Opportunistic mycoses

General characteristics and ecology of pathogens

The group of opportunistic mycoses unites diseases whose etiological factor is represented by fungi that normally do not exhibit pronounced pathogenicity in healthy humans. The main genera of micromycetes capable of causing these conditions include Aspergillus, Mucor, Penicillium, Fusarium, and Candida.

The ecological reservoirs of these microorganisms are quite diverse. Most of them are widely distributed in the external environment. Fungal spores and mycelium can be found in soil, fresh water, atmospheric air, and on decaying plant debris. At the same time, certain representatives, in particular yeast-like fungi of the genus Candida, are full members of the normal (facultative) microflora of the human body, colonizing mucous membranes and skin.

Pathogenetic conditions and risk factors

For an opportunistic fungus to transition into an aggressive form and initiate the infectious process, specific pathogenetic conditions that weaken the host organism are required. Key risk factors include:

• Immunodeficiency states. These include both primary and secondary immunodeficiencies, including post-organ transplantation states requiring immunosuppression.
• Medication impact. Irrational and prolonged antibiotic therapy disrupts normal microbiocenosis, freeing up ecological niches for fungi. Hormone therapy, cytostatic therapy, and radiation therapy also act as triggers.
• Medical manipulations. The widespread use of invasive diagnostic and treatment methods (catheterization, probing, surgical interventions) disrupts tissue barrier functions and creates entry gates for infection.

Classification of main nosologies

Depending on the genus of the pathogen, several main forms of opportunistic mycoses are distinguished. The systematization is presented in the table below:

Diagnostics and treatment (using cryptococcosis as an example)

Approaches to the detection and treatment of severe mycoses can be examined using the concluding section on cryptococcosis. The diagnostic search includes a complex of modern methods:

1. Immunodiagnostics. Aimed at detecting specific antigens or antibodies. Latex agglutination reaction and enzyme-linked immunosorbent assay (ELISA) are used. The key marker is the pathogen's capsular polysaccharide — glucuronoxylomannan.
2. Biological assay. Consists of infecting laboratory animals. Administration of the material is performed intravenously or intracerebrally.
3. Molecular genetic methods. DNA hybridization provides high specificity.

Etiotropic therapy of mycoses requires the use of potent antimycotics. The drugs of choice are amphotericin B, fluconazole, itraconazole, and flucytosine. The choice of a specific agent depends on the severity of the course and the isolated pathogen species.

Class and exam questions

What else to study on this topic

• Clinical manifestations and pathogenesis of candidiasis
• Features of the pathogen of Pneumocystis pneumonia (Pneumocystis jiroveci)
• Pathogenesis of mycotoxicoses caused by fungi of the genus Fusarium
• Differential diagnostics of zygomycoses and aspergillosis
• Mechanisms of action of amphotericin B and fluconazole

Other topics in the section "Opportunistic mycoses (candidiasis, aspergillosis, pneumocystosis, etc.)"

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