Practice 5 structured short- and long-answer medical questions on Weekly Year 3: Medical Mycology Exam - October 2, 2026 (Sections B & C). Review model answe...
Answer: Yeast are unicellular fungi that typically reproduce by budding, forming blastoconidia (e.g., Candida albicans). Moulds are multicellular, filamentous fungi composed of hyphae (either septate or aseptate) that grow by apical extension and reproduce via spores (e.g., Aspergillus fumigatus).
Answer: Azole antifungals inhibit the fungal enzyme 14-alpha-demethylase, which is crucial for the synthesis of ergosterol, a vital component of the fungal cell membrane. This inhibition leads to the accumulation of toxic 14-alpha-methyl sterols and depletion of ergosterol, disrupting membrane integrity and function. An example is Fluconazole or Itraconazole.
Answer: Three risk factors for invasive candidiasis include: 1. **Immunosuppression:** Especially neutropenia, chemotherapy, solid organ or hematopoietic stem cell transplantation, corticosteroid use. 2. **Presence of central venous catheters:** Acts as a nidus for biofilm formation and entry point. 3. **Broad-spectrum antibiotic use:** Disrupts the normal commensal bacterial flora, allowing Candida overgrowth. (Other valid answers include: prolonged hospitalization, major surgery, total parenteral nutrition, severe burns, renal failure, diabetes mellitus.)
Answer: In tissue sections or BAL fluid, *Aspergillus fumigatus* typically presents as narrow (3-6 µm), septate hyphae that branch dichotomously at acute angles (approximately 45 degrees). Conidia and conidiophores are generally not seen in tissue unless there is growth into an air cavity (e.g., aspergilloma).
Answer: **Epidemiology:** * *Cryptococcus neoformans* is an encapsulated yeast found ubiquitously in the environment, particularly associated with pigeon droppings and decaying wood. Infection is typically acquired via inhalation of desiccated yeast cells or spores. It is a global pathogen, with a high incidence in immunocompromised individuals, especially those with advanced HIV/AIDS. **Clinical Manifestations (in immunocompromised hosts, e.g., HIV/AIDS):** * **Central Nervous System (CNS):** Most common and severe manifestation. Presents as chronic meningoencephalitis. Symptoms include headache (often severe), fever, nausea, vomiting, neck stiffness, photophobia, cranial nerve palsies, seizures, and altered mental status (confusion, lethargy, personality changes, coma). Hydrocephalus due to elevated intracranial pressure (ICP) is common. * **Pulmonary:** Often the initial site of infection, though frequently asymptomatic or mild (cough, dyspnea, pleuritic chest pain). Can range from solitary nodules to diffuse interstitial infiltrates. * **Disseminated Disease:** Can spread to virtually any organ. Common sites include skin (papules, pustules, ulcers resembling molluscum contagiosum), bone, prostate, and eyes (chorioretinitis). * **Cryptococcoma:** Mass lesions in the brain or elsewhere. **Diagnostic Approaches:** * **Lumbar Puncture (LP) and Cerebrospinal Fluid (CSF) Analysis:** The cornerstone for CNS disease. * **Microscopy:** India ink stain of CSF to visualize the characteristic encapsulated yeast (halo around the yeast cells). Sensitivity can be variable. * **Cryptococcal Antigen (CrAg) Detection:** Highly sensitive and specific test for detecting cryptococcal polysaccharide capsule antigen in CSF and serum (latex agglutination, enzyme immunoassay (EIA), lateral flow assay). A positive serum CrAg can predict CNS disease. * **Culture:** CSF culture on Sabouraud dextrose agar is definitive for growth of *C. neoformans*. Growth typically occurs within 24-72 hours. * **Blood Tests:** Serum CrAg and blood cultures (especially in disseminated disease or fungemia). * **Pulmonary Samples:** Sputum, bronchoalveolar lavage (BAL) fluid, or lung biopsy for microscopy, culture, or antigen detection in cases of pulmonary involvement. * **Imaging:** CT or MRI of the brain may show hydrocephalus, cryptococcomas, or enhancement of meninges. **Treatment Principles:** Treatment is typically divided into three phases: 1. **Induction Therapy:** Aims to rapidly reduce fungal burden and symptoms. * Standard regimen: Amphotericin B deoxycholate (or liposomal Amphotericin B) in combination with Flucytosine for at least 2 weeks. * Management of elevated intracranial pressure is crucial, often requiring repeated therapeutic lumbar punctures or shunting. 2. **Consolidation Therapy:** Follows induction to eradicate residual infection. * Typically, high-dose oral Fluconazole (e.g., 400-800 mg daily) for 8 weeks. 3. **Maintenance/Secondary Prophylaxis:** Prevents relapse, especially in immunocompromised individuals. * Low-dose oral Fluconazole (e.g., 200 mg daily) for at least 1 year, or until immune reconstitution (e.g., CD4+ count >100 cells/µL for >3 months in HIV patients). Adjustments may be made based on host immune status, severity of disease, and drug tolerability.