Enumerate cause of opportunities mycosis
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I now have sufficient information from the textbooks to provide a thorough answer. Here is a comprehensive enumeration of the causes (predisposing conditions/risk factors) of opportunistic mycoses, with the causative fungi organized by type of immune defect:
Causes of Opportunistic Mycoses
Opportunistic mycoses are fungal infections caused by organisms of inherently low or limited virulence that exploit a weakened host. They occur when normal host defenses are impaired. The specific fungus and disease pattern are largely determined by the type of immune defect present.
- Medical Microbiology 9e, p. 647 (Table 57.4)
- Jawetz, Melnick & Adelberg's Medical Microbiology 28e, p. 706
A. Impaired Cell-Mediated Immunity (T-cell defects)
| Predisposing Condition | Associated Fungi |
|---|---|
| HIV/AIDS (CD4+ <200 cells/µL) | Candida spp., Cryptococcus neoformans, Pneumocystis jirovecii, Aspergillus spp., Talaromyces marneffei |
| Organ transplantation (on immunosuppressants) | Candida, Aspergillus, Cryptococcus, Pneumocystis jirovecii, Mucorales |
| Corticosteroid therapy (long-term/high-dose) | Aspergillus spp., Candida, Mucorales |
| Immunosuppressive therapy (e.g., calcineurin inhibitors, TNF-alpha blockers) | Aspergillus, Candida |
| Congenital T-cell deficiencies (DiGeorge, SCID) | Candida, Pneumocystis |
B. Impaired Neutrophil Function / Neutropenia
| Predisposing Condition | Associated Fungi |
|---|---|
| Hematologic malignancies (leukemia, lymphoma) | Aspergillus spp. (most important), Candida, Mucorales, Fusarium |
| Chemotherapy-induced neutropenia | Aspergillus fumigatus (key risk - angioinvasive disease), Candida |
| Hematopoietic stem cell transplantation (HSCT) | Aspergillus (prolonged neutropenia, GVHD), Candida |
| Aplastic anemia | Aspergillus, Candida |
| Chronic granulomatous disease (CGD) | Aspergillus spp. |
C. Disruption of Normal Flora / Mucosal Barriers
| Predisposing Condition | Associated Fungi |
|---|---|
| Broad-spectrum antibiotic use | Candida albicans (endogenous overgrowth) |
| Indwelling vascular catheters / prosthetic devices | Candida spp. (candidemia) |
| Total parenteral nutrition (TPN) | Candida |
| Surgery / burns | Candida, Aspergillus |
| Premature neonates (immature barriers) | Candida |
D. Metabolic and Endocrine Disorders
| Predisposing Condition | Associated Fungi |
|---|---|
| Diabetes mellitus (especially ketoacidosis) | Mucorales (Rhizopus, Mucor, Lichtheimia) - rhinocerebral mucormycosis is classic |
| Iron overload / deferoxamine therapy | Mucorales (Rhizopus) - deferoxamine acts as siderophore for fungi |
| Renal failure / uremia | Candida, Mucorales |
| Malnutrition | Candida, Pneumocystis jirovecii |
E. Special Clinical Situations
| Predisposing Condition | Associated Fungi |
|---|---|
| COPD / structural lung disease | Aspergillus (chronic pulmonary aspergillosis, ABPA) |
| Influenza or COVID-19 (ICU patients) | Aspergillus spp. (COVID-19-associated pulmonary aspergillosis - CAPA) |
| Liver failure / cirrhosis | Candida, Aspergillus, Cryptococcus |
| Extremes of age (neonates, elderly) | Candida |
| Hyper-IgE syndrome / CMC | Candida (chronic mucocutaneous candidiasis) |
Key Fungi and Their Characteristic Host Defects
| Fungus | Primary Host Defect |
|---|---|
| Candida spp. | Disrupted mucosal barriers, antibiotics, T-cell defects, catheters |
| Aspergillus spp. | Neutropenia (most critical), corticosteroids, lung transplant |
| Cryptococcus neoformans | T-cell defects (HIV/AIDS, transplant) |
| Pneumocystis jirovecii | T-cell defects (CD4+ <200 in HIV, steroids) |
| Mucorales (Rhizopus, Mucor) | Diabetes/ketoacidosis, neutropenia, deferoxamine use, iron overload |
| Fusarium spp. | Profound neutropenia, HSCT |
| Talaromyces marneffei | HIV/AIDS (Southeast Asia) |
| Trichosporon spp. | Neutropenia, HSCT |
| Scedosporium spp. | Transplant, near-drowning, chronic lung disease |
Summary Principle
The key concept is that virtually any fungus can become an opportunistic pathogen given sufficient host immune compromise. The most common opportunistic pathogens are Candida spp., Aspergillus spp., Cryptococcus neoformans, and Pneumocystis jirovecii. The incidence and variety of opportunistic fungal infections continue to grow each year as more patients survive with prolonged immunosuppression from cancer treatment, transplantation, and HIV.
- Jawetz, Melnick & Adelberg's Medical Microbiology 28e: "In patients with HIV/AIDS, susceptibility and incidence of opportunistic mycoses are inversely correlated with the CD4+ lymphocyte count. AIDS patients with CD4+ counts less than 200 cells/µL are highly susceptible."
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