An allergic reaction to mosquito bites can cause an ulcerative and crusted dermatitis of the pinnae, nose, and rarely the footpads and eyelids of cats. Lesions progress from papules to plaques to crusted ulcers that coalesce to affect extensive areas. Pruritus is variable, and regional lymphadenopathy may occur. Histologically, the lesions are characterized by severe superficial and deep perivascular to interstitial eosinophilic dermatitis, often associated with flame figures, folliculitis, and furunculosis. The differential diagnoses include pemphigus foliaceus, herpesvirus ulcerative dermatitis, other causes of eosinophilic dermatitis (food allergy, atopy, idiopathic), notoedric mange, and dermatophytosis. Treatment includes keeping the animal inside and using a pyrethrin repellent when exposure to mosquitoes is anticipated. Systemic glucocorticoids may be necessary in severe cases. (Also see Flies: Mosquitoes.)

Last full review/revision July 2011 by Sheila Torres, DVM, PhD, DACVD; Scott A. Dee, DVM, MS, PhD, DACVM