A Lesson in Fungi: What are Dermatophytes?

Dermatophytes (name based on the Greek for ‘skin plants’) are a common label for a group of three types of fungus that commonly causes skin disease in animals and humans. These anamorphic (asexual or imperfect fungi) genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera. Species capable of reproducing sexually belong in the teleomorphic genus Arthroderma, of the Ascomycota (see Teleomorph, anamorph and holomorph for more information on this type of fungal life cycle).

Dermatophytes cause infections of the skin like athletes foot, hair like and nails like due to their ability to obtain nutrients from keratinized material. The organisms colonize the keratin tissues and inflammation is caused by host response to metabolic by-products. They are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate viable tissue of an immunocompetent host. Invasion does elicit a host response ranging from mild to severe. Acid proteinases, elastase, keratinases, and other proteinases reportedly act as virulence factors. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or a defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection.

Dermatophytes get under the nail fold at the end of the nail and grow underneath the nail. When they take hold, the nail become thick, yellowish-brown or darker in color, deformed and foul smelling. Debris may collect beneath the nail plate, white marks frequently appear on the nail plate, and the infection is capable of spreading to other toenails, the skin, or even the fingernails.

Types of Dermatophyte Infections:

  • Athlete’s foot or tinea pedis
    Contrary to the name, it does not affect just athletes. Tinea pedis affects men more than women. Frequently affects the webs between the toes first, before spreading to the sole of the foot in a “moccasin” pattern.
  • Jock itch or tinea cruris
    Frequently, the feet are also involved. The theory is that the feet get infected first from contact with the ground. The fungus spores are carried to the groin from scratching, from putting on underclothing or pants. Frequently extend from the groin to the perianal skin and gluteal cleft.
  • Facial ringworm or tinea faciei
    Can be misdiagnosed for other conditions like psoriasis, discoid lupus, etc. Can be aggravated by treatment with topical steroid or immunosuppressive creams.

Related books

Medically Important Fungi
D. Larone
ISBN: 978-1-555-81660-5
Read online

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