Infectious Diseases Practice Questions

Q: In a granuloma, from which cell type are the epithelioid and giant cells derived?

Monocytes. **Explanation:** The formation of a **granuloma** is a hallmark of Type IV (delayed-type) hypersensitivity reactions, typically seen in chronic infections like Tuberculosis or Sarcoidosis. **1. Why Monocytes are correct:** The central cell of a granuloma is the **activated macrophage**. When an offending agent (like *M. tuberculosis*) cannot be easily eliminated, T-helper 1 (Th1) cells secrete **Interferon-gamma (IFN-̳)** [1]. This cytokine activates circulating **monocytes**, which migrate into the tissue and transform into: * **Epithelioid cells:** Macrophages that have gained increased secretory capacity but lost phagocytic ability [1]. They resemble epithelial cells with abundant pink cytoplasm and slipper-shaped nuclei. * **Giant cells:** Formed by the fusion of multiple activated macrophages (e.g., Langhans giant cells with peripheral nuclei or Foreign body giant cells with disorganized nuclei) [1]. **2. Why other options are incorrect:** * **T cells (A):** While Th1 cells are essential for *initiating* the granuloma by secreting IFN-̳, they do not physically transform into epithelioid or giant cells [1]. * **B cells (B) & Plasma cells (C):** These are involved in humoral immunity. While they may be found in the "lymphocytic rim" surrounding a granuloma, they do not differentiate into the characteristic epithelioid cells [1]. **High-Yield Facts for NEET-PG:** * **Key Cytokine:** IFN-̳ is the most important cytokine for macrophage activation and granuloma formation. * **TNF-̑:** Essential for *maintaining* the structural integrity of a granuloma (Anti-TNF drugs can cause breakdown of granulomas and reactivation of TB). * **Langhans Giant Cell:** Characteristic of "immune" granulomas (TB); nuclei are arranged in a **horseshoe pattern** [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109.

Q: The Maltese cross morphology is characteristic of which of the following parasitic infections?

Babesiosis. **Explanation:** The **Maltese cross** appearance is a pathognomonic finding in **Babesiosis**, a tick-borne zoonosis caused by *Babesia microti*. This morphology occurs when the parasite undergoes asexual reproduction (merogony) within host erythrocytes, resulting in a **tetrad of merozoites** joined at their bases. **Why the other options are incorrect:** * **Pneumocystis carinii (jirovecii):** On silver stains (GMS), these appear as crushed ping-pong balls or cup-shaped cysts with a central dark spot, but they do not form tetrads. * **Leishmaniasis:** Characterized by **LD bodies** (amastigotes) within macrophages. These are oval bodies with a distinct nucleus and a rod-shaped kinetoplast, not a cross shape. * **Cryptococcosis:** While *Cryptococcus neoformans* exhibits a "Maltese cross" appearance under **polarized light** when stained with specific dyes (due to the birefringence of its capsule), it is a fungus, not a parasite. In the context of parasitic morphology on a standard blood smear, the term specifically refers to Babesia. **NEET-PG High-Yield Pearls:** * **Vector:** *Ixodes scapularis* tick (the same vector as Lyme disease). * **Diagnosis:** Thick and thin peripheral blood smears (Giemsa/Wright stain). * **Distinction from Malaria:** Unlike *Plasmodium falciparum*, Babesia lacks hemozoin pigment and does not have a gametocyte stage [1]. * **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria. It is particularly severe in asplenic patients. * **Treatment:** Atovaquone + Azithromycin (preferred) or Clindamycin + Quinine. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 400.

Q: Rasmussen's aneurysm involves which of the following?

Pulmonary artery aneurysm. **Explanation:** **Rasmussen’s aneurysm** is a clinical phenomenon associated with **chronic cavitary pulmonary tuberculosis**. It refers to an inflammatory pseudoaneurysm of a **pulmonary artery** branch located within the wall of a tuberculous cavity. 1. **Why the correct answer is right:** In chronic tuberculosis, the progressive inflammation and necrosis (caseation) of the lung parenchyma eventually erode the walls of adjacent pulmonary arteries. As the surrounding lung tissue is destroyed, the arterial wall thins and weakens, leading to a localized dilation or "aneurysm." If this aneurysm ruptures into the cavity, it results in massive, life-threatening **hemoptysis**. 2. **Why the incorrect options are wrong:** * **Option A (Bronchial artery):** While bronchial arteries are the most common source of *general* hemoptysis in TB (due to hypertrophy under high pressure), they do not form the specific "Rasmussen’s aneurysm." * **Option C & D (Vertebral/Posterior intercostal):** These are systemic arteries. While vertebral arteries can be involved in cervical trauma or connective tissue disorders, and intercostal arteries in Coarctation of the Aorta, they have no pathological link to pulmonary TB cavities. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Usually occurs in the upper lobes (where TB cavities are most common). * **Pathology:** It is technically a *pseudoaneurysm* because it lacks all three layers of the arterial wall. * **Radiology/Management:** Diagnosed via CT Angiography; the treatment of choice for an unstable patient is **Bronchial/Pulmonary Artery Embolization (BAE)**. * **Differential:** Do not confuse with **Dieulafoy’s lesion** (a vascular malformation in the bronchus) which can also cause massive hemoptysis.

Question 1

What is the most common tumor associated with AIDS?

Accepted Answer

Kaposi's sarcoma

Answer

Carcinoma

Answer

Melanoma

Answer

Ewing's sarcoma

Question 2

A 24-year-old man is infected with HIV during a sexual encounter. During the asymptomatic latent phase of his infection, the virus is actively proliferating and can be found in association with which of the following?

Accepted Answer

Follicular dendritic cells in lymph nodes

Answer

B lymphocytes

Answer

Ganglion cells

Answer

Oligodendrocytes

Question 3

In a granuloma, from which cell type are the epithelioid and giant cells derived?

Accepted Answer

Monocytes

Answer

T cells

Answer

B cells

Answer

Plasma cells

Question 4

Which disease is transmitted by all components of blood?

Accepted Answer

Malaria

Answer

Syphilis

Answer

Toxoplasma

Answer

H. pylori

Question 5

The Maltese cross morphology is characteristic of which of the following parasitic infections?

Accepted Answer

Babesiosis

Answer

Pneumocystis carinii

Answer

Leishmaniasis

Answer

Cryptococcosis

Question 6

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 7

A 52-year-old man presents with fever and cough productive of thick, gelatinous sputum that has worsened over 4 days. Physical examination reveals a temperature of 38.2°C. Auscultation of the chest shows diffuse crackles at the right lung base. Laboratory studies show a WBC count of 13,240/mm³ with 71% segmented neutrophils, 8% bands, 15% lymphocytes, and 6% monocytes. A sputum Gram stain reveals Gram-negative bacilli with mucoid capsules. His condition improves after a course of gentamicin therapy. Which of the following complications of this infection is he most likely to develop?

Accepted Answer

Abscess formation

Answer

Adenocarcinoma

Answer

Bullous emphysema

Answer

Cavitary granulomas

Question 8

Rasmussen's aneurysm involves which of the following?

Accepted Answer

Pulmonary artery aneurysm

Answer

Bronchial artery aneurysm

Answer

Vertebral artery aneurysm

Answer

Posterior intercostal artery aneurysm

Question 9

Warthin-Finkeldey giant cells are seen in which of the following conditions?

Accepted Answer

Measles

Answer

Mumps

Answer

Rubella

Answer

Polio

Question 10

All of the following organisms can cause serious infection in chronic granulomatous disease except?

Accepted Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Pseudomonas

Answer

Haemophilus influenzae

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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