Dermatophytes are classified in three genera: Trichophyton (with the important species T. mentagrophytes, T. rubrum, T. schoenleinii, T. tonsurans); Microsporum; and Epidermophyton (E. floccosum). Some dermatophyte species are anthropophilic, others zoophilic. The natural habitat of the geophilic species M. gypseum is the soil.
Morphology and culture. The dermatophytes are filamentous fungi. They grow readily on fungal nutrient mediums at 25–30 8C. After 5–14 days, cultures with a woolly appearance, in different colors, usually develop. Pathogenesis and clinical pictures. Dermatomycoses are infections that are transmitted directly by human contact, animal-human contact or indirectly on inanimate objects (clothes, carpets, moisture, and dust in showers, swimming pools, wardrobes, gyms).
The localization of the primary foci corresponds to the contact site. Thus feet, uncovered skin (hair, head, facial skin) are affected most frequently. Different species can cause the same clinical picture. Frequent dermatomycoses include:
Dermatomycoses can be treated with locally applied antimycotic agents. In cases of massive infections of the hair, and above all of the nails, the oral allylamine terbinafine or azoles can be used. Griseofulvin is rarely used today
pidemiology and prevention. Dermatophytes occur naturally all over the world. The geophilic dermatophyte, M. gypseum, can cause infections in persons in constant, intensive contact with the soil (e.g., gardeners). Prophylactic measures for all dermatomycoses consist in avoiding direct contact with the pathogen. Regular disinfection of showers and wardrobes can contribute to prevention of athlete’s foot, a very frequent infection.
Other Cutaneous Mycoses
Pityriasis (or tinea) versicolor is a surface infection of the skin caused by Malassezia furfur. This infection is observed mainly in the tropics but is known all over the world. It causes hypopigmentations. M. furfur is dependent for its metabolic needs on a source of long-chain fatty acids. This fungus is actually a component of the skin’s normal flora.
The pathogenesis of the infections has not yet been clarified. Tinea nigra, which occurs mainly in the tropics, is caused by Exophiala werneckii. Infection results in brown to black, maculous efflorescences on the skin. White and black piedras is an infection of the hair caused by Trichosporon beigelii or Piedraia hortae.
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Viruses are complexes consisting of protein and an RNA or DNA genome. They lack both cellular structure and independent metabolic processes. They replicate solely by exploiting living cells based on the information in the viral genome
Viruses are autonomous infectious particles that differ widely from other microorganisms in a number of characteristics: they have no cellular structure, consisting only of proteins and nucleic acid (DNA or RNA). They have no metabolic systems of their own, but rather depend on the synthetic mechanism of a living host cell, whereby the viruses exploit normal cellular metabolism by delivering their own genetic information, i.e., nucleic acid, into the host cell.
components of new viruses in accordance with the genetic information it contains.
One thus might call viruses “vagabond genes.” Viruses infect bacteria (so-called bacteriophages), plants, animals, and humans. The following pages cover mainly the human pathogen ists the essential characteristics of viruses.