Fungal Infections

General Mycology - Funky Fundamentals

• Eukaryotes; chitin wall; ergosterol membrane (antifungal target).
• Types:
  • Yeasts: Unicellular, budding (Candida, Cryptococcus).
  • Molds: Multicellular, hyphae, spores (Aspergillus, Mucorales).
  • Dimorphic: Yeast at 37°C (host), mold at 25°C (env). 📌 Mold in Cold, Yeast in Heat.
• Pathogenesis: Adherence, invasion, mycotoxins.

⭐ Dimorphic fungi (e.g., Histoplasma, Blastomyces) exist as yeast in vivo (37°C) and mold in vitro/environment (25°C).

Superficial & Cutaneous Mycoses - Itchy & Scratchy Crew

• Superficial Mycoses: Stratum corneum, hair surface.
  • Pityriasis versicolor (Malassezia furfur): Hypo/hyperpigmented patches; "spaghetti & meatballs" (KOH).
  • Tinea nigra (Hortaea werneckii): Brown/black macules, palms/soles.
  • Piedra: Hair shaft nodules (White: Trichosporon; Black: Piedraia).
• Cutaneous Mycoses (Dermatophytosis): Keratinized tissues (skin, hair, nails).
  • Genera: Trichophyton, Microsporum, Epidermophyton.
  • Lesions: Tinea (ringworm) - capitis, corporis, pedis, unguium.

  ⭐ Trichophyton rubrum is the most common cause of dermatophytosis worldwide.

Subcutaneous Mycoses - Lumpy Bumpy Foes

• Caused by traumatic implantation of fungi into skin/subcutaneous tissue.
• Sporotrichosis: Sporothrix schenckii. "Rose gardener's disease". Lymphocutaneous spread (nodules along lymphatics). Cigar-shaped yeasts, asteroid bodies. Tx: Itraconazole.
• Chromoblastomycosis: Dematiaceous fungi (e.g., Fonsecaea). Verrucous, cauliflower-like lesions. Sclerotic bodies (Medlar bodies, copper pennies). Tx: Itraconazole.
• Mycetoma (Eumycetoma): True fungi (e.g., Madurella mycetomatis). Triad: tumefaction, draining sinuses, granules (grains). Tx: Surgery + antifungals.

⭐ Splendore-Hoeppli phenomenon (asteroid bodies) seen in sporotrichosis involves antigen-antibody complexes around the fungal element (yeast).

Systemic Dimorphic Mycoses - Shape-Shifting Pathogens

Thermally dimorphic: mold in cold (environment, 25°C), yeast in heat (tissue, 37°C). Inhalation of spores causes primary lung infection, can disseminate.

• Histoplasma capsulatum: Ohio/Mississippi river valleys. Bird/bat droppings.

  ⭐ Histoplasma capsulatum is characteristically found intracellularly within macrophages.

• Blastomyces dermatitidis: North America. Broad-based budding yeast.
• Coccidioides immitis/posadasii: Southwestern USA, Mexico. Spherules with endospores.
• Paracoccidioides brasiliensis: South America. "Pilot's wheel" or "Mariner's wheel" yeast.

Opportunistic Mycoses - Immune System's Nightmare

• Primarily infect immunocompromised (HIV/AIDS, transplant, chemotherapy).
• Candida: Oral thrush, esophagitis, disseminated. Pseudohyphae, budding yeast.
• Aspergillus: ABPA, aspergilloma, invasive. Acute angle (<45°) branching septate hyphae.
• Cryptococcus neoformans: Meningitis (India ink). Pigeon droppings.
• Mucormycosis: Rhinocerebral. Broad, non-septate hyphae, right-angle (90°) branching. DKA risk.
• Pneumocystis jirovecii (PJP): Pneumonia (CD4 < 200 cells/μL). Ground-glass CXR.

⭐ Aspergillus fumigatus is the most common cause of invasive aspergillosis, particularly in neutropenic patients and transplant recipients_._

Antifungals & Lab Diagnosis - Fungal Foes & Fixes

• Lab Diagnosis:
  • Microscopy: KOH (clears debris), India Ink (capsules).
  • Culture: SDA (key culture).
  • Antigens: Galactomannan (Aspergillus), CrAg (Cryptococcus).
  • Biopsy: PAS, GMS stains.
• Antifungals - Key Classes:
  • Polyenes (Amphotericin B): Bind ergosterol → pores. Nephrotoxic.
  • Azoles (Fluconazole): Inhibit ergosterol synthesis. CYP450 DDI.
  • Echinocandins (Caspofungin): Inhibit β-(1,3)-D-glucan (cell wall).
  • Flucytosine: → 5-FU; DNA/RNA synth ↓.

⭐ Voriconazole is drug of choice for invasive Aspergillosis.

High-Yield Points - ⚡ Biggest Takeaways

• India Ink for Cryptococcus (meningitis in HIV). KOH mount for dermatophytes.
• Aspergillus: Acute angle branching hyphae; causes ABPA, aspergilloma, invasive disease.
• Mucormycosis: Rhino-orbito-cerebral in diabetics (DKA); broad, non-septate hyphae, right-angle branching.
• Candida: Oral thrush, vulvovaginitis; pseudohyphae and budding yeasts.
• Dimorphic fungi: Yeast in heat (37°C), mold in cold (25°C).
• Sporothrix schenckii: Rose gardener's disease (lymphocutaneous); cigar-shaped yeasts.