7 topics with concise reviews: definitions, key facts, and class questions.
This section is dedicated to deep (systemic) mycoses that primarily affect internal organs. Most of them are endemic diseases tied to specific climatic and geographical zones, and their causative agents exhibit thermal dimorphism.
Here we cover the etiology, pathogenesis, and microbiological diagnosis of classical systemic endemic mycoses: histoplasmosis, blastomycosis, coccidioidomycosis, and paracoccidioidomycosis. This section also includes cryptococcosis (which occurs globally but is studied here due to the severity of systemic central nervous system involvement) and mycetoma, a chronic granulomatous infection of the tissues of the foot.
Commonly asked in class: Instructors will certainly emphasize thermal dimorphism (mycelial phase in the soil, yeast phase in the human body). Expect questions on the differential diagnosis of primary pulmonary lesions from tuberculosis, as well as methods for detecting the thick polysaccharide capsule of Cryptococcus neoformans (India ink negative staining). Pay special attention to the morphology of tissue forms—this is the basis for successfully solving microscopy tasks.
What serves as the reservoir for mycetoma pathogens?
The natural reservoir of the disease-causing microorganisms is the environment—soil and vegetation.
Where do the causative agents of systemic endemic mycoses inhabit in nature?
The primary habitat of pathogens is soil, various decomposing organic substrates, and in some cases, bird droppings.
Why is the fungus called capsulatum if it has no capsule?
This is a historically established name. The discoverers mistook the halo effect around the cell in tissues for a capsule, but it was later found that the fungus has no true capsule.
At what temperature does the pathogen form the mycelial phase?
The transition to the mycelial form occurs during cultivation on nutrient media at room temperature, i.e., at 20–25 °C.
Is a patient with coccidioidomycosis contagious to others?
No, the patient is completely non-contagious. The hazard is posed solely by arthrospores (the mycelial phase), which form in the external environment at 25 °C, whereas the human body harbors the non-contagious tissue phase (spherules).
Can one contract paracoccidioidomycosis through contact with an infected person?
No, this disease is not transmitted from person to person. Infection is only possible through contact with the natural reservoir (inhalation of dust containing the pathogen or trauma to mucous membranes by infected plant parts).
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