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Fungal Disease - Malasseziasis (Malassezia dermatitis)

Introduction

Malassezia pachydermatis is yeast that is normally found in low numbers in the external ear canals, in perioral areas, in perianal regions, and in moist skin folds. Skin disease occurs in dogs when a hypersensitivity reaction to the organisms develops, or when cutaneous overgrowth occurs.

In dogs, Malassezia overgrowth is almost always associated with an underlying cause, such as atopy, food allergy, endocrinopathy, keratinization disorder, metabolic disease, or prolonged therapy with corticosteroids. In cats, skin disease is caused by Malassezia overgrowth that may occur secondary to an underlying disease (e.g., feline immunodeficiency virus, diabetes mellitus, an internal malignancy).

In particular, generalized Malassezia dermatitis may occur in cats with thymoma-associated dermatosis or paraneoplastic alopecia.

Malasseziasis is common in dogs, especially among West Highland White terriers, Dachshunds, English setters, Basset hounds, American cocker spaniels, Shih tzus, Springer spaniels, and German shepherds. These breeds may be predisposed.

Malasseziasis is rare in cats.

Clinical signs

Dogs

Moderate to severe pruritus is seen, with regional or generalized alopecia, excoriations, erythema, and seborrhea.

With chronicity, affected skin may become lichenified, hyperpigmented, and hyperkeratotic (leathery or elephant-like skin).

An unpleasant body odor is usually present.

Lesions may involve the interdigital spaces, ventral neck, axillae, perineal region, or leg folds.

Paronychia with dark brown nail bed discharge may be present.

Concurrent yeast otitis externa is common.

Cats

Symptoms include black, waxy otitis externa, chronic chin acne, alopecia, and multifocal to generalized erythema and seborrhea.

Differential diagnosis

Differentials include other causes of pruritus and seborrhea, such as demodicosis, superficial pyoderma, dermatophytosis, ectoparasites, and allergies.

Diagnosis

Rule out other differentials.

Cytology (tape preparation, impression smear): yeast overgrowth is confirmed by the finding of round to oval budding yeasts (100). In yeast hypersensitivity, organisms may be difficult to find.

Dermato histopathology: superficial perivascular to interstitial lymphohistiocytic dermatitis with yeasts and occasionally pseudohyphae in keratin. Organisms may be few in number and difficult to find.

Fungal culture: M. pachydermatis.

Allergy test demonstrating a hypersensitivity to Malassezia.

Treatment

Any underlying cause (allergies, endocrinopathy, keratinization defect) must be identified and corrected.

For mild cases, topical therapy alone is often effective. The patient should be bathed every 2 to 3 days with shampoo that contains 2% ketoconazole, 1% ketoconazole/ 2% chlorhexidine, 2% miconazole, 2% to 4% chlorhexidine, or 1% selenium sulfide (dogs only). Shampoos that have two active ingredients provide better efficacy. Treatment should be continued until the lesions resolve and follow-up skin cytology reveals no organisms (approximately 4 weeks).

The treatment of choice for moderate to severe cases is ketoconazole (dogs) or fluconazole 10 mg/ kg PO with food every 24 hours, Treatment should be continued until lesions resolve and follow-up skin cytology reveals no organisms (approximately 4 weeks).

Alternatively, treatment with terbinafine 5–40 mg/ kg PO every 24 hours or itraconazole (Sporanox) 5–10 mg/kg every 24 hours for 4 weeks may be effective.

Pulse therapy protocols using several drugs and a variety of schedules have been published; however, these often take longer to resolve the active infection.

Prognosis: is good if the underlying cause can be identified and corrected. Otherwise, regular once- or twice-weekly anti yeast shampoo baths may be needed to prevent relapse. This disease is not considered contagious to other animals or to humans, except for immune-compromised individuals.


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