Epidemiology and Clinical Presentation
The disease is historically known as South American blastomycosis. The primary natural reservoir of Paracoccidioides brasiliensis is soil, as well as various decaying plants.
Human infection occurs through two main routes:
- Aerogenic (dust-borne inhalation): infection enters the body when inhaling contaminated dust.
- Contact: infection via mechanical trauma to the oral mucosa (e.g., the habit of chewing harvested plants).
The infection has a long incubation period, ranging from one month to several years. A crucial epidemiological feature is that an infected person is completely non-contagious to others.
Clinically, paracoccidioidomycosis presents as a deep mycosis. Granulomas form in the affected tissues. The pathological process most frequently localizes in the lungs, skin (particularly the face), and the mucous membranes of the nose and mouth. A prominent clinical manifestation is the formation of painless ulcers on the mucous membranes.
Morphology and Dimorphism
The fungus Paracoccidioides brasiliensis is a dimorphic microorganism. This means its morphological properties change dramatically depending on the ambient temperature and environmental conditions.
1. Tissue Form (within the human body) In affected organs, the fungus exists in the yeast form. These are large spherical or oval cells measuring 30 to 60 µm. They reproduce via multiple budding. Numerous daughter buds form around a large mother cell and are connected to it by a broad base.
2. Culture Form (on artificial nutrient media) Fungal behavior in vitro depends on the incubation temperature:
- At 20–25 °C (on Sabouraud agar): the pathogen grows in the mycelial phase. A septate mycelium develops, producing sessile conidia and chlamydospores.
- At 37 °C (on blood agar): transformation into the yeast phase occurs. Cells measuring 40–50 µm are formed, featuring small buds attached by a narrowed base.
Microbiological Diagnostics and Treatment
To confirm the diagnosis, various clinical specimens are sent to the laboratory: pus, scrapings from ulcer surfaces, and biopsies of affected tissues.
Microscopic Method This is a critical diagnostic step. The following approaches are used:
- Examination of native preparations with potassium hydroxide (KOH) added. This reveals thin-walled yeast-like cells.
- Examination of stained smears. Gram, Giemsa, hematoxylin and eosin, Grocott-Gomori methenamine silver (GMS) stains, as well as fluorescence microscopy with acridine orange, are utilized.
Key diagnostic feature during microscopy: detection of specific budding cells resembling a "ship's wheel".
Serological Method Designed to detect specific antibodies in the patient's blood serum. Laboratory practice employs:
- Precipitation reaction;
- Complement fixation test (CFT);
- Immunodiffusion test (ID);
- Enzyme-linked immunosorbent assay (ELISA).
Principles of Treatment Systemic antifungal drugs are used to treat South American blastomycosis. Clinicians' armamentarium includes amphotericin B, ketoconazole, and itraconazole.