Infectious Diseases Practice Questions

Q: What stain is used for degenerated fungi in tissue?

Gomori methenamine silver. **Explanation:** The identification of fungi in histopathological sections depends on the staining of the fungal cell wall. **Why Gomori Methenamine Silver (GMS) is correct:** GMS is considered the **gold standard** and the most sensitive stain for detecting fungi in tissue. The principle involves the oxidation of carbohydrates in the fungal cell wall to aldehydes, which then reduce the silver nitrate to metallic silver. Because GMS provides an intense black contrast against a green background, it can visualize even **degenerated, non-viable, or dead fungi** that have lost their cytoplasmic detail and fail to stain with other methods. **Analysis of Incorrect Options:** * **Periodic acid-Schiff (PAS):** While excellent for highlighting the polysaccharides in fungal walls (staining them bright magenta), PAS requires intact cell wall structures. It is often less effective than GMS for degenerated organisms or those with low fungal loads. * **Hematoxylin and Eosin (H&E):** Most fungi are poorly visualized on H&E as they appear pale or nearly transparent (except for some pigmented fungi like dematiaceous molds). It cannot reliably identify degenerated fungal elements. * **Mucicarmine:** This is a selective stain used specifically for **capsular material**. In mycology, its primary use is identifying *Cryptococcus neoformans*, which has a carminophilic polysaccharide capsule. **NEET-PG High-Yield Pearls:** * **Best stain for fungal morphology:** GMS (Black/Brown). * **Best stain for *Cryptococcus* capsule:** Mayer’s Mucicarmine (Rose red). * **Best stain for *Pneumocystis jirovecii*:** GMS (shows "crushed ping-pong ball" appearance). * **Rapid screening of skin/hair/nails:** 10% KOH mount. * **Fluorescent stain for fungi:** Calcofluor White (binds to chitin).

Q: All of the following are associated with primary tuberculosis EXCEPT:

Cavitary lesion. **Explanation:** The distinction between primary and secondary (reactivation) tuberculosis is a frequent high-yield topic in NEET-PG. **Why "Cavitary lesion" is the correct answer:** Cavitary lesions are the hallmark of **Secondary (Post-primary) Tuberculosis** [3]. Cavitation occurs due to a robust cell-mediated immune response (Type IV hypersensitivity) leading to extensive tissue necrosis. In contrast, **Primary TB** typically presents as a localized parenchymal lesion (Ghon focus) with associated lymphadenopathy (Ghon complex) [1], but rarely results in cavitation because the initial immune response is usually insufficient to cause such extensive tissue destruction. **Analysis of incorrect options:** * **Pleural effusion:** This is a common manifestation of primary TB, often resulting from the rupture of a subpleural focus into the pleural space. * **Fibrocaseous lesion:** Primary TB begins with a Ghon focus, which is pathologically a fibrocaseous granuloma [1]. While secondary TB also shows caseation, it is a fundamental feature of the primary infection as the body attempts to wall off the bacilli. * **Phlyctenular conjunctivitis:** This is a known **hypersensitivity reaction** to the tubercle bacilli protein [2]. It is considered a "delayed-type hypersensitivity" manifestation that can occur during the primary infection stage. **High-Yield Clinical Pearls for NEET-PG:** * **Ghon Complex:** Parenchymal lesion + Lymphangitis + Hilar lymphadenopathy [1]. * **Ranke Complex:** A healed, calcified Ghon complex (visible on X-ray) [1]. * **Location:** Primary TB usually affects the **lower or middle lobes**, whereas Secondary TB favors the **apical/posterior segments of the upper lobes** (due to higher oxygen tension). * **Epithelioid cells:** These are modified macrophages and are the characteristic diagnostic cell type found in TB granulomas [1].

Question 1

What stain is used for degenerated fungi in tissue?

Accepted Answer

Gomori methenamine silver

Answer

Periodic acid-Schiff (PAS)

Answer

Hematoxylin and Eosin (H & E)

Answer

Mucicarmine

Question 2

Lepra cells found in lepromatous leprosy are?

Accepted Answer

Macrophages

Answer

Neutrophils

Answer

Lymphocytes

Answer

Plasma cells

Question 3

All of the following are associated with primary tuberculosis EXCEPT:

Accepted Answer

Cavitary lesion

Answer

Pleural effusion

Answer

Fibrocaseous lesion

Answer

Phlyctenular conjunctivitis

Question 4

The center of a tubercular granuloma is typically formed by which component?

Accepted Answer

Necrotic zone

Answer

T-lymphocytes

Answer

B-lymphocytes

Answer

Langhan's giant cells

Question 5

A 7-year-old child has had worsening performance in school for the past 4 months due to decreased vision. Examination of the right eye shows diffuse punctate inflammation of the cornea and pannus, which is a growth of fibrovascular tissue from the conjunctiva onto the cornea. Microscopic examination of a corneal scraping shows lymphocytes, plasma cells, neutrophils, and scattered corneal epithelial cells that have cytoplasmic inclusion bodies. Which of the following infectious agents is most likely to produce these findings?

Accepted Answer

Chlamydia trachomatis

Answer

Cytomegalovirus

Answer

Herpes simplex virus

Answer

Rubella virus

Question 6

"Ghon focus" is associated with which of the following conditions?

Accepted Answer

Tuberculosis

Answer

Gonorrhea

Answer

Syphilis

Answer

AIDS

Question 7

Miliary tuberculosis is classified as:

Accepted Answer

Post-primary tuberculosis

Answer

Primary tuberculosis

Answer

Extra-pulmonary tuberculosis

Answer

None of the above

Question 8

Which disease is transmitted by all components of blood?

Accepted Answer

Malaria

Answer

Syphilis

Answer

Toxoplasma

Answer

H. pylori

Question 9

A 42-year-old man presents with a constant bad taste in his mouth for the past month. Physical examination reveals white, fluffy patches on the sides of his tongue that cannot be scraped off. A biopsy shows squamous epithelial hyperkeratosis, parakeratosis, and koilocytosis. Immunohistochemical staining for Epstein-Barr virus (EBV) is positive. Which of the following is the most likely risk factor for his oral lesions?

Accepted Answer

HIV infection

Answer

Chronic alcohol abuse

Answer

Diabetes mellitus

Answer

Pernicious anemia

Question 10

Which of the following is associated with leprosy?

Accepted Answer

All of the above

Answer

Foamy histiocytes

Answer

Epithelioid cells

Answer

Noncaseating granulomas

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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