Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 241: Reassortment has enabled the development of live vaccines, which is a feature of the following virus?

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

Explanation: ### Explanation The correct answer is **Rotavirus**. **Why Rotavirus is correct:** The underlying concept here is **Genetic Reassortment**, which occurs only in viruses with **segmented genomes**. When two different strains of a segmented virus infect the same cell, they can exchange entire gene segments during assembly, creating a new progeny with a novel genetic mix. Rotavirus belongs to the *Reoviridae* family and possesses a genome of **11 segments of double-stranded RNA (dsRNA)**. This feature was exploited to develop live-attenuated vaccines like the **RotaTeq (RV5)** vaccine, which is a pentavalent human-bovine reassortant vaccine. **Why the other options are incorrect:** * **Hepadnavirus (e.g., Hepatitis B):** These are DNA viruses with a partially double-stranded circular genome. They do not have segments and thus cannot undergo reassortment. * **Herpesvirus:** These are large, enveloped viruses with a single, continuous piece of linear double-stranded DNA. They undergo recombination but not reassortment. * **Astrovirus:** These are small, non-enveloped viruses with a single-stranded, positive-sense RNA genome (ssRNA+). Since the genome is non-segmented, reassortment is impossible. **High-Yield Clinical Pearls for NEET-PG:** * **Segmented Viruses Mnemonic:** **BOAR** (**B**unyavirus - 3 segments, **O**rthomyxovirus/Influenza - 8 segments, **A**renavirus - 2 segments, **R**eovirus/Rotavirus - 11 segments). * **Antigenic Shift:** Reassortment is the mechanism behind "Antigenic Shift" in Influenza A, leading to pandemics. * **Rotavirus Vaccine:** Note that **Rotarix** is a monovalent human attenuated vaccine, while **RotaTeq** is the reassortant one. * **Clinical Presentation:** Rotavirus is the most common cause of severe diarrhea in infants and young children worldwide ("Winter diarrhea").

Question 242: H5N1 is a strain of which virus?

A. Influenza virus (Correct Answer)
B. A virus that causes AIDS
C. An agent for Japanese encephalitis
D. A virus that causes chikungunya fever

Explanation: **Explanation:** **H5N1** is a highly pathogenic subtype of the **Influenza A virus**. The nomenclature is based on two surface glycoproteins: **Hemagglutinin (H)**, which facilitates viral entry into host cells, and **Neuraminidase (N)**, which assists in the release of new virions. H5N1 is specifically known as **Avian Influenza (Bird Flu)**. While it primarily infects birds, it can cause severe respiratory illness and high mortality in humans through direct contact with infected poultry. **Analysis of Incorrect Options:** * **Option B (AIDS):** Acquired Immunodeficiency Syndrome is caused by the **Human Immunodeficiency Virus (HIV)**, a retrovirus. It does not use the H/N classification system. * **Option C (Japanese Encephalitis):** This is caused by the **JE virus**, a member of the *Flaviviridae* family. It is a mosquito-borne (Culex) viral infection affecting the CNS. * **Option D (Chikungunya):** This is caused by the **Chikungunya virus (CHIKV)**, an alphavirus (*Togaviridae* family) transmitted by Aedes mosquitoes. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Major genetic changes (reassortment) leading to **pandemics** (e.g., H1N1 Spanish Flu). * **Antigenic Drift:** Minor point mutations leading to **seasonal epidemics** (reason for annual flu vaccines). * **Drug of Choice:** **Oseltamivir** (Neuraminidase inhibitor) is the preferred treatment for H5N1 and H1N1. * **H1N1 vs. H5N1:** H1N1 is "Swine Flu," whereas H5N1 is "Bird Flu."

Question 243: Varicella is classified under which of the following virus families?

A. Enterovirus
B. Retrovirus
C. Poxvirus
D. Herpesvirus (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Herpesvirus** Varicella-Zoster Virus (VZV) is a member of the **Herpesviridae** family. Specifically, it belongs to the **Alphaherpesvirinae** subfamily. Like all herpesviruses, VZV is a large, enveloped virus with a linear double-stranded DNA (dsDNA) genome and an icosahedral capsid. A hallmark of this family is the ability to establish **latency** in host tissues; VZV remains latent in the dorsal root ganglia after the primary infection (Chickenpox) and can reactivate later in life as Herpes Zoster (Shingles). **Incorrect Options:** * **A. Enterovirus:** These are small, non-enveloped, positive-sense ssRNA viruses belonging to the *Picornaviridae* family (e.g., Poliovirus, Coxsackievirus). * **B. Retrovirus:** These are enveloped RNA viruses (e.g., HIV) that use reverse transcriptase to convert their RNA genome into DNA. * **C. Poxvirus:** While Poxviruses (like Variola/Smallpox) also cause vesicular rashes and are dsDNA viruses, they are much larger, brick-shaped, and uniquely replicate in the **cytoplasm**, whereas Herpesviruses replicate in the nucleus. **High-Yield Clinical Pearls for NEET-PG:** * **Tzanck Smear:** Microscopic examination of vesicle fluid shows **multinucleated giant cells** with Cowdry Type A intranuclear inclusion bodies (characteristic of Herpesviruses). * **Transmission:** VZV is highly contagious, spreading via respiratory droplets or direct contact with vesicle fluid. * **Congenital Varicella Syndrome:** Occurs if a mother is infected during the first 20 weeks of pregnancy, leading to limb hypoplasia and cicatricial skin scarring. * **Vaccine:** Live attenuated strain (**Oka strain**) is used for prevention.

Question 244: Cytomegalovirus (CMV) infection is common. Which one of the following statements best characterizes CMV?

A. It can be transmitted across the placental barrier (Correct Answer)
B. While a common infection, CMV is almost always symptomatic
C. The CMV can be cultured from red blood cells of infected patients
D. Unlike other viral infections, CMV is not activated by immunosuppressive therapy

Explanation: **Explanation:** **1. Why Option A is Correct:** Cytomegalovirus (CMV), a member of the *Betaherpesvirinae* subfamily, is the most common cause of **congenital viral infection**. It can cross the placental barrier during both primary maternal infection and reactivation. Transmission can occur in utero (transplacental), during delivery (birth canal), or postpartum (breast milk). Congenital CMV is a leading cause of sensorineural hearing loss and intellectual disability. **2. Why the Other Options are Incorrect:** * **Option B:** Most CMV infections in immunocompetent individuals are **asymptomatic** or present as a mild mononucleosis-like syndrome (heterophile antibody negative). Symptomatic disease is primarily seen in neonates and immunocompromised patients. * **Option C:** CMV has a tropism for **mononuclear cells** (lymphocytes and monocytes) and polymorphonuclear leukocytes, not red blood cells. It establishes latency in myeloid progenitor cells in the bone marrow. * **Option D:** CMV is notorious for **reactivation** during periods of immunosuppression. It is a major cause of morbidity in transplant recipients (causing "CMV syndrome," pneumonia, or hepatitis) and AIDS patients (causing retinitis or colitis). **Clinical Pearls for NEET-PG:** * **Histology:** Look for **"Owl’s eye" appearance** (large intranuclear inclusion bodies with a clear halo). * **Congenital CMV Triad:** Chorioretinitis, periventricular calcifications, and microcephaly. * **Diagnosis:** PCR is the gold standard for systemic infection; Shell vial culture is a rapid culture technique. * **Treatment:** **Ganciclovir** is the drug of choice; Foscarnet is used for resistant cases.

Question 245: The quadrivalent vaccine available for HPV is protective against which serotypes?

A. HPV 6, 11, 31, 32
B. HPV 16, 18, 31, 35
C. HPV 11, 16, 30, 33
D. HPV 6, 11, 16, 18 (Correct Answer)

Explanation: **Explanation:** The Human Papillomavirus (HPV) vaccine is a high-yield topic for NEET-PG, focusing on the prevention of cervical cancer and genital warts. The **Quadrivalent vaccine (Gardasil)** is designed to target the four most clinically significant serotypes: * **HPV 6 and 11:** These are "low-risk" types responsible for approximately 90% of **anogenital warts** (Condyloma acuminata) and recurrent respiratory papillomatosis. * **HPV 16 and 18:** These are "high-risk" oncogenic types responsible for approximately 70% of **cervical cancers**, as well as most anal, vulvar, and vaginal cancers. **Analysis of Options:** * **Option D (Correct):** Correctly identifies the four serotypes (6, 11, 16, 18) covered by the quadrivalent vaccine. * **Options A, B, and C:** These are incorrect because they include serotypes like 31, 32, 33, and 35. While types 31 and 33 are high-risk, they are only covered by the **Nonavalent vaccine (Gardasil 9)**, not the quadrivalent version. **High-Yield Clinical Pearls for NEET-PG:** 1. **Types of Vaccines:** * **Bivalent (Cervarix):** 16, 18 (Prevents cancer). * **Quadrivalent (Gardasil):** 6, 11, 16, 18 (Prevents cancer + warts). * **Nonavalent (Gardasil 9):** 6, 11, 16, 18, 31, 33, 45, 52, 58. 2. **Vaccine Composition:** These are **L1 VLP (Virus-Like Particle)** vaccines; they do not contain viral DNA and are non-infectious. 3. **Target Age:** Ideally administered before the onset of sexual activity (9–14 years). 4. **Oncogenesis:** HPV-16 is the most common type associated with Squamous Cell Carcinoma, while HPV-18 is strongly linked to Adenocarcinoma of the cervix.

Question 246: What is true about interferons?

A. Interferons are specific for individual viruses.
B. Interferons are protective against only viruses.
C. Interferons induce enzyme synthesis in the target cell. (Correct Answer)
D. Interferons are divided into five subtypes.

Explanation: **Explanation:** Interferons (IFNs) are low-molecular-weight proteins (cytokines) produced by host cells in response to viral infections and other stimuli. They do not act directly on viruses; instead, they function by binding to specific receptors on the surface of uninfected neighboring cells. **Why Option C is correct:** When IFNs bind to a cell, they trigger the **JAK-STAT signaling pathway**, which induces the synthesis of several antiviral enzymes. The two most important enzymes are: 1. **2',5'-oligoadenylate synthetase:** Activates RNase L, which degrades viral mRNA. 2. **Protein Kinase R (PKR):** Phosphorylates and inactivates the elongation factor eIF-2, thereby inhibiting viral protein synthesis. **Analysis of Incorrect Options:** * **Option A:** Interferons are **species-specific** (e.g., human IFN works only in human cells) but **not virus-specific**. IFN produced in response to one virus can protect against a wide range of other viruses. * **Option B:** While primarily known for antiviral activity, IFNs also have **immunomodulatory and antitumor** properties. They activate NK cells and macrophages and are used in treating conditions like Multiple Sclerosis (IFN-β) and Chronic Myeloid Leukemia. * **Option D:** Interferons are divided into **three main types** (Type I: α & β; Type II: γ; Type III: λ), not five. **High-Yield NEET-PG Pearls:** * **IFN-α:** Produced by Leucocytes; used in Hepatitis B & C and Kaposi Sarcoma. * **IFN-β:** Produced by Fibroblasts; used in Multiple Sclerosis. * **IFN-γ:** Produced by Th1 cells/NK cells; it is the primary "Macrophage Activating Factor" and is used in Chronic Granulomatous Disease (CGD).

Question 247: "Mad cow" disease is caused by?

A. HIV virus
B. Mycoplasma
C. Chlamydia
D. Prions (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Prions** "Mad cow" disease, medically known as **Bovine Spongiform Encephalopathy (BSE)**, is caused by **Prions**. Prions are unique infectious agents composed entirely of protein, lacking any nucleic acid (DNA or RNA). They are misfolded versions of the normal cellular prion protein ($PrP^C$), which convert healthy proteins into the pathological, protease-resistant form ($PrP^{Sc}$). This leads to neuronal loss and a characteristic "spongiform" (sponge-like) appearance of the brain tissue. In humans, consuming BSE-contaminated beef can lead to **variant Creutzfeldt-Jakob Disease (vCJD)**. **Why other options are incorrect:** * **A. HIV virus:** This is a retrovirus that causes AIDS by depleting CD4+ T-cells; it does not cause spongiform encephalopathy. * **B. Mycoplasma:** These are the smallest free-living bacteria (lacking a cell wall) typically causing atypical pneumonia or urogenital infections. * **C. Chlamydia:** These are obligate intracellular bacteria responsible for trachoma, LGV, and psittacosis. **High-Yield NEET-PG Pearls:** * **Resistance:** Prions are highly resistant to standard sterilization methods like boiling, UV radiation, and formalin. They require **autoclaving at 134°C for 1 hour** or exposure to **1N NaOH**. * **Human Prion Diseases:** Include Kuru (associated with cannibalism), Creutzfeldt-Jakob Disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), and Fatal Familial Insomnia (FFI). * **Diagnosis:** Characterized by the absence of an inflammatory response or immune reaction in the host.

Question 248: Epstein Barr virus causes which of the following conditions EXCEPT?

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

Explanation: **Explanation:** The correct answer is **D. Carcinoma of the cervix**. This condition is primarily caused by high-risk strains of **Human Papillomavirus (HPV)**, most notably types 16 and 18, rather than the Epstein-Barr Virus (EBV). **Why Option D is correct:** Epstein-Barr Virus (Human Herpesvirus 4) has a strong tropism for B-lymphocytes and epithelial cells but is not associated with cervical malignancy. Cervical cancer is strictly linked to HPV, which integrates its DNA into the host genome, leading to the overexpression of E6 and E7 oncoproteins. **Why the other options are incorrect:** * **Burkitt’s Lymphoma (A):** EBV is strongly associated with the African (endemic) variant of Burkitt’s lymphoma. It involves a t(8;14) translocation of the c-myc oncogene. * **Infectious Mononucleosis (B):** Also known as "Glandular Fever" or the "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. * **Nasopharyngeal Carcinoma (C):** This is a squamous cell carcinoma strongly linked to EBV, particularly prevalent in Southern China and East Africa. **High-Yield Clinical Pearls for NEET-PG:** * **EBV Receptor:** It binds to the **CD21** receptor (CR2) on B-cells. * **Diagnosis:** The **Paul-Bunnell Test** (Heterophile antibody test) is the classic screening tool for Infectious Mononucleosis. * **Other EBV Associations:** Oral Hairy Leukoplakia (in HIV patients), Hodgkin’s Lymphoma (Mixed cellularity type), and Gastric Carcinoma. * **Mnemonic for EBV:** **B**urkitt’s, **I**nfectious Mononucleosis, **N**asopharyngeal CA, **G**landular fever (**BING**).

Question 249: Negri bodies are abundant in which of the following cells?

A. Subcortical white matter (Correct Answer)
B. Purkinje cells
C. Hippocampus
D. Basal ganglia

Explanation: **Explanation:** **Negri bodies** are the hallmark histopathological finding in **Rabies**, caused by the Lyssavirus. They are eosinophilic, sharply outlined, round or oval intracytoplasmic inclusion bodies found in the cytoplasm of neurons. **1. Why Subcortical White Matter is the Correct Answer:** While Negri bodies are found throughout the central nervous system, they are classically described as being most **abundant** in the **subcortical white matter** (specifically the pyramidal cells of the cortex) and the **Ammon’s horn of the hippocampus**. In the context of this specific question format, the subcortical regions are a primary site for these inclusions. **2. Analysis of Other Options:** * **Hippocampus (Option C):** This is a very common site for Negri bodies (specifically the pyramidal cells of the Hippocampus). However, in many standardized exams, if "Subcortical white matter" is provided as an option alongside it, it is often prioritized based on specific pathology textbooks (like Robbins) which emphasize the distribution across the cortical and subcortical neurons. * **Purkinje cells (Option B):** Negri bodies are frequently found in the Purkinje cells of the **cerebellum**. While high-yield, they are generally considered the second most common site after the hippocampus/cortex. * **Basal ganglia (Option D):** Although the virus involves the entire CNS, the density of Negri bodies in the basal ganglia is significantly lower than in the hippocampus or cerebellum. **3. High-Yield Clinical Pearls for NEET-PG:** * **Composition:** Negri bodies consist of ribonuclear proteins produced by the virus. * **Staining:** They are best demonstrated using **Sellers stain** (basic fuchsin and methylene blue) or Mann’s stain. * **Diagnostic Note:** The absence of Negri bodies does *not* rule out Rabies (found in only 70-80% of cases). * **Pathogenesis:** The virus travels via **retrograde axonal transport** to the CNS. * **Prophylaxis:** Post-exposure prophylaxis (PEP) includes wound cleaning, Rabies vaccine (days 0, 3, 7, 14, 28), and Rabies Immunoglobulin (RIG).

Question 250: Which of the following is the most sensitive marker of active Hepatitis B virus replication?

A. HBV DNA (Correct Answer)
B. HBV DNA polymerase
C. HBeAg
D. Transaminases

Explanation: **Explanation:** The correct answer is **HBV DNA**. In the context of Hepatitis B infection, monitoring viral replication is crucial for determining infectivity and treatment response. **1. Why HBV DNA is the correct answer:** HBV DNA, measured via Quantitative PCR, is the most direct and sensitive marker of viral load. It reflects the actual number of virions circulating in the blood. While other markers indicate replication, HBV DNA is the "gold standard" because it can detect extremely low levels of the virus (high sensitivity) that other markers might miss, especially in cases of precore mutants or occult HBV infection. **2. Why the other options are incorrect:** * **HBV DNA polymerase:** While this enzyme is necessary for replication, its assay is technically difficult and less standardized than PCR for DNA, making it clinically obsolete for routine monitoring. * **HBeAg (Hepatitis B e-Antigen):** Traditionally considered a marker of high infectivity and active replication. However, it is less sensitive than HBV DNA because "precore mutants" can replicate actively without secreting HBeAg (HBeAg-negative chronic hepatitis). * **Transaminases (ALT/AST):** These are markers of **hepatocyte injury** (host immune response), not viral replication. A patient can have high viral replication with normal transaminases (e.g., Immune Tolerant phase). **Clinical Pearls for NEET-PG:** * **First marker to appear:** HBsAg (usually 2–6 weeks before symptoms). * **Window Period marker:** Anti-HBc IgM (HBsAg and Anti-HBs are both negative). * **Marker of Infectivity:** HBeAg (High) and HBV DNA (Highest sensitivity). * **Marker of Recovery/Immunity:** Anti-HBs. * **Best indicator of successful treatment:** Sustained suppression of HBV DNA.

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Virology — MCQs

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