The two most common cutaneous fungal infections in small animals are dermatophytosis and Malassezia dermatitis. Malassezia is a yeast organism that has recently been implicated as a cause of dermatitis in cats and dogs. From veterinary point of view, Malassezia pachydermatis has the greatest significance. It has been standing in the focus of interest since the early 1990s, mostly because of the frequency of otitis externa and dermatitis caused by this yeast in dogs.
Malassezia pachydermatis dermatitis in dogs is an extremely itchy skin disease. It is often associated with inflammation, yellowish-gray greasy scales, dark pigmentation of the skin, self-trauma, and hair loss. In cats, disease produced by Malassezia is most often seen as ear infections, severe acne, and generalized redness and scaling. Severe disease may be associated with underlying FIV infection. Dogs with corneal ulcer are more likely to develop Malassezia pachydermatis dermatitis which suggests its possible role at least as an aggravating factor in the disease. Malassezia has little zoonotic potential, but it can be dangerous to people with weakened immune system.
Diagnosis is based on tests (impression smears, tape strip cytology, or discharge from the ears). It may be difficult to find this organism in biopsy samples. Culturing skin debris may be unreliable since small numbers of this yeast on the skin are considered normal. Although the yeast may appear as a primary pathogen, an underlying disease should always be suspected and several tests may be necessary to exclude other diseases. The skin can be cleared from the yeast (at least in the short term) with ketoconazole for 10-14 days or topical shampoos containing miconazole or ketoconazole. Recently, terbinafine has been effectively used to decrease itchiness. In a few cases, complete cure may occur and no further treatment may be necessary. Because most cases of Malassezia dermatitis are secondary to an underlying disease, recurrence is common unless the cause can be resolved.
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Australian researchers have examined the activity of Australian tea tree oil, the essential oil of Melaleuca alternifolia, against several strains of Malassezia pachydermatis. All tested strains showed remarkably high susceptibility to tea tree oil. With these results the excellent antibacterial activity of tea tree oil is extended to a new group of fungal pathogens colonizing mainly mammals' skin. During the last ten years there was an increasing popularity of tea tree oil containing human health care products.
Although rare, cases of life-threatening fungemia in people have been attributed to Malassezia pachydermatis, for which dogs are a natural host. Zoonotic transfer has been documented from dogs to immunocompromised patients by healthcare workers who own dogs. These investigations show that the Malassezia species causing most skin disease in humans, including the most common cause of dandruff and seborrhoeic dermatitis, is M. globosa. Symptomatic scalp infections are often treated with selenium disulfide or ketoconazole containing shampoos. Other treatments include ciclopirox olamine, coal tar, zinc pyrithione (ZPT), miconazole, or tea tree oil medicated shampoos.
- Richard G. Harvey, P. J. McKeever. A Colour Handbook of Skin Diseases of the Dog and Cat
- Mycologic disorders of the skin, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA.
- Comparison of the clinical efficacy of oral terbinafine and ketoconazole combined with cephalexin in the treatment of Malassezia dermatitis in dogs by Rosales MS, Marsella R, Kunkle G, Harris BL, Nicklin CF, Lopez J. (a pilot study, Vet Dermatol. 2005 Jun;16(3):171-6.)
- Higher incidence of Malassezia pachydermatis in the eyes of dogs with corneal ulcer than in healthy dogs. Prado MR, Brito EH, Girao MD, Monteiro AJ, Sidrim JJ, Rocha MF. School of Veterinary Medicine, Post-Graduation Program in Veterinary Science, State University of Ceara, Ceara, Brazil
- Pathological and clinical aspects of the diseases caused by Malassezia species.Dorogi J., Dr. Juhasz Tamas Clinic for Small Animals, Budapest, Hungary
- Antifungal effect of Australian tea tree oil on Malassezia pachydermatis isolated from canines suffering from cutaneous skin disease. Weseler A, Geiss HK, Saller R, Reichling J. Institute of Pharmaceutical Biology, Ruprecht-Karls-University Heidelberg, Germany
- Malassezia pachydermatis Carriage in Dog Owners. Daniel O. Morris et al.