Infection

Clinical signs result from penetration and digestion of the non-viable outer skin layer and of hair shafts by infective fungal elements. Often, there is some trauma to the skin, including bites from fleas, clipping wounds, etc.

Arthrospores (the infective element) are present on the broken hairs, collars, and brushes from infected or carrier animals and contamination of the environment from these sources is common Arthrospores invade hair shafts and stratum corneum (the outer-most layer of the epidermis...see "Skin Basics" page).Some strains can also invade "living" tissue as well. Immune and inflammatory responses to organisms and their metabolic by-products contribute, in part, to the appearance of gross lesions (see below). In rare instances, an infected hair follicle may rupture and spread organisms to tissue beneath the skin (subcutaneous tissue) producing a firm, sometimes painful nodule known as a "pseudomycetoma". The disease is highly contagious, and Microsporum canis, the most common species in cats, is zoonotic, meaning that infections are transmissible to other species, including humans. (Not all dermatophyte species are transmitted between animals)