Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 751: Severe Acute Respiratory Syndrome (SARS) is caused by which of the following?

A. H1N1
B. Respiratory Syncytial Virus (RSV)
C. Parainfluenza virus
D. Coronavirus (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Coronavirus** Severe Acute Respiratory Syndrome (SARS) is caused by the **SARS-associated coronavirus (SARS-CoV)**. Coronaviruses are large, enveloped, positive-sense single-stranded RNA viruses characterized by club-shaped surface projections (peplomers) that give them a "crown-like" appearance under electron microscopy. SARS-CoV emerged in 2003 as a zoonotic pathogen (likely originating in bats and transmitted via civet cats), causing severe lower respiratory tract infection characterized by high fever, dyspnea, and progressive pneumonia. **Why other options are incorrect:** * **A. H1N1:** This is a subtype of **Influenza A virus** (Orthomyxoviridae). While it causes significant respiratory outbreaks (e.g., the 2009 Swine Flu pandemic), it is genetically and structurally distinct from coronaviruses. * **B. Respiratory Syncytial Virus (RSV):** A member of the Pneumoviridae family, RSV is the most common cause of **bronchiolitis and pneumonia in infants** and young children, characterized by the formation of syncytia (multinucleated giant cells). * **C. Parainfluenza virus:** Part of the Paramyxoviridae family, these viruses are the primary cause of **Croup (Laryngotracheobronchitis)** in children, typically presenting with a "barking" cough and inspiratory stridor. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** SARS-CoV and SARS-CoV-2 both utilize the **ACE-2 (Angiotensin-Converting Enzyme 2)** receptor to enter host cells. * **MERS-CoV:** Another highly pathogenic coronavirus (Middle East Respiratory Syndrome) uses the **DPP-4 receptor**. * **Morphology:** Coronaviruses have the **largest genome** among all RNA viruses. * **Diagnosis:** Gold standard is **RT-PCR** from respiratory specimens.

Question 752: HIV post-exposure prophylaxis can be given up to what duration?

A. 1-2 hours
B. 14 hours
C. 18 hours
D. 72 hours (Correct Answer)

Explanation: **Explanation:** The correct answer is **72 hours**. Post-exposure prophylaxis (PEP) is a medical intervention aimed at preventing HIV infection after a potential exposure (e.g., needle-stick injury, sexual assault). **Why 72 hours is correct:** The effectiveness of PEP is highly time-dependent. The goal is to initiate antiretroviral therapy (ART) before the virus can disseminate from the initial site of entry to the regional lymph nodes and establish a systemic infection. Clinical guidelines and animal models indicate that the window of opportunity for PEP is **up to 72 hours**. Beyond this timeframe, the virus is likely to have integrated into the host genome, making PEP significantly less effective or ineffective. **Analysis of Incorrect Options:** * **A, B, and C (1-2, 14, and 18 hours):** While PEP is most effective when started as soon as possible (ideally within **2 hours**), these options are incorrect because they represent the "ideal" window rather than the "maximum" duration. PEP is still recommended and indicated up to the 72-hour mark. **High-Yield Clinical Pearls for NEET-PG:** * **Ideal Timing:** "The sooner, the better." Ideally within 2 hours of exposure. * **Duration of Treatment:** Once started, PEP must be continued for a total of **28 days**. * **Standard Regimen (NACO/WHO):** Usually a 3-drug regimen (e.g., Tenofovir + Lamivudine + Dolutegravir). * **Testing Protocol:** Baseline HIV testing is mandatory for the exposed person. Follow-up testing is typically done at 6 weeks, 3 months, and sometimes 6 months. * **Contraindication:** PEP is not indicated if the source person is confirmed to be HIV-negative.

Question 753: Which of the following viruses does not cause chronic hepatitis?

A. Hepatitis B virus (HBV)
B. Hepatitis C virus (HCV)
C. Hepatitis D virus (HDV)
D. Hepatitis E virus (HEV) (Correct Answer)

Explanation: **Explanation:** The correct answer is **Hepatitis E virus (HEV)**. The underlying medical concept is the mode of transmission and the nature of the viral infection. HEV is primarily transmitted via the **fecal-oral route** and typically causes an acute, self-limiting infection. In immunocompetent individuals, it does not progress to chronicity. * **Hepatitis E (Option D):** While it is generally acute, a high-yield exception for NEET-PG is that HEV can cause chronic hepatitis **only in immunocompromised individuals** (e.g., organ transplant recipients). However, in the general population, it is not a cause of chronic liver disease. * **Hepatitis B (Option A):** HBV is a DNA virus that can lead to chronic infection in about 5-10% of adults and up to 90% of neonates (vertical transmission). * **Hepatitis C (Option B):** HCV is notorious for chronicity, with approximately **75-85%** of infected individuals developing chronic hepatitis, often leading to cirrhosis and hepatocellular carcinoma. * **Hepatitis D (Option C):** HDV is a defective virus that requires HBV (HBsAg) for replication. Both co-infection and super-infection can lead to chronic states, with super-infection carrying a very high risk of rapid progression to chronic liver failure. **High-Yield Clinical Pearls for NEET-PG:** 1. **HEV in Pregnancy:** HEV (Genotype 1 and 2) is associated with high mortality (up to 20%) in pregnant women due to fulminant hepatic failure. 2. **Vowels to the Bowels:** Hepatitis **A** and **E** are transmitted via the fecal-oral route and generally do not cause chronic disease. 3. **Consonants to the Blood:** Hepatitis **B, C, and D** are transmitted parenterally and are the primary causes of chronic hepatitis.

Question 754: Which serotype of Dengue virus is considered the most virulent?

A. Dengue virus serotype 1
B. Dengue virus serotype 2 (Correct Answer)
C. Dengue virus serotype 3
D. Dengue virus serotype 4

Explanation: **Explanation:** **Dengue virus (DENV)** is a single-stranded RNA virus belonging to the family *Flaviviridae*, with four distinct serotypes (DENV-1 to DENV-4). While all serotypes can cause disease, **Dengue virus serotype 2 (DENV-2)** is clinically recognized as the most virulent. **Why DENV-2 is the correct answer:** Epidemiological studies and clinical data consistently link DENV-2 to more severe disease manifestations, such as **Dengue Hemorrhagic Fever (DHF)** and **Dengue Shock Syndrome (DSS)**. DENV-2 is associated with higher viral loads and a more robust inflammatory response. Furthermore, it is the serotype most frequently implicated in secondary infections where **Antibody-Dependent Enhancement (ADE)** occurs—a process where non-neutralizing antibodies from a previous infection (usually DENV-1) facilitate the entry of DENV-2 into host macrophages, leading to a "cytokine storm." **Analysis of Incorrect Options:** * **DENV-1:** Often associated with primary infections and large outbreaks, but generally results in classic Dengue Fever rather than severe complications. * **DENV-3:** Known to cause severe disease and neurological manifestations, but statistically ranks behind DENV-2 in terms of global virulence and shock syndrome frequency. * **DENV-4:** Generally considered the least virulent serotype, often resulting in milder clinical symptoms. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (primary) and *Aedes albopictus*. * **Most common serotype in India:** Historically DENV-2, though DENV-1 and DENV-3 also circulate widely. * **Diagnosis:** NS1 Antigen (Days 1–5); IgM/IgG ELISA (after Day 5). * **Tourniquet Test:** A positive test (≥10 petechiae per square inch) is a classic bedside indicator of capillary fragility in Dengue. * **ADE Phenomenon:** Explains why a second infection with a *different* serotype is more dangerous than the first.

Question 755: Parvovirus causes all of the following except?

A. Aplastic anemia
B. Erythema infectiosum
C. Roseola infantum (Correct Answer)
D. Arthralgia

Explanation: **Explanation:** The correct answer is **Roseola infantum** because it is caused by **Human Herpesvirus 6 (HHV-6)**, and occasionally HHV-7, not Parvovirus B19. Roseola typically presents in infants with a high fever followed by the sudden appearance of a maculopapular rash as the fever subsides. **Analysis of Options:** * **A. Aplastic anemia:** Parvovirus B19 infects and lyses **erythroid progenitor cells** in the bone marrow. In patients with high red cell turnover (e.g., Sickle Cell Disease, Spherocytosis), this leads to a life-threatening **Transient Aplastic Crisis**. * **B. Erythema infectiosum (Fifth Disease):** This is the most common clinical presentation of Parvovirus B19 in children, characterized by the classic **"slapped-cheek" appearance** followed by a reticular (lace-like) body rash. * **D. Arthralgia:** In adults (especially women), Parvovirus B19 infection often presents as acute, symmetrical polyarthritis involving the small joints of the hands, mimicking Rheumatoid Arthritis. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** Parvovirus B19 binds to the **P-antigen** (globoside) on erythroblasts. * **Hydrops Fetalis:** If a pregnant woman is infected, the virus can cross the placenta, causing severe fetal anemia, high-output cardiac failure, and fetal hydrops. * **Virology:** Parvovirus is the **smallest DNA virus** and is unique for being **Single-Stranded (ssDNA)** and non-enveloped. * **Pure Red Cell Aplasia:** Can occur in immunocompromised individuals (e.g., HIV patients) due to chronic Parvovirus B19 infection.

Question 756: Which of the following statements regarding the prion protein is true?

A. It is a protein product coded in viral DNA.
B. It catalyzes the abnormal folding of other proteins. (Correct Answer)
C. It protects disulfide bonds from oxidation.
D. It cleaves normal proteins.

Explanation: **Explanation** Prions (Proteinaceous Infectious Particles) are unique pathogens because they lack nucleic acids (DNA or RNA). The correct answer is **Option B** because the pathogenesis of prion diseases (like Creutzfeldt-Jakob Disease) centers on the **conformational change** of the normal cellular prion protein ($PrP^C$) into an abnormal, misfolded isoform ($PrP^{Sc}$). 1. **Mechanism of Action:** $PrP^{Sc}$ acts as a template. When it comes into contact with normal $PrP^C$ (which is rich in alpha-helices), it catalyzes its conversion into the infectious $PrP^{Sc}$ form (rich in beta-pleated sheets). This creates a self-propagating cascade leading to protein aggregation and neurodegeneration. **Analysis of Incorrect Options:** * **Option A:** Prions are **not** coded by viral DNA. They are encoded by the host's own genome (the *PRNP* gene on chromosome 20). * **Option C:** Prions do not have a primary role in protecting disulfide bonds. In fact, the transition from $PrP^C$ to $PrP^{Sc}$ involves significant structural destabilization and the formation of insoluble amyloid plaques. * **Option D:** Prions do not act as proteases (enzymes that cleave proteins). Instead, $PrP^{Sc}$ is notoriously **resistant to proteases** (Protease K resistant), which allows it to accumulate in the brain. **High-Yield Clinical Pearls for NEET-PG:** * **Structure:** $PrP^C$ (Alpha-helix) $\rightarrow$ $PrP^{Sc}$ (Beta-sheet). * **Resistance:** Prions are highly resistant to standard sterilization (autoclaving, UV light, and formalin). They require **1N NaOH for 1 hour** or **porous load autoclaving at 134°C**. * **Histology:** Characterized by "spongiform encephalopathy" (vacuolation of neurons) without an inflammatory response. * **Diagnosis:** Detection of **14-3-3 protein** in CSF is a key marker for CJD.

Question 757: Which of the following produces pocks on the chorioallantoic membrane of a chick embryo?

A. Myxovirus
B. Varicella
C. Herpes simplex (Correct Answer)
D. Cytomegalovirus

Explanation: **Explanation:** The cultivation of viruses in embryonated eggs is a classic virological technique. The **Chorioallantoic Membrane (CAM)** is specifically used for the growth of viruses that produce visible lesions called **pocks**. Each pock represents a single infectious virus particle, and their morphology (size, shape, and color) helps in identification. **Why Herpes simplex is correct:** **Herpes Simplex Virus (HSV)**, along with Poxviruses (like Variola and Vaccinia), is characterized by its ability to produce distinct pocks on the CAM. HSV typically produces small, white, non-necrotic pocks. This is a high-yield diagnostic feature used to differentiate it from other members of the Herpes family. **Why the other options are incorrect:** * **Myxoviruses (Influenza/Mumps):** These are typically grown in the **allantoic or amniotic cavity**, not the CAM. They do not produce pocks; their growth is detected via hemagglutination. * **Varicella-Zoster Virus (VZV):** Unlike HSV, VZV is highly cell-associated and does not grow well in embryonated eggs or produce pocks on the CAM. * **Cytomegalovirus (CMV):** CMV is highly species-specific and only grows in human fibroblast cell cultures. It does not grow on the CAM of a chick embryo. **High-Yield NEET-PG Pearls:** 1. **Pock-forming viruses:** Variola (large, opaque), Vaccinia (large, necrotic), and HSV (small, white). 2. **Amniotic cavity:** Primary site for the initial isolation of the Influenza virus. 3. **Allantoic cavity:** Used for the production of vaccines (Yellow fever, Influenza). 4. **Yolk sac:** Used for cultivating Chlamydia, Rickettsia, and some viruses (e.g., Hantavirus).

Question 758: Dengue virus belongs to which family of viruses?

A. Alphaviridae
B. Reoviridae
C. Flaviviridae (Correct Answer)
D. Bunyaviridae

Explanation: **Explanation:** **Correct Answer: C. Flaviviridae** Dengue virus (DENV) is a single-stranded, positive-sense RNA virus belonging to the genus *Flavivirus* within the **Flaviviridae** family. It is an arbovirus (arthropod-borne) primarily transmitted by the *Aedes aegypti* mosquito. The family Flaviviridae is characterized by enveloped viruses with icosahedral nucleocapsids. **Analysis of Incorrect Options:** * **A. Alphaviridae (Togaviridae):** This family includes viruses like **Chikungunya** and Rubella. While Chikungunya shares the same vector (*Aedes*) and similar clinical symptoms (fever, joint pain) with Dengue, it belongs to a different taxonomic family. * **B. Reoviridae:** These are non-enveloped, double-stranded RNA viruses. The most clinically significant member for NEET-PG is **Rotavirus**, the leading cause of severe diarrhea in infants. * **D. Bunyaviridae:** This family includes viruses like **Hantavirus**, Crimean-Congo hemorrhagic fever, and California encephalitis. They are typically negative-sense, segmented RNA viruses. **High-Yield Clinical Pearls for NEET-PG:** * **Serotypes:** There are four distinct serotypes (DEN-1 to DEN-4). Infection with one provides lifelong immunity to that specific serotype but only temporary cross-protection to others. * **Antibody-Dependent Enhancement (ADE):** Secondary infection with a different serotype increases the risk of **Dengue Hemorrhagic Fever (DHF)** and Dengue Shock Syndrome (DSS) due to non-neutralizing antibodies. * **Diagnosis:** **NS1 Antigen** is the marker of choice for early diagnosis (Days 1–5). IgM/IgG ELISA is used after Day 5. * **Vector:** *Aedes aegypti* is a "daytime biter" and breeds in artificial collections of clean water.

Question 759: Which antigen of the rabies virus stimulates antibody production?

A. Lipoprotein
B. Glycoprotein (Correct Answer)
C. Phosphoprotein
D. Intranuclear protein

Explanation: **Explanation:** The rabies virus is a bullet-shaped, negative-sense single-stranded RNA virus belonging to the *Rhabdoviridae* family. Its structure consists of five major proteins: Nucleoprotein (N), Phosphoprotein (P), Matrix protein (M), Glycoprotein (G), and RNA-dependent RNA polymerase (L). **Why Glycoprotein is the correct answer:** The **G protein (Glycoprotein)** forms the spike-like projections on the viral envelope. It is the most critical antigen because it mediates viral attachment to the host cell (acetylcholine receptors) and is the **only protein that induces and reacts with neutralizing antibodies**. This makes it the primary component used in modern cell-culture vaccines to confer protective immunity. **Analysis of Incorrect Options:** * **Lipoprotein:** While the virus has a lipid bilayer envelope derived from the host cell membrane, it is not the specific antigen responsible for stimulating protective neutralizing antibodies. * **Phosphoprotein (P):** This is an internal protein associated with the viral polymerase complex. While it is antigenic, it does not stimulate neutralizing antibodies. * **Intranuclear protein:** This is a distractor. Rabies is an RNA virus that replicates in the **cytoplasm**, not the nucleus. The characteristic Negri bodies are intracytoplasmic inclusions. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusions found most commonly in the **Hippocampus (Ammon’s horn)** and Cerebellum (Purkinje cells). * **Receptor:** Rabies virus binds to **Nicotinic Acetylcholine Receptors (nAChR)** at the neuromuscular junction. * **Centripetal Spread:** The virus travels via retrograde axonal transport to the CNS. * **Vaccine:** Modern vaccines (e.g., Purified Chick Embryo Cell Vaccine) are inactivated and standardized based on the G protein content.

Question 760: Genetic reassortment is seen with which virus?

A. Astrovirus
B. Herpes virus
C. Rotavirus (Correct Answer)
D. Hepadnavirus

Explanation: **Explanation:** The core concept behind this question is **Genetic Reassortment**, which occurs only in viruses with **segmented genomes**. When two different strains of a segmented virus infect the same host cell, they can exchange entire gene segments during replication, leading to the emergence of new subtypes. **Why Rotavirus is correct:** Rotavirus belongs to the *Reoviridae* family. It possesses a **segmented, double-stranded RNA (dsRNA) genome** consisting of **11 segments**. This segmentation allows for frequent genetic reassortment, contributing to the diversity of strains and the potential for "antigenic shift." **Analysis of Incorrect Options:** * **Astrovirus:** These are small, non-enveloped viruses with a **single-stranded, non-segmented (+) RNA** genome. Without segments, reassortment cannot occur. * **Herpes virus:** These are large, enveloped viruses with a **linear, double-stranded DNA** genome. While they can undergo genetic recombination, they do not have segmented genomes for reassortment. * **Hepadnavirus (e.g., Hepatitis B):** These have a **circular, partially double-stranded DNA** genome. They replicate via reverse transcription but are non-segmented. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Segmented Viruses:** "**BOAR**" * **B**unyaviridae (3 segments) * **O**rthomyxoviridae (Influenza: 8 segments) * **A**renaviridae (2 segments) * **R**eoviridae (Rotavirus: 11 segments; Coltivirus: 12 segments) * **Antigenic Shift vs. Drift:** Reassortment is the mechanism behind **Antigenic Shift** (major changes), whereas point mutations cause **Antigenic Drift** (minor changes). * Rotavirus is the most common cause of severe diarrhea in infants and young children worldwide ("Wheel-like" appearance on EM).

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Virology — MCQs

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