Infectious Diseases Practice Questions

Q: Which of the following conditions is associated with the presence of a Drcke granuloma?

Cerebral malaria. **Explanation:** **Cerebral malaria**, caused by *Plasmodium falciparum*, is characterized by the sequestration of parasitized red blood cells in the cerebral microvasculature [1]. A hallmark histopathological finding in the brain is the **Dürck granuloma** (also known as Dürck node). These are not true granulomas in the immunological sense; rather, they are small foci of **perivascular demyelination and microglial proliferation** surrounding a central area of necrosis or a small hemorrhage (petechiae) caused by microvascular occlusion. **Analysis of Incorrect Options:** * **A. Cat scratch disease:** Characterized by **stellate (star-shaped) necrotizing granulomas** in the lymph nodes, typically caused by *Bartonella henselae*. * **C. Churg-Strauss syndrome (EGPA):** Associated with **allergic granulomas** (extravascular palisading granulomas) and eosinophilic infiltration, but not Dürck nodes. * **D. Coccidioidomycosis:** A fungal infection that typically presents with **suppurative and caseating granulomas** containing thick-walled spherules filled with endospores. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogenesis:** Sequestration occurs due to the expression of **PfEMP-1** (P. falciparum erythrocyte membrane protein 1) on RBCs, which binds to endothelial receptors like **ICAM-1** and **CD36**. [1] * **Gross Pathology:** The brain in cerebral malaria often shows a characteristic **"slate-gray" discoloration** due to the deposition of **hemozoin** (malarial pigment). [1] * **Dürck Granuloma Components:** Central capillary necrosis/hemorrhage + surrounding microglial response + reactive astrocytes. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 400.

Q: Stellate granuloma is found in which condition?

Cat scratch disease. **Explanation:** **Cat scratch disease (CSD)**, caused by the Gram-negative bacterium *Bartonella henselae*, is the classic condition associated with **stellate granulomas**. Pathologically, these are characterized by central irregular (star-shaped) areas of **suppurative necrosis** (containing neutrophils) surrounded by a rim of palisading epithelioid histiocytes and lymphocytes. This unique combination of granulomatous and suppurative inflammation is a hallmark of CSD, typically seen in the regional lymph nodes draining the site of a cat scratch or bite. **Analysis of Incorrect Options:** * **Leprosy:** Characterized by non-caseating granulomas (Tuberculoid) or diffuse histiocytic infiltration without well-formed granulomas (Lepromatous). Stellate morphology is not seen. * **Coccidioidomycosis:** Typically presents with granulomas containing thick-walled **spherules** filled with endospores. While it can cause suppuration, it does not form the characteristic stellate pattern. * **Histoplasmosis:** Features granulomas containing small, intracellular yeast cells (2-4 µm) with a "pseudo-capsule," often found within macrophages. **High-Yield Clinical Pearls for NEET-PG:** * **Differential Diagnosis of Stellate Granulomas:** Apart from Cat scratch disease, stellate granulomas are also seen in **Lymphogranuloma Venereum (LGV)** and occasionally in **Tularemia**. * **Warthin-Starry Stain:** This silver stain is the gold standard for visualizing *Bartonella henselae* in tissue sections. * **Clinical Presentation:** CSD usually presents as painful regional lymphadenopathy (most commonly axillary or cervical) in a child or young adult following contact with a kitten.

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).

Question 1

A neonate born at 36 weeks' gestation manifests severe hydrops fetalis, hepatosplenomegaly, generalized icterus, and scattered ecchymoses of the skin. Laboratory studies show a hemoglobin concentration of 9.4 g/dL and platelet count of 67,000/mm3. Ultrasound of the head shows ventricular enlargement. Death occurs 14 days after birth. At autopsy, there is extensive subependymal necrosis, with microscopic evidence of encephalitis. Within the areas of necrosis, there are large cells containing intranuclear inclusions. Congenital infection with which of the following organisms is most likely to produce these findings?

Accepted Answer

Cytomegalovirus

Answer

Herpes simplex virus

Answer

HIV

Answer

Parvovirus

Question 2

Which of the following statements regarding BK virus infection is true?

Accepted Answer

Causes nephropathy in transplant patients

Answer

Causes progressive multifocal leukoencephalopathy

Answer

20-25% of transplant cases are associated with BK virus nephropathy

Answer

Is a single-stranded DNA virus

Question 3

How does Systemic Miliary TB spread?

Accepted Answer

Artery

Answer

Vein

Answer

Bronchus

Answer

Lymphatic

Question 4

Which of the following conditions is associated with the presence of a Drcke granuloma?

Accepted Answer

Cerebral malaria

Answer

Cat scratch disease

Answer

Churg-Strauss syndrome

Answer

Coccidioidomycosis

Question 5

Which is the best marker for early septicemia?

Accepted Answer

Procalcitonin

Answer

C-reactive protein

Answer

D-dimer

Answer

All of the above

Question 6

Bronchopneumonia due to measles occurs due to which of the following mechanisms?

Accepted Answer

Immunomodulation

Answer

Sinusitis

Answer

Bronchial obstruction

Answer

Aspiration

Question 7

Stellate granuloma is found in which condition?

Accepted Answer

Cat scratch disease

Answer

Leprosy

Answer

Coccidomycosis

Answer

Histoplasmosis

Question 8

In miliary tuberculosis, what is the typical size of the granulomas?

Accepted Answer

1-2 mm

Answer

3-4 mm

Answer

0-1 mm

Answer

4-5 mm

Question 9

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 10

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

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?