Malassezia are commensal yeasts that are part of the normal fungal flora of the skin, ears, oral cavity and body orifices. It is believed to have a symbiotic relationship with commensal staphylococcal organisms; both organisms produce mutually beneficial growth factors and micro-environmental changes. For decades, Malassezia organisms were recognized on the skin of cats, but because they were considered part of the normal flora, their involvement in skin disease went unrecognized.
Yeast organisms do not invade the deeper tissues of the skin and live on only the superficial skin layers. Malassezia dermatitis is believed to be caused by inflammation from hypersensitivity to yeast products and antigens. All cats have this organism on their skin but not all cats have or will develop yeast dermatitis; there needs to be an abnormal host response for disease to occur. Overgrowth is always triggered by some internal or external factor
The presence of yeast dermatitis on cat is always due to an underlying disease or trigger. There are several breeds of cats that are predisposed to yeast overgrowth (e.g. Devon Rex cats, Himalayan). Cats with systemic illnesses such as feline leukemia, feline immunodeficiency virus, diabetes mellitus, or neoplasia may be presented, not for the underlying disease, but rather for clinical signs associated with yeast overgrowth. Overgrowth of yeast is a common complication of cats with diabetes mellitus. One of the most common causes of yeast overgrowth in cats is allergic skin disease due to environmental allergies, food intolerances, and/or flea allergy dermatitis.
The two major hallmark clinical signs of yeast overgrowth in cats are pruritus and black waxy debris. Other clinical signs include:
- Recurrent pruritic otitis externa
- Chronic recurrent otitis media
- Chronic chin acne
- Facial fold dermatitis
- Black nail bed debris (often first noticed as ‘toe nail biting’)
- Idiopathic pruritus and scaling on the hair coat
- Diffuse erythema with or without a greasy hair coat
In most cases the diagnosis of yeast overgrowth in cats is not difficult. There are two components: the presence of the organism in any number and concurrent compatible clinical signs. The organism is readily identified by cytological examination of skin cytology. This can include ear swab cytology, skin impression smears, tape cytology (clear tape), and skin cytology obtained by scraping the skin or nail bed using a skin scraping spatula. For everyone’s safety, scalpel blades should not be used in cats to obtain skin samples for either skin cytology or skin scrapings. (Fisherbrand Microspatula Flat End)
Cats have a number of different species of Malassezia that can be isolated from their skin. What is important to note is that the yeast may vary from size from large to small budding organisms to round organisms resembling large cocci. Yeast are most readily found adhered to skin cells.
The treatment plan involves consideration of a number of factors.
- Is the overgrowth limited to a focal area allowing for topical therapy?
- Is the severity of clinical signs warrant both systemic and topical therapy?
- What is the suspected underlying cause? If so, treatment will only temporarily resolve the problem and yeast overgrowth will recur.
- If systemic therapy is needed, is there a need to coordinate it with other therapy?
- What is the overall health of the cat?
Treatment options include topical therapy, systemic therapy, or a combination of both.
Local topical therapy is often used for ears and includes the use of an otic glucocorticoid and antifungal.
Generalized topical therapy alone generally focuses on the use of shampoo therapy however there is a newer product (Douxo® Chlorhexidine PS with climbazole (antifungal) Mousse) that is treats both yeast and bacterial overgrowth. This is well tolerated by cats and allows for treatment of both yeast and bacterial overgrowth concurrently.
The systemic drug of choice for cats is itraconazole 3-5 mg/kg orally once daily for 15 to 30 days. Usually there is a dramatic improvement within 7-10 days
It is important to remember that yeast overgrowth is often associated with concurrent overgrowth of bacteria and treatment for both may be needed. In addition, of an underlying disease is recurrent yeast overgrowth.
One of the most recent developments in the treatment of chronic yeast overgrowth due to allergies is the use of oral allergy drops in cats. Prior to the development of this novel therapy, it was not possible to hyposensitize cats to Malassezia because this antigen could not be used in allergy shots.