Mycology-MHA-2024

Introduction to Mycology

  • Definition: Mycology is the study of fungi, including molds and yeasts.

  • Distribution: Fungi are present in air, dust, fomites, and the normal flora of humans.

  • Pathogenicity: Most fungi are non-pathogenic, with some being opportunistic pathogens, especially in immunocompromised individuals.

Emerging Fungal Pathogens

  • Opportunistic fungal pathogens require impaired host defenses to cause infection.

  • Account for 10% of nosocomial infections.

Fungal Diseases

  • Primary True Pathogens: Histoplasmosis, Blastomycosis, Coccidiomycosis, Paracoccidiomycosis.

  • Opportunistic Pathogens: Candidiasis, Aspergillosis, Cryptococcosis.

Morphology

  • Yeasts: Unicellular, spherical or ovoid.

  • Hyphae: Multicellular, thread-like structures.

Reproduction

  • Fungi reproduce via sexual and asexual modes.

Diagnosis

  1. Skin scrapings or pus (microscopy).

  2. Skin testing for hypersensitivity.

  3. Serology: Useful for specific fungal diseases but varies in efficacy; common tests include latex agglutination (IgM detection).
    4. Direct fluorescent microscopy.
    5. Biopsy and histopathology: Identifies tissue-invading fungi.
    6. Culture: Definitive diagnosis using Sabouraud dextrose agar, often with antibiotics to prevent bacterial contamination.

    Portals of Entry

    1. Primary Mycoses: Respiratory tract (inhalation of spores).

    2. Subcutaneous: Traumatic introduction.

    3. Cutaneous and Superficial: Contamination of the skin surface.

    Human Mycoses

    • Superficial Mycoses:

      • Involves skin, hair, and nails without systemic threat.

      • Includes conditions like Tinea versicolor and Piedra (white and black types).

      • Diagnosis involves microscopy; treatment uses topical preparations.

    • Cutaneous Mycoses:

      • Affect keratinized tissues (skin, hair, nails).

      • Caused by dermatophytes (Epidermophyton, Microsporum, Trichophyton).

      • Common diseases: Ringworm, Candida infections of nails.

      • Spread through infected individuals, animals, or objects.

      • Controlled by cleanliness and treatment.

    • Subcutaneous Mycoses:

      • Infections beneath the skin, e.g., Sporotrichosis caused by Sporothrix schenckii.

      • Involves granulomatous lesions and lymphatic spread.

    • Systemic (Deep) Mycoses:

      • Life-threatening fungal infections in internal organs, often in immunocompromised patients.

      • Caused by dimorphic fungi like Histoplasma capsulatum.

      • Spread via inhalation of spores.

    • Opportunistic Mycoses:

      • Caused by fungi that are normally non-pathogenic, e.g., Candida albicans.

      • Can invade bloodstream or tissues, especially in immunocompromised individuals.

    Candida Infections

    • Oral Thrush: White deposits on mucous membranes.

    • Virulence Factors:

      • Biofilm formation.

      • Dimorphism (yeast and hyphae).

      • Hydrolytic enzymes (e.g., Aspartyl proteinases).

      • Toxins like Candidalysin.

    • Diagnosis and Treatment:

      • Identified via Sabouraud's agar and molecular methods.

      • Treated with antifungals like Nystatin, Ketoconazole, or Amphotericin B.

    Control and Prevention

    • Maintain a balanced microbiome and strong host defenses to prevent fungal overgrowth.