Medical Mycology: Fungal Infections

• Medical mycology is the branch of medicine focused on the study, diagnosis, and treatment of fungal infections in humans and animals.

Fungal Infections

• Fungal infections, also known as mycoses, can range from superficial skin conditions to life-threatening systemic diseases.
• These infections are caused by pathogenic fungi, which include yeasts, molds, and dimorphic fungi.
• Mycoses are categorized based on the location of the infection: superficial, cutaneous, subcutaneous, and systemic.
• Superficial mycoses affect the outermost layers of the skin or hair, causing cosmetic rather than invasive damage.
• Cutaneous mycoses extend deeper into the epidermis, hair, and nails, caused by dermatophytes.
• Subcutaneous mycoses involve the dermis, subcutaneous tissues, and sometimes bone, often introduced through trauma.
• Systemic mycoses affect internal organs and can disseminate throughout the body, often entering through the lungs.
• Opportunistic mycoses occur in individuals with weakened immune systems, caused by fungi that are typically harmless.

Diagnostic Techniques

• Direct Microscopy involves the direct examination of clinical specimens to identify fungal elements.
• Samples are prepared with various stains like KOH (potassium hydroxide), Gram stain, or periodic acid-Schiff (PAS).
• Fungal Culture is used to grow and identify fungal species from clinical specimens.
• Different media such as Sabouraud dextrose agar (SDA) are used to support fungal growth.
• Cultures help in identifying the specific fungus causing the infection and perform susceptibility testing.
• Histopathology involves examining tissue samples under a microscope to detect fungal elements and tissue damage.
• Stains like Grocott's methenamine silver (GMS) and hematoxylin and eosin (H&E) are commonly used.
• Molecular Diagnostics such as PCR can detect fungal DNA in clinical samples, offering rapid and specific identification.
• MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) identifies fungi based on their protein profiles.
• Serological Tests detect antibodies or antigens in serum to diagnose systemic fungal infections.

Epidemiology of Fungal Diseases

• Fungal infections are distributed worldwide, but some are more prevalent in certain geographic regions.
• Factors influencing the epidemiology include climate, occupation, lifestyle, and immune status.
• Climate affects the distribution of fungi in the environment.
• Occupational exposure increases risk, such as farmers inhaling spores from soil.
• Immunocompromised individuals are at higher risk of opportunistic infections.
• Common fungal infections include dermatophytoses (athlete's foot, ringworm), candidiasis (thrush, yeast infections), and aspergillosis.
• Less common but serious infections include cryptococcosis, histoplasmosis, and mucormycosis.
• Incidence of invasive fungal infections has increased due to more immunocompromised individuals.
• Travel and migration contribute to the spread of endemic fungi to new areas.

Pathogenesis

• Fungal pathogenesis is the process by which fungi cause disease in a host.
• It involves several steps: adherence, invasion, tissue damage, and evasion of host defenses.
• Adherence to host cells is the first step, often mediated by fungal adhesins that bind to host receptors.
• Invasion involves penetration of host tissues, using enzymes like proteases, elastases, and phospholipases.
• Tissue damage results from fungal enzymes, toxins, and the host's immune response.
• Fungi evade host defenses through various mechanisms.
• Capsule production inhibits phagocytosis.
• Biofilm formation protects against antifungals and immune cells.
• Dimorphism allows adaptation to different host environments.
• Immune response plays a critical role in determining the outcome of fungal infections.
• Innate immunity involves phagocytes, complement, and cytokines.
• Adaptive immunity involves T cells and antibodies.
• Immunocompromised individuals are more susceptible to severe fungal infections.