Malassezia Dermatitis and Malassezia Otic Overgrowth

PATHOGENESIS

Malassezia yeast colonize the skin and external ear canals of animals in very low numbers. Overt “infection”, sometimes referred to as “overgrowth” is defined by increased numbers of the yeast on the skin surface in conjunction with inflammation. In a diseased state, alterations of the skin’s surface microclimate contribute to increased susceptibility to yeast infection. 1 Primary diseases that cause increased moisture, altered surface lipids, and/or disruption of stratum corneum barrier function encourage secondary overgrowth of the organism. In some dogs with atopic dermatitis (AD), antigens produced by M. pachydermatis may be recognized by the immune system as allergens (ie., Malassezia hypersensitivity), in which case a highly inflammatory and pruritic response can be mounted to relatively low numbers of yeast organisms, blurring the line between cytological definitions of “colonization” and “infection”. 2 While a definitive (immunological) relationship between Malassezia yeast and atopic dermatitis has not been described in cats, feline MD does appear to occur secondary to underlying pruritic/inflammatory dermatoses. […]