Infectious Diseases Practice Questions

Q: Which of the following is a special stain used to diagnose fungal hyphae in tissues?

Methenamine silver. **Explanation:** **1. Why Methenamine Silver (GMS) is correct:** Gomori Methenamine Silver (GMS) is the gold standard special stain for identifying fungal organisms in tissue sections [1]. The underlying principle is an **oxidation-reduction reaction**: chromic acid oxidizes the polysaccharides (glucans) in the fungal cell wall to form aldehydes. These aldehydes then reduce the silver nitrate in the methenamine silver solution to metallic silver, staining the fungal hyphae and spores **black** against a green background [1]. It is highly sensitive for *Candida, Aspergillus, and Pneumocystis jirovecii*. **2. Analysis of Incorrect Options:** * **Masson Trichrome:** Used primarily to differentiate between **collagen (blue/green)** and smooth muscle (red). It is the stain of choice for diagnosing liver cirrhosis (fibrosis). * **Congo Red:** Specifically used to identify **Amyloid** deposits. Under polarized light, it exhibits a characteristic "apple-green birefringence." * **Alcian Blue:** Used to detect **acidic mucopolysaccharides** (mucin). It is commonly used to diagnose Barrett's esophagus (staining goblet cells) and certain types of mesotheliomas. **3. NEET-PG High-Yield Pearls:** * **PAS (Periodic Acid-Schiff):** Another common stain for fungi; it stains the cell walls **magenta/bright pink** [1]. * **Mucicarmine:** Specifically used to identify the capsule of ***Cryptococcus neoformans*** (stains it bright red) [1]. * **India Ink:** Used for rapid identification of *Cryptococcus* in CSF (negative staining). * **Oil Red O / Sudan Black:** Used for staining **lipids/fats** (requires frozen sections). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 362, 393-394.

Q: All of the following are true about amoebiasis except?

Coagulative necrosis. **Explanation:** The correct answer is **D (Coagulative necrosis)** because *Entamoeba histolytica* characteristically causes **liquefactive necrosis**, not coagulative. The parasite releases proteolytic enzymes (histolysins) and pore-forming proteins (amoebapores) that dissolve host tissues, leading to a liquid, necrotic mass. Coagulative necrosis is typically associated with ischemia (infarction) in solid organs. **Analysis of other options:** * **A. Flask-shaped ulcers:** This is the classic pathological hallmark of intestinal amoebiasis. The parasite penetrates the mucosal layer and spreads laterally in the submucosa, creating an ulcer with a narrow neck and a broad base. * **B. Disease affects the caecum and ascending colon:** These are the most common sites for intestinal amoebiasis because the slow transit of fecal matter in the large intestine allows the trophozoites more time to colonize and invade the mucosa. * **C. Anchovy pus in the liver:** This refers to the characteristic appearance of an Amoebic Liver Abscess (ALA) aspirate. It is a sterile, odorless, reddish-brown fluid composed of liquefied hepatocytes and blood, resembling anchovy sauce. **NEET-PG High-Yield Pearls:** * **Diagnostic Gold Standard:** Stool microscopy for **quadrinucleate cysts** (chronic/carrier) or **trophozoites with ingested RBCs** (active dysentery). * **Liver Abscess:** Usually occurs in the **right lobe** (due to portal blood flow) and is "sterile" (trophozoites are found in the abscess wall, not the pus). * **Treatment:** Metronidazole/Tinidazole for tissue stages; Diloxanide furoate or Paromomycin for luminal stages (to prevent relapse).

Q: Which of the following stains is used to demonstrate yeast forms of Cryptococci in tissue sections?

Mucicarmine. **Explanation:** **1. Why Mucicarmine is correct:** *Cryptococcus neoformans* is unique among pathogenic fungi because it possesses a thick **polysaccharide capsule** composed of glucuronoxylomannan. **Mayer’s Mucicarmine** stain specifically targets these acidic mucopolysaccharides, staining the capsule a vibrant **rose-red/pink** against a yellow background. This is the gold standard for demonstrating the yeast forms in tissue sections (histopathology), helping to differentiate it from other non-encapsulated yeasts like *Candida*. **2. Why the other options are incorrect:** * **Perl’s Prussian Blue:** Used to detect **Iron** (ferric ions). It is the stain of choice for identifying hemosiderin in tissues (e.g., in Hemochromatosis). * **Sudan Black B:** A lipophilic stain used to demonstrate **Lipids/Fats**. In hematology, it is used to differentiate Acute Myeloid Leukemia (AML) from Acute Lymphoblastic Leukemia (ALL). * **Masson Fontana:** Used to detect **Melanin**. While *Cryptococcus* does produce melanin in its cell wall (visible with this stain), Mucicarmine is more specific and classically associated with the capsule in tissue sections. **Clinical Pearls for NEET-PG:** * **India Ink:** Used for CSF (negative staining); highlights the translucent capsule against a dark background. * **Gomori Methenamine Silver (GMS) & PAS:** General fungal stains that stain the cell wall of *Cryptococcus* but not the capsule. * **Latex Agglutination Test:** Detects the capsular antigen in CSF/Serum; more sensitive than India Ink. * **Culture:** Sabouraud Dextrose Agar (SDA) shows creamy, mucoid colonies. Niger Seed/Bird Seed Agar is used to demonstrate melanin production (brown-black colonies).

Q: Which of the following statements is NOT TRUE regarding primary Herpes Simplex Virus (HSV) infections?

Occurs epidemically.. **Explanation:** The correct answer is **C (Occurs epidemically)** because Herpes Simplex Virus type 1 (HSV-1) infections are **endemic**, not epidemic. HSV is ubiquitous worldwide; most individuals are infected in childhood through direct contact with infected secretions (like saliva). It does not occur in large-scale seasonal outbreaks or localized epidemics but rather persists in the population through continuous transmission and lifelong latency. **Analysis of other options:** * **Option A & B:** Primary HSV-1 infection in children most commonly manifests as **Acute Herpetic Gingivostomatitis** [1]. It characteristically involves the **anterior portion of the mouth**, including the gingiva (gums), tongue, and labial mucosa, presenting with painful vesicles that rupture into ulcers [1]. * **Option D:** Primary infections are frequently preceded by **prodromal symptoms** such as high-grade fever, malaise, irritability, and regional lymphadenopathy before the appearance of oral lesions [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Latency:** HSV-1 remains latent in the **Trigeminal ganglion**, while HSV-2 typically resides in the **Sacral ganglia**. * **Diagnosis:** The gold standard for rapid bedside diagnosis is the **Tzanck Smear**, which shows **Multinucleated Giant Cells** with Cowdry Type A inclusion bodies [1]. * **Histopathology:** Look for "acantholysis," "ballooning degeneration" of keratinocytes, and "margination of chromatin" [1]. * **Encephalitis:** HSV-1 is the most common cause of sporadic fatal viral encephalitis, typically involving the **temporal lobes** [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 365-366. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, p. 1278.

Question 1

Which of the following is a special stain used to diagnose fungal hyphae in tissues?

Accepted Answer

Methenamine silver

Answer

Masson Trichrome

Answer

Congo red

Answer

Alcian blue

Question 2

All of the following are true about amoebiasis except?

Accepted Answer

Coagulative necrosis

Answer

Flask-shaped ulcers

Answer

Disease affects the caecum and ascending colon

Answer

Anchovy pus in the liver

Question 3

Glomus cells are found in which of the following?

Accepted Answer

Carotid body tumor

Answer

Thyroid carcinoma

Answer

Liver carcinoma

Answer

None of the above

Question 4

Which of the following stains is used to demonstrate yeast forms of Cryptococci in tissue sections?

Accepted Answer

Mucicarmine

Answer

Perl's

Answer

Sudan black

Answer

Masson Fontana

Question 5

A child presents with a 15-day history of cough and examination reveals cervical lymphadenopathy. Lymph node biopsy shows Langerhans giant cells. What is the most likely diagnosis?

Accepted Answer

Tuberculosis

Answer

Leprosy

Answer

Sarcoidosis

Answer

Syphilis

Question 6

In primary tuberculosis, all of the following may be seen except?

Accepted Answer

Cavitation

Answer

Caseation

Answer

Calcification

Answer

Langhans giant cell

Question 7

A 20-year-old man who has multiple sexual partners and does not use barrier precautions has had a non-tender ulcer on his penis for the past week. On physical examination, the 0.6-cm lesion has a firm, erythematous base and sharply demarcated borders. The lesion is scraped, and the microscopic darkfield examination is positive for motile spirochetes. Which of the following inflammatory processes is most likely to accompany this infection?

Accepted Answer

Perivascular inflammation with plasma cells

Answer

Acute inflammation with abscess formation

Answer

Granulomatous inflammation with caseation

Answer

Gummatous inflammation with necrosis

Question 8

In Tuberculosis, what type of cells primarily provide immunity?

Accepted Answer

CD4+ cells

Answer

CD8+ cells

Answer

IgG antibodies

Answer

IgM antibodies

Question 9

Foaming liver is seen in which of the following conditions?

Accepted Answer

Gas gangrene

Answer

Organophosphorus Poisoning

Answer

Actinomycosis

Answer

Anthrax

Question 10

Which of the following statements is NOT TRUE regarding primary Herpes Simplex Virus (HSV) infections?

Accepted Answer

Occurs epidemically.

Answer

Primarily affects the anterior portion of the mouth.

Answer

Causes acute gingivostomatitis.

Answer

Is often preceded by prodromal symptoms.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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