Regarding the clinical features and epidemiology of dermatophytosis in India, all of the following are true EXCEPT:
A. Tinea corporis typically presents with a well-demarcated erythematous patch with central clearing and raised borders
B. Tinea pedis is more common in warm, humid climates and in individuals with poor foot hygiene
C. Dermatophytes are obligate intracellular parasites that cannot survive outside the host
D. Trichophyton rubrum is the most common dermatophyte isolated in India
Explanation
Dermatophyte Biology and Epidemiology
Key Point
Dermatophytes are NOT obligate intracellular parasites. They are keratinophilic fungi that live in the stratum corneum, hair, and nails — all dead, keratinized tissue. They can survive outside the host in contaminated fomites, floors, and shared spaces for extended periods.
Correct Statements Explained
Trichophyton rubrum dominance:
T. rubrum accounts for ~60–70% of dermatophyte infections in India Inamadar & Palit, Indian J Dermatol
Followed by T. mentagrophytes and M. canis
Tinea corporis presentation:
Classic "ringworm" lesion: erythematous patch with central clearing (hypopigmentation) and raised, scaly, inflammatory border
Annular or serpiginous morphology is pathognomonic
Tinea pedis epidemiology:
Warm, humid climate → increased maceration and moisture retention
Poor foot hygiene, occlusive footwear, and communal bathing areas are major risk factors in India
Why Option 2 Is Wrong
High-YieldNEET PG
Dermatophytes are keratinophilic (not obligate intracellular) fungi. They:
1.
Colonize dead keratinized tissue (stratum corneum, hair shaft, nail plate)
2.
Can be cultured on Sabouraud dextrose agar in vitro
3.
Survive on fomites (floors, towels, combs) for weeks to months
4.
Do NOT invade living epidermis or dermis (unlike some Candida species)
This distinction is critical for understanding transmission and environmental control measures.
Dermatophyte infections spread via direct contact with infected skin, fomites, or infected animals — not via bloodstream or systemic dissemination in immunocompetent hosts.
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