Emerging Fungal Infections — MCQs
Which antifungal binds to ergosterol, causing fungal cell membrane damage?
A 15-year-old boy presented with fever and chills for 3 days. On examination, he was found to have delayed skin pinch time and dry oral mucosa. Identify the pathogen involved based on the provided peripheral blood smear image.
A 55-year-old woman presents with persistent cough, fever, and hemoptysis. Sputum shows branching septate hyphae. What is the likely pathogen?
1-3 beta-d-glucan assay is done for which infection?
A 65-year-old diabetic man presents with black necrotic tissue on his palate. What is the most likely causative organism?
A 70 year old farmer, presented to you with complaints of yellowish discolouration of his finger nails for the past 6 months, he also gives history of recurrent episodes of itching in the groin for which he used to take local home made herbal remedy. On examination 3 of his toe nails also show similar change with tunneling. Which among the following is the best test for rapid confirmation of your diagnosis?
Beta 1,3 Glucan test is positive in all except?
What should be the minimum value of HbA1c to safely carry out a surgical procedure in an emergency setting?
All are ophthalmological emergencies except -
Kerion is a type of:
Emerging Fungal Infections Indian Medical PG Practice Questions and MCQs
Question 1: Which antifungal binds to ergosterol, causing fungal cell membrane damage?
- A. Caspofungin
- B. Terbinafine
- C. Fluconazole
- D. Amphotericin B (Correct Answer)
Explanation: Amphotericin B - **Amphotericin B** is a polyene antifungal that directly binds to **ergosterol**, the primary sterol in fungal cell membranes [2]. - This binding creates pores in the membrane, leading to leakage of intracellular components and ultimately **fungal cell death** [2]. Caspofungin - **Caspofungin** is an echinocandin, which inhibits the synthesis of **β-(1,3)-D-glucan**, a vital component of the fungal cell wall. - Its mechanism of action is distinct from ergosterol binding and primarily targets cell wall integrity rather than the cell membrane directly. Terbinafine - **Terbinafine** is an allylamine antifungal that inhibits **squalene epoxidase**, an enzyme involved in ergosterol synthesis. - By blocking this enzyme, it prevents the formation of ergosterol, leading to an accumulation of toxic squalene and disrupting membrane function, but it does not directly bind to ergosterol. Fluconazole - **Fluconazole** is an azole antifungal that inhibits **lanosterol 14-α-demethylase**, a cytochrome P450 enzyme responsible for an earlier step in ergosterol synthesis [1]. - This action prevents ergosterol production, impairing membrane function, but it does not involve direct binding to pre-existing ergosterol [1].
Question 2: A 15-year-old boy presented with fever and chills for 3 days. On examination, he was found to have delayed skin pinch time and dry oral mucosa. Identify the pathogen involved based on the provided peripheral blood smear image.
- A. Babesia
- B. Plasmodium vivax (Correct Answer)
- C. Plasmodium falciparum
- D. Salmonella typhi
Explanation: ***Plasmodium vivax*** - The image shows **enlarged red blood cells** infected with various stages of *Plasmodium vivax*, including trophozoites and schizonts displaying **ameboid forms**. - The presence of **Schüffner's dots**, though not distinctly visible in this specific resolution, is characteristic of *P. vivax* infection. - *P. vivax* preferentially infects **reticulocytes** and young red blood cells, leading to the characteristic RBC enlargement. *Babesia* - *Babesia* infection typically presents with **ring forms** in red blood cells that lack pigment and often form **tetrads** (Maltese cross appearance), which are not seen here. - While it can cause fever and chills, the morphology of the parasites in the image is inconsistent with *Babesia*. *Plasmodium falciparum* - *P. falciparum* characteristically presents with **multiple small ring forms** in a single red blood cell and **crescent-shaped gametocytes**. - It infects red blood cells of all ages, does not typically enlarge the red blood cells, and early trophozoites (*ring forms*) are the most common stage seen in peripheral blood, which differs from the image. *Salmonella typhi* - *Salmonella typhi* is a bacterium that causes **typhoid fever** and is a systemic infection. - It does not infect red blood cells or present with intraerythrocytic parasites on a peripheral blood smear; diagnosis is typically made by **blood culture**.
Question 3: A 55-year-old woman presents with persistent cough, fever, and hemoptysis. Sputum shows branching septate hyphae. What is the likely pathogen?
- A. Aspergillus fumigatus (Correct Answer)
- B. Candida albicans
- C. Histoplasma capsulatum
- D. Mucor species
Explanation: ***Aspergillus fumigatus*** - The presence of **branching septate hyphae** in sputum, along with symptoms of **persistent cough, fever, and hemoptysis**, is highly characteristic of an *Aspergillus* infection, particularly in immunocompromised patients or those with pre-existing lung conditions. - This fungus often colonizes the respiratory tract and can cause various diseases, including **allergic bronchopulmonary aspergillosis (ABPA)**, **aspergilloma** (fungus ball), or **invasive aspergillosis**. - The hyphae branch at **acute angles (45°)** and are **septate**, which is the key distinguishing feature. *Candida albicans* - While *Candida albicans* is a common fungal pathogen, it typically presents as **yeast** or **pseudohyphae** on microscopy, not branching septate hyphae. - It usually causes **mucocutaneous infections** like thrush or candidemia, with pulmonary involvement being less common and usually presenting differently from the described symptoms. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that appears as **small intracellular yeast forms** within macrophages in tissue or sputum, not branching septate hyphae. - It is endemic to certain regions (e.g., Ohio and Mississippi River valleys) and typically causes **pulmonary histoplasmosis**, which can mimic tuberculosis, but microscopic findings differ significantly. *Mucor species* - **Mucor species** are characterized by **broad, ribbon-like, aseptate (non-septate) hyphae** with irregular branching at right angles, which is distinct from the branching septate hyphae described. - These fungi typically cause **mucormycosis** (zygomycosis), an aggressive infection often seen in immunocompromised individuals, especially diabetics with ketoacidosis, and can involve the rhinocerebral region, lungs, or skin.
Question 4: 1-3 beta-d-glucan assay is done for which infection?
- A. Invasive candidiasis (Correct Answer)
- B. Penicillium
- C. Cryptococcus
- D. Rhinocerebral mucormycosis
Explanation: ***Invasive candidiasis*** - The **1-3 beta-D-glucan assay** detects a component of the cell wall of many fungi, including **Candida** species, making it useful for diagnosing invasive candidiasis. - Elevated levels in a patient with risk factors for fungal infection can indicate an active **candidal infection**. *Penicillium* - While **Penicillium** is a fungus, specific antigens or metabolic products differentiate its infection from others. - Diagnosis of **penicilliosis** often relies on culture or molecular methods rather than the 1-3 beta-D-glucan assay, which has broader utility. *Cryptococcus* - **Cryptococcus neoformans** has a polysaccharide capsule that is the target of specific antigen tests, particularly the **cryptococcal antigen test (CrAg)**. - The cell wall of Cryptococcus contains very little **beta-D-glucan**, making the assay less sensitive for cryptococcal infections. *Rhinocerebral mucormycosis* - **Mucormycosis** is caused by fungi belonging to the order Mucorales, whose cell walls contain very little **beta-D-glucan**. - The 1-3 beta-D-glucan assay is generally **not positive** in cases of mucormycosis, making it a poor diagnostic tool for this infection.
Question 5: A 65-year-old diabetic man presents with black necrotic tissue on his palate. What is the most likely causative organism?
- A. Cryptococcus neoformans
- B. Candida albicans
- C. Mucor species (Correct Answer)
- D. Aspergillus fumigatus
Explanation: ***Mucor species*** - The presence of **black necrotic tissue** on the palate in a diabetic patient is highly suggestive of **mucormycosis**, an aggressive fungal infection caused by *Mucor* species. - **Diabetes mellitus**, particularly with ketoacidosis, is a major risk factor for mucormycosis due to impaired phagocytic function and increased iron availability. *Cryptococcus neoformans* - This fungus is primarily associated with **cryptococcal meningitis** or pneumonia, especially in immunocompromised individuals. - It does not typically cause **black necrotic lesions** on the palate. *Candida albicans* - While *Candida albicans* can cause oral infections (**thrush**), these typically present as white, creamy patches that can be scraped off, not black necrotic tissue. - Oral candidiasis is common in diabetics but does not usually involve tissue necrosis. *Aspergillus fumigatus* - *Aspergillus* species can cause invasive infections, particularly in immunocompromised patients, often affecting the lungs or sinuses. - While it can cause **necrotic lesions**, the characteristic rapid progression and specific presentation in the palate of a diabetic with black necrotic tissue points more strongly towards *Mucor*.
Question 6: A 70 year old farmer, presented to you with complaints of yellowish discolouration of his finger nails for the past 6 months, he also gives history of recurrent episodes of itching in the groin for which he used to take local home made herbal remedy. On examination 3 of his toe nails also show similar change with tunneling. Which among the following is the best test for rapid confirmation of your diagnosis?
- A. Tzanck smear
- B. KOH mount (Correct Answer)
- C. Woods lamp
- D. Biopsy
Explanation: ***KOH mount*** - A **KOH mount** (potassium hydroxide) dissolves keratinocytes, allowing for direct visualization of fungal elements such as **hyphae** and **spores** under a microscope. This is the **most rapid and cost-effective test** for confirming fungal infections like **onychomycosis**. - The patient's presentation with **yellowish discoloration** and **"tunneling"** of nails (suggesting onycholysis and subungual hyperkeratosis), along with a history of recurrent groin itching (potentially **tinea cruris**), strongly points to a fungal infection. *Tzanck smear* - A **Tzanck smear** is primarily used to detect multinucleated giant cells in **herpesvirus infections** (e.g., herpes simplex, varicella-zoster). - It is not useful for identifying fungal elements responsible for nail discoloration or suspected onychomycosis. *Woods lamp* - A **Woods lamp** uses ultraviolet light to detect specific fluorescent substances, particularly useful for diagnosing certain **bacterial infections** (e.g., *Corynebacterium minutissimum* in erythrasma) or some **tinea capitis** species (*Microsporum*). - Most common dermatophytes causing onychomycosis **do not fluoresce** under a Wood's lamp, making it an unreliable diagnostic tool in this scenario. *Biopsy* - A **nail biopsy** (with histology and special stains like PAS) is a highly accurate diagnostic method for onychomycosis, especially when other tests are inconclusive. - However, it is an **invasive procedure**, takes more time for results, and is generally not the **most rapid** initial test compared to a KOH mount.
Question 7: Beta 1,3 Glucan test is positive in all except?
- A. Pneumocystis Jirovecii
- B. Candida
- C. Mucormycosis (Correct Answer)
- D. Aspergillus
Explanation: ***Mucormycosis*** - Fungi causing mucormycosis belong to the order **Mucorales**, which structurally lack **beta-D-glucan** in their cell walls. - Due to the absence of beta-D-glucan, the **beta-1,3-D-glucan assay** will yield a negative result in cases of mucormycosis. *Pneumocystis jirovecii* - This fungus contains significant amounts of **beta-D-glucan** in its cell wall, making the test usually positive during active infection. - A positive **beta-D-glucan test** can be a useful diagnostic marker for **Pneumocystis pneumonia (PCP)**, especially in immunocompromised patients. *Candida* - **Candida species** possess a cell wall rich in **beta-D-glucan**, leading to a positive test result during active infection. - The **beta-D-glucan assay** is a valuable adjunctive test for diagnosing invasive candidiasis. *Aspergillus* - The cell wall of **Aspergillus** contains **beta-D-glucan**, causing the test to be positive in cases of invasive aspergillosis. - A positive **beta-D-glucan test** can aid in the early diagnosis and management of invasive aspergillosis, particularly in high-risk patients.
Question 8: What should be the minimum value of HbA1c to safely carry out a surgical procedure in an emergency setting?
- A. <7
- B. <8
- C. <10 (Correct Answer)
- D. <8
Explanation: ***<10*** - In an **emergency setting**, the priority is to proceed rapidly with surgery; current guidelines suggest that an **HbA1c <10%** is acceptable to proceed without significant delay for optimization. - While lower HbA1c is ideal, delaying an emergency procedure to achieve an HbA1c below 10% is generally **not recommended**, as the benefits of urgent surgery outweigh the risks associated with this level of glycemic control [1]. *<7* - An HbA1c of **<7% is the general target** for optimal glycemic control in most diabetic patients, especially in an elective setting. - Achieving this level in an emergency would likely require **delaying surgery**, which is not feasible or safe when immediate intervention is needed. *<8* - An HbA1c of **<8%** represents good control for many individuals, particularly older adults or those with comorbidities. - While better than 10%, it is not the absolute minimum required to proceed with an **emergency surgery**, as timely intervention is paramount. *<8* - An HbA1c of **<8%** represents good control for many individuals, particularly older adults or those with comorbidities. - While better than 10%, it is not the absolute minimum required to proceed with an **emergency surgery**, as timely intervention is paramount.
Question 9: All are ophthalmological emergencies except -
- A. Endophthalmitis
- B. CRVO (Correct Answer)
- C. Acute congestive glaucoma
- D. CRAO
Explanation: ***CRVO*** - Central Retinal Vein Occlusion (CRVO) is characterized by painless **vision loss** due to retinal hemorrhage and edema, but it is generally *not* considered an immediate, vision-threatening emergency in the same vein as the other options. - While it requires prompt evaluation and management to preserve vision, CRVO allows for a less urgent intervention compared to conditions that can lead to permanent vision loss within hours. *Endophthalmitis* - **Endophthalmitis** is a severe inflammation of the intraocular fluids and tissues, typically caused by infection, and can lead to rapid and irreversible vision loss if not treated urgently. - It presents with pain, redness, reduced vision, and hypopyon (pus in the anterior chamber), necessitating immediate antibiotic treatment and surgical intervention. *Acute congestive glaucoma* - **Acute congestive glaucoma** (acute angle-closure glaucoma) involves a sudden increase in intraocular pressure, causing severe pain, redness, corneal edema, and profound vision loss. - If left untreated, the high pressure can cause irreversible damage to the optic nerve within hours, making it a true ocular emergency. *CRAO* - **Central Retinal Artery Occlusion (CRAO)** is a sudden, painless loss of vision in one eye due to blockage of the central retinal artery, leading to retinal ischemia. - It is an ocular emergency because irreversible retinal damage and vision loss can occur within 90-120 minutes of the occlusion, requiring immediate intervention to restore blood flow.
Question 10: Kerion is a type of:
- A. Viral infection
- B. Fungal infection (Correct Answer)
- C. Bacterial infection
- D. Parasitic infection
Explanation: ***Fungal infection*** - Kerion is a severe inflammatory **tinea capitis** (ringworm of the scalp) caused by a fungal infection. - It presents as a boggy, elevated, and painful lesion with pustules and could lead to **scarring alopecia**. *Viral infection* - Viral infections typically manifest with conditions like **herpes zoster**, **varicella**, or **molluscum contagiosum**, which have distinct clinical features and are not characterized as kerion. - Kerion's inflammatory, pustular nature and typical location on the scalp are not consistent with common viral dermatoses. *Bacterial infection* - Bacterial infections of the skin could cause conditions like **impetigo** or **folliculitis**, which are generally less extensive and lack the specific inflammatory boggy plaque typical of kerion. - While secondary bacterial infection can occur in kerion, the primary etiology is fungal, not bacterial. *Parasitic infection* - Parasitic infections of the scalp usually involve **lice** (pediculosis capitis) or **scabies**, which cause intense itching and excoriations but do not result in a kerion-like boggy, inflammatory mass. - The pathology of kerion involves a fungal invasion of hair follicles, distinct from parasitic infestation.
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