Clinical presentation and localization
Rubrophytosis has characteristic clinical manifestations that are important to recognize. The pathological process involves specific structures of the human body.
Preferred localization of the infection:
- Skin integument of the trunk.
- Skin of the upper and lower extremities.
- Nail plates.
- Vellus hair (unlike other dermatophytes, which more commonly affect terminal hair).
Typical lesions form on the affected areas of the skin. They appear as small, pink macules with well-demarcated borders. Specific rash elements — small vesicles and drying crusts — can be found on the surface and edges of these lesions.
Microscopic appearance
Microscopy is of key importance for the laboratory diagnosis of rubromycosis. The morphology of Trichophyton rubrum differs significantly depending on whether the patient's clinical material is examined or the fungus has been grown on a nutrient medium.
In pathological material (skin scales): Examination of scrapings reveals fibers of septate mycelium that branch actively. Arthrospores — elements formed as a result of the breakdown of hyphae into separate fragments — are significantly less common in the specimen.
In pure culture: When Trichophyton rubrum is grown in vitro, the mycelium retains its structure (thin, branching, septate filaments), but characteristic spore-bearing structures appear:
- Microconidia: small, pear-shaped or oval spores. They do not occur singly but form clusters.
- Macroconidia: large, elongated spores of extended shape, reaching up to 6 × 50 µm in size.
- Chlamydospores: these thick-walled resting structures are not characteristic of young colonies and begin to form only during the aging of the fungal culture.
To remember what Trichophyton rubrum affects, use the mnemonic: vellus hair, nails, trunk (and extremities).
Class and exam questions
Is rubrophytosis a zoonotic disease?
No, this is a strict anthroponosis. The infection source is exclusively an infected human.
What type of hair does Trichophyton rubrum affect?
Unlike the agents of microsporia or superficial trichophytosis, the causative agent of rubromycosis specifically affects vellus hair.
How does the microscopy of scales differ from that of a pure culture?
Only septate mycelium and occasionally arthrospores are visible in the scales. In pure culture, microconidia (pear-shaped clusters), macroconidia (6 × 50 µm), and chlamydospores (upon aging) appear.
What else to study on this topic
- Structure and functions of septate mycelium in dermatophytes
- The process of pear-shaped microconidia formation
- Morphological differences between arthrospores and chlamydospores during culture aging
- Pathogenesis of vellus hair involvement
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