Introduction to Clinical Mycology

Learning Outcomes

• Compare and contrast yeast and fungi: Understand their cellular structure, modes of reproduction, and ecological roles.

• Provide examples of superficial and systemic fungal infections: Identify fungal infections in clinical scenarios, differentiating between superficial (e.g., athlete's foot) and systemic infections (e.g., cryptococcosis).

• Discuss opportunistic fungi, particularly Candida albicans and its role in thrush among AIDS patients: Examine how opportunistic fungi exploit weakened immune defenses in immunocompromised individuals.

Overview of Fungi

Definitions

• Mycology: Study of fungi, encompassing taxonomy, biology, and diseases they cause in humans.

• Mycologists: Scientists specializing in fungi.

• Mycoses: Diseases caused by fungal infections.

• Etymology of terms: "mycosis" derives from Greek "mykos" (fungus) + "-osis" (condition or disease).

Fungi Characteristics

• Species Diversity: Approx. 1.5 million known species, ~300 pathogenic to humans.

• Environmental Importance: Essential for nutrient cycling, organic matter decomposition, and ecological relationships (e.g., mycorrhizae).

Fungal Structure

Cells and Wall

• Eukaryotic Cells: Defined nucleus, phospholipid bilayer, contains ergosterol (target for antifungal medications).

• Cell Wall: Primarily made of chitin and carbohydrates, providing structure and immune recognition.

• Capsule: Antiphagocytic virulence factor aiding in immune evasion.

Classification of Fungi

• Types of Fungi:

  • Yeast: Unicellular, reproduce via budding; examples include Candida albicans.

  • Moulds (Filamentous Fungi): Multicellular with hyphae; engage in organic material degradation.

  • Dimorphic Fungi: Switch between yeast and mould forms (e.g., Histoplasma capsulatum).

Fungal Infections

Types

• Superficial Mycoses: Affect outer layers of skin, hair, nails (e.g., Tinea corporis, candidiasis).

• Systemic Mycoses: Affect internal organs, can be life-threatening (e.g., histoplasmosis, cryptococcosis).

• Invasive Fungal Infections: Opportunistic pathogens causing infections in immunocompromised individuals; notable examples include candidemia and disseminated candidiasis.

Importance

• Increasing Cases: Rise in infections in patients undergoing chemotherapy and organ transplants.

• Manageable Issues: Advances in diagnostics and antifungal treatments improve patient outcomes.

Diagnosis of Fungal Infections

• Methods:

  • Clinical observations of lesions and symptoms.

  • Laboratory tests including microscopic examination and culture.

  • Variable sampling based on infection site (skin scrapings, blood, sputum).