Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 151: A patient from Himachal Pradesh gets a thorn prick and subsequently presents with a verrucous lesion on feet which on microscopy revealed "Copper penny bodies". The diagnosis is

A. Sporothrix
B. Chromoblastomycosis (Correct Answer)
C. Verruca vulgaris
D. Eumycetoma

Explanation: ***Chromoblastomycosis*** - The presence of **"copper penny bodies" (sclerotic bodies or Medlar bodies)** on microscopy is pathognomonic for chromoblastomycosis. - This chronic fungal infection typically presents as **verrucous lesions** on the skin, often in exposed areas like the feet, following **traumatic inoculation**, such as a thorn prick. *Eumycetoma* - Characterized by the formation of **grains or granules** composed of fungal hyphae within subcutaneous tissue, usually with **multiple draining sinuses**. - While it can be caused by a thorn prick and affect the feet, it does not typically show "copper penny bodies" on microscopy. *Sporothrix* - Causes **sporotrichosis**, which often presents as **lymphocutaneous nodules** that ulcerate and follow lymphatic drainage, or fixed cutaneous lesions. - Microscopic examination typically reveals **cigar-shaped budding yeasts** in tissue, not copper penny bodies. *Verruca vulgaris* - This is a common **viral wart** caused by the **Human Papillomavirus (HPV)**, presenting as a raised, rough, cauliflower-like papule [1]. - Histologically, it shows **koilocytes** (HPV-infected keratinocytes), but no fungal elements like "copper penny bodies." [1] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, p. 1178.

Question 152: Refrigerated blood stored up to 48 hours before transfusion can destroy which of the following ?

A. Hepatitis B
B. P. Vivax
C. Treponema pallidum (Correct Answer)
D. HIV

Explanation: ***Treponema pallidum*** - *Treponema pallidum*, the causative agent of **syphilis**, is highly sensitive to cold temperatures and **does not survive well in refrigerated blood** stored for more than a few days (typically 24-48 hours). - This characteristic makes the risk of **transfusion-transmitted syphilis** extremely low for stored blood components. *Hepatitis B* - **Hepatitis B virus (HBV)** is very hardy and can survive for extended periods, even in refrigerated blood. - Blood donations are routinely screened for HBV to prevent **transfusion-associated hepatitis**. *P. Vivax* - *Plasmodium vivax*, one of the species causing **malaria**, can survive in refrigerated blood, as the parasites can remain viable within red blood cells [1]. - Transmission of malaria through blood transfusion is a known risk, especially in endemic areas, and is not mitigated by refrigeration alone. *HIV* - **Human Immunodeficiency Virus (HIV)** can survive in refrigerated whole blood and blood components for the duration of their typical storage periods. - Therefore, strict screening of blood donors for HIV antibodies and antigens is crucial to prevent **transfusion-related HIV transmission**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400.

Question 153: A person died of HIV infection. Lung Autopsy performed in this person showed intranuclear basophilic inclusions. His CD4 count was less than 100/uL. Which is the most probable diagnosis?

A. Herpes infection
B. CMV (Correct Answer)
C. Pneumocystis jirovecii
D. ARDS

Explanation: ***CMV*** - **Cytomegalovirus (CMV)** infection commonly causes **intranuclear basophilic inclusions** (owl's eye inclusions) in infected cells, particularly in the lungs of immunocompromised patients like those with advanced HIV. - A CD4 count **below 100 cells/µL** signifies severe immunosuppression, making the patient highly susceptible to opportunistic infections such as CMV pneumonia [1]. *Herpes infection* - Herpes viruses also cause intranuclear inclusions, but these are typically **eosinophilic (Cowdry type A bodies)**, not basophilic [2]. - While herpes can cause pneumonia in immunocompromised individuals, the specific description of basophilic inclusions points away from herpes and towards CMV. *Pneumocystis jirovecii* - *Pneumocystis jirovecii* causes **pneumonia** (PJP), a common opportunistic infection in HIV patients with low CD4 counts, but it does **not form intranuclear inclusions** in host cells [1]. - Histologically, PJP is characterized by foamy intra-alveolar exudates containing cysts and trophozoites, not viral inclusions [1]. *ARDS* - **Acute Respiratory Distress Syndrome (ARDS)** is a clinical syndrome characterized by acute lung injury and respiratory failure, and it is a *consequence* of severe underlying conditions, not a primary infectious diagnosis. - ARDS is diagnosed based on clinical and radiological findings (bilateral infiltrates, severe hypoxemia) and **does not present with specific intranuclear inclusions** as a diagnostic pathological feature. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 318-319. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 365-366.

Question 154: Rickettsial infections cause 30% mortality due to?

A. Endothelial injury (Correct Answer)
B. Renal failure
C. Hemodynamic instability
D. Endocarditis

Explanation: ***Endothelial injury*** - **Rickettsiae** are obligate intracellular bacteria that primarily target and replicate within **endothelial cells**, leading to widespread **endothelial injury** [1]. - This damage results in increased **vascular permeability**, **edema**, and subsequent organ dysfunction, contributing to the high mortality rate in severe cases [1]. *Renal failure* - While **renal failure** can be a complication of severe rickettsial infections due to **hypoperfusion** and direct injury, it is a *consequence* of the initial widespread endothelial damage, not the primary cause of high mortality [1]. - The systemic nature of the endothelial damage affects multiple organs, including the kidneys, leading to multifactorial organ dysfunction rather than isolated renal pathology as the main driver of death [1]. *Hemodynamic instability* - **Hemodynamic instability**, characterized by **hypotension** and **shock**, is a critical manifestation of severe rickettsial infection [1]. However, this instability is a *result* of the widespread **fluid extravasation** and **vasodilation** caused by extensive **endothelial injury**. - The direct damage to the endothelium precedes and drives the hemodynamic changes that contribute to patient demise [1]. *Endocarditis* - **Endocarditis** (inflammation of the heart's inner lining) is an infrequent complication of rickettsial infections and is not considered a primary contributor to the high 30% mortality observed. - The main pathology in rickettsial diseases involves systemic **vasculitis** and microvascular damage rather than focal inflammation of the heart valves, differentiating it from common causes of high mortality. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 392-393.

Question 155: What is the classic histopathological finding in chancroid?

A. Polymorphonuclear infiltrate with vasculitis
B. Plasma cells at base of ulcer
C. Intraepidermal neutrophilic microabscesses (Correct Answer)
D. Giant cells with intranuclear inclusion bodies

Explanation: ***Intraepidermal neutrophilic microabscesses*** - Chancroid, caused by **Haemophilus ducreyi**, is characterized histopathologically by a three-zone pattern: a superficial layer of **neutrophilic microabscesses**, a mid-zone of **granulation tissue with prominent edematous blood vessels**, and a deep zone of **lymphocytic and plasma cell infiltration**. - The presence of **neutrophilic microabscesses** in the superficial zone is the most classic and distinctive diagnostic feature of chancroid. *Polymorphonuclear infiltrate with vasculitis* - While a polymorphonuclear (neutrophilic) infiltrate is present in chancroid, **vasculitis** (inflammation of blood vessels) is not a primary or classic distinguishing histological feature. - This description is too general and does not capture the specific three-zone pattern and microabscess formation characteristic of chancroid. *Plasma cells at base of ulcer* - Plasma cells are part of the chronic inflammatory response seen in the **deepest layer** of the chancroid ulcer, but they are not the most characteristic or diagnostic finding. - The presence of plasma cells alone does not differentiate chancroid from other chronic inflammatory conditions or other sexually transmitted infections. *Giant cells with intranuclear inclusion bodies* - **Giant cells with intranuclear inclusion bodies** are characteristic of **herpes simplex virus (HSV) infections**, particularly in a **Tzanck smear** or biopsy. - This finding is specific to viral infections and is not associated with the bacterial etiology of chancroid.

Question 156: Which of the following is a primary cause of decreased glucose levels in CSF?

A. TB meningitis
B. Fungal meningitis
C. Viral meningitis
D. Bacterial meningitis (Correct Answer)

Explanation: ***Bacterial meningitis*** - **Bacteria** actively consume glucose for their rapid metabolic needs and proliferation within the cerebrospinal fluid (CSF). - The inflammatory process in bacterial meningitis also increases the **metabolism of glucose** by host cells and leukocytes in the CSF [1]. *TB meningitis* - While TB meningitis can cause decreased CSF glucose, the reduction is usually **less severe and slower** in onset compared to bacterial meningitis. - The causative agent, *Mycobacterium tuberculosis*, has a **slower metabolic rate** and growth compared to typical bacterial pathogens. *Fungal meningitis* - Fungi can consume glucose from the CSF, leading to decreased levels, but this is generally **less pronounced** and develops more chronically than in acute bacterial infections. - Fungal infections in the CSF are often **insidious** and progress slowly, leading to a more gradual consumption of glucose. *Viral meningitis* - In viral meningitis, **CSF glucose levels are typically normal**, or only slightly decreased [1], [2]. - Viruses are intracellular parasites and do not consume glucose from the CSF in the same way that bacteria or fungi do [2]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 708-711. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1274-1275.

Question 157: What is the mechanism by which cholera toxin leads to diarrhea?

A. Stimulates intestinal fluid secretion
B. Inhibits intestinal absorption of water
C. Increases chloride secretion into the intestinal lumen (Correct Answer)
D. Inhibits sodium absorption in the intestines

Explanation: ***Increases chloride secretion into the intestinal lumen*** - Cholera toxin **irreversibly activates adenylate cyclase** in enterocytes, leading to increased intracellular cyclic AMP (cAMP) levels [1]. - Elevated cAMP stimulates the **cystic fibrosis transmembrane conductance regulator (CFTR) channel**, causing excessive chloride ions to be secreted into the intestinal lumen [1]. *Stimulates intestinal fluid secretion* - While cholera toxin ultimately leads to increased intestinal fluid secretion, this option describes the **overall effect** rather than the specific molecular mechanism. - The fluid secretion is a *consequence* of the altered ion transport, primarily chloride secretion [1]. *Inhibits intestinal absorption of water* - Water absorption is indeed impaired, but this is a **secondary effect** due to the osmotic drag created by the increased luminal electrolyte concentration [1]. - The primary action of the toxin is on electrolyte movement, not direct inhibition of water channels. *Inhibits sodium absorption in the intestines* - Cholera toxin primarily *promotes secretion* rather than directly inhibiting sodium absorption to the extent of causing massive diarrhea. - While some sodium absorption might be indirectly affected, the dominant mechanism is the **active secretion of chloride ions** [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 792-793.

Question 158: Which staining technique is considered the most reliable for detecting Cytomegalovirus (CMV) inclusions in tissue samples?

A. Hematoxylin and eosin staining (H&E)
B. Periodic acid-Schiff (PAS) staining
C. Giemsa staining
D. Immunohistochemistry (IHC) (Correct Answer)

Explanation: ***Immunohistochemistry (IHC)*** - **IHC** uses specific antibodies to detect **viral antigens** present within infected cells, offering high **sensitivity** and **specificity** for CMV [1]. - It effectively highlights **CMV-infected cells**, even those without classic viral inclusions, making it the most reliable method [1]. *Hematoxylin and eosin staining (H&E)* - While H&E can identify classic **CMV inclusions** (e.g., "owl's eye" appearance), its **sensitivity** is limited, especially in early or focal infections [1]. - It relies on morphological changes which might be subtle or absent, leading to potential **false negatives**. *Periodic acid-Schiff (PAS) staining* - PAS staining is primarily used to detect **carbohydrates** like glycogen, mucin, and fungal elements, not viral components [1]. - It is not specific for viral inclusions and would not reliably detect **CMV infection**. *Giemsa staining* - Giemsa stain is useful for identifying certain bacteria, parasites, and fungi, and can show some nuclear morphology, but it is not specific for **CMV viral inclusions** [1]. - It lacks the **specificity** and **sensitivity** of IHC for detecting viral antigens and distinguishing CMV from other cellular changes. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 362.

Question 159: A 32-year-old female presents with abdominal pain and fever. Imaging reveals multiple cystic lesions in the liver. Biopsy shows laminated hyaline membranes and scolices. What is the most likely cause?

A. Entamoeba histolytica
B. Echinococcus granulosus (Correct Answer)
C. Schistosoma mansoni
D. Taenia solium

Explanation: ***Echinococcus granulosus*** - The presence of **cystic lesions** in the liver and **laminated hyaline membranes** in the biopsy are indicative of a hydatid cyst caused by Echinococcus granulosus [1,2]. - The **scolices** observed confirm a diagnosis of hydatid disease, which is specifically associated with this parasite [1]. *Taenia solium* - Primarily causes **cysticercosis**, which typically presents with **cysts in the brain** or muscles rather than the liver [4]. - It is characterized by the presence of **larval cysts** but does not create laminated membranes or scolices in liver lesions. *Entamoeba histolytica* - Causes **amoebic liver abscesses**, which are solid lesions rather than cystic lesions observed in this case [3]. - Typically associated with dysentery and does not produce **laminated hyaline membranes** or scolices. *Schistosoma mansoni* - Causes **schistosomiasis**, typically leading to **portal hypertension** and not cystic formations in the liver. - Histological findings are related to granulomatous inflammation rather than laminated membranes or scolices. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 404-405. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 403-404. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 801-802. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 404.

Question 160: Which of the following is the carrying agent for Lyme disease?

A. Anopheles
B. Ixodes scapularis ticks (Correct Answer)
C. Louse
D. Rat flea

Explanation: ***Ixodes scapularis ticks*** - *Ixodes scapularis* ticks (deer ticks) are the primary **vectors for Lyme disease** (caused by *Borrelia burgdorferi*) in North America [1]. - In Europe, *Ixodes ricinus* is the main vector for Lyme disease. - Lyme disease presents with characteristic **erythema migrans** rash, followed by potential neurological, cardiac, and arthritic complications [1]. - Lyme arthritis commonly affects large joints, particularly the **knee**, causing inflammatory arthritis [1]. *Anopheles* - **Anopheles mosquitoes** are the primary vectors for **malaria**, not Lyme disease [2]. - Malaria is caused by *Plasmodium* parasites and presents with fever, chills, and hemolytic anemia [2]. *Louse* - **Lice** are vectors for diseases such as **epidemic typhus** (caused by *Rickettsia prowazekii*) and **relapsing fever** (caused by *Borrelia recurrentis*) [3]. - They are not associated with the transmission of Lyme disease. *Rat flea* - **Rat fleas** (e.g., *Xenopsylla cheopis*) are the primary vectors for **bubonic plague** (caused by *Yersinia pestis*) and **murine typhus**. - These insects do not transmit Lyme disease. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 389-390. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 400. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 392-393.

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