Infectious Diseases Practice Questions

Q: All of the following are associated with primary tuberculosis EXCEPT:

Cavitary lesion. **Explanation:** The distinction between primary and secondary (reactivation) tuberculosis is a frequent high-yield topic in NEET-PG. **Why "Cavitary lesion" is the correct answer:** Cavitary lesions are the hallmark of **Secondary (Post-primary) Tuberculosis** [3]. Cavitation occurs due to a robust cell-mediated immune response (Type IV hypersensitivity) leading to extensive tissue necrosis. In contrast, **Primary TB** typically presents as a localized parenchymal lesion (Ghon focus) with associated lymphadenopathy (Ghon complex) [1], but rarely results in cavitation because the initial immune response is usually insufficient to cause such extensive tissue destruction. **Analysis of incorrect options:** * **Pleural effusion:** This is a common manifestation of primary TB, often resulting from the rupture of a subpleural focus into the pleural space. * **Fibrocaseous lesion:** Primary TB begins with a Ghon focus, which is pathologically a fibrocaseous granuloma [1]. While secondary TB also shows caseation, it is a fundamental feature of the primary infection as the body attempts to wall off the bacilli. * **Phlyctenular conjunctivitis:** This is a known **hypersensitivity reaction** to the tubercle bacilli protein [2]. It is considered a "delayed-type hypersensitivity" manifestation that can occur during the primary infection stage. **High-Yield Clinical Pearls for NEET-PG:** * **Ghon Complex:** Parenchymal lesion + Lymphangitis + Hilar lymphadenopathy [1]. * **Ranke Complex:** A healed, calcified Ghon complex (visible on X-ray) [1]. * **Location:** Primary TB usually affects the **lower or middle lobes**, whereas Secondary TB favors the **apical/posterior segments of the upper lobes** (due to higher oxygen tension). * **Epithelioid cells:** These are modified macrophages and are the characteristic diagnostic cell type found in TB granulomas [1].

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.

Question 1

All of the following are associated with primary tuberculosis EXCEPT:

Accepted Answer

Cavitary lesion

Answer

Pleural effusion

Answer

Fibrocaseous lesion

Answer

Phlyctenular conjunctivitis

Question 2

The center of a tubercular granuloma is typically formed by which component?

Accepted Answer

Necrotic zone

Answer

T-lymphocytes

Answer

B-lymphocytes

Answer

Langhan's giant cells

Question 3

A 7-year-old child has had worsening performance in school for the past 4 months due to decreased vision. Examination of the right eye shows diffuse punctate inflammation of the cornea and pannus, which is a growth of fibrovascular tissue from the conjunctiva onto the cornea. Microscopic examination of a corneal scraping shows lymphocytes, plasma cells, neutrophils, and scattered corneal epithelial cells that have cytoplasmic inclusion bodies. Which of the following infectious agents is most likely to produce these findings?

Accepted Answer

Chlamydia trachomatis

Answer

Cytomegalovirus

Answer

Herpes simplex virus

Answer

Rubella virus

Question 4

"Ghon focus" is associated with which of the following conditions?

Accepted Answer

Tuberculosis

Answer

Gonorrhea

Answer

Syphilis

Answer

AIDS

Question 5

Miliary tuberculosis is classified as:

Accepted Answer

Post-primary tuberculosis

Answer

Primary tuberculosis

Answer

Extra-pulmonary tuberculosis

Answer

None of the above

Question 6

Which disease is transmitted by all components of blood?

Accepted Answer

Malaria

Answer

Syphilis

Answer

Toxoplasma

Answer

H. pylori

Question 7

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 8

Which of the following is associated with leprosy?

Accepted Answer

All of the above

Answer

Foamy histiocytes

Answer

Epithelioid cells

Answer

Noncaseating granulomas

Question 9

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 10

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

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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