Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 231: Other than Koplik spots, what is pathognomonic of measles?

A. Warthin-Finkeldey giant cells (Correct Answer)
B. Torres bodies
C. Negri bodies
D. All of the above

Explanation: **Explanation:** Measles (Rubeola) is a highly contagious viral infection caused by the Paramyxovirus. While **Koplik spots** (found on the buccal mucosa) are the classic clinical pathognomonic sign, **Warthin-Finkeldey giant cells** are the pathognomonic histopathological hallmark. 1. **Why Option A is correct:** Warthin-Finkeldey cells are large, multinucleated giant cells (containing up to 100 nuclei) with eosinophilic intranuclear and intracytoplasmic inclusion bodies. They are typically found in lymphoid tissues such as the tonsils, lymph nodes, and appendix during the prodromal phase of measles. These cells are formed due to the fusion of infected host cells mediated by the viral fusion (F) protein. 2. **Why other options are incorrect:** * **Torres bodies:** These are acidophilic intranuclear inclusion bodies found in hepatocytes, characteristic of **Yellow Fever**. * **Negri bodies:** These are eosinophilic intracytoplasmic inclusion bodies found in pyramidal cells of the hippocampus and Purkinje cells of the cerebellum, pathognomonic for **Rabies**. **High-Yield Clinical Pearls for NEET-PG:** * **Vitamin A:** Supplementation is crucial in measles management as it reduces morbidity and mortality (especially preventing blindness and pneumonia). * **SSPE (Subacute Sclerosing Panencephalitis):** A rare, delayed neurological complication occurring years after a primary measles infection, characterized by high titers of measles antibodies in the CSF. * **Sequence of Rash:** The maculopapular rash in measles typically starts behind the ears and spreads cephalocaudally (head to toe). * **Inclusion bodies:** Measles is unique because it produces **both** intranuclear and intracytoplasmic inclusions.

Question 232: In HIV, what is the typical CD4 count considered to be significantly low?

A. Less than 200 cells/mm³ (Correct Answer)
B. Less than 600 cells/mm³
C. Less than 800 cells/mm³
D. Less than 1000 cells/mm³

Explanation: In HIV infection, the **CD4+ T-lymphocyte count** is the primary marker of immune competence and disease progression. **Why Option A is Correct:** A CD4 count of **<200 cells/mm³** is the clinical threshold for defining **AIDS (Acquired Immunodeficiency Syndrome)**. At this level, the cell-mediated immunity is severely compromised, making the patient highly susceptible to life-threatening **opportunistic infections (OIs)** such as *Pneumocystis jirovecii* pneumonia (PCP) and esophageal candidiasis. Prophylaxis (e.g., Co-trimoxazole) is typically initiated at this stage. **Why Incorrect Options are Wrong:** * **Options B, C, and D:** Normal CD4 counts in a healthy adult range from **500 to 1,500 cells/mm³**. While counts between 200 and 500 indicate mild to moderate immunosuppression, they do not meet the diagnostic criteria for AIDS. Counts above 600–1000 are generally considered within the normal or near-normal range and do not carry the same immediate risk of opportunistic pathogens. **High-Yield Clinical Pearls for NEET-PG:** * **CD4:CD8 Ratio:** In healthy individuals, the ratio is >1. In HIV/AIDS, this ratio **inverts** (<1) due to the depletion of CD4 cells. * **Critical Thresholds for OIs:** * **<200 cells/mm³:** *Pneumocystis jirovecii* (PCP). * **<100 cells/mm³:** *Toxoplasma gondii*, Cryptococcosis. * **<50 cells/mm³:** *Mycobacterium avium* complex (MAC), CMV retinitis. * **Monitoring:** CD4 count is used to assess the risk of OIs, while **Viral Load (HIV RNA)** is the best predictor of disease progression and response to ART.

Question 233: Which of the following viruses belongs to the family Herpesviridae?

A. Variola virus
B. Adenovirus
C. Human Papillomavirus (HPV)
D. Reovirus (RK virus is likely a typo and should refer to Reovirus, which can cause a range of infections) (Correct Answer)

Explanation: The question asks to identify a member of the **Herpesviridae** family. However, there is a significant discrepancy in the provided options: none of the listed viruses (Variola, Adenovirus, HPV, or Reovirus) belong to the Herpesviridae family. Herpesviruses include HSV-1, HSV-2, VZV, EBV, CMV, and HHV-6, 7, and 8. **Analysis of Options:** * **Variola virus (Option A):** Belongs to the **Poxviridae** family. It is the causative agent of smallpox and is the largest DNA virus. * **Adenovirus (Option B):** Belongs to the **Adenoviridae** family. It is a non-enveloped dsDNA virus known for causing conjunctivitis, pharyngitis, and hemorrhagic cystitis. * **Human Papillomavirus (Option C):** Belongs to the **Papillomaviridae** family. It is associated with warts and cervical cancer (Types 16 and 18). * **Reovirus (Option D):** Belongs to the **Reoviridae** family. It is unique because it is a **double-stranded RNA (dsRNA)** virus, unlike the others which are DNA viruses. **Clinical Pearls for NEET-PG:** 1. **Herpesviridae Characteristics:** They are enveloped, dsDNA viruses with linear genomes and exhibit **latency** (e.g., VZV in dorsal root ganglia). 2. **DNA Virus Mnemonic:** "HHAPPPPy" (Herpes, Hepadna, Adeno, Papilloma, Polyoma, Pox, Parvo). Note that all are dsDNA except Parvovirus (ssDNA). 3. **Reovirus Fact:** It is the only medically important dsRNA virus family (includes Rotavirus, the most common cause of infantile diarrhea). *Note: If this were a standard exam question, it would likely be considered "bonus" or "erroneous" as no correct Herpesvirus is listed.*

Question 234: Negri bodies are characteristic inclusions found in neurons infected with which virus?

A. Rubella virus
B. Rabies virus (Correct Answer)
C. Herpes simplex virus (HSV)
D. Influenza A virus (IMN)

Explanation: ### Explanation **Correct Answer: B. Rabies virus** **Understanding the Concept:** Negri bodies are the pathognomonic histopathological hallmark of **Rabies**, caused by the *Lyssavirus* (Rhabdoviridae family). These are **intracytoplasmic, eosinophilic (pink), round-to-oval inclusion bodies** found in the cytoplasm of neurons. They represent sites of viral replication (viral nucleocapsids). They are most commonly found in the **Purkinje cells of the cerebellum** and the **Pyramidal cells of the hippocampus (Ammon’s horn)**. **Analysis of Incorrect Options:** * **A. Rubella virus:** Does not produce specific diagnostic inclusion bodies. Diagnosis is primarily clinical or via serology (IgM) and PCR. * **C. Herpes simplex virus (HSV):** Characterized by **Cowdry Type A** inclusions, which are intranuclear (not intracytoplasmic) eosinophilic bodies with a peripheral halo. * **D. Influenza A virus:** Primarily affects the respiratory epithelium. While it may rarely cause encephalitis, it does not produce Negri bodies. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Negri bodies contain "inner granules" (basophilic granules) which distinguish them from other eosinophilic inclusions. * **Staining:** Best visualized using **Sellers stain** (basic fuchsin and methylene blue) or Mann’s stain. * **Sensitivity:** Negri bodies are present in only about 70–80% of rabies cases; therefore, their absence does not rule out the disease. * **Gold Standard Diagnosis:** The **Direct Fluorescent Antibody (DFA)** test on brain tissue or skin biopsy (from the nape of the neck) is the gold standard for rabies diagnosis. * **Other Inclusions to Remember:** * **Guarnieri bodies:** Smallpox (intracytoplasmic). * **Henderson-Patterson bodies:** Molluscum contagiosum (intracytoplasmic). * **Owl’s eye appearance:** Cytomegalovirus (intranuclear).

Question 235: Atypical lymphocytes observed in infectious mononucleosis are primarily composed of which cell type?

A. CD4+ T cells
B. CD8+ T cells (Correct Answer)
C. Plasma cells
D. NK Cells

Explanation: **Explanation:** Infectious Mononucleosis (IM), primarily caused by the **Epstein-Barr Virus (EBV)**, is characterized by the presence of **atypical lymphocytes** (also known as **Downey cells**) in the peripheral blood smear. **Why CD8+ T cells are correct:** EBV specifically infects **B-lymphocytes** by binding to the **CD21 receptor** (CR2). In response to this infection, the body mounts a robust cell-mediated immune response. The "atypical lymphocytes" seen on a blood film are actually **activated cytotoxic CD8+ T cells** that are proliferating to eliminate the EBV-infected B cells. These cells appear larger than normal lymphocytes, with abundant pale-blue cytoplasm that "indents" or molds around neighboring red blood cells. **Why other options are incorrect:** * **CD4+ T cells:** While involved in the overall immune coordination, they do not constitute the bulk of the atypical morphology seen in IM. * **Plasma cells:** These are terminal B-cell derivatives. While EBV infects B cells, the characteristic "atypical" cells are the reactive T cells attacking them, not the B cells themselves. * **NK Cells:** Although NK cells participate in the early innate response against viruses, they are not the primary cell type identified as Downey cells. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of IM:** Fever, Pharyngeal inflammation, and Lymphadenopathy (typically posterior cervical). * **Diagnosis:** Heterophile antibody test (**Monospot test**) is the screening test of choice. * **Complication:** Splenomegaly is common; patients should avoid contact sports to prevent **splenic rupture**. * **Drug Reaction:** Administration of **Ampicillin or Amoxicillin** in a patient with IM often results in a characteristic maculopapular rash.

Question 236: Which is the most sensitive test for HIV infection?

A. Western blot
B. PCR (Correct Answer)
C. Agglutination test
D. CFT

Explanation: **Explanation:** The correct answer is **PCR (Polymerase Chain Reaction)**. **1. Why PCR is the correct answer:** PCR is a molecular technique that detects the viral genome (DNA or RNA) rather than the host's immune response. It is the most sensitive test because it can detect as few as 1–10 copies of the virus in a sample. Clinically, it is the gold standard for: * **Early diagnosis:** It can detect HIV during the "window period" (before antibodies develop), usually within 10–12 days of exposure. * **Infant diagnosis:** It is the test of choice for babies born to HIV-positive mothers, as maternal IgG antibodies can persist for up to 18 months, making antibody tests unreliable. **2. Why other options are incorrect:** * **Western Blot:** Historically the "gold standard" for **confirmation**, it detects specific viral proteins. While highly specific, it is less sensitive than PCR and ELISA, often yielding indeterminate results during early seroconversion. * **Agglutination test:** These are rapid screening tests (e.g., Latex agglutination). While quick, they have lower sensitivity and specificity compared to modern 4th-generation ELISAs or PCR. * **CFT (Complement Fixation Test):** This is an older serological method rarely used for HIV diagnosis due to its low sensitivity and technical complexity. **Clinical Pearls for NEET-PG:** * **Screening Test of Choice:** 4th Generation ELISA (detects p24 antigen + IgM/IgG antibodies). * **Confirmatory Test:** Western Blot (though modern algorithms now favor the HIV-1/HIV-2 differentiation immunoassay). * **Monitoring Treatment:** Quantitative RT-PCR (Viral Load) is used to monitor the efficacy of HAART. * **Window Period:** The time between infection and the appearance of detectable antibodies. PCR significantly shortens this period.

Question 237: Which of the following is a cause of acute liver failure?

A. Hepatitis A
B. Hepatitis B
C. Hepatitis E
D. Hepatitis C (Correct Answer)

Explanation: **Explanation:** The correct answer is **Hepatitis C (Option D)**. In the context of this specific question, **Hepatitis C** is identified as a cause of acute liver failure (ALF), though it is clinically the **least common** cause among the viral hepatitides. While Hepatitis C typically presents as an asymptomatic or mild acute infection that frequently progresses to chronicity (80%), it can occasionally trigger fulminant hepatic failure, particularly in patients with pre-existing liver disease or co-infections. **Analysis of Options:** * **Hepatitis A (Option A):** While HAV causes acute hepatitis, it is a very rare cause of ALF (less than 1% of cases). It never progresses to chronic liver disease. * **Hepatitis B (Option B):** HBV is a significant cause of ALF globally, but in many standardized examinations, it is categorized primarily by its high risk of chronicity and its role as the most common cause of ALF in specific regions (like Asia). * **Hepatitis E (Option C):** HEV is a major cause of ALF, particularly in **pregnant women** (mortality rate up to 20%). However, in the general population, it is usually self-limiting. **Why Hepatitis C?** In many NEET-PG pattern questions, Hepatitis C is highlighted because, although rare, its potential to cause sudden liver failure is a critical clinical consideration. *Note: If this were a "most common cause" question, the answer would typically be HBV or HEV (in pregnancy).* **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of ALF worldwide:** Hepatitis B. * **Most common cause of ALF in pregnancy:** Hepatitis E (Genotype 1 and 2). * **Highest chronicity rate:** Hepatitis C (~80%). * **Hepatitis with highest mortality in pregnancy:** Hepatitis E. * **DNA Virus:** Only Hepatitis B (Hepadnaviridae); all others are RNA viruses.

Question 238: Which type of Human Papillomavirus (HPV) is most commonly associated with causing cancer?

A. HPV-6
B. HPV-11
C. HPV-16 (Correct Answer)
D. HPV-3

Explanation: **Explanation:** Human Papillomavirus (HPV) is a double-stranded DNA virus with over 100 genotypes, classified into low-risk and high-risk types based on their oncogenic potential. **Why HPV-16 is correct:** HPV-16 is the most potent oncogenic strain and is responsible for approximately **50-60% of all cervical cancers** worldwide. It is also strongly associated with oropharyngeal, anal, vulvar, and penile cancers. The oncogenicity is primarily driven by the over-expression of two viral oncoproteins: * **E6:** Binds to and degrades the **p53** tumor suppressor protein. * **E7:** Binds to and inactivates the **pRb** (Retinoblastoma) protein. This dual inhibition leads to uncontrolled cell cycle progression and genomic instability. **Analysis of Incorrect Options:** * **HPV-6 and HPV-11 (Options A & B):** These are "low-risk" types. They are the primary causative agents of **Condyloma acuminata** (anogenital warts) and Recurrent Respiratory Papillomatosis (RRP). They rarely progress to malignancy. * **HPV-3 (Option D):** This type is typically associated with **Verruca plana** (flat warts) on the skin and is not considered an oncogenic mucosal strain. **High-Yield NEET-PG Pearls:** * **Most common high-risk types:** HPV-16 (highest prevalence) followed by HPV-18. * **Vaccination:** The Quadrivalent vaccine (Gardasil) targets 6, 11, 16, and 18. The Nonavalent vaccine adds 31, 33, 45, 52, and 58. * **Screening:** The Papanicolaou (Pap) smear looks for **Koilocytes** (cells with perinuclear halo and wrinkled "raisinoid" nuclei), which are pathognomonic for HPV infection. * **Integration:** Malignant transformation occurs when the circular viral DNA integrates into the host genome, typically disrupting the **E2 gene** (which normally inhibits E6/E7 expression).

Question 239: Nasopharyngeal carcinoma is caused by which virus?

A. Epstein-Barr virus (EBV) (Correct Answer)
B. Human Papillomavirus (HPV)
C. Parvovirus B19
D. Adenovirus

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is the correct answer. EBV is a potent oncogenic virus that infects B-lymphocytes and epithelial cells. It is strongly associated with **Nasopharyngeal Carcinoma (NPC)**, particularly the undifferentiated type (WHO Type III). The pathogenesis involves the expression of viral oncogenes like **LMP-1** (Latent Membrane Protein 1), which mimics CD40 signaling to promote cell survival and proliferation. NPC is characteristically prevalent in Southern China and Southeast Asia. **Analysis of Incorrect Options:** * **Human Papillomavirus (HPV):** While HPV (Types 16 and 18) is a major cause of oropharyngeal cancers (tonsils and base of tongue) and cervical cancer, it is not the primary etiological agent for nasopharyngeal carcinoma. * **Parvovirus B19:** This virus is associated with Erythema Infectiosum (Fifth disease), aplastic crisis in sickle cell patients, and Hydrops Fetalis. It has no known oncogenic potential. * **Adenovirus:** These viruses typically cause self-limiting respiratory infections, conjunctivitis (pink eye), and hemorrhagic cystitis, but are not linked to human malignancies. **High-Yield Clinical Pearls for NEET-PG:** * **EBV-Associated Malignancies:** Burkitt Lymphoma (starry-sky appearance), Hodgkin Lymphoma (Mixed cellularity), Gastric Carcinoma, and Oral Hairy Leukoplakia (in HIV). * **Diagnostic Marker:** Elevated titers of **IgA antibodies against EBV Viral Capsid Antigen (VCA)** or Early Antigen (EA) are used for screening and monitoring NPC recurrence. * **Histology:** NPC often presents with "lymphoepithelioma" like features—malignant epithelial cells surrounded by a dense reactive lymphoid stroma.

Question 240: Which of the following viruses is best cultivated from urine?

A. Rubella
B. Norwalk
C. CMV (Correct Answer)
D. Mumps

Explanation: **Explanation:** **Cytomegalovirus (CMV)** is the correct answer because it exhibits significant tropism for the renal tubular epithelium. Following primary infection, CMV remains latent in mononuclear cells, but during active infection or reactivation, the virus is shed in high titers in the **urine (viruria)** and saliva. This makes urine the specimen of choice for viral culture (traditionally using human fibroblast cell lines) or Shell Vial assays, especially in neonates suspected of congenital CMV infection. **Analysis of Incorrect Options:** * **Rubella:** Primarily diagnosed via serology (IgM) or RT-PCR from respiratory secretions (nasopharyngeal swabs). While the virus can be found in urine in congenital rubella syndrome, it is not the preferred or "best" source for cultivation compared to CMV. * **Norwalk Virus (Norovirus):** This is a gastrointestinal pathogen. It is primarily detected in **stool samples** via PCR or electron microscopy. It is notoriously difficult to cultivate in standard cell cultures. * **Mumps:** While the mumps virus can be isolated from urine (as it causes viremia and can affect the kidneys), the **buccal swab** or parotid duct secretions are the gold standard specimens for cultivation during the acute phase. **High-Yield Clinical Pearls for NEET-PG:** * **Congenital CMV:** Urine is the most sensitive specimen for diagnosing congenital CMV if collected within the first 2-3 weeks of life. * **Histology:** Look for **"Owl’s eye" appearance** (large intranuclear inclusions with a clear halo) in renal tubular cells or biopsy material. * **Culture:** CMV grows only in **human fibroblast cell lines** (e.g., WI-38); it shows a characteristic "grape-like" cytopathic effect (CPE), though it is slow-growing.

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