[Update on the diagnosis of dermatomycosis].
Dermatomycosis are mycotic diseases of skin caused by a few mycetes: dermatophytes, and some opportunistic fungi as Malassezia, Candida (not C. albicans), Trichosporon, Rhodutorula, Cryptococcus or Aspergillus, Geotrichum, Alternaria, etc. Dermatophytes are a group of closely related filamentous fungi that invade keratinized tissue (skin, hair, nails) of humans and other animals and produce infection called dermatophytosis or ringworm or "tinea". The etiological agents of dermatophytosis are classified in three genera: Microsporum, Trichophyton and Epidermophyton (Deuteromycetes). On the basis of their primary habitat dermatophytes are divided in Anthropophilic dermatophytes (parasitic organisms that infect humans), Zoophilic dermatophytes (parasitic organisms that infect animals, but also humans: agents of zoonosis) and Geophilic dermatophytes (saprobic fungi associated with keratinous materials in soil). In the soil there are also structure associated with contagion, ("spore", "arthroconidium", or "clamydospore") of anthropophilic and zoophilic dermatophytes that may persist for years, in the environment, in hair or skin scales. Since on the skin of animals there are many saprobic organisms (Malassezia) and many fungi may infect the fur, it is important to make an accurate diagnosis. Dermatophytosis are communicable diseases acquired from infected animals or from fomites. Infections caused by dermatophytes is a ringworm. These infections may range from mild and superficial, almost subclinical, to a few areas of scaling to a highly inflammatory reaction with extensive areas of scarring and alopecia. Granuloma formations (mycetoma-like) may occur especially in cats. Dermatophytes, as filamentous fungi, undergo radial fungi: collection of skin material is best made by collecting the scales near the edges of the rings. Hairs are best sampled by plucking; a scalpel may be used to scrape scales; brushes have also been used. Sample materials are best transported in dry packet. The Wood's light may be used to identify infected fluorescent hairs. Direct microscopy, although false negative up to 50% of cases, is a highly efficient screening technique. Scraping and hairs should mixed to 10-15% KOH. Culture is a valuable adjunct to direct microscopy and is essential to identify more dermatophytes. A medium selective against most nondermatophytic moulds and bacteria is used as a primary isolation medium. Many typical isolates of common dermatophytes can be identified directly from primary isolation media. Identification characters include: colony pigmentation, texture, morphological structure (macroconidia, microconidia, spirals, pectinate branches, etc). Nutritional requiment, growth in special media, "in vitro" perforation, mating studies are procedures used to identify atypical isolates. Serological approaches have revealed difficulties. Many kinds of molecular biologic techniques have been made available for clinical diagnosis recently; almost all of these techniques involve the polymerase chain reaction (PCR).
Dipartimento di Sanità Pubblica Veterinaria e Patologia Animale, Università di Bologna.
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Tampieri
D000505:Alopecia / Q000209:etiology / Q000382:microbiology / Q000662:veterinary; D000818:Animals; D000829:Animals, Domestic / Q000382:microbiology; D000908:Antibodies, Fungal / Q000097:blood; D004271:DNA, Fungal / Q000032:analysis; D003881:Dermatomycoses / Q000175:diagnosis* / Q000453:epidemiology / Q000473:pathology / Q000635:transmission / Q000662:veterinary; D004199:Disease Vectors; D006801:Humans; D009172:Mycology / Q000379:methods*
D000908:Antibodies, Fungal; D004271:DNA, Fungal