Epidemiology and Clinical Presentation
The disease is historically known as South American blastomycosis. The primary reservoir of the fungus Paracoccidioides brasiliensis in nature is soil, as well as various decaying plants.
Human infection occurs via two main routes:
- Aerogenous (dust-borne): the infection enters the body through inhalation of contaminated dust.
- Contact: transmission via mechanical trauma to the oral mucosa (e.g., from the habit of chewing gathered plants).
The infection has a long incubation period, which can range from one month to several years. A crucial epidemiological feature is that an infected person is entirely non-contagious to others.
Clinically, paracoccidioidomycosis manifests as a deep mycosis. Granulomas form in the affected tissues. The pathological process is most frequently localized in the lungs, on the skin (the face is particularly often affected), as well as on the nasal and oral mucosa. One of the prominent clinical manifestations 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 drastically depending on ambient temperature and environmental conditions.
1. Tissue form (inside the human body) In the affected organs, the fungus exists in the yeast form. These are large spherical or oval cells ranging from 30 to 60 µm in size. They reproduce by multiple budding. Numerous daughter buds form around a large mother cell, connected to it by a wide base.
2. Culture form (on artificial nutrient media) The behavior of the fungus in vitro depends on the incubation temperature:
- At 20–25 °C (on Sabouraud agar): the pathogen grows in the mycelial phase. Septate mycelium is formed, along with sessile conidia and chlamydospores.
- At 37 °C (on blood agar): transformation into the yeast phase occurs. Cells measuring 40–50 µm are formed, with small buds located on 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 biopsy samples of affected tissues.
Microscopic method This is a crucial stage of diagnostics. The following approaches are used:
- Examination of native preparations with the addition of potassium hydroxide (KOH). This allows the detection of yeast-like cells surrounded by a thin wall.
- Examination of stained smears. Gram staining, Romanowsky-Giemsa staining, hematoxylin and eosin staining, Gomori methenamine silver (GMS) staining, and fluorescence microscopy with acridine orange are used.
The key diagnostic sign upon microscopy is the detection of specific budding cells resembling a "ships wheel" (steering wheel).
Serological method Aimed at detecting specific antibodies in the patient's blood serum. Laboratory practice utilizes:
- Precipitin test (PT);
- Complement fixation test (CFT);
- Immunodiffusion test (ID);
- Enzyme-linked immunosorbent assay (ELISA).
Treatment principles Systemic antifungals are used to treat South American blastomycosis. The clinician's arsenal includes amphotericin B, ketoconazole, and itraconazole.
Briefly: answers to topical questions
What types of clinical specimens are sent to the laboratory for the diagnosis of paracoccidioidomycosis?
For the microbiological diagnosis of paracoccidioidomycosis, the following are sent to the laboratory:
- pus;
- tissue biopsies;
- ulcer scrapings.
Microscopy of the material reveals yeast-like cells; the key diagnostic sign is multiple budding cells resembling a "ships wheel".
To easily remember the tissue form of *Paracoccidioides brasiliensis*, imagine a ship's "steering wheel": a large mother yeast cell is in the center, and multiple daughter buds with wide bases extend from it in all directions, resembling the handles of a steering wheel.
Class and exam questions
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).
How to obtain the mycelial phase of this fungus in the laboratory?
To obtain the mycelial phase, clinical material must be inoculated onto Sabouraud agar and incubated at 20–25 °C.
Which visual sign upon microscopy indicates paracoccidioidomycosis?
The key sign is the presence of large yeast cells reproducing by multiple budding. Visually, this structure is described as a "steering wheel" or "ships wheel".
What else to study on this topic
- Pathogenesis of mycotic granuloma formation in the lungs and skin
- Differential diagnosis with North American blastomycosis
- Mechanism of action of systemic antimycotics (amphotericin B and azoles)
- Features of serological diagnostics in deep mycoses (CFT, ID)
Study the full topic in the «Microbiology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Paracoccidioidomycosis" and 4,383 more subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 141 video lectures on the subject
Other topics in the section «Systemic endemic mycoses (histoplasmosis, blastomycosis, coccidioidomycosis, cryptococcosis)»
Entire section «Systemic endemic mycoses (histoplasmosis, blastomycosis, coccidioidomycosis, cryptococcosis)»Free video lessons: microbiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.