Infectious Diseases Practice Questions

Q: Indirectly cytopathic viruses kill cells by provoking which of the following?

An immune response. Viruses cause cell injury and death via two primary mechanisms: **Directly cytopathic** and **Indirectly cytopathic**. [1] **1. Why the Correct Answer is Right:** In **indirectly cytopathic** infections, the virus itself does not cause significant damage to the host cell during its replication cycle. Instead, the cell death is a result of the host’s own **immune response**. The virus expresses foreign antigens on the cell surface (via MHC Class I molecules), which are recognized by **CD8+ Cytotoxic T-lymphocytes (CTLs)**. These CTLs then kill the infected cell to eliminate the viral reservoir. A classic example is **Hepatitis B**, where the hepatocyte damage is not caused by the virus, but by the T-cell-mediated immune attack against infected liver cells. **2. Why the Incorrect Options are Wrong:** * **A. Injury to DNA:** While some viruses (like oncogenic viruses) can integrate into or damage host DNA, this is not the defining mechanism of "indirect" cytopathicity. [1] * **C. Injury to the cell membrane:** This is typically a feature of **directly cytopathic** viruses (e.g., Poliovirus or Rhinoviruses) that interfere with host protein synthesis or cause membrane lysis during viral release. [1] * **D. An influx of potassium:** Cell injury usually leads to an **efflux of potassium** and an **influx of calcium** and sodium due to the failure of ATP-dependent pumps. **High-Yield Clinical Pearls for NEET-PG:** * **Directly Cytopathic:** Damage is proportional to viral replication (e.g., Polio, CMV). [1] * **Indirectly Cytopathic:** Damage is proportional to the host immune vigor (e.g., HBV, HCV). * **Councilman bodies:** These are apoptotic hepatocytes often seen in viral hepatitis, representing the end result of this indirect T-cell mediated killing. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 356-357.

Q: What is the typical cell found in the lymphoid tissue of a case of measles?

Warthin Finkeldey cells. ### Explanation **Correct Answer: C. Warthin-Finkeldey cells** **Warthin-Finkeldey cells** are the pathognomonic histological hallmark of **Measles (Rubeola)**. These are large, multinucleated giant cells formed by the fusion of infected lymphocytes and macrophages. They are typically found in lymphoid tissues such as the tonsils, lymph nodes, spleen, and appendix during the prodromal phase of the disease. These cells can contain up to 100 nuclei and may show both intracytoplasmic and intranuclear eosinophilic inclusion bodies. **Analysis of Incorrect Options:** * **A. Guarnieri bodies:** These are eosinophilic cytoplasmic inclusion bodies found in epithelial cells infected with **Variola (Smallpox)** or Vaccinia virus. They represent the site of viral replication in the cytoplasm. * **B. Cowdry bodies:** These are intranuclear eosinophilic inclusions. **Cowdry Type A** is associated with **Herpes Simplex Virus (HSV)** and Varicella-Zoster Virus (VZV), while **Cowdry Type B** is seen in Poliovirus and Adenovirus. * **D. Councilman bodies:** These are eosinophilic, apoptotic hepatocytes (acidophilic bodies) typically seen in the liver of patients with **Yellow Fever** or Viral Hepatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Measles Inclusions:** Unlike many viruses, Measles produces **both** intranuclear and intracytoplasmic inclusion bodies. * **Koplik’s spots:** Small white spots on an erythematous base (grains of salt on a red sea) found on the buccal mucosa opposite the lower 2nd molar; they are the clinical pathognomonic sign. * **Complications:** The most common complication is Otitis Media; the most common cause of death is Pneumonia (Hecht’s giant cell pneumonia). * **SSPE:** Subacute Sclerosing Panencephalitis is a late-onset, progressive neurological complication caused by a defective measles virus.

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.

Question 1

Indirectly cytopathic viruses kill cells by provoking which of the following?

Accepted Answer

An immune response

Answer

Injury to DNA

Answer

Injury to the cell membrane

Answer

An influx of potassium

Question 2

What is the typical cell found in the lymphoid tissue of a case of measles?

Accepted Answer

Warthin Finkeldey cells

Answer

Guarnieri bodies

Answer

Cowdry bodies

Answer

Councilman bodies

Question 3

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 4

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 5

How does Systemic Miliary TB spread?

Accepted Answer

Artery

Answer

Vein

Answer

Bronchus

Answer

Lymphatic

Question 6

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 7

Which is the best marker for early septicemia?

Accepted Answer

Procalcitonin

Answer

C-reactive protein

Answer

D-dimer

Answer

All of the above

Question 8

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

Accepted Answer

Immunomodulation

Answer

Sinusitis

Answer

Bronchial obstruction

Answer

Aspiration

Question 9

Stellate granuloma is found in which condition?

Accepted Answer

Cat scratch disease

Answer

Leprosy

Answer

Coccidomycosis

Answer

Histoplasmosis

Question 10

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

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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