Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 901: What is the most common agent responsible for Bronchiolitis?

A. RSV (Respiratory Syncytial Virus) (Correct Answer)
B. Adenovirus
C. Herpesvirus
D. Influenza virus

Explanation: **Explanation:** **1. Why RSV is the correct answer:** Respiratory Syncytial Virus (RSV) is the single most common cause of bronchiolitis worldwide, accounting for approximately **50–80% of all cases**. It primarily affects infants and children under two years of age, with a peak incidence between 2 to 6 months. The virus causes inflammation, edema, and necrosis of the epithelial cells lining the small airways (bronchioles), leading to the classic clinical presentation of wheezing, tachypnea, and chest retractions. **2. Why the other options are incorrect:** * **Adenovirus:** While it can cause severe bronchiolitis and "Bronchiolitis Obliterans" (a chronic obstructive lung disease), it is a much less frequent cause than RSV. It more commonly presents as pharyngoconjunctival fever. * **Herpesvirus:** These viruses (like HSV or CMV) typically cause systemic infections or pneumonia in immunocompromised hosts but are not standard causative agents for acute bronchiolitis in infants. * **Influenza virus:** Although it causes significant respiratory morbidity and can lead to viral pneumonia, it is a less common cause of isolated bronchiolitis compared to RSV and Parainfluenza. **3. Clinical Pearls for NEET-PG:** * **Seasonality:** RSV outbreaks typically occur in **winter and early spring**. * **Diagnosis:** Primarily clinical; however, **Rapid Antigen Detection Tests (RADT)** or PCR from nasopharyngeal swabs are used for confirmation. * **Microscopy:** Look for **multinucleated giant cells (syncytia)** formed by the fusion of infected cells (due to the viral F-protein). * **Treatment:** Mainly supportive (oxygen, hydration). **Ribavirin** (nebulized) is reserved for severe cases or high-risk infants. * **Prophylaxis:** **Palivizumab** (a monoclonal antibody against the F-protein) is used for high-risk preterm infants.

Question 902: Shingles are manifestations of which viral infection?

A. Infectious Mononucleosis
B. Herpes zoster (Correct Answer)
C. Chicken pox
D. Smallpox

Explanation: **Explanation:** **Shingles** (also known as Herpes Zoster) is the clinical manifestation of the reactivation of the **Varicella-Zoster Virus (VZV)**, a member of the *Herpesviridae* family (Human Herpesvirus 3). 1. **Why Option B is Correct:** The primary infection with VZV causes **Chickenpox**. Following the resolution of the primary illness, the virus remains **latent** in the **dorsal root ganglia** or cranial nerve ganglia. Years or decades later, usually due to waning immunity or stress, the virus reactivates and travels down the sensory nerve to the skin, resulting in Shingles. This presents as a painful, unilateral vesicular rash that follows a specific **dermatomal distribution**. 2. **Why Other Options are Incorrect:** * **Option A (Infectious Mononucleosis):** Caused by the Epstein-Barr Virus (EBV/HHV-4). It typically presents with a triad of fever, pharyngitis, and lymphadenopathy, not a dermatomal rash. * **Option C (Chickenpox):** This is the **primary** infection caused by VZV. While the causative agent is the same, "Shingles" specifically refers to the **reactivation** phase. * **Option D (Smallpox):** Caused by the Variola virus (a Poxvirus). It is characterized by a centrifugal distribution of synchronous pustules and has been globally eradicated since 1980. **Clinical Pearls for NEET-PG:** * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions (common to VZV and HSV). * **Post-Herpetic Neuralgia (PHN):** The most common complication of Shingles, defined as pain persisting >90 days after the rash. * **Ramsay Hunt Syndrome:** Reactivation involving the geniculate ganglion (CN VII), leading to facial palsy and vesicles in the external auditory canal. * **Hutchinson’s Sign:** Vesicles on the tip of the nose indicating ophthalmic involvement (Trigeminal nerve, V1 branch).

Question 903: Certain viruses have been isolated in crystalline form and have been found to be what?

A. Nucleotides
B. Phospholipids
C. Scleroproteins
D. Nucleoproteins (Correct Answer)

Explanation: **Explanation:** The correct answer is **Nucleoproteins**. **1. Why Nucleoproteins is correct:** Viruses are fundamentally composed of a nucleic acid core (DNA or RNA) surrounded by a protein coat called a capsid. This structural combination is termed a **nucleoprotein**. In 1935, Wendell Stanley first isolated the Tobacco Mosaic Virus (TMV) in crystalline form, demonstrating that viruses are not simple cells but complex biochemical molecules. Because they lack cytoplasm and organelles, they can be crystallized like proteins while retaining their infectivity once introduced into a host cell. **2. Why other options are incorrect:** * **Nucleotides (A):** These are the building blocks of nucleic acids (monomers). A virus contains a complete polymer (genome), not just individual nucleotides, and must have a protein shell to be a complete virion. * **Phospholipids (B):** While enveloped viruses possess a lipid bilayer derived from the host cell membrane, the core structural identity of all viruses (including non-enveloped ones) is defined by the nucleoprotein complex. * **Scleroproteins (C):** These are fibrous structural proteins found in animals (e.g., keratin, collagen). They are not components of viral structures. **3. High-Yield Clinical Pearls for NEET-PG:** * **Wendell Stanley:** The scientist credited with the first crystallization of a virus (Nobel Prize 1946). * **Capsid:** Composed of subunits called **capsomeres**. * **Virion:** The complete, infectious virus particle. * **Prions:** Differ from viruses as they are composed *entirely* of protein, lacking any nucleic acid. * **Viroids:** Differ from viruses as they consist *only* of naked RNA without a protein coat.

Question 904: Epstein-Barr virus causes all the following conditions EXCEPT:

A. Burkitt's lymphoma
B. Nasopharyngeal carcinoma
C. Carcinoma of the cervix (Correct Answer)
D. Infectious mononucleosis

Explanation: **Explanation:** The correct answer is **Carcinoma of the cervix** because it is primarily caused by **Human Papillomavirus (HPV)**, specifically high-risk types 16 and 18. Epstein-Barr Virus (EBV), also known as Human Herpesvirus 4 (HHV-4), is a potent oncogenic virus, but it does not have a causal link to cervical malignancies. **Analysis of Options:** * **Burkitt’s Lymphoma (Option A):** EBV is strongly associated with the endemic (African) form of Burkitt’s lymphoma. It involves the translocation of the c-myc oncogene (typically t[8;14]). * **Nasopharyngeal Carcinoma (Option B):** EBV is a major etiological factor for the undifferentiated type of nasopharyngeal carcinoma, particularly prevalent in Southern China and Southeast Asia. * **Infectious Mononucleosis (Option D):** Also known as "Glandular Fever" or "Kissing Disease," this is the primary acute infection caused by EBV, characterized by fever, pharyngitis, lymphadenopathy, and atypical lymphocytes (Downey cells) on a peripheral smear. **High-Yield Clinical Pearls for NEET-PG:** * **EBV Receptor:** It binds to the **CD21** receptor (CR2) on B-cells and nasopharyngeal epithelial cells. * **Diagnosis:** The **Paul-Bunnell Test** (detecting heterophile antibodies) is the classic screening test for Infectious Mononucleosis. * **Other EBV Associations:** Oral Hairy Leukoplakia (in HIV patients), Hodgkin’s Lymphoma (Mixed cellularity subtype), and Gastric Carcinoma. * **Rule of Thumb:** If a question asks about cervical cancer, always look for HPV; if it asks about EBV, think of B-cell lymphomas and Nasopharyngeal cancer.

Question 905: Which of the following is an oncogenic RNA virus?

A. Hepatitis B virus
B. Human papilloma virus
C. Epstein Barr virus
D. Hepatitis C virus (Correct Answer)

Explanation: **Explanation:** The core concept tested here is the classification of oncogenic viruses based on their genetic material (DNA vs. RNA). **Correct Answer: D. Hepatitis C virus (HCV)** Hepatitis C is a member of the *Flaviviridae* family and is a **single-stranded RNA virus**. It is a major cause of chronic hepatitis, cirrhosis, and **Hepatocellular Carcinoma (HCC)**. Unlike most oncogenic viruses, HCV does not integrate its genome into the host DNA; instead, it promotes carcinogenesis through chronic inflammation, oxidative stress, and the action of non-structural proteins (like NS5A) that interfere with cell cycle regulation. **Incorrect Options:** * **A. Hepatitis B virus (HBV):** While it causes HCC, it is a **dsDNA virus** (Hepadnaviridae). It integrates into the host genome and produces the HBx protein, which inactivates the p53 tumor suppressor. * **B. Human Papilloma Virus (HPV):** This is a **dsDNA virus**. High-risk types (16, 18) cause cervical and oropharyngeal cancers via E6 and E7 oncoproteins, which inhibit p53 and pRb respectively. * **C. Epstein-Barr Virus (EBV):** This is a **dsDNA virus** (Herpesviridae). It is associated with Burkitt lymphoma, Nasopharyngeal carcinoma, and Hodgkin lymphoma. **High-Yield Clinical Pearls for NEET-PG:** * **Oncogenic RNA Viruses:** Only two are majorly recognized: **HCV** and **HTLV-1** (Human T-cell Lymphotropic Virus type 1, which causes Adult T-cell Leukemia/Lymphoma). * **Direct vs. Indirect:** HTLV-1 is a direct transforming virus (contains oncogenes), while HCV is considered an indirect carcinogen (mediated by chronic injury). * **Mnemonic:** Most oncogenic viruses are DNA viruses (HBV, HPV, EBV, HHV-8, MCV) EXCEPT for HCV and HTLV-1.

Question 906: A 45-year-old male presents for an HIV test. He reports unprotected sexual contact with another man three weeks prior. Antibodies against which of the following viral components will be detected first by ELISA or Western blot?

A. gp120
B. p24
C. p55
D. gp41 (Correct Answer)

Explanation: **Explanation:** The correct answer is **gp41**. In the natural course of HIV infection, the immune system produces antibodies against various viral proteins. Among these, **anti-gp41 antibodies** are the first to appear and reach detectable levels by conventional ELISA or Western blot, typically within 3–4 weeks of infection. **Why gp41 is correct:** * **gp41 (Transmembrane protein):** It is highly immunogenic. During the "seroconversion" phase, antibodies against the envelope proteins (gp41 and gp120) develop early. Specifically, anti-gp41 is the earliest antibody detected by standard diagnostic assays. **Analysis of Incorrect Options:** * **p24 (Capsid protein):** While the **p24 antigen** itself is the first viral marker to appear in the blood (detected by 4th generation ELISA during the window period), the **antibody** against p24 usually appears slightly after anti-gp41. * **gp120 (Surface protein):** Antibodies to gp120 develop early alongside gp41, but they generally reach detectable thresholds later than anti-gp41. * **p55:** This is a precursor polypeptide (Gag precursor) that is cleaved into p24, p17, and p7. It is not a primary target for early diagnostic antibody detection. **NEET-PG High-Yield Pearls:** 1. **Sequence of Markers:** RNA (7-10 days) → p24 Antigen (14-16 days) → Antibodies (3-4 weeks). 2. **Window Period:** The time between infection and the appearance of detectable antibodies. 4th generation ELISA (p24 Ag + Ab) has significantly shortened this. 3. **Western Blot Criteria:** A positive result requires antibodies against at least two of the following: **p24, gp41, or gp120/160**. 4. **Screening vs. Confirmatory:** ELISA is the screening test of choice (high sensitivity), while Western Blot is the traditional confirmatory test (high specificity).

Question 907: Rabies vaccine is prepared from which strain of virus?

A. Street virus
B. Fixed Virus (Correct Answer)
C. Wild virus
D. All of the above

Explanation: **Explanation:** The correct answer is **Fixed Virus**. In virology, the Rabies virus exists in two forms based on its laboratory modification: **Street virus** and **Fixed virus**. 1. **Why Fixed Virus is correct:** The "Fixed" virus is a street virus that has been serially passaged (usually 40–50 times) through the brains of rabbits. This process "fixes" the incubation period to a short, predictable duration (4–6 days). Crucially, while it remains immunogenic, it loses its ability to replicate in extraneural tissue and does not form Negri bodies. Because of its stable characteristics and high antigenicity, it is used for the preparation of both **Anti-Rabies Vaccines (ARV)** and diagnostic antigens. 2. **Why other options are incorrect:** * **Street Virus (A & C):** This is the virus as it exists in nature (wild virus) isolated from infected animals or humans. It has a long and highly variable incubation period (20–60 days), produces **Negri bodies**, and is highly pathogenic. It cannot be used for vaccines because its behavior is unpredictable and too virulent. * **All of the above (D):** Only the modified "Fixed" strain is safe and standardized for vaccine production. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic for Rabies; found in the cytoplasm of neurons (Hippocampus/Purkinje cells). They are present in **Street virus** infections but **absent** in Fixed virus infections. * **Vaccine Strains:** Common fixed strains used include the **Pitman-Moore (PM) strain**, Pasteur strain, and Flury strain. * **Neural vs. Non-neural:** Modern vaccines (like HDCV or PCEV) are inactivated fixed viruses grown in cell cultures, replacing the older, side-effect-prone neural (Semple) vaccines.

Question 908: Which of the following statements are true regarding Severe Acute Respiratory Syndrome (SARS)?

A. Severe acute respiratory syndrome (Correct Answer)
B. Documented respiratory route spread
C. Effective vaccine available
D. Cause atypical pneumonia, Group coronavirus

Explanation: **Explanation:** Severe Acute Respiratory Syndrome (SARS) is a viral respiratory disease caused by the **SARS-associated coronavirus (SARS-CoV)**, a member of the *Coronaviridae* family. 1. **Why Option A is correct:** SARS is the clinical acronym for **Severe Acute Respiratory Syndrome**. It first emerged in 2002 in Guangdong Province, China. It is characterized by high fever, malaise, and progressive respiratory failure. 2. **Why Option B is incorrect:** While the respiratory route (droplets) is the primary mode of transmission, SARS is unique because it also has documented **fecal-oral and fomite spread**. The 2003 Amoy Gardens outbreak in Hong Kong famously demonstrated aerosolization via sewage systems. 3. **Why Option C is incorrect:** Despite extensive research following the 2003 outbreak, **no effective vaccine** was ever commercially released for SARS-CoV-1. Management remains primarily supportive. 4. **Why Option D is incorrect:** While SARS-CoV causes atypical pneumonia, it belongs to **Group 2 (Betacoronavirus)**. The phrasing "Group coronavirus" in the option is often considered too vague or technically incomplete in competitive exams compared to the definitive name of the syndrome. **High-Yield NEET-PG Pearls:** * **Receptor:** SARS-CoV (and SARS-CoV-2) uses the **ACE-2 receptor** (Angiotensin-Converting Enzyme 2) found in the lower respiratory tract to enter host cells. * **Incubation Period:** Typically 2 to 7 days. * **Diagnosis:** RT-PCR is the gold standard for early detection; serology (ELISA) is used for retrospective diagnosis. * **Animal Reservoir:** The natural reservoir is the **Horseshoe Bat**, with the **Civet cat** acting as the intermediate host.

Question 909: The Paul Bunnell test is used for the diagnosis of which condition?

A. Malta fever
B. Leptospirosis
C. Enteric fever
D. Infectious mononucleosis (Correct Answer)

Explanation: **Explanation:** The **Paul-Bunnell test** is a classic diagnostic tool for **Infectious Mononucleosis (IM)**, caused by the Epstein-Barr Virus (EBV). **Why Infectious Mononucleosis is correct:** The test detects **heterophile antibodies** in the patient's serum. These are IgM antibodies produced during an EBV infection that have the unique property of agglutinating red blood cells (RBCs) from other species, specifically **sheep RBCs**. While the Paul-Bunnell test is non-specific, it is highly characteristic of IM. A more refined version used today is the **Monospot test** (using horse RBCs). **Why other options are incorrect:** * **Malta fever (Brucellosis):** Diagnosed via the Standard Agglutination Test (SAT) or Rose Bengal Plate Test, which detect antibodies against *Brucella* species. * **Leptospirosis:** The gold standard is the Microscopic Agglutination Test (MAT), which uses live cultures of *Leptospira*. * **Enteric fever (Typhoid):** Diagnosed using the **Widal test**, which detects antibodies against the O and H antigens of *Salmonella Typhi*. **High-Yield Clinical Pearls for NEET-PG:** * **Heterophile-Negative Mononucleosis:** If a patient has IM-like symptoms but a negative Paul-Bunnell test, the most common cause is **Cytomegalovirus (CMV)**. * **Atypical Lymphocytes:** Peripheral blood smears in IM typically show **Downey cells** (activated T-cells). * **Differential Absorption:** To distinguish Paul-Bunnell antibodies from Forssman antibodies, absorption with **guinea pig kidney extract** is used (Davidsohn modification). Paul-Bunnell antibodies are *not* absorbed by guinea pig kidney.

Question 910: Which virus has a wheel-like shape?

A. Tobacco mosaic virus
B. Adenovirus
C. Rotavirus (Correct Answer)
D. Rabies virus

Explanation: **Explanation:** The correct answer is **Rotavirus**. The name "Rotavirus" is derived from the Latin word **"Rota,"** which means **wheel**. Under electron microscopy, the virus exhibits a characteristic appearance resembling a wheel with a distinct rim and radiating spokes. This unique morphology is due to its triple-layered icosahedral protein capsid (outer, middle, and inner layers). **Analysis of Options:** * **Tobacco mosaic virus:** This is a plant virus characterized by a **rod-shaped** (helical) symmetry. * **Adenovirus:** This is a non-enveloped DNA virus with an **icosahedral** shape. It is famously described as looking like a **"space satellite"** or a "soccer ball" due to the fibers (pentons) projecting from its vertices. * **Rabies virus:** This virus belongs to the Rhabdoviridae family and has a classic **bullet-shaped** morphology. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** Reoviridae. * **Genome:** Double-stranded RNA (dsRNA), which is **segmented** (11 segments). * **Clinical Significance:** Rotavirus is the most common cause of severe, dehydrating **diarrhea in infants and young children** worldwide. * **Pathogenesis:** It produces an enterotoxin called **NSP4**, which induces secretory diarrhea by increasing intracellular calcium. * **Diagnosis:** Most commonly diagnosed via detection of viral antigen in stool using **ELISA** or Latex Agglutination. * **Vaccines:** Live attenuated oral vaccines (e.g., Rotarix, RotaTeq) are part of the Universal Immunization Programme (UIP).

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Virology — MCQs

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