Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 541: Which of the following viruses has an RNA genome and also produces an RNA replicative intermediate?

A. Cytomegalovirus
B. Hepadnavirus
C. Retrovirus
D. Togavirus (Correct Answer)

Explanation: **Explanation:** The core concept tested here is the **replication strategy** of different virus families. **1. Why Togavirus is Correct:** Togaviruses (e.g., Rubella, Chikungunya) are **positive-sense single-stranded RNA (+ssRNA)** viruses. To replicate their genome, they must first synthesize a complementary **negative-sense RNA strand**, which serves as a **replicative intermediate**. This intermediate then acts as a template for the synthesis of multiple new positive-sense genomic RNA strands using the viral enzyme RNA-dependent RNA polymerase (RdRp). **2. Analysis of Incorrect Options:** * **Cytomegalovirus (CMV):** This is a member of the *Herpesviridae* family. It has a **double-stranded DNA (dsDNA)** genome and replicates in the nucleus using DNA-dependent DNA polymerase; it does not utilize an RNA replicative intermediate for genome doubling. * **Hepadnavirus (Hepatitis B):** While it involves an RNA step (pre-genomic RNA), it is a **DNA virus**. It uses **reverse transcription** to convert an RNA intermediate back into DNA. * **Retrovirus (HIV):** Although it has an RNA genome, it replicates via a **DNA intermediate** (provirus) integrated into the host genome using reverse transcriptase. It does not use an RNA-to-RNA replicative intermediate for genome replication. **Clinical Pearls for NEET-PG:** * **All RNA viruses** (except Retroviruses and Orthomyxoviruses) replicate in the **cytoplasm**. * **Positive-sense RNA viruses** (Toga, Flavi, Picorna, Corona) are directly infectious because their genome can function immediately as mRNA. * **Rubella (Togavirus)** is a classic "TORCH" infection characterized by the triad of cataracts, sensorineural deafness, and congenital heart disease (PDA).

Question 542: The Norwalk virus is a

A. DNA virus
B. RNA virus (Correct Answer)
C. Prion
D. Bacteriophage induced virus

Explanation: **Explanation:** The **Norwalk virus** (now officially known as **Norovirus**) belongs to the **Caliciviridae** family. It is a small, non-enveloped, **single-stranded, positive-sense RNA virus**. It is the most common cause of epidemic non-bacterial gastroenteritis worldwide, often associated with outbreaks in closed settings like cruise ships, schools, and nursing homes. **Why the other options are incorrect:** * **DNA virus:** Most gastrointestinal viruses (like Norovirus and Rotavirus) are RNA viruses. Common DNA viruses include the Herpesvirus, Poxvirus, and Hepadnavirus families. * **Prion:** Prions are misfolded infectious proteins devoid of nucleic acids (DNA/RNA). They cause Transmissible Spongiform Encephalopathies (TSEs) like Creutzfeldt-Jakob Disease, not acute gastroenteritis. * **Bacteriophage induced virus:** Bacteriophages are viruses that infect bacteria. While some bacterial toxins (like Shiga toxin or Diphtheria toxin) are encoded by bacteriophages (lysogenic conversion), the Norwalk virus is a primary human enteric pathogen. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** It has a characteristic "cup-shaped" indentation on electron microscopy (Calici = Chalice/Cup). * **Transmission:** Primarily **fecal-oral route**; it has a very low infectious dose (as few as 10-100 particles can cause disease). * **Clinical Feature:** Characterized by "explosive" watery diarrhea and projectile vomiting. * **Resistance:** It is highly resistant to environmental freezing and chlorine levels typically used in water treatment. * **Epidemiology:** It is the leading cause of foodborne illness outbreaks globally.

Question 543: The likelihood of becoming an HBsAg carrier after acute HBV infection is high in which of the following groups?

A. Neonates
B. Chronic hemodialysis patients
C. Persons with HIV infection
D. All of the above (Correct Answer)

Explanation: **Explanation:** The risk of progressing from an acute Hepatitis B Virus (HBV) infection to a chronic carrier state (defined as HBsAg persistence for >6 months) is inversely proportional to the **competence of the host’s cell-mediated immunity (CMI)**. 1. **Neonates (Option A):** This is the highest-risk group. Approximately **90%** of infants infected perinatally become chronic carriers. This is due to an immature immune system that develops "immune tolerance" to the virus, failing to clear the infected hepatocytes. 2. **Chronic Hemodialysis Patients (Option B):** Patients with end-stage renal disease (ESRD) often exhibit uremia-induced immune dysfunction. Their impaired T-cell response leads to a higher rate of chronicity (approx. 10–20%) compared to healthy adults. 3. **Persons with HIV Infection (Option C):** HIV-induced depletion of CD4+ T-cells severely impairs the body's ability to mount an effective cytotoxic T-lymphocyte response against HBV, significantly increasing the likelihood of persistent infection. **Conclusion:** Since all three groups have compromised or immature immune systems, they are all at a significantly higher risk of becoming HBsAg carriers compared to healthy immunocompetent adults (where the risk is <5%). **High-Yield Clinical Pearls for NEET-PG:** * **Age vs. Chronicity:** Neonates (90%) > Children aged 1-5 (25-30%) > Adults (<5%). * **Serological Marker:** Persistence of **HBsAg** for more than 6 months defines the carrier state. * **The "Window Period":** The interval when both HBsAg and Anti-HBs are negative; **Anti-HBc IgM** is the only marker present. * **Ground Glass Hepatocytes:** Histological hallmark of chronic HBV infection due to HBsAg accumulation in the endoplasmic reticulum.

Question 544: Enterovirus causes which of the following conditions?

A. Acute hemorrhagic conjunctivitis (Correct Answer)
B. Acute follicular conjunctivitis
C. Posterior follicular conjunctivitis
D. Epidemic keratoconjunctivitis

Explanation: **Explanation:** **Enterovirus 70** and **Coxsackievirus A24** are the primary causative agents of **Acute Hemorrhagic Conjunctivitis (AHC)**. This condition is characterized by a sudden onset of foreign body sensation, periorbital swelling, and pathognomonic subconjunctival hemorrhages. It is highly contagious, often occurring in large-scale epidemics in crowded settings with poor hygiene. **Analysis of Options:** * **Option A (Correct):** Enterovirus 70 is the classic cause of AHC. It is unique because it can rarely be associated with a polio-like paralysis (Radiculomyelitis). * **Option B & C (Incorrect):** Follicular conjunctivitis is a general reaction of the conjunctiva to various stimuli. While many viruses (including Adenovirus) cause a follicular response, "Acute Follicular Conjunctivitis" is most classically associated with **Adenovirus** (Pharyngoconjunctival fever) or primary **Herpes Simplex Virus**. * **Option D (Incorrect):** **Epidemic Keratoconjunctivitis (EKC)** is caused by **Adenovirus serotypes 8, 19, and 37**. It is distinguished from AHC by the presence of significant corneal involvement (keratitis) and preauricular lymphadenopathy, but it lacks the prominent hemorrhagic component seen with Enteroviruses. **High-Yield Clinical Pearls for NEET-PG:** * **Enterovirus 70:** Associated with "Apollo Conjunctivitis" (so named because it was first described during the Apollo 11 mission era). * **Adenovirus 8:** The most common cause of Epidemic Keratoconjunctivitis (EKC). * **Hand-Foot-Mouth Disease:** Caused by Coxsackievirus A16 and Enterovirus 71. * **Herpangina:** Caused by Coxsackievirus A.

Question 545: Which of the following is a leading cause of pneumonia primarily in infants?

A. Rabies
B. Rhinovirus
C. Cytomegalovirus
D. Respiratory syncytial virus (Correct Answer)

Explanation: **Explanation:** **Respiratory Syncytial Virus (RSV)** is the correct answer because it is the most common cause of lower respiratory tract infections (LRTI), including **bronchiolitis and pneumonia**, in infants and children under the age of one. It belongs to the *Paramyxoviridae* family (genus *Orthopneumovirus*). The virus causes the formation of **syncytia** (multinucleated giant cells) in the respiratory epithelium, leading to inflammation, edema, and excessive mucus production that easily obstructs the small airways of infants. **Analysis of Incorrect Options:** * **Rabies:** A neurotropic rhabdovirus that causes fatal encephalitis. It does not cause pneumonia; it is transmitted via animal bites and travels via retrograde axonal transport to the CNS. * **Rhinovirus:** The most frequent cause of the "common cold" (upper respiratory tract infection). While it can occasionally exacerbate asthma, it is rarely the primary cause of pneumonia in infants compared to RSV. * **Cytomegalovirus (CMV):** While CMV can cause interstitial pneumonia, it typically occurs in **immunocompromised** patients (e.g., post-transplant) or as part of congenital CMV syndrome, rather than being the leading cause of community-acquired pneumonia in healthy infants. **High-Yield Clinical Pearls for NEET-PG:** * **Seasonality:** RSV outbreaks typically occur in winter and early spring. * **Diagnosis:** Rapid antigen detection tests or RT-PCR from nasopharyngeal aspirates are preferred. * **Treatment:** Management is primarily supportive (oxygen, hydration). **Ribavirin** (aerosolized) is reserved for severe cases or high-risk infants. * **Prophylaxis:** **Palivizumab** (a monoclonal antibody against the RSV F-protein) is used for high-risk premature infants. * **Pathology:** Look for "Syncytia" and "intracytoplasmic inclusion bodies" in histopathology.

Question 546: Antibody mediated enhancement is a feature of which of the following viral infections?

A. Yellow fever
B. Dengue hemorrhagic fever (Correct Answer)
C. Omsk hemorrhagic fever
D. Japanese encephalitis

Explanation: **Explanation:** **Antibody-Dependent Enhancement (ADE)** is a phenomenon where non-neutralizing antibodies from a previous infection facilitate the entry of a virus into host cells, leading to increased viral replication and a more severe clinical presentation. **Why Dengue Hemorrhagic Fever (DHF) is correct:** Dengue virus has four distinct serotypes (DEN-1 to DEN-4). When a person is infected with a second, different serotype, the pre-existing antibodies from the primary infection do not neutralize the new serotype. Instead, these antibodies bind to the new virus and then attach to the **Fc receptors** on macrophages and monocytes. This acts like a "Trojan Horse," actively pulling the virus into the cells. This leads to a massive release of cytokines (**Cytokine Storm**), resulting in increased vascular permeability, plasma leakage, and the clinical manifestations of DHF and Dengue Shock Syndrome (DSS). **Why other options are incorrect:** * **Yellow Fever, Omsk Hemorrhagic Fever, and Japanese Encephalitis:** While these are all members of the *Flaviviridae* family, they do not typically exhibit the ADE phenomenon in clinical practice. Their pathogenesis is primarily driven by direct viral cytopathic effects or standard immunopathological responses rather than antibody-facilitated entry. **High-Yield Clinical Pearls for NEET-PG:** * **The "Halstead Hypothesis":** This is the formal name for the theory explaining ADE in Dengue. * **Target Cells:** Monocytes and Macrophages are the primary sites of enhanced replication. * **Vaccine Implication:** ADE is the primary reason why the Dengue vaccine (Dengvaxia) is only recommended for individuals with laboratory-confirmed prior Dengue infection. * **Other Viruses:** ADE has also been observed in Zika virus and some Coronaviruses, but Dengue remains the classic, most frequently tested example.

Question 547: Variola virus is classified as which of the following genera?

A. Orthopoxvirus (Correct Answer)
B. Parapoxvirus
C. Yatapoxvirus
D. Avipoxvirus

Explanation: **Explanation:** **Variola virus**, the causative agent of Smallpox, belongs to the family **Poxviridae**, subfamily Chordopoxvirinae, and the genus **Orthopoxvirus**. This genus is clinically significant as it includes viruses that exhibit significant cross-reactivity and cross-protection. 1. **Why Orthopoxvirus is correct:** The genus *Orthopoxvirus* includes Variola (Smallpox), Vaccinia (used for the smallpox vaccine), Monkeypox, and Cowpox viruses. These viruses are characterized by their large, brick-shaped structure and double-stranded DNA genome. Because they share common antigens, infection or vaccination with one member (e.g., Vaccinia) provides immunity against others (e.g., Variola). 2. **Why other options are incorrect:** * **Parapoxvirus:** Includes Orf virus (contagious pustular dermatitis) and Pseudocowpox (Milker’s nodules). These are typically ovoid and have a spiral-like surface structure. * **Yatapoxvirus:** Includes Tanapox and Yaba monkey tumor virus; these primarily affect primates and occasionally humans in specific geographic regions. * **Avipoxvirus:** These viruses (e.g., Fowlpox) infect birds and do not cause disease in humans. **High-Yield Clinical Pearls for NEET-PG:** * **Smallpox Eradication:** Smallpox was officially declared eradicated by the WHO on **May 8, 1980**. It is the only human infectious disease to be completely eradicated. * **Intracytoplasmic Inclusions:** Variola produces characteristic eosinophilic inclusion bodies called **Guarnieri bodies**. * **Clinical Presentation:** Smallpox is distinguished from Chickenpox (Varicella) by its **centrifugal distribution** (more lesions on the face and extremities) and the fact that all lesions in one area are at the **same stage of development**. * **Vaccine:** The vaccine uses **live Vaccinia virus**, not Variola virus.

Question 548: Which of the following is not a clinical manifestation of parvovirus infection?

A. Erythema infectiosum
B. Polyarthropathy
C. Pure red cell aplasia
D. Tropical sprue (Correct Answer)

Explanation: **Explanation:** **Parvovirus B19** is a small, single-stranded DNA virus that specifically targets and replicates in **erythroid progenitor cells** by binding to the **P-antigen** (globoside) on the cell surface. **Why Tropical Sprue is the Correct Answer:** Tropical sprue is a malabsorption syndrome characterized by chronic diarrhea and megaloblastic anemia, primarily seen in tropical regions. Its etiology is linked to persistent bacterial overgrowth in the small intestine, not viral infections. Parvovirus B19 has no clinical association with intestinal malabsorption or tropical sprue. **Analysis of Incorrect Options:** * **Erythema Infectiosum (Fifth Disease):** This is the most common presentation in children, characterized by a "slapped-cheek" rash followed by a reticular, lace-like rash on the trunk and limbs. * **Polyarthropathy:** In adults (especially women), Parvovirus B19 often presents as symmetrical inflammatory arthritis affecting small joints, mimicking rheumatoid arthritis. * **Pure Red Cell Aplasia (PRCA):** Because the virus destroys erythroblasts, it can cause a transient aplastic crisis in patients with high red cell turnover (e.g., Sickle Cell Anemia). In immunocompromised individuals, it can lead to chronic PRCA and severe anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Hydrops Fetalis:** If a pregnant woman is infected, the virus can cross the placenta, leading to severe fetal anemia, high-output cardiac failure, and fetal death. * **Receptor:** The cellular receptor for Parvovirus B19 is the **P-antigen**. Individuals lacking this antigen are naturally immune. * **Diagnosis:** IgM antibodies are used for acute infection; PCR is preferred for immunocompromised patients with PRCA.

Question 549: Susceptible cultured cells infected with which of the following viruses would exhibit hemadsorption with the appropriate erythrocyte?

A. Sindbis virus
B. Influenza virus (Correct Answer)
C. Measles virus
D. Respiratory syncytial virus

Explanation: **Explanation:** The correct answer is **Influenza virus**. **Mechanism of Hemadsorption:** Hemadsorption is a phenomenon where erythrocytes (RBCs) adhere to the surface of virus-infected host cells. This occurs because certain viruses, primarily those in the **Orthomyxoviridae** and **Paramyxoviridae** families, express a viral protein called **Hemagglutinin (HA)** on the host cell membrane during the budding process. When appropriate RBCs are added to the culture, they bind to these HA spikes, creating a "clumping" effect on the cell surface. This serves as a rapid presumptive test for viral replication before a cytopathic effect (CPE) is visible. **Analysis of Options:** * **Influenza virus (Correct):** As a member of Orthomyxoviridae, it possesses Hemagglutinin which strongly mediates hemadsorption. * **Sindbis virus:** An Alphavirus (Togaviridae). While it has envelope glycoproteins, it is not typically identified via the hemadsorption test in standard diagnostic virology. * **Measles virus:** Although it belongs to Paramyxoviridae and has a hemagglutinin (H) protein, it typically causes characteristic **syncytia (multinucleated giant cells)** and inclusion bodies. In the context of standard NEET-PG questions, Influenza is the classic prototype for hemadsorption. * **Respiratory Syncytial Virus (RSV):** A Paramyxovirus that **lacks** Hemagglutinin and Neuraminidase (it only has the G-protein). Therefore, it cannot perform hemadsorption. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hemadsorption vs. Hemagglutination:** Hemadsorption happens on the **surface of infected cells**, while hemagglutination is the clumping of RBCs by **free viral particles** in a solution. 2. **Viruses showing Hemadsorption:** Influenza, Parainfluenza, and Mumps. 3. **RSV Key Fact:** It is the most common cause of bronchiolitis in infants and is characterized by **syncytia formation**, not hemadsorption.

Question 550: Which virus spreads via the neural route?

A. Rabies virus (Correct Answer)
B. Poliovirus
C. Adenovirus
D. Enterovirus

Explanation: **Explanation:** The correct answer is **Rabies virus**. The defining characteristic of Rabies pathogenesis is its **centripetal spread** via the nervous system. After an animal bite, the virus replicates locally in muscle tissue before binding to nicotinic acetylcholine receptors at the neuromuscular junction. It then travels via **retrograde axonal transport** through the sensory or motor nerves to the spinal cord and eventually the brain, leading to fatal encephalitis. **Analysis of Options:** * **Poliovirus & Enteroviruses:** While Poliovirus is neurotropic (targeting the anterior horn cells of the spinal cord), its primary route of spread within the body is **hematogenous** (viremia). It enters via the feco-oral route, replicates in the Peyer’s patches, and reaches the CNS through the bloodstream, not primarily via peripheral nerves. * **Adenovirus:** This virus typically spreads via respiratory droplets or feco-oral routes and causes pharyngitis, conjunctivitis, or gastroenteritis. It does not exhibit neural spread. **High-Yield Clinical Pearls for NEET-PG:** * **Axonal Transport:** Rabies uses the dynein motor protein for retrograde transport to the CNS. * **Negri Bodies:** These are pathognomonic intracytoplasmic eosinophilic inclusions found in the hippocampus (Ammon’s horn) and Purkinje cells of the cerebellum. * **Other Neural Spreaders:** Besides Rabies, **Herpes Simplex Virus (HSV)** and **Varicella-Zoster Virus (VZV)** also utilize neural pathways to establish latency in sensory ganglia (e.g., Trigeminal or Dorsal Root Ganglia). * **Incubation Period:** The length of the incubation period in Rabies is directly proportional to the distance of the bite site from the CNS.

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Virology — MCQs

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