Mycology

Mycology

Systemic Mycoses

  • Definition: Systemic mycoses are fungal infections that can spread to multiple systems in the body, often manifesting from inhalation of fungi.

Types of Fungi to Cover Systemic Mycoses

  • Blastomyces dermatitidis: Fungi causing blastomycosis.

  • Histoplasma capsulatum: Fungi associated with histoplasmosis.

  • Coccidioides immitis: Fungi responsible for coccidioidomycosis (Valley fever).

  • Paracoccidioides brasiliensis: Causes paracoccidioidomycosis.

Other Mycoses Types

  • Cutaneous Mycoses: Infections limited to the skin.

  • Opportunistic Mycoses: Infections occurring in immunocompromised individuals, including:

    • Malassezia furfur

    • Dermatophyte Genera

    • Sporothrix schenckii

    • Cryptococcus neoformans

    • Aspergillus fumigatus

    • Candida albicans

    • Pneumocystis jirovecii

    • Prions

Systemic Mycoses Details

General Features

  • Dimorphic: Fungi can exist in a mold form in the environment and as yeast or spherules in human tissues.

  • Primary Pathogens: Can cause infections in healthy and immunocompromised hosts and typically spread from the lungs.

  • Endemic Pathogens: Fungi confined to specific geographic regions with infections acquired by inhalation of spores.

Antifungal Treatment

  • Amphotericin B: An antifungal that binds to sterols (ergosterols) in fungal cell membranes, leading to disruption of the cell membrane.

Geographic Distribution of Endemic Mycoses

  • Distribution of diseases like blastomycosis and histoplasmosis varies significantly across regions such as the Upper Great Lakes, Mexico, and Central and South America.

Specific Pathogens

Blastomyces dermatitidis

Morphology

  • Yeasts: At 37°C, yeasts are budded off from the parent cell with broad bases and thick cell walls for resistance to phagocytosis.

  • Mold Phase: At 25°C, presents as hyphae and conidia - saprobic and parasitic phase.

Epidemiology & Transmission

  • Found predominantly in southern and mid-western USA, especially in moist soil.

    • Geographic regions: Ohio, Africa, Europe, and Middle East.

  • Infection occurs through inhalation of aerosolized conidia.

  • Risk Factors: Living in endemic regions, exposure to soil, prevalent in dogs.

  • Endemic: Clear geographic boundaries; hyperendemic areas exist where risk is heightened.

Pathogenesis

  • Infection Cycle: Inhalation transforms conidia to the yeast phase, eliciting neutrophilic responses and dissemination via macrophages to skin, bone, urinary tract.

Clinical Disease: North American Blastomycosis

  • Asymptomatic in many cases; pulmonary symptoms resemble flu.

  • Severe cases can lead to adult respiratory distress syndrome with high fever and cough.

  • Chronic cases may mimic tuberculosis or lung cancer.

Diagnosis

  • Microscopic detection in tissues or clinical samples, confirmed by culture.

  • Treatment: Amphotericin B.

Histopathology

  • Yeasts surrounded by neutrophils, featuring multiple nuclei.

Histoplasma capsulatum

Morphology

  • Thermally dimorphic; exists as a mold at 25°C and as yeast in tissues at 37°C.

  • Features two types of conidia: macroconidia and microconidia, which are budding yeast forms in tissue.

Epidemiology & Transmission

  • Endemic in central USA, Mexico, and parts of South America.

  • Found in soils enriched with nitrogen, particularly near bird and bat droppings.

Pathogenesis

  • Inhalation of microconidia leads to phagocytosis by macrophages and neutrophils, allowing yeasts to germinate intracellularly.

Clinical Disease

  • Asymptomatic in up to 90% of low-inoculum exposures; higher exposures lead to flu-like symptoms, potentially acute respiratory distress syndrome.

  • Chronic pulmonary symptoms can include persistent lymphadenopathy or disseminated histoplasmosis with mucocutaneous lesions.

Diagnosis

  • Involves microscopy, culture, serology, and antigen detection; treated primarily with Amphotericin B.

Coccidioides immitis

Morphology

  • Dimorphic, with mold in nature producing infectious arthroconidia and endosporulating spherules in culture and tissues.

Epidemiology & Transmission

  • Predominantly in Southwestern US, mainly during late summer and early fall.

  • Significant incidence in endemic areas; infected mainly via inhalation.

  • Risk Factors: Certain occupational exposures, pregnancy conditions, and immunosuppression.

Clinical Disease

  • Presents as Valley Fever; typically asymptomatic but can result in self-limited flu-like illness or severe pulmonary disease.

Diagnosis

  • Direct microscopic examination, nucleic acid hybridization, culture, and treatment with Amphotericin B.