Infectious Diseases Practice Questions

Q: Which of the following infectious diseases is the most likely cause of granuloma formation?

Leprosy. ***Leprosy*** - Leprosy is a classic example of a chronic infection that leads to **granuloma formation**, particularly in its tuberculoid and borderline tuberculoid forms [1]. - The immune response to *Mycobacterium leprae* involves the formation of **macrophage-rich granulomas** to contain the infection, often affecting the skin and nerves [2]. *Syphilis* - While syphilis can cause **gummas**, which are granulomatous lesions, these are typically seen in tertiary syphilis and are less characteristic of granuloma formation across all stages compared to leprosy [3]. - Gummas are often **necrotic** and can be widespread, but the primary pathology of syphilis involves vasculitis and inflammation rather than classic granulomatous tissue reaction. *Cat scratch disease* - Caused by *Bartonella henselae*, this infection typically leads to **lymphadenopathy** with **stellate microabscesses** and sometimes epithelioid granulomas, but the granulomas are usually less prominent and distinct than those seen in leprosy. - The histological features are dominated by **suppurative necrosis** within lymphoid tissue rather than well-formed, non-caseating granulomas. *Trench fever* - Trench fever, caused by *Bartonella quintana*, primarily presents with **fever**, **bone pain**, and a **maculopapular rash**. - It does not typically cause **granuloma formation**; the pathology is more related to bacteremia and inflammation of vascular endothelium. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 638-639. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360.

Q: In spinal tuberculosis, the commoner route of spread is:

Blood. ***Blood*** - Spinal tuberculosis, also known as **Pott's disease**, primarily spreads via the **hematogenous route** [1] from a primary infection elsewhere, most commonly the lungs [1]. - Bacilli reach the vertebral bodies through the **arterial circulation** or via the **paravertebral (Batson's) venous plexus**, which allows retrograde spread without passing through the lungs. - The rich vascular supply of the vertebral bodies, particularly the **metaphyseal regions adjacent to intervertebral discs**, facilitates the deposition and growth of **Mycobacterium tuberculosis**. - This accounts for the typical involvement of two adjacent vertebrae with disc destruction in spinal TB [2]. *Lymphatics* - While lymphatic spread is important in other forms of tuberculosis, it is **not the primary route** for the initial seeding of the spine. - Lymphatic involvement tends to be secondary to established bony lesions or occurs in cases of extensive soft tissue involvement with paravertebral abscess formation. *Direct spread* - Direct spread is **rare** in spinal tuberculosis and typically occurs from an adjacent infected structure, such as a psoas abscess that erodes into the spine or from mediastinal lymph nodes. - It is not the most common initial mode of dissemination to the vertebrae. *All of the options* - While other routes like lymphatics and direct spread can contribute in specific circumstances, **hematogenous spread (via blood)** is overwhelmingly the most common and primary route for spinal tuberculosis. - The question asks for the "commoner route," which is definitively the bloodstream. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 379-380. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1197-1198.

Q: The following pathological features are associated with Plasmodium falciparum except-

Tissue phase. ***Tissue phase*** (Correct Answer - NOT associated with P. falciparum) - While *Plasmodium falciparum* does have a **hepatic (liver) phase** in its life cycle, the term "**tissue phase**" specifically refers to the **persistent dormant liver stage (hypnozoites)** seen in **relapsing malarias** [1]. - **Hypnozoites** are found in *Plasmodium vivax* and *Plasmodium ovale* but **NOT in *P. falciparum***. - These dormant forms can reactivate months or years later, causing relapse—a feature absent in *P. falciparum* infection. *Cytoadherence* (Incorrect - IS associated with P. falciparum) - This is a **key virulence factor** of *P. falciparum*, where **infected red blood cells (iRBCs)** bind to the **vascular endothelium** via adhesion molecules (PfEMP1) [1]. - This binding leads to **sequestration** in deep capillaries and avoidance of splenic clearance, contributing to severe malaria pathology [1]. *Sequestration* (Incorrect - IS associated with P. falciparum) - Refers to the confinement of **iRBCs** in the **deep microvasculature** of vital organs such as the brain, lungs, and kidneys. - Results from **cytoadherence** and is the primary mechanism behind severe complications like **cerebral malaria** in *P. falciparum*. *Rosetting* (Incorrect - IS associated with P. falciparum) - Involves **iRBCs** binding to uninfected red blood cells, forming **rosette structures**. - This phenomenon impedes blood flow in capillaries and contributes to **microvascular obstruction** and tissue hypoxia in severe *P. falciparum* infections. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400.

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

Silver methenamine. ***Silver methenamine*** - **Grocott's methenamine silver (GMS) stain** is widely used to visualize **fungal elements** in tissue sections. - It works by staining the **polysaccharides** in the fungal cell walls, making them appear **black** against a green or grayish-green background. *Masson trichome* - This stain is primarily used to differentiate **collagen fibers** from smooth muscle and other tissues. - It stains **collagen blue or green**, cytoplasm red, and nuclei black, and is not suitable for identifying fungi. *Congo Red* - **Congo Red stain** is used to identify **amyloid deposits** in tissues, which appear red-pink and show apple-green birefringence under polarized light [1]. - It does not specifically stain fungal hyphae. *Alizarin Red* - **Alizarin Red S stain** is used to demonstrate the presence of **calcium deposits** in tissues. - It stains calcium salts **orange-red** or scarlet, and is not utilized for fungal identification. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 268-269.

Q: Which of the following is true regarding globi in a patient with lepromatous leprosy?

Consists of macrophages filled with AFB. ***Consists of macrophages filled with AFB*** - **Globi** are characteristic microscopic structures found in lepromatous leprosy, representing large aggregates of **Mycobacterium leprae** within **macrophages** [1]. - These macrophages are heavily parasitized with **acid-fast bacilli (AFB)**, which are the bacteria causing leprosy [1]. *Consists of lipid-laden macrophages* - While macrophages in leprosy can contain lipids, **globi** specifically refer to the aggregation of these macrophages *filled primarily with bacteria*, not just lipid droplets [1]. - The lipid content is secondary to the bacterial accumulation and degradation, not the defining characteristic of a globus. *Consists of neutrophils filled with bacteria* - **Neutrophils** are the primary phagocytes in acute bacterial infections, but they are generally less involved in chronic granulomatous diseases like leprosy compared to macrophages [2]. - **Globi** are fundamentally macrophage-derived structures, not neutrophil-derived. *Consists of activated lymphocytes* - **Lymphocytes** are crucial for the immune response in leprosy, particularly in the tuberculoid form, but they do not form globi [1]. - **Globi** represent bacterial burden within host cells, which are typically macrophages, not aggregates of lymphocytes [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360.

Q: Lepra cells are -

Histiocytes. ***Histiocytes*** - **Histiocytes** (a type of **macrophage**) are the primary cells infected by *Mycobacterium leprae* [1]. - Within these cells, the bacteria can multiply and form large aggregates, leading to the characteristic foamy appearance of **"lepra cells"** when viewed microscopically [1]. *Neutrophils* - **Neutrophils** are primarily involved in the acute inflammatory response and phagocytosis of bacteria, but they are not the main host cell for *Mycobacterium leprae*. - They are typically associated with pyogenic infections rather than chronic granulomatous diseases like leprosy. *Plasma cells* - **Plasma cells** are differentiated B lymphocytes responsible for producing antibodies. - While they play a role in the immune response to various infections, they are not directly infected by *Mycobacterium leprae* or involved in the formation of lepra cells. *Lymphocytes* - **Lymphocytes** (T and B cells) are crucial for adaptive immunity and the cell-mediated immune response in leprosy. - However, they are not the cells that directly harbor and are transformed into "lepra cells" by the *Mycobacterium leprae* bacteria. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386.

Q: "Medlar bodies" are seen in

Chromblastomycosis. ***Chromblastomycosis*** - "**Medlar bodies**" (also known as muriform cells or sclerotic bodies) are characteristic findings in the tissue biopsy of patients with **chromoblastomycosis**. - These are thick-walled, septate, dark brown fungal cells that reproduce by septation and are crucial for the diagnosis of this chronic fungal infection. *Coccidiomycosis* - This deep fungal infection is characterized by thick-walled **spherules containing endospores** in tissue, rather than Medlar bodies [1]. - It primarily affects the lungs but can disseminate to other organs. *Sporotrichosis* - The classic histological finding in sporotrichosis is the presence of **cigar-shaped budding yeasts** in tissue, especially in the suppurative granulomas. - **Asteroid bodies**, which are yeasts surrounded by eosinophilic material, may also be seen. *Histoplasmosis* - This fungal infection is identified by small, **intracellular budding yeasts** (2-4 µm) found within macrophages in tissue samples [1]. - It commonly affects the lungs and can disseminate, particularly in immunocompromised individuals [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 717.

Q: Ghon's focus with hilar lymphadenopathy is known as -

Tuberculoid Leprosy (TL). ***Tuberculoid Leprosy (TL)*** - This question describes a finding related to **tuberculosis**, not leprosy. **Ghon's focus** and **hilar lymphadenopathy** are classic signs of primary tuberculosis infection [1]. - While this option is incorrect in the context of the question's premise (it discusses tuberculosis, not leprosy), among the leprosy types provided, none directly relate to the described imaging findings [2]. Assuming a misinterpretation and seeking the correct leprosy definition. *Borderline Tuberculoid Leprosy* - This form of leprosy lies between tuberculoid and borderline lepromatous leprosy, characterized by a few **skin lesions** and moderate nerve involvement [2]. - It does not involve **Ghon's focus** or **hilar lymphadenopathy**, which are features of tuberculosis [1]. *Lepromatous Leprosy (LL)* - This is a severe, multi-bacillary form of leprosy with diffuse infiltration of skin, multiple **nodules**, and widespread **nerve damage** [2]. - It has no association with **Ghon's focus** or **hilar lymphadenopathy**. *Indeterminate Leprosy* - This is the earliest form of leprosy, characterized by a single patch or a few poorly defined **skin lesions**, with minimal or no nerve involvement [2]. - It does not present with **Ghon's focus** or **hilar lymphadenopathy**.

Q: Systemic miliary TB occurs when the spread of Mycobacterium tuberculosis happens via which route?

Hematogenous. ***Hematogenous*** - **Miliary TB** is characterized by the widespread dissemination of *Mycobacterium tuberculosis* to multiple organs via the **bloodstream (hematogenous route)**. - Hematogenous spread allows bacilli to be carried throughout the systemic circulation, leading to the formation of small, millet-seed-sized lesions in various tissues including lungs, liver, spleen, bone marrow, and other organs. - This typically occurs when bacilli from a primary focus erode into a blood vessel and gain access to the circulation. *Direct dissemination* - This route involves the local spread of infection from one tissue or organ directly to an adjacent one, without entering the bloodstream. - It does not account for the widespread, systemic involvement seen in miliary TB. *Lymphatic* - **Lymphatic spread** typically leads to involvement of regional lymph nodes and can contribute to dissemination, but it is not the primary route for the widespread, systemic involvement characteristic of miliary TB. - While bacilli can reach the bloodstream via the thoracic duct, the key mechanism for systemic miliary spread is direct hematogenous dissemination. *Aerial* - **Aerial spread** primarily refers to the transmission of *Mycobacterium tuberculosis* from person to person via airborne droplets, or the initial infection of the lungs. - It is the route of initial infection for pulmonary TB, not the mechanism for systemic dissemination within an infected individual leading to miliary disease.

Question 1

Which of the following infectious diseases is the most likely cause of granuloma formation?

Accepted Answer

Leprosy

Answer

Syphilis

Answer

Cat scratch disease

Answer

Trench fever

Question 2

Earliest feature of TB:

Accepted Answer

Lymphocytosis

Answer

Caseation

Answer

Granuloma

Answer

Langerhans' Giant cells

Question 3

In spinal tuberculosis, the commoner route of spread is:

Accepted Answer

Blood

Answer

Lymphatics

Answer

All of the options

Answer

Direct spread

Question 4

The following pathological features are associated with Plasmodium falciparum except-

Accepted Answer

Tissue phase

Answer

Cytoadherence

Answer

Sequestration

Answer

Rosetting

Question 5

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

Accepted Answer

Silver methenamine

Answer

Masson trichrome

Answer

Congo Red

Answer

Alizarin Red

Question 6

Which of the following is true regarding globi in a patient with lepromatous leprosy?

Accepted Answer

Consists of macrophages filled with AFB

Answer

Consists of lipid-laden macrophages

Answer

Consists of neutrophils filled with bacteria

Answer

Consists of activated lymphocytes

Question 7

Lepra cells are -

Accepted Answer

Histiocytes

Answer

Neutrophils

Answer

Plasma cells

Answer

Lymphocytes

Question 8

"Medlar bodies" are seen in

Accepted Answer

Chromblastomycosis

Answer

Coccidiomycosis

Answer

Sporotrichosis

Answer

Histoplasmosis

Question 9

Ghon's focus with hilar lymphadenopathy is known as -

Accepted Answer

Tuberculoid Leprosy (TL)

Answer

Borderline Tuberculoid Leprosy

Answer

Lepromatous Leprosy (LL)

Answer

Indeterminate Leprosy

Question 10

Systemic miliary TB occurs when the spread of Mycobacterium tuberculosis happens via which route?

Accepted Answer

Hematogenous

Answer

Direct dissemination

Answer

Lymphatic

Answer

Aerial

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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