Chapter 9. Dermatophytes and Dermatophytosis: A New Look at an Old Mycosis


Germana Costa Paixão,1,2, Marcos Fábio Gadelha Rocha1,2, José Júlio Costa Sidrimand Raimunda Sâmia Nogueira Brilhante1
1Department of Pathology and Legal Medicine, Federal University of Ceará, Fortaleza, Ceará, Brazil
2State University of Ceará, Fortaleza, Ceará, Brazil

Part of the book: The Book of Fungal Pathogens


Dermatophytes are closely related filamentous fungi characterized by their ability to invade and infect keratinized tissues. They belong to the oldest groups of microorganisms known to be pathogenic to humans and animals, causing dermatophytosis in between 20 and 25% of the world’s human population. The frequency and spectrum of distribution of these fungi in the population vary with geography, socioeconomic and climatic conditions and ecology. Dermatophytes are divided into three groups: anthropophilic, zoophilic and geophilic. The most recent phylogenetic taxonomy of dermatophytes classifies them into seven genera or clades, namely Arthroderma, Epidermophyton, Lophophyton, Microsporum, Nannizzia, Paraphyton and Trichophyton, placing these fungi at a new level of interest. The clinical aspects of dermatophytosis are varied and result from keratin destruction associated with an inflammatory response, more or less intense depending on the parasite/host binomial, which can compromise glabrous skin, nails and hair. There are two clinical classification systems of dermatophytosis. One of them follows the English current, according to which all infections are called tinea (in Latin), associated with another word (also in Latin) that indicates the anatomical site of the lesion, such as tinea corporis (location on the body), tinea capitis (scalp) and tinea unguium (nails). The other is the French system, by which dermatophytoses are classified as Tinea (any lesion that affects the scalp and/or beard and mustache region); epidermophytoses (lesions found on glabrous skin); onychomycosis (injury to the nails), and finally subcutaneous and deep dermatophytoses (lesions that affect the subcutaneous cell space or other deep organs, generally occurring in immunocompromised patients). Traditionally, dermatophytes are identified based on clinical symptoms caused by their infection, ecological preferences, in vitro morphological characteristics and the physiological behavior of the species. However, phenotypic instability, together with the microbial plasticity presented by some species, can produce overly generalized and erroneous classifications, making the identification of these fungi challenging, even for experienced mycologists. Therefore, the morphophenotypic characterization of dermatophytes has limitations and should no longer be used as the only taxonomic criterion. Instead, it is desirable to combine different approaches, including the study of genotypic and protein profiles, for the precise identification of these fungi. This accurate identification is essential for the establishment of effective programs for control and prevention of dermatophytoses, as well as for determining the most appropriate and effective antifungal therapies. Regarding the treatment of these infections, a variety of oral and topical antifungal agents can be used, such as imidazoles (clotrimazole, miconazole, etc.), triazoles (fluconazole, itraconazole and efinaconazole), allylamines (terbinafine and naphthyfine) and griseofulvin, with the treatment being guided by the species involved, ideally associating systemic agents with adjuvant topical treatments.

Keywords: dermatophytes, dermatophytosis, taxonomy, epidemiology, clinical symptoms, diagnosis, treatment


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