Clinical and epidemiological characteristics
The disease known in classical medicine as favus or tinea favosa is a classic anthroponosis. This means that the source of infection is exclusively human. The maximum risk group includes primarily children, whose immune system and skin barrier functions are still developing. This pathology has a pronounced chronic nature, requiring prolonged medical observation.
The main localization of the pathological process includes several anatomical zones at once. The pathogen is capable of actively colonizing and destroying:
- The patient's glabrous skin.
- Hair (with penetration into the structure of the hair shaft itself).
- Nail plates.
An absolute pathognomonic clinical sign of favus development is the formation of the so-called scutulum (from Latin for a small shield). Visually, it is a characteristic formation of a distinct yellow color. According to its histological and microbiological composition, the scutulum is a complex conglomerate. Detailed examination reveals a massive accumulation of fungal spores, intertwined mycelial threads, as well as desquamated cells of the affected epidermis and fat elements.
Features of microscopic diagnostics
Laboratory verification of the diagnosis is based on a thorough microscopic examination of biological material taken from the patient. The picture varies significantly depending on the specific substrate being analyzed.
- Examination of skin scales. When studying scrapings from glabrous skin under a microscope, a specific picture is visualized: branching mycelium with clearly defined septa is detected. In addition, arthrospores are present in this material, indicating an active process of hyphal fragmentation.
- Hair examination (favus type). The lesion of the hair shaft in favus has its unique specificity, which in mycology is designated as the "favus type". A key feature is the localization of fungal elements strictly inside the hair itself. Upon microscopy within the thickness of the hair shaft, not only septate mycelium and dense clusters of spores are found, but also characteristic gas bubbles, the appearance of which is an important diagnostic marker specifically for this pathogen.
Cultural properties of the pathogen
When isolating a pure culture of Trichophyton schoenleinii on nutrient media, the mycologist evaluates the characteristic morphological features of fungal growth. The vegetative body (mycelium) of the pathogen is septate, meaning it is divided into separate cellular compartments.
Special attention is paid to the shape of the threads. The mycelium in favus is typically characterized by specific thickenings and abundant branching. These morphological changes lead to the formation of figures that have received figurative names in laboratory practice:
- "Chandeliers" (branchings resembling classical candlesticks).
- "Deer antlers" (massive, dichotomously branching structures).
Sporulation in culture is represented by several types of elements. Arthrospore mycelium forms, protective chlamydospores appear, and large macroconidia are produced. The dimensions of macroconidia average 8×50 µm, which is an important morphometric parameter for identification.
Briefly: answers to topical questions
What laboratory diagnostic methods are used to verify favus?
Microscopic, mycological, and a number of additional methods are used to verify favus.
- Microscopic method — rapid diagnostics of clinical material (scrapings, hair, nails) after treatment with a 10–15% KOH solution. In favus, fungal elements and gas bubbles are detected inside the hair.
- Mycological method — inoculation onto nutrient media for species identification based on growth characteristics.
- Serological method — detection of specific antibodies using complement fixation test (CFT), indirect hemagglutination assay (IHA), precipitation reaction (PR), indirect immunofluorescence assay (IFA), and enzyme-linked immunosorbent assay (ELISA).
- Allergy diagnostics — skin allergy tests with fungal allergens.
- Biological test — inoculation of laboratory animals (mice, guinea pigs) into the skin, nails, or hair.
On which selective nutrient media is Trichophyton schoenleinii cultivated?
Specialized mycological nutrient media are used to cultivate the favus pathogen.
- Sabouraud agar — the main elective medium for isolating fungi.
- Wort agar — an additional medium for inoculating clinical material.
Inoculation is performed using the mycological (cultural) method. Incubation is carried out at a temperature of 25 °C, and the growth duration ranges from 1 to 3 weeks. The purpose of cultivation is species identification of the pathogen based on its growth characteristics on these media.
Imagine a DEER (deer antlers) with a CHANDELIER holding a yellow SHIELD (scutulum), and GAS BUBBLES getting tangled in its hair (favus type).
Class and exam questions
Which sign is considered pathognomonic for favus?
An absolute specific sign is the formation of a yellow scutulum (crust) consisting of spores, mycelium, fat, and epidermal cells.
What is the peculiarity of hair damage according to the "favus type"?
In the "favus type", fungal elements (septate mycelium, spore clusters) are located inside the hair, where the formation of gas bubbles is also characteristic.
What specific forms of mycelium are detected during cultivation?
The culture of Trichophyton schoenleinii is characterized by mycelial branching with thickenings, forming figures resembling "chandeliers" and "deer antlers".
What else to study on this topic
- Detailed composition and formation process of the yellow scutulum in tinea favosa.
- Differences between the intrapilary location of elements in the favus type versus endothrix.
- Morphological characteristics of macroconidia (8×50 µm) and chlamydospores.
- The mechanism of gas bubble formation in the affected hair shaft.
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