General Characteristics and Ecology of Pathogens
The group of opportunistic mycoses unites diseases whose etiological factor is fungi that do not normally possess marked pathogenicity for healthy individuals. The main genera of micromycetes capable of causing these conditions include Aspergillus, Mucor, Penicillium, Fusarium, and Candida.
Ecological reservoirs of these microorganisms are diverse. Most of them are widespread in the external environment. Fungal spores and mycelium can be found in soil, fresh water, atmospheric air, and decaying plant debris. At the same time, certain representatives, particularly yeast-like fungi of the genus Candida, are permanent 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 develop an infectious process, specific pathogenetic conditions that weaken the host organism are required. Key risk factors include:
- Immunodeficiency states. This includes both primary and secondary immunodeficiencies, including post-organ transplantation states requiring immunosuppression.
- Drug exposure. Irrational and prolonged antibiotic therapy disrupts the normal microbiocenosis, freeing ecological niches for fungi. Hormonal 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 the barrier functions of tissues and opens the portal of entry for infection.
Classification of Main Nosologies
Depending on the genus of the pathogen, several main forms of opportunistic mycoses are distinguished. The systematic breakdown is presented in the table below:
| Genus of Pathogen | Nosological Form (Disease) |
|---|---|
| Candida | Candidiasis |
| Zygomycetes (Rhizopus, Mucor) | Zygomycosis (phycomycosis) |
| Aspergillus | Aspergillosis |
| Penicillium | Penicilliosis |
| Fusarium | Fusarium infection, myrotoxicosis |
| Pneumocystis jirovecii (carinii) | Pneumocystis pneumonia |
Diagnosis and Treatment (with Cryptococcosis as an Example)
Approaches to identifying and treating severe mycoses can be examined using cryptococcosis as an example. The diagnostic workup includes a complex of modern methods:
- Immunodiagnostics. Aimed at detecting specific antigens or antibodies. Latex agglutination and enzyme-linked immunosorbent assay (ELISA) are used. The key marker is the pathogen's capsular polysaccharide — glucuronoxylomannan.
- Biological assay. Involves inoculating laboratory animals. Administration of the material is carried out intravenously or intracerebrally.
- Molecular genetic methods. DNA hybridization provides high specificity.
Etiotropic therapy of mycoses requires potent antifungals. Drugs of choice include amphotericin B, fluconazole, itraconazole, and flucytosine. The choice of a specific agent depends on the severity of the course and the isolated pathogen species.