General principles of epidemiology
The etiological structure of superficial mycoses is quite diverse: about 40 different species of dermatophytes are capable of causing pathological processes in humans. Infection with these fungi occurs through several main routes:
- Direct contact: transmission of the pathogen occurs directly through physical contact with an infected person or animal.
- Contact-fomite transmission: infection is transmitted indirectly via contaminated everyday objects (hairbrushes, shared towels, shoes).
- Environmental contact: infection occurs through interaction with soil inhabited by spores of pathogenic fungi.
A major risk factor for the development of mycoses is the regular visiting of public places with high humidity levels. Such facilities traditionally include bathhouses, shower rooms, and swimming pools, which provide ideal conditions for the survival and transmission of dermatophytes.
Anthropophilic dermatophytes
The ecological classification divides dermatophytes into three groups depending on the natural reservoir of infection. The first group is anthropophilic dermatophytes. Their only source is humans, and transmission of the pathogen occurs exclusively from human to human.
The main anthropophilic pathogens and the diseases they cause include:
- Microsporum: caused by fungi such as Microsporum audouinii and Microsporum ferrugineum.
- Trichophytosis: the etiological agents are Trichophyton tonsurans and Trichophyton violaceum.
- Favus: the classic pathogen is Trichophyton schoenleinii.
Fungi causing infections of the feet and nails (onychomycosis) deserve special attention:
- Trichophyton mentagrophytes var. interdigitale is the main cause of tinea pedis.
- Epidermophyton floccosum causes tinea cruris as well as nail plate infections.
- Trichophyton rubrum is the causative agent of rubrophytosis.
Zoophilic dermatophytes
The second group is represented by zoophilic dermatophytes. The natural reservoir and source of infection in this case are various animals. Humans become infected through direct contact with an infected animal.
A specific and very characteristic example of such an interaction is Trichophyton verrucosum. This fungus is transmitted from cattle and causes a disease in humans known as "calf ringworm".
The main zoophilic reservoirs are distributed as follows:
- Microsporum:
- Microsporum canis — the main reservoir includes cats, dogs, and horses.
- Microsporum gallinae — affects poultry.
- Microsporum nanum — pigs serve as the source of infection.
- Trichophytosis:
- Trichophyton verrucosum — cattle.
- Trichophyton equinum — horses.
- Trichophyton mentagrophytes (its zoophilic variants) — circulates among rodents, mice, and hedgehogs.
Geophilic dermatophytes
The third ecological group consists of geophilic dermatophytes. Their natural reservoir and permanent habitat is the soil. Human infection occurs upon direct contact with contaminated soil.
A striking example of geophilic infection is the contamination with the fungus Microsporum gypseum. Transmission of this pathogen often occurs during agricultural or gardening soil work with bare hands, which is why the resulting disease received the informal name "gardener's microsporum".
The main geophilic fungi capable of causing microsporum in humans include species such as Microsporum cookei, Microsporum gypseum, and Microsporum fulvum.
Briefly: answers to topical questions
What laboratory diagnostic methods are used to detect and identify dermatophytes?
Microscopic, cultural, and a number of additional methods are used to detect and identify dermatophytes.
- Microscopic method — rapid diagnostics of material (scrapings, hair, nails) after treatment with a 10–15% KOH solution to detect fungal elements.
- Mycological method — inoculation onto Sabouraud media or wort agar for species identification based on growth characteristics.
- Serological method — detection of antibodies using complement fixation test (CFT), indirect hemagglutination test (IHA), precipitation test, indirect immunofluorescence assay (IFA), ELISA.
- Allergy diagnostics — skin allergy tests with fungal allergens.
- Biological assay — inoculation of laboratory animals (guinea pigs, mice).
Which pathogens are capable of causing tinea cruris?
Tinea cruris is caused by the anthropophilic fungus Epidermophyton floccosum.
- Anthropophilic dermatophytes (Epidermophyton floccosum) — predominantly affect the inguinal folds and shins, less frequently the interdigital folds and nails.
Microscopy of pathological material from this pathogen reveals septate branching mycelium and rectangular arthrospores arranged in chains. According to its anatomical localization, this disease is also classified as inguinal dermatomycosis (tinea cruris).
Which groups of antimycotic drugs are used for etiotropic treatment of dermatophytoses?
Systemic and topical agents from several chemical groups are used for the etiotropic treatment of dermatophytoses.
- Azoles (imidazole and triazole derivatives) — clotrimazole, ketoconazole, econazole, miconazole, fluconazole, itraconazole.
- Allylamines (N-methylnaphthalene derivatives) — terbinafine, naftifine.
- Benzylamine derivatives — butenafine.
- Morpholine derivatives — amorolfine.
- Undecylenic acid derivatives — undecin, zincundan, mycoseptin.
Griseofulvin is also used in the treatment of superficial mycoses. The choice of drug formulation depends on the localization of the process; if necessary, topical therapy is combined with systemic drugs.
Ecological groups of dermatophytes are easy to remember by their specific examples: Anthropophiles — humans only (tinea pedis, onychomycoses), Zoophiles — animals (T. verrucosum — "calf ringworm"), Geophiles — soil (M. gypseum — "gardener's microsporum").
Class and exam questions
Why is it necessary for a physician to know the ecological classification of dermatophytes when a mycosis is suspected?
This is a key point for taking an accurate epidemiological history. Understanding whether a fungus belongs to anthropophiles, zoophiles, or geophiles allows for precisely determining the source of infection — an infected person, an animal, or contact with soil.
Which causative agents most frequently cause tinea pedis and nail involvement?
The main anthropophilic pathogens of these conditions are Trichophyton mentagrophytes var. interdigitale (tinea pedis), Epidermophyton floccosum (nail damage, tinea cruris), and Trichophyton rubrum (rubrophytosis).
What is the reservoir for the zoophilic fungus Microsporum canis?
The main source of infection and natural reservoir for the pathogen Microsporum canis are cats, dogs, and horses.
How does infection with "gardener's microsporia" occur?
The disease is caused by the geophilic dermatophyte Microsporum gypseum. Infection occurs when handling contaminated soil with bare hands.
What else to study on this topic
- Clinical presentation of various types of microsporia
- Pathogenetic mechanisms and manifestations of rubrophytosis and favus
- Specific laboratory diagnostics of dermatophytosis
- Prevention of zoophilic mycoses in agriculture
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