Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 291: Which virus is a single-stranded RNA orthomyxovirus, and is responsible for annual epidemics necessitating vaccination due to antigenic drift and shift?

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

Explanation: **Explanation:** The **Influenza virus** is the correct answer as it perfectly matches the description provided. It belongs to the **Orthomyxoviridae** family and possesses a **segmented, single-stranded, negative-sense RNA genome**. The segmented nature of its genome is the key driver behind its genetic variability: * **Antigenic Drift:** Minor mutations in the Hemagglutinin (HA) and Neuraminidase (NA) genes leading to annual epidemics. * **Antigenic Shift:** Major genetic reassortment (only in Influenza A) between different strains, leading to pandemics. These changes necessitate the formulation of a new vaccine every year. **Why the other options are incorrect:** * **Measles virus (Option A):** Belongs to the *Paramyxoviridae* family. While it is an ssRNA virus, it is antigenically stable (only one serotype exists), meaning the vaccine provides lifelong immunity. * **Respiratory Syncytial Virus (RSV) (Option B):** Also a member of *Paramyxoviridae*. It lacks a segmented genome and does not undergo antigenic shift. * **Parainfluenza virus (Option D):** Another *Paramyxoviridae* member. It causes croup (laryngotracheobronchitis) but does not exhibit the significant antigenic variation seen in Influenza. **High-Yield NEET-PG Pearls:** * **Genome:** Influenza has **8 segments** (A and B) or 7 segments (C). Segmented genomes are a prerequisite for **Antigenic Shift**. * **Replication:** Unlike most RNA viruses, Influenza replicates its genome in the **nucleus** of the host cell. * **Drug of Choice:** Oseltamivir (Neuraminidase inhibitor) is used for both prophylaxis and treatment. * **Vaccine:** The most common is the **Inactivated (killed)** vaccine; the Live Attenuated Influenza Vaccine (LAIV) is administered intranasally.

Question 292: Which of the following is NOT true of chickenpox rash?

A. Centripetal in distribution
B. Palms and soles are mostly spared
C. Pleomorphic rash
D. Scabs are infectious (Correct Answer)

Explanation: The correct answer is **D. Scabs are infectious**. ### Explanation In Chickenpox (caused by the Varicella-Zoster Virus), the infectivity period extends from **1–2 days before the appearance of the rash** until **all lesions have crusted (scabbed) over**. Unlike the fluid in vesicles and pustules, which contains live virus, the **scabs (crusts) are not infectious**. Once the rash has completely scabbed, the patient is no longer considered a source of transmission. ### Analysis of Incorrect Options * **A. Centripetal in distribution:** This is a hallmark of chickenpox. The rash begins on the trunk (where it is most dense) and spreads peripherally to the face and limbs. This is the opposite of Smallpox, which is centrifugal. * **B. Palms and soles are mostly spared:** Chickenpox typically avoids the palms and soles. If a vesicular rash involves these areas, clinicians should consider Hand-Foot-Mouth Disease (Coxsackievirus) or Syphilis. * **C. Pleomorphic rash:** This refers to the presence of multiple stages of lesions (macules, papules, vesicles, and crusts) simultaneously in the same anatomical area. This occurs because the rash appears in successive "crops." ### NEET-PG High-Yield Pearls * **Dew-drop on a rose petal:** Classic description of the varicella vesicle on an erythematous base. * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions (also seen in HSV). * **Starry Sky Appearance:** Refers to the pleomorphic nature of the rash. * **Incubation Period:** Typically 14–16 days (Range 10–21 days). * **Congenital Varicella Syndrome:** Characterized by cicatricial skin scarring, limb hypoplasia, and chorioretinitis.

Question 293: Which of the following would you consider to be general properties of viruses?

A. New virus particle arises directly (by division) from pre-existing viruses.
B. Fall in to the general size range of 200-3000 angstrom units. (Correct Answer)
C. Contain equal proportions of protein, lipopolysaccharide, and nucleic acids.
D. Contain DNA but no RNA.

Explanation: **Explanation:** Viruses are unique, obligate intracellular parasites characterized by their simple structure and specific replication cycle. Understanding their fundamental properties is crucial for NEET-PG. **Why Option B is Correct:** Viruses are significantly smaller than bacteria. Their size is typically measured in nanometers (nm) or Angstroms (Å). The general size range for viruses is **20-300 nm**, which converts to **200-3000 Angstrom units** (1 nm = 10 Å). For example, the Parvovirus is roughly 200 Å, while the Poxvirus (one of the largest) is about 3000 Å. **Analysis of Incorrect Options:** * **Option A:** Unlike bacteria or eukaryotic cells, viruses **do not divide by binary fission**. Instead, they replicate through a complex process of "disassembly and assembly" within a host cell, where viral components are synthesized separately and then organized into new virions. * **Option C:** Viruses are primarily composed of a **nucleic acid core** (genome) and a **protein coat** (capsid). While some possess a lipid envelope, they do not contain equal proportions of these materials, nor do they typically contain lipopolysaccharides (which are characteristic of Gram-negative bacteria). * **Option D:** A fundamental rule of virology is that a virus contains **either DNA or RNA**, but never both as its primary genome. **High-Yield Clinical Pearls for NEET-PG:** * **Smallest Virus:** Parvovirus (approx. 18-26 nm). * **Largest Virus:** Poxvirus (approx. 200-400 nm); it is large enough to be seen under a light microscope. * **Filterability:** Viruses pass through filters that retain bacteria (e.g., Chamberland filters), a property used historically to define them. * **Eclipse Phase:** The period between the entry of a virus into a host cell and the appearance of the first infectious progeny; during this time, no infectious virus can be recovered from the cell.

Question 294: Basophilic inclusion bodies are seen in which virus?

A. Adenovirus (Correct Answer)
B. Poliovirus
C. Measles virus
D. Herpes virus

Explanation: **Explanation:** In virology, inclusion bodies are distinct structures formed during viral replication, serving as "viral factories." Their staining characteristics (acidophilic vs. basophilic) and location (intranuclear vs. intracytoplasmic) are high-yield diagnostic markers for the NEET-PG exam. **1. Why Adenovirus is correct:** Adenoviruses are non-enveloped DNA viruses that replicate entirely within the host cell nucleus. They produce characteristic **intranuclear basophilic (blue-staining) inclusion bodies**. These are often described as "smudge cells" (large, dark, dense inclusions that obscure the nuclear detail), particularly seen in *Adenovirus* pneumonia or urinary tract infections. **2. Analysis of Incorrect Options:** * **Poliovirus:** As an Enterovirus (RNA virus), it replicates in the cytoplasm. It typically does not produce prominent diagnostic inclusion bodies used in routine histopathology. * **Measles virus:** Characterized by **Warthin-Finkeldey giant cells** (multinucleated). It is unique because it produces **both intranuclear and intracytoplasmic acidophilic** (eosinophilic) inclusion bodies (Cowdry type A). * **Herpes virus:** Produces **acidophilic (eosinophilic) intranuclear** inclusion bodies, famously known as **Cowdry Type A** (or "owl’s eye" appearance in CMV, though CMV is also a herpesvirus). **High-Yield Clinical Pearls for NEET-PG:** * **Basophilic Intranuclear:** Adenovirus, Molluscum contagiosum (Henderson-Patterson bodies - though these are technically intracytoplasmic, they are a common basophilic trap). * **Acidophilic Intranuclear (Cowdry A):** HSV, VZV, Yellow Fever (Councilman bodies). * **Acidophilic Intracytoplasmic:** Rabies (Negri bodies), Variola (Guarnieri bodies), Molluscum contagiosum (Henderson-Patterson). * **Both (Intranuclear + Intracytoplasmic):** Measles, CMV.

Question 295: What is the most common virus responsible for molluscum contagiosum?

A. Molluscum contagiosum virus type 1 (Correct Answer)
B. Molluscum contagiosum virus type 2
C. Molluscum contagiosum virus type 3
D. Molluscum contagiosum virus type 4

Explanation: **Explanation:** Molluscum contagiosum is a common viral skin infection caused by the **Molluscum Contagiosum Virus (MCV)**, which belongs to the *Poxviridae* family (Genus: *Molluscipoxvirus*). **Why Option A is correct:** There are four main genotypes of MCV (MCV-1 to MCV-4). **MCV-1** is the most prevalent genotype globally, responsible for approximately **75–90% of all clinical cases**. It is the primary cause of infections in children, typically transmitted through direct skin-to-skin contact or fomites. **Why Options B, C, and D are incorrect:** * **MCV-2:** While less common than MCV-1, it is more frequently isolated in adults and is often associated with sexual transmission. It is also more prevalent in immunocompromised individuals (e.g., HIV patients). * **MCV-3 and MCV-4:** These genotypes are extremely rare and are infrequently isolated in clinical practice. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Characterized by small, firm, pearly, **umbilicated papules** (central depression). * **Histopathology:** Pathognomonic **Henderson-Paterson bodies** (large, intracytoplasmic eosinophilic inclusion bodies) are seen in the epidermis. * **Virology:** MCV is a **large, complex, dsDNA virus** that replicates in the **cytoplasm** (unlike most DNA viruses which replicate in the nucleus). * **Clinical Context:** In adults, lesions in the genital area are considered a Sexually Transmitted Infection (STI). Widespread or giant molluscum should prompt an investigation for underlying **HIV/AIDS**.

Question 296: Rabies is identified by which of the following inclusions?

A. Guarneri bodies
B. Negri bodies (Correct Answer)
C. Cowdry A bodies
D. Cowdry B bodies

Explanation: **Explanation:** **1. Why Negri bodies are correct:** Negri bodies are the pathognomonic histological hallmark of **Rabies**, caused by the Lyssavirus. These are **intracytoplasmic, eosinophilic, round-to-oval inclusion bodies** typically found in the neurons of the central nervous system. They are most commonly observed in the **Purkinje cells of the cerebellum** and the **pyramidal cells of the hippocampus (Ammon’s horn)**. They represent sites of viral replication and consist of viral nucleocapsids. **2. Why the other options are incorrect:** * **Guarneri bodies:** These are intracytoplasmic inclusions seen in **Variola (Smallpox)** and Vaccinia virus infections. * **Cowdry A bodies:** These are "owl’s eye" **intranuclear** eosinophilic inclusions associated with **Herpes Simplex Virus (HSV)**, Varicella-Zoster Virus (VZV), and Cytomegalovirus (CMV). * **Cowdry B bodies:** These are intranuclear inclusions seen in **Adenovirus** and Poliovirus infections. **3. High-Yield Clinical Pearls for NEET-PG:** * **Shape:** Rabies virus is **bullet-shaped** (Rhabdoviridae family). * **Transmission:** Primarily via the bite of a rabid animal; the virus travels via **retrograde axonal transport** to the CNS. * **Diagnosis:** While Negri bodies are classic, the **Gold Standard** for diagnosis in animals/humans is the **Direct Fluorescent Antibody (DFA)** test on brain tissue or skin biopsy from the nape of the neck. * **Prophylaxis:** Rabies is 100% fatal once symptoms appear, making post-exposure prophylaxis (PEP) with wound cleaning, HRIG, and modern cell culture vaccines (e.g., Purified Chick Embryo Cell Vaccine) vital.

Question 297: Which of the following is an integrase inhibitor used to treat HIV?

A. Maraviroc
B. Ritonavir
C. Raltegravir (Correct Answer)
D. Enfluviritide

Explanation: **Explanation:** The correct answer is **Raltegravir**. **1. Why Raltegravir is correct:** Raltegravir belongs to the class of **Integrase Strand Transfer Inhibitors (INSTIs)**. The HIV life cycle requires the viral enzyme **integrase** to incorporate the reverse-transcribed viral DNA into the host cell's genome. By inhibiting this enzyme, Raltegravir prevents the formation of the HIV provirus, effectively halting viral replication. Other drugs in this class include Dolutegravir and Elvitegravir. **2. Why the other options are incorrect:** * **Maraviroc (Option A):** This is a **CCR5 Antagonist** (Entry Inhibitor). It binds to the CCR5 receptor on the surface of T-cells, preventing the HIV gp120 protein from attaching. It is only effective against "R5-tropic" strains. * **Ritonavir (Option B):** This is a **Protease Inhibitor (PI)**. While it has antiviral activity, it is primarily used in low doses as a "pharmacokinetic enhancer" (booster) because it inhibits the CYP3A4 enzyme, increasing the plasma levels of other PIs. * **Enfuvirtide (Option D):** This is a **Fusion Inhibitor**. It binds to the **gp41** subunit of the viral envelope glycoprotein, preventing the fusion of the viral envelope with the host cell membrane. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action (MOA) Mnemonic:** Remember **"-tegra-"** in Ral**tegra**vir stands for In**tegra**se inhibitor. * **Drug of Choice:** Dolutegravir (an INSTI) is now a preferred component of first-line ART regimens globally due to its high genetic barrier to resistance. * **Side Effects:** Integrase inhibitors are generally well-tolerated but can be associated with an increase in **creatine kinase (CK)** levels and rare neuropsychiatric effects.

Question 298: Dengue hemorrhagic fever is caused by which virus family?

A. Alphavirus
B. Flavivirus (Correct Answer)
C. Bunyavirus
D. Orbivirus

Explanation: **Explanation:** **Dengue virus** is a member of the **Flaviviridae** family (genus *Flavivirus*). It is a single-stranded, positive-sense RNA virus transmitted primarily by the *Aedes aegypti* mosquito. Dengue Hemorrhagic Fever (DHF) typically occurs due to "Antibody-Dependent Enhancement" (ADE), where a secondary infection with a different serotype (out of the four: DEN 1-4) leads to an exaggerated immune response, increased vascular permeability, and thrombocytopenia. **Analysis of Options:** * **Flavivirus (Correct):** This family includes major human pathogens like Dengue, Yellow Fever, West Nile, Zika, and Japanese Encephalitis viruses. They are characterized by being enveloped, icosahedral viruses. * **Alphavirus:** Part of the *Togaviridae* family; includes viruses like **Chikungunya**, which presents with similar joint pain but rarely causes the plasma leakage seen in DHF. * **Bunyavirus:** This family includes the Crimean-Congo hemorrhagic fever (CCHF) and Hantavirus. While they cause hemorrhagic fevers, they are distinct from the Flavivirus genus. * **Orbivirus:** A genus within the *Reoviridae* family (e.g., Bluetongue virus), primarily affecting ruminants and not associated with Dengue. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (Day biter; breeds in artificial collections of clean water). * **Diagnosis:** **NS1 Antigen** is the marker of choice for early diagnosis (Days 1–5). IgM/IgG ELISA is used after Day 5. * **Tourniquet Test:** A positive test (≥10 petechiae per square inch) is a clinical indicator of capillary fragility in DHF. * **Saddle-back fever:** Refers to the biphasic fever pattern often seen in Dengue. * **Most common complication:** Plasma leakage leading to Dengue Shock Syndrome (DSS).

Question 299: Epidemic pleurodynia is caused by which virus?

A. Coxsackie B virus (Correct Answer)
B. Coxsackie A virus
C. Polio virus
D. Enterovirus

Explanation: **Explanation:** **Epidemic Pleurodynia** (also known as Bornholm disease or "Devil’s Grip") is a clinical syndrome characterized by the sudden onset of severe, paroxysmal, lancinating chest and upper abdominal pain, often accompanied by fever and malaise. 1. **Why Coxsackie B is correct:** The primary causative agents of epidemic pleurodynia are the **Group B Coxsackieviruses** (specifically types B1–B6). These viruses infect the intercostal muscles, leading to acute inflammation (myositis). The pain is typically pleuritic in nature, worsening with deep inspiration or movement, which explains the clinical nomenclature. 2. **Why other options are incorrect:** * **Coxsackie A virus:** These are primarily associated with **Herpangina** and **Hand-Foot-and-Mouth Disease (HFMD)**. While there is some overlap, they do not typically cause pleurodynia. * **Polio virus:** This virus selectively targets the anterior horn cells of the spinal cord, leading to asymmetrical flaccid paralysis; it does not cause primary muscle inflammation like pleurodynia. * **Enterovirus:** While Coxsackieviruses belong to the *Enterovirus* genus, "Enterovirus" as an option is too broad. In NEET-PG, when a specific subtype (Coxsackie B) is provided, it is the preferred answer over the general genus. **High-Yield Clinical Pearls for NEET-PG:** * **Coxsackie B** is also the most common viral cause of **Myocarditis** and **Pericarditis**. * **Coxsackie A16** is the most common cause of Hand-Foot-and-Mouth Disease. * **Bornholm Disease** is named after the Danish island where an outbreak was famously described. * **Diagnosis:** Usually clinical, but can be confirmed via RT-PCR from throat or stool samples. Treatment is purely supportive (NSAIDs for pain).

Question 300: Which of the following tests can be used for the diagnosis of chickenpox?

A. FAM (Correct Answer)
B. ELISA
C. Widal
D. PCR

Explanation: **Explanation:** **Chickenpox**, caused by the **Varicella-Zoster Virus (VZV)**, is primarily diagnosed clinically, but laboratory confirmation is essential in atypical or severe cases. **Why FAM is the correct answer:** **FAM (Fluorescent Antibody to Membrane Antigen)** is considered one of the most sensitive and specific serological tests for detecting antibodies against VZV. It detects antibodies directed against the glycoproteins expressed on the surface of VZV-infected cells. While the **Tzanck smear** (showing multinucleated giant cells) is a common bedside test, FAM is the "gold standard" serological method for determining immunity and diagnosing infection. **Analysis of Incorrect Options:** * **ELISA:** While ELISA is commonly used to detect VZV IgG/IgM, in the context of specific competitive exams, FAM is often highlighted as the more specialized/superior serological reference for VZV. * **Widal:** This is a tube agglutination test used for the diagnosis of **Enteric fever (Typhoid)**, caused by *Salmonella typhi*, not viral infections. * **PCR:** While PCR is the most sensitive method for detecting VZV DNA (especially from vesicle fluid), the question specifically points toward **FAM** as the classic academic answer associated with VZV serology in traditional microbiology curricula. **High-Yield Clinical Pearls for NEET-PG:** * **Tzanck Smear:** Look for **Cowdry Type A** intranuclear inclusion bodies and multinucleated giant cells (also seen in HSV). * **Rash Pattern:** Characterized as "centripetal" distribution with "pleomorphism" (all stages of rash—papule, vesicle, crust—seen simultaneously). * **Dew-drop on a rose petal:** Classic description of the varicella vesicle. * **Congenital Varicella Syndrome:** Associated with limb hypoplasia, cicatricial skin scarring, and microcephaly if the mother is infected in early pregnancy.

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Virology — MCQs

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