THE DERMATOPHYTES

The etiologic agents of the dermatophytoses (ringworm) are classified in three anamorphic (asexual or imperfect) genera, Epidermophyton, Mic rosporum, and Trichophyton. Species capable of reproducing sexually be long in the teleomorphic genus, Arthroderma, of the Ascomycota. On the basis of primary habitat association, they may be grouped as geophili c (soil associated), zoophilic, and anthropophilic. Adaptation to grow th on humans by most geophilic species resulted in diminished lass of sporulation, sexuality, and other soil-associated characteristics. The dermatophytes have the ability to invade keratinized tissue (skin, ha ir, and nails) but are usually restricted to the nonliving comified la yer of the epidermis because of their inability to penetrate viable ti ssue of an immunocompetent host. However, invasion does elicit a host response ranging from mild to severe. Acid proteinases, elastase, kera tinases, and other proteinases reportedly act as virulence factors. Th e development of cell-mediated immunity correlated with delayed hypers ensitivity and an inflammatory response is associated with clinical cu re, whereas the lack of or a defective cell-mediated immunity predispo ses the host to chronic or recurrent dermatophyte infection. Chronic d ermatophytosis is mostly caused by Trichophyton rubrum, and there is s ome evidence that mannan produced by this fungus suppresses or diminis hes the inflammatory response. Since dermatophytes cause a communicabl e disease, modes of transmission and control are discussed as well as a survey of recent trends in therapy. Collection of specimens, culture media, and rests for identification are also presented. Genetic studi es have led to an understanding of incompatibility mechanisms, pleomor phism and variation, resistance to griseofulvin, and virulence. Molecu lar biology has contributed to our knowledge of the taxonomy and phylo genetic relationships of dermatophytes.