely, FAD presents as eosinophilic plaąues (Figs 9 : 8,9), linear granulomas (Fig. 9 : 10) or facial pruritus. Unlike in the dog, the cat with FAD rarely presents with secondary bacterial infections. As cats tend to groom themselves very thoroughly, it is often difficult to demonstrate fleas or flea faeces. Owners sometimes describe weight loss and restlessness in affected animals ".

Diagnosis

History

Historical factors, suggestive of FAD, are of the utmost importance in both establishing a diagnosis and instituting treatment.

The presence of in-contact dogs or cats in the emironment is an important element of the diagnosis and, as infestation in the cat is often inapparent, these animals may help permanently maintain the flea popu-lation. An in-contact cat, even if treated for fleas, constitutes an important risk factor for recurrence ¹²

The seasons of flea development are very variable, depending on geographical region and environ-mental conditions. Peaks may occur between March and October. However, increased pruritus in Winter does not rule out FAD and may be due to a rise in ambient temperaturę of the habitat^l3.

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