Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1181: Which of the following agents does not cause pneumonia?

A. Mumps virus (Correct Answer)
B. Measles virus
C. Respiratory Syncytial Virus (RSV)
D. Influenza virus

Explanation: **Explanation:** The correct answer is **A. Mumps virus**. **1. Why Mumps virus is the correct answer:** Mumps is primarily a systemic viral infection caused by a Rubulavirus (Paramyxoviridae family). Its hallmark clinical presentation is **nonsuppurative parotitis** (painful swelling of the salivary glands). While the virus disseminates hematogenously, its primary targets are glandular tissues and the central nervous system. Common complications include **orchitis** (most common in post-pubertal males), oophoritis, meningitis, and pancreatitis. Crucially, Mumps virus is **not** a respiratory pathogen and does not cause pneumonia. **2. Why the other options are incorrect:** * **Measles virus (B):** A leading cause of childhood mortality, Measles frequently causes pneumonia, either directly (Giant cell pneumonia/Hecht's pneumonia) or via secondary bacterial infections due to transient immunosuppression. * **Respiratory Syncytial Virus (RSV) (C):** RSV is the most common cause of bronchiolitis and pneumonia in infants and young children worldwide. * **Influenza virus (D):** Influenza is a classic cause of viral pneumonia and can also predispose patients to severe secondary bacterial pneumonia (most commonly by *S. aureus* or *S. pneumoniae*). **High-Yield Clinical Pearls for NEET-PG:** * **Mumps:** Most common cause of **aseptic meningitis** in unvaccinated populations. * **Warthin-Finkeldey cells:** Pathognomonic multinucleated giant cells found in lymphoid tissues in **Measles**. * **RSV Diagnosis:** Rapid antigen detection or PCR; characterized by formation of syncytia (fusion of cells). * **Steeple Sign:** Seen on X-ray in Croup (Laryngotracheobronchitis), caused by Parainfluenza virus.

Question 1182: Which one of the following is a double-stranded RNA virus?

A. Hepatitis A
B. Hepatitis E
C. Reovirus (Correct Answer)
D. Coronavirus

Explanation: **Explanation:** The correct answer is **Reovirus**. In virology, the majority of RNA viruses are single-stranded (ssRNA). **Reoviruses** (which include **Rotavirus**) are the notable exception, characterized by a **segmented, double-stranded RNA (dsRNA)** genome and a double-layered icosahedral capsid. **Why the other options are incorrect:** * **Hepatitis A (Picornavirus):** This is a non-enveloped, **positive-sense single-stranded RNA (+ssRNA)** virus. It is primarily transmitted via the fecal-oral route. * **Hepatitis E (Hepevirus):** Similar to Hepatitis A, it is a non-enveloped **+ssRNA** virus. It is significant in pregnancy due to the high risk of fulminant hepatic failure. * **Coronavirus:** These are enveloped, **+ssRNA** viruses. They possess the largest genomes among RNA viruses and are known for their characteristic "club-shaped" surface projections (peplomers). **High-Yield Clinical Pearls for NEET-PG:** 1. **Mnemonic for dsRNA:** Remember **"REO"** – **R**espiratory **E**nteric **O**rphan. 2. **Rotavirus:** A member of the Reoviridae family, it is the most common cause of severe infantile diarrhea worldwide. It features **11 segments** of dsRNA. 3. **Wheel-like appearance:** Under electron microscopy, Rotavirus exhibits a characteristic "wheel-and-spoke" appearance (Latin *rota* means wheel). 4. **Segmented Genomes:** Other segmented RNA viruses include **B**unyavirus, **O**rthomyxovirus (Influenza), and **A**renavirus (Mnemonic: **BOAR**). Only Reovirus among these is double-stranded.

Question 1183: Which types of Human Papillomavirus (HPV) are considered low-risk sexually transmitted types?

A. 6 & 11 (Correct Answer)
B. 16 & 18
C. 26 & 53
D. 73 & 82

Explanation: **Explanation:** Human Papillomavirus (HPV) is a double-stranded DNA virus that infects epithelial cells. It is classified into "Low-risk" and "High-risk" types based on its oncogenic potential (ability to cause cancer). **1. Why Option A is Correct:** **HPV types 6 and 11** are the most common **low-risk** types. They are non-oncogenic because their E6 and E7 proteins have a low affinity for p53 and Rb tumor suppressor proteins, respectively. Instead of malignancy, they cause benign epithelial proliferations, most notably **Condyloma acuminatum** (anogenital warts) and **Laryngeal Papillomatosis**. **2. Analysis of Incorrect Options:** * **Option B (16 & 18):** These are the most important **high-risk** types. They are responsible for approximately 70% of cervical cancers worldwide. HPV 16 is specifically associated with squamous cell carcinoma, while HPV 18 is often linked to adenocarcinoma. * **Option C & D (26, 53, 73, 82):** These are classified as "probable" or "potential" high-risk types. While less common than 16 and 18, they are still associated with cervical intraepithelial neoplasia (CIN) and are not considered low-risk. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** HPV E6 inhibits **p53** (pro-apoptotic), and E7 inhibits **pRb** (cell cycle regulator). * **Koilocytes:** The pathognomonic finding on a Pap smear (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Vaccines:** * *Bivalent (Cervarix):* 16, 18. * *Quadrivalent (Gardasil):* 6, 11, 16, 18. * *Nonavalent (Gardasil-9):* 6, 11, 16, 18, 31, 33, 45, 52, 58. * **Skin Warts:** HPV 1, 2, 3, and 4 are typically responsible for non-genital cutaneous warts (verruca vulgaris).

Question 1184: What is the incubation period of herpes zoster?

A. 7-14 days (Correct Answer)
B. 1 month
C. 1-2 years
D. 3-6 months

Explanation: ### Explanation **Correct Answer: A. 7-14 days** **Understanding the Concept:** Herpes Zoster (Shingles) is caused by the reactivation of the **Varicella-Zoster Virus (VZV)**, which remains latent in the sensory dorsal root ganglia following a primary infection (Chickenpox). While the "incubation period" for primary Varicella is typically 10–21 days, the term in the context of Zoster reactivation refers to the time from viral replication in the ganglia to the appearance of the characteristic dermatomal rash. In clinical practice and standardized examinations, the period for this eruptive phase is recognized as **7–14 days**. **Analysis of Incorrect Options:** * **B. 1 month:** This is too long for the acute reactivation phase of a herpesvirus. * **C. 1-2 years:** Reactivation can occur decades after the primary infection, but the "incubation" (the interval between the trigger/reactivation and clinical manifestation) is much shorter. * **D. 3-6 months:** This timeframe is more characteristic of the incubation periods for Hepatitis B or C, not VZV. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Infection:** Chickenpox (Varicella); **Reactivation:** Shingles (Herpes Zoster). * **Hallmark:** Unilateral, painful, vesicular rash restricted to a **single dermatome** (most commonly thoracic). * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusion bodies (shared with HSV-1 and HSV-2). * **Complication:** The most common chronic complication is **Post-Herpetic Neuralgia (PHN)**. * **Ramsey Hunt Syndrome:** VZV involvement of the geniculate ganglion (CN VII), leading to facial palsy and vesicles in the external auditory canal. * **Vaccine:** Live attenuated strains (e.g., Oka strain) are used for prevention.

Question 1185: Which of the following is a marker of acute hepatitis B infection?

A. DNA polymerase (Correct Answer)
B. Hepatitis core antigen
C. Anti HBs
D. IgG to core antigen

Explanation: **Explanation:** The presence of **DNA polymerase** is a direct indicator of active viral replication. In Hepatitis B (HBV), DNA polymerase is found within the core of the virus; its detection in the serum occurs during the early phase of acute infection, coinciding with the peak of viral load and infectivity. While HBsAg is the most common screening marker, DNA polymerase (and HBV DNA) serves as a highly specific marker for the replicative phase of acute hepatitis. **Analysis of Options:** * **Hepatitis core antigen (HBcAg):** This is a "sequestrated" antigen. It is found inside the hepatocyte but **does not circulate freely in the blood**. Therefore, it cannot be used as a serum marker for diagnosis. * **Anti-HBs:** These are protective antibodies that appear after the disappearance of HBsAg. They indicate **recovery and immunity** (either from past infection or vaccination), not an acute infection. * **IgG to core antigen (Anti-HBc IgG):** This marker indicates a **past or chronic infection**. In acute infection, the predominant antibody to the core antigen is of the **IgM** class. **Clinical Pearls for NEET-PG:** * **First marker to appear:** HBsAg. * **Marker of infectivity:** HBeAg and HBV DNA (DNA polymerase). * **Window Period marker:** Anti-HBc IgM (HBsAg and Anti-HBs are both negative). * **Best indicator of vaccination:** Anti-HBs (with all other markers negative). * **Only marker present in all phases of infection (except vaccination):** Anti-HBc (Total).

Question 1186: What is the primary receptor for HIV attachment?

A. CD4 (Correct Answer)
B. CD3
C. CD5
D. CD56

Explanation: **Explanation:** The primary step in HIV infection is the attachment of the viral envelope glycoprotein **gp120** to the **CD4 molecule** on the surface of host cells. This interaction is highly specific and determines the viral tropism for T-helper lymphocytes, macrophages, and dendritic cells. **Why CD4 is correct:** The CD4 molecule acts as the **primary high-affinity receptor**. Upon binding to CD4, gp120 undergoes a conformational change that allows it to subsequently bind to **co-receptors** (CCR5 or CXCR4). This sequential binding is essential for the fusion peptide (gp41) to penetrate the host cell membrane. **Why other options are incorrect:** * **CD3:** This is a pan-T cell marker associated with the T-cell receptor (TCR) complex involved in signal transduction. It does not bind HIV. * **CD5:** A marker found on T cells and a small subset of B cells (B-1 cells); it plays a role in modulating immune responses but not in viral entry. * **CD56:** The primary marker for **Natural Killer (NK) cells**. While NK cells are part of the innate immune response to HIV, they are not the primary targets for viral attachment via gp120. **High-Yield Clinical Pearls for NEET-PG:** * **Co-receptors:** **CCR5** is used by M-tropic strains (early infection), while **CXCR4** is used by T-tropic strains (late-stage/AIDS). * **Genetic Resistance:** Individuals with a **CCR5-Δ32 mutation** are resistant to infection by M-tropic HIV-1. * **Maraviroc:** A drug that acts as a CCR5 antagonist, preventing viral entry. * **Target Cells:** Besides CD4+ T cells, HIV infects **Microglial cells** in the brain (the reservoir for HIV-associated neurocognitive disorders).

Question 1187: Which of the following viruses can be grown only in suckling mice?

A. Coxsackie virus (Correct Answer)
B. Rhinovirus
C. Echovirus
D. Poliovirus

Explanation: **Explanation:** The correct answer is **Coxsackie virus**. In virology, the use of laboratory animals is a traditional method for virus isolation. **Suckling mice** (mice less than 48 hours old) are uniquely susceptible to certain viruses that do not grow well in standard cell cultures or embryonated eggs. 1. **Why Coxsackie virus is correct:** The classification of Coxsackie viruses into Groups A and B is historically based on the specific pathology they induce in suckling mice. * **Group A:** Causes widespread **myositis** in skeletal muscles, leading to flaccid paralysis. * **Group B:** Causes focal myositis, **steatitis** (inflammation of brown fat), and encephalitis, leading to spastic paralysis. While some strains have been adapted to cell culture, suckling mouse inoculation remains the "gold standard" and, for many strains, the only reliable growth method. 2. **Why other options are incorrect:** * **Rhinovirus:** These are primarily grown in human diploid cell lines (e.g., WI-38) at a lower temperature (33°C) to mimic the nasal passage. * **Echovirus:** The name stands for "Enteric Cytopathic Human Orphan" virus. They were named "orphan" because they were originally isolated in **cell cultures** and were not initially associated with specific diseases in animal models (unlike Coxsackie). * **Poliovirus:** While it can infect monkeys, it is routinely grown in primate-derived cell cultures (e.g., Monkey kidney cells or HeLa cells). **High-Yield Clinical Pearls for NEET-PG:** * **Coxsackie A:** Associated with Herpangina and Hand-Foot-Mouth Disease. * **Coxsackie B:** The most common viral cause of Myocarditis and Pleurodynia (Bornholm disease). * **Mnemonic:** Group **A** = **A**ll muscles (Flaccid); Group **B** = **B**ody fat/Brain/Heart (Spastic).

Question 1188: What is the sequence of genetic material replication followed by a retrovirus upon entering a host cell?

A. RNA to DNA to RNA (Correct Answer)
B. RNA to DNA
C. DNA to RNA
D. DNA to RNA to DNA

Explanation: **Explanation:** The hallmark of a **Retrovirus** (e.g., HIV, HTLV) is its ability to reverse the normal flow of genetic information (Central Dogma). 1. **Why Option A is Correct:** Upon entering the host cell, the retrovirus releases its single-stranded positive-sense **RNA** genome. The viral enzyme **Reverse Transcriptase** (RNA-dependent DNA polymerase) converts this RNA into double-stranded **DNA**. This DNA (provirus) integrates into the host genome. Finally, the host’s cellular machinery transcribes this integrated DNA back into new viral **RNA** (genomic RNA and mRNA for protein synthesis). Thus, the sequence is **RNA → DNA → RNA**. 2. **Why Other Options are Incorrect:** * **Option B (RNA to DNA):** This is only the first half of the cycle (Reverse Transcription). Without the final step of transcribing DNA back to RNA, new virions cannot be assembled. * **Option C (DNA to RNA):** This is the standard "Central Dogma" followed by DNA viruses (e.g., Herpesvirus) and host cells, not retroviruses. * **Option D (DNA to RNA to DNA):** This is the replication cycle of **Hepadnaviruses** (e.g., Hepatitis B). They contain a DNA genome, use an RNA intermediate (pre-genome), and use reverse transcriptase to go back to DNA. **High-Yield Clinical Pearls for NEET-PG:** * **Reverse Transcriptase** has three activities: RNA-dependent DNA polymerase, RNase H (degrades the original RNA template), and DNA-dependent DNA polymerase. * **Integrase** is the enzyme responsible for incorporating viral DNA into the host chromosome. * **Hepatitis B** is the only DNA virus that utilizes reverse transcriptase, but its sequence is DNA → RNA → DNA.

Question 1189: All the following statements are true for the viral genome in HIV, except?

A. They are diploid
B. They consist of DNA dependent DNA polymerase activity (Correct Answer)
C. They consist of three major genes-gag, pol and env characteristic of all retroviruses
D. They are the most complex of human retroviruses

Explanation: ### Explanation The correct answer is **B. They consist of DNA dependent DNA polymerase activity.** **1. Why Option B is the correct answer (The "Except" statement):** The HIV virus is a retrovirus, meaning its genome consists of **RNA**, not DNA. To replicate, it utilizes a unique enzyme called **Reverse Transcriptase (RT)**. Reverse transcriptase primarily functions as an **RNA-dependent DNA polymerase (RdDP)**, which transcribes the viral single-stranded RNA into a complementary DNA (cDNA) strand. While RT does possess some DNA-dependent DNA polymerase activity to synthesize the second strand of DNA, the characteristic and defining enzymatic activity of the viral genome/virion is its ability to convert RNA to DNA. In the context of NEET-PG, the hallmark of Retroviridae is **RNA-dependent DNA polymerase**. **2. Analysis of Incorrect Options:** * **Option A (Diploid):** HIV is unique among viruses because it is **diploid**, containing two identical copies of positive-sense single-stranded RNA (+ssRNA). * **Option C (Major Genes):** All retroviruses share three structural genes: **gag** (group-specific antigen - capsid/matrix), **pol** (polymerase - enzymes like RT, protease, integrase), and **env** (envelope glycoproteins gp120/gp41). * **Option D (Complexity):** HIV is considered a **complex retrovirus** because, in addition to the three standard genes, it contains six accessory/regulatory genes (*tat, rev, nef, vif, vpr, vpu*) that modulate pathogenicity and replication. **3. Clinical Pearls & High-Yield Facts:** * **Reverse Transcriptase** lacks proofreading activity, leading to high mutation rates and drug resistance. * **p24 antigen** (encoded by the *gag* gene) is the earliest serological marker detected in the "window period." * **gp120** is responsible for attachment to the CD4 receptor, while **gp41** mediates fusion and entry. * **Integrase** (encoded by *pol*) is the enzyme responsible for incorporating viral DNA into the host cell genome (provirus).

Question 1190: Which of the following cancers is caused by Epstein-Barr Virus (EBV)?

A. Cervical cancer
B. Nasopharyngeal cancer (Correct Answer)
C. Lung cancer
D. Uterine cancer

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is a potent oncogenic virus with a strong tropism for B-lymphocytes and epithelial cells. 1. **Why Nasopharyngeal Cancer is Correct:** EBV is strongly associated with **Nasopharyngeal Carcinoma (NPC)**, particularly the undifferentiated type (WHO Type III). The virus establishes a latent infection in the nasopharyngeal epithelial cells. The expression of viral oncogenes, such as **LMP-1 (Latent Membrane Protein 1)**, mimics CD40 signaling, leading to constitutive activation of cell survival pathways (NF-κB), which drives malignant transformation. 2. **Why Other Options are Incorrect:** * **Cervical Cancer:** Primarily caused by high-risk strains of **Human Papillomavirus (HPV)**, specifically types 16 and 18. * **Lung and Uterine Cancer:** These are generally associated with environmental factors (smoking), hormonal imbalances, or genetic mutations (TP53, KRAS) rather than viral etiologies. **High-Yield Clinical Pearls for NEET-PG:** * **EBV-Associated Malignancies:** * **Burkitt Lymphoma:** Classic "starry sky" appearance; associated with t(8;14) translocation. * **Hodgkin Lymphoma:** Specifically the Mixed Cellularity subtype. * **Primary CNS Lymphoma:** Common in HIV/AIDS patients. * **Gastric Carcinoma:** EBV is linked to ~10% of cases. * **Diagnostic Markers:** The **Monospot Test** (detects heterophile antibodies) is used for Infectious Mononucleosis (Glandular Fever), also caused by EBV. * **Cell Receptor:** EBV enters B-cells via the **CD21** receptor (CR2).

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Virology — MCQs

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