Virology Practice Questions

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

Coronavirus. **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.

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

72 hours. **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.

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

Hepatitis E virus (HEV). **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.

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

Dengue virus serotype 2. **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.

Q: Parvovirus causes all of the following except?

Roseola infantum. **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.

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

It catalyzes the abnormal folding of other proteins.. **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.

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

Herpes simplex. **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).

Q: Dengue virus belongs to which family of viruses?

Flaviviridae. **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.

Q: Which antigen of the rabies virus stimulates antibody production?

Glycoprotein. **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.

Q: Genetic reassortment is seen with which virus?

Rotavirus. **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).

Question 1

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

Accepted Answer

Coronavirus

Answer

H1N1

Answer

Respiratory Syncytial Virus (RSV)

Answer

Parainfluenza virus

Question 2

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

Accepted Answer

72 hours

Answer

1-2 hours

Answer

14 hours

Answer

18 hours

Question 3

Which of the following viruses does not cause chronic hepatitis?

Accepted Answer

Hepatitis E virus (HEV)

Answer

Hepatitis B virus (HBV)

Answer

Hepatitis C virus (HCV)

Answer

Hepatitis D virus (HDV)

Question 4

Which serotype of Dengue virus is considered the most virulent?

Accepted Answer

Dengue virus serotype 2

Answer

Dengue virus serotype 1

Answer

Dengue virus serotype 3

Answer

Dengue virus serotype 4

Question 5

Parvovirus causes all of the following except?

Accepted Answer

Roseola infantum

Answer

Aplastic anemia

Answer

Erythema infectiosum

Answer

Arthralgia

Question 6

Which of the following statements regarding the prion protein is true?

Accepted Answer

It catalyzes the abnormal folding of other proteins.

Answer

It is a protein product coded in viral DNA.

Answer

It protects disulfide bonds from oxidation.

Answer

It cleaves normal proteins.

Question 7

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

Accepted Answer

Herpes simplex

Answer

Myxovirus

Answer

Varicella

Answer

Cytomegalovirus

Question 8

Dengue virus belongs to which family of viruses?

Accepted Answer

Flaviviridae

Answer

Alphaviridae

Answer

Reoviridae

Answer

Bunyaviridae

Question 9

Which antigen of the rabies virus stimulates antibody production?

Accepted Answer

Glycoprotein

Answer

Lipoprotein

Answer

Phosphoprotein

Answer

Intranuclear protein

Question 10

Genetic reassortment is seen with which virus?

Accepted Answer

Rotavirus

Answer

Astrovirus

Answer

Herpes virus

Answer

Hepadnavirus

Virology — MCQs

Virology — MCQs

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