Tropical Fungal Infections

Tropical Fungal Infections - Hot & Humid Horrors

• Endemic mycoses in tropical/subtropical regions.
• Etiology: Traumatic implantation of saprophytic fungi (soil, decaying vegetation).
• Risk factors: Barefoot walking, agricultural work, minor trauma, humidity, poverty.
• Common types (subcutaneous):
  • Mycetoma
  • Chromoblastomycosis
  • Sporotrichosis
• General: Chronic, insidious onset, often difficult to treat.

⭐ Mycetoma is characterized by the triad of tumefaction, draining sinuses, and grains/granules.

Mycetoma - Foot's Fungal Fortress

Chronic, suppurative, granulomatous infection of subcutaneous tissues, fascia, bone. 📌 Mycetoma Triad: Tumor (painless subcutaneous tumefaction), Sinuses (multiple), Grains (discharged colonies).

• Types & Etiology:
  • Eumycetoma (Fungal):
    • Madurella mycetomatis (most common, black grains).
    • Aspergillus, Fusarium (pale grains).
  • Actinomycetoma (Bacterial, filamentous):
    • Nocardia brasiliensis, Actinomadura madurae (yellow/white/red grains). Clinically similar.
• Diagnosis: Clinical; grain examination (color, microscopy); imaging (X-ray 'dot-in-circle' sign); culture; biopsy.
• Management:
  • Eumycetoma: Itraconazole / Voriconazole + surgical debridement. Often resistant.
  • Actinomycetoma: Welsh regimen (Amikacin + Co-trimoxazole). Good response.

⭐ Madurella mycetomatis is the most common cause of eumycetoma worldwide.

Chromoblastomycosis - Cauliflower Calamity

• Definition: Chronic localized fungal infection of skin & subcutaneous tissue.
• Etiology: Dematiaceous (pigmented) fungi.
  • Fonsecaea pedrosoi (most common).
  • Phialophora verrucosa.
  • Cladophialophora carrionii.
• Clinical Features:
  • Slow-growing verrucous (warty), cauliflower-like plaques/nodules.
  • Often on lower extremities.
  • 'Black dots' (hemorrhagic points) on surface.
• Histopathology:
  • Sclerotic bodies (Medlar bodies / copper pennies / muriform cells): thick-walled, pigmented, septate fungal cells. 📌 Chromo = Copper pennies (Medlar bodies).

  ⭐ Sclerotic bodies (Medlar bodies or copper pennies) are pathognomonic for Chromoblastomycosis.

• Diagnosis: Clinical presentation, KOH microscopy, skin biopsy (revealing sclerotic bodies), fungal culture.
• Management: Difficult; often requires combination therapy.
  • Systemic antifungals: Itraconazole, Terbinafine.
  • Local therapies: Cryotherapy, heat therapy (e.g., topical 5-FU + heat), surgical excision for small lesions.

Sporotrichosis - Thorny Trouble Trail

• Etiology: Sporothrix schenckii (dimorphic fungus).
• Transmission: "Rose Gardener's Disease" (thorn pricks); zoonotic (cats).
  • 📌 Sporo-THRIX on a thorn, follows a lymph TRIX (track).
• Clinical Forms:
  • Lymphocutaneous (commonest): Chancre at inoculation → linear nodules along lymphatics ("sporotrichoid spread").
  • Fixed Cutaneous: Solitary, chronic lesion; no lymphatic spread.
• Diagnosis:
  • Culture (Gold Standard): Yeast at $37^\circ C$, mold at $25^\circ C$.
  • Biopsy: Cigar-shaped yeasts; asteroid bodies (Splendore-Hoeppli).
• Management:
  • Cutaneous/Lymphocutaneous: Itraconazole (DOC). SSKI (alternative).
  • Disseminated: Amphotericin B, then Itraconazole.

⭐ Exam Favourite: "Sporotrichoid spread" (lymphatic) is characteristic but also seen in Nocardiosis, Leishmaniasis, atypical Mycobacteria.

High‑Yield Points - ⚡ Biggest Takeaways

• Tinea imbricata: T. concentricum causes concentric, scaly rings ("Tokelau").
• Lobomycosis: Lacazia loboi leads to keloidal, verrucous nodules; microscopy shows "chain-of-coins" yeast.
• Chromoblastomycosis: Dematiaceous fungi (e.g., Fonsecaea) cause cauliflower-like lesions; histology shows sclerotic bodies (copper pennies).
• Mycetoma: Characterized by tumefaction, draining sinuses, and grains; distinguish eumycetoma (fungal) from actinomycetoma.
• Sporotrichosis: Sporothrix schenckii causes lymphocutaneous spread ("rose gardener's disease"); asteroid bodies on histology.
• Rhinosporidiosis: R. seeberi presents as friable, strawberry-like nasal/ocular polyps; large sporangia with endospores.