Pathogenesis and Risk Factors
Dermatophyte fungi are classified as keratinophiles. This means they require keratin for survival, which they break down using the enzyme keratinase. The depth of the lesion is strictly limited: fungi never penetrate deeper than the basement membrane of the epidermis.
Various factors contribute to the development of the disease:
- External (exogenous): hyperhidrosis, skin maceration, microtraumas.
- Internal (endogenous): decreased overall bodily resistance, endocrine disorders.
- Iatrogenic: prolonged antibiotic therapy disrupting the normal microflora.
Clinical Manifestations and Localization
Clinically, dermatomycoses are typically classified by anatomical lesion sites (topographic classification):
- Tinea corporis (trunk, limbs).
- Tinea facialis and Tinea barbae (face and beard area).
- Tinea capitis (scalp).
- Tinea manus and Tinea pedis (hands and feet).
- Tinea cruris (groin area).
- Tinea unguium (nail infection, or onychomycosis).
Symptomatology depends on the affected structures:
- Glabrous skin: severe pruritus, desquamation, fissuring, as well as vesicles and pustules. Inflammation can range from pronounced to nearly imperceptible.
- Hair: hair shafts break off, forming foci of alopecia.
- Nails (onychomycosis): the nail plate loses transparency, discolors, thickens, and becomes brittle. The primary culprits here are most often Trichophyton rubrum and Trichophyton interdigitale.
Laboratory diagnostics
The diagnosis is confirmed using microbiological tests.
Microscopic method (rapid) Skin scrapings, broken hairs, or nail clippings are collected for analysis. The material is immersed in a 10–15% KOH solution (for 10–15 minutes) to dissolve the obstructing keratin. The microscope is used to search for mycelial threads, blastospores, and conidia (macro- and micro-). The arrangement of spores on the hair can suggest the causative agent:
- In Trichophyton, arthroconidia lie in parallel chains (Ectothrix — outside the hair, Endothrix — inside).
- In Microsporum, spores form a mosaic outside the shaft.
- In favus, fungal elements and characteristic gas bubbles are visible inside the hair.
Culture method Inoculation of material onto media (e.g., Sabouraud or wort agar). Incubation at 25 °C takes 1 to 3 weeks. This method is necessary for precise identification of the fungal species based on colony morphology.
Additional methods: serology (ELISA, CFT for antibody detection), skin allergy tests, and inoculation of laboratory animals (bioassay).
Treatment and Prevention
Therapy is selected depending on the site of the lesion:
- Scalp: systemic drugs are indicated (fluconazole, terbinafine, griseofulvin, itraconazole).
- Onychomycosis: a combination of topical agents and systemic antimycotics (ketoconazole, terbinafine, fluconazole, griseofulvin).
- Feet: topical creams or ointments (Mycospor, Nizoral, Lamisil) are usually sufficient, but in severe cases, systemic antimycotics and antihistamines are added.
Prevention includes observing personal hygiene (including wearing strictly personal footwear), early detection of patients, examination of contacts, and mandatory disinfection in the infection focus.
Briefly: answers to topical questions
Which species of fungi are the main causative agents of microsporum infection?
The main causative agents of microsporia are fungi of the genus Microsporum, which are divided into three groups depending on the infection reservoir.
- Anthropophilic species (Microsporum audouinii, Microsporum ferrugineum) — infect humans exclusively.
- Zoophilic species (Microsporum canis) — reservoir animals include cats and dogs, as well as humans.
- Geophilic species (Microsporum cookei, Microsporum fulvum, Microsporum nanum, Microsporum gypseum) — soil dwellers, transmitted via contact with soil (causing "gardener's microsporia").
What rapid diagnostic methods are used to detect dermatomycoses?
Microscopy is used for the rapid diagnosis of dermatomycoses. Skin scrapings, scales, hair, and nails are used as the test material. To dissolve keratin, specimens are pre-treated with a 10–15% KOH solution for 10–15 minutes. Microscopy reveals the following elements:
- mycelial threads;
- arthroconidia;
- macroconidia and microconidia;
- blastospores.
Additionally, when examining hair, the arrangement of spores is taken into account: the genus Trichophyton is characterized by arthroconidia in parallel chains, the genus Microsporum by a mosaic arrangement of spores outside the hair, and favus by fungal elements and gas bubbles inside the hair.
Class and exam questions
Why do dermatophyte fungi infect only the upper layers of the skin?
These fungi are keratinophiles—they feed on keratin. Since keratin is present only in the epidermis and its appendages, they cannot penetrate deeper than the basement membrane.
Why is the scraping treated with a KOH solution for rapid diagnosis?
The alkali (10–15% KOH) dissolves the keratin of the skin, hair, or nails within 10–15 minutes, making fungal elements (mycelium, spores) visible under a microscope.
What are the main causative agents of onychomycosis?
Nails can be infected by any dermatophyte, but the most frequent culprits are Trichophyton rubrum and Trichophyton interdigitale.
What else to study on this topic
- Mechanisms of delayed-type hypersensitivity in fungal infections
- Differential microscopy of Trichophyton and Microsporum
- Serological reactions (CFT, HAI, ELISA) in the diagnosis of mycoses
- Specifics of conducting biological tests on laboratory animals
Study the full topic in the «Microbiology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Dermatomycoses: Pathogenesis, Clinical Features, and Diagnostics" and 4,383 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 141 video lectures on the subject
Other topics in the section "Epidermophytoses (microsporia, trichophytosis, favus, rubroophytosis, etc.)"
Free video lessons: microbiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.