## Dermatophyte Classification and Clinical Patterns ### Correct Statements (Options 0, 1, 3) **Option 0 — Trichophyton rubrum:** - Most common dermatophyte globally (accounts for ~70% of dermatophytosis) - Anthropophilic (human-to-human transmission) - Causes chronic, indolent infections with minimal inflammation - Affects skin, nails, and hair **Option 1 — Microsporum canis:** - Zoophilic dermatophyte (reservoir: cats and dogs) - Causes human infection through direct contact with infected animals - More common in children - Produces inflammatory lesions **Option 3 — Trichophyton mentagrophytes:** - Geophilic dermatophyte (found in soil) - Can also be zoophilic (from rodents) - Causes severe inflammatory tinea pedis, especially in web spaces - Known for vesicular and bullous presentations ### Why Option 2 is INCORRECT **Key Point:** Epidermophyton floccosum is an anthropophilic dermatophyte that causes **skin infections, NOT primarily nails**. It commonly affects: - Groin (tinea cruris) — most frequent site - Feet (tinea pedis) - Body (tinea corporis) - Rarely involves nails (unlike T. rubrum or T. mentagrophytes) The statement falsely claims it "primarily affects nails and rarely involves skin," which is the **opposite of clinical reality**. ### Mnemonic for Dermatophyte Ecology **AAG** = **A**nthropophilic, **A**zoophilic, **G**eophilic - **Anthropophilic:** T. rubrum, T. mentagrophytes var. mentagrophytes, E. floccosum - **Zoophilic:** M. canis, T. mentagrophytes var. quinckeanum, T. verrucosum - **Geophilic:** T. mentagrophytes var. mentagrophytes, M. gypseum ### High-Yield Table: Common Dermatophytes | Organism | Ecology | Common Sites | Inflammation | Nails? | |----------|---------|--------------|--------------|--------| | T. rubrum | Anthropophilic | Groin, feet, nails | Low | Yes | | T. mentagrophytes | Geophilic/Zoophilic | Feet, nails | High | Yes | | E. floccosum | Anthropophilic | Groin, feet | Low | Rare | | M. canis | Zoophilic | Body, scalp | High | No | [cite:Robbins 10e Ch 25]
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