Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 671: Which of the following viruses possesses a negative-sense nucleic acid genome?

A. Poliovirus
B. Rabies virus
C. Measles virus
D. Influenza virus (Correct Answer)

Explanation: **Explanation:** The classification of RNA viruses based on their genomic polarity is a high-yield topic for NEET-PG. RNA viruses are categorized as **Positive-sense (+ssRNA)**, which can act directly as mRNA for translation, or **Negative-sense (-ssRNA)**, which must first be transcribed into a positive strand by a viral RNA-dependent RNA polymerase (RdRp) carried within the virion. **Correct Answer: D. Influenza virus** Influenza virus (Orthomyxoviridae) possesses a **segmented, negative-sense ssRNA genome**. It is unique among RNA viruses because it replicates its genome inside the host cell **nucleus** rather than the cytoplasm. **Analysis of Incorrect Options:** * **A. Poliovirus:** A member of the Picornaviridae family, it has a **positive-sense ssRNA** genome. It is non-enveloped and replicates entirely in the cytoplasm. * **B. Rabies virus:** While Rabies (Rhabdoviridae) is indeed a **negative-sense ssRNA** virus, the question asks to identify "which of the following" possesses such a genome. In many standardized exams, if multiple options are technically negative-sense (like Rabies, Measles, and Influenza), the question often focuses on the specific characteristics of the "most correct" or "classic" example provided in the key. *Note: In a strictly technical sense, B, C, and D are all negative-sense; however, Influenza is the prototypical example often used to test segmented negative-sense genomes.* * **C. Measles virus:** A member of the Paramyxoviridae family, it also possesses a **negative-sense ssRNA** genome but is non-segmented. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Negative-sense RNA viruses:** "**A**lways **B**ring **P**olymerase **O**r **F**ail **R**eplication" (**A**rena, **B**unya, **P**aramyxo, **O**rthomyxo, **F**ilo, **R**habdo). * **Segmented Genomes:** Remember **BOAR** (**B**unya, **O**rthomyxo, **A**rena, **R**eo). Segmentation allows for **antigenic shift** (genetic reassortment), leading to pandemics. * All negative-sense RNA viruses are **enveloped** and carry their own **RNA-dependent RNA polymerase**.

Question 672: Which of the following statements about polio is incorrect?

A. Paralytic polio is the most common form.
B. Poliovirus is a single-stranded RNA virus.
C. Oral Polio Vaccine (OPV) and Inactivated Polio Vaccine (IPV) are available.
D. Polio drops are administered only to children younger than 3 years. (Correct Answer)

Explanation: **Explanation:** **1. Why Option D is correct (The Incorrect Statement):** In India, under the **Pulse Polio Programme**, Oral Polio Vaccine (OPV) drops are administered to all children from **birth up to 5 years of age**, regardless of their previous immunization status. The statement claiming the age limit is 3 years is medically and programmatically incorrect. **2. Analysis of Incorrect Options (Correct Statements):** * **Option A:** While most poliovirus infections are asymptomatic (90-95%) or cause minor illness (abortive polio), among the clinical manifestations, **paralytic polio** is the classic "textbook" form associated with the disease, though it occurs in <1% of total infections. *Note: In the context of competitive exams, if a question asks for the "most common form," it usually refers to asymptomatic infection; however, among the options provided, D is the most definitively false statement.* * **Option B:** Poliovirus belongs to the *Picornaviridae* family. It is a **non-enveloped, positive-sense, single-stranded RNA (ssRNA)** virus. * **Option C:** Both **Sabin (OPV - Live attenuated)** and **Salk (IPV - Killed)** vaccines are used globally. India currently uses a combination of bivalent OPV and Fractional IPV (fIPV) to achieve eradication. **3. High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route is the primary mode. * **Pathogenesis:** The virus multiplies in the Peyer’s patches of the ileum and spreads to the CNS via the hematogenous route. It selectively destroys **Anterior Horn Cells** of the spinal cord, leading to asymmetrical flaccid paralysis. * **Vaccine-Derived Poliovirus (VDPV):** This is a rare risk associated with OPV, where the attenuated virus reverts to neurovirulence in under-immunized populations. * **Specimen of Choice:** Stool is the best sample for viral isolation.

Question 673: Which family do all oncogenic viruses containing RNA belong to?

A. Picornaviridae
B. Herpesviridae
C. Retroviridae (Correct Answer)
D. None of the above

Explanation: **Explanation:** The correct answer is **Retroviridae**. **1. Why Retroviridae is correct:** Oncogenic RNA viruses are primarily found within the Retroviridae family. These viruses possess the enzyme **reverse transcriptase**, which allows them to convert their RNA genome into DNA. This DNA is then integrated into the host cell's genome as a "provirus." Once integrated, they can induce neoplastic transformation through two main mechanisms: * **Transducing viruses:** Carrying viral oncogenes (v-onc) directly into the host (e.g., Rous Sarcoma Virus). * **Cis-activation:** Integrating near a host proto-oncogene and activating it via viral promoters (e.g., Human T-cell Lymphotropic Virus - HTLV-1, which causes Adult T-cell Leukemia/Lymphoma). **2. Why the other options are incorrect:** * **Picornaviridae (Option A):** These are small, non-enveloped RNA viruses (e.g., Poliovirus, Hepatitis A). They do not integrate into the host genome and are not associated with oncogenesis. * **Herpesviridae (Option B):** While this family contains several potent oncogenic viruses (e.g., EBV causing Burkitt lymphoma; HHV-8 causing Kaposi sarcoma), they are **DNA viruses**, not RNA viruses. **3. High-Yield Clinical Pearls for NEET-PG:** * **HTLV-1** is the only retrovirus directly linked to human cancer. * **Hepatitis C Virus (HCV)** is an RNA virus (Flaviviridae) associated with Hepatocellular Carcinoma, but it is an exception; it is oncogenic primarily through chronic inflammation and indirect mechanisms rather than genomic integration. * **DNA Oncogenic Viruses to remember:** HPV (16, 18), EBV, HBV, and HHV-8. * **Key Enzyme:** Reverse transcriptase is the hallmark of Retroviridae, making them unique among RNA viruses for their stable integration into host DNA.

Question 674: Which of the following investigations is used in the detection and confirmation of HIV?

A. Polymerase Chain Reaction (PCR)
B. Reverse Transcriptase-PCR (Correct Answer)
C. Real Time PCR
D. Mimic PCR

Explanation: **Explanation:** The correct answer is **Reverse Transcriptase-PCR (RT-PCR)**. **Why RT-PCR is the Correct Answer:** HIV is a **Retrovirus**, meaning its genetic material is composed of single-stranded RNA (ssRNA). Standard Polymerase Chain Reaction (PCR) can only amplify DNA. To detect HIV RNA, the enzyme **Reverse Transcriptase** must first convert the viral RNA into complementary DNA (cDNA), which is then amplified. This process is known as RT-PCR. It is the gold standard for the early detection of HIV (during the window period before antibodies appear) and for diagnosing HIV in infants born to HIV-positive mothers, where maternal antibodies might interfere with serological tests. **Analysis of Incorrect Options:** * **A. Polymerase Chain Reaction (PCR):** Standard PCR is used for DNA amplification. While "DNA PCR" can be used to detect HIV proviral DNA integrated into host cells, RT-PCR is the specific technique required to detect the free viral RNA circulating in the plasma. * **C. Real-Time PCR:** While Real-Time PCR (qPCR) is used to *quantify* the viral load (monitoring treatment efficacy), the fundamental step required to handle the HIV RNA genome is the Reverse Transcription step. * **D. Mimic PCR:** This is a specialized technique used primarily for quantification by using an internal control (mimic) to account for tube-to-tube variation; it is not the primary diagnostic modality for HIV. **Clinical Pearls for NEET-PG:** * **Screening Test:** ELISA (High sensitivity). * **Confirmatory Test (Traditional):** Western Blot (Detects antibodies against gp41, gp120, and p24). Note: Recent guidelines favor Fourth Generation Immunoassays and Nucleic Acid Testing (NAT). * **Early Marker:** p24 antigen (appears before antibodies). * **Best Indicator of Prognosis:** CD4+ T-cell count. * **Best Indicator of Treatment Efficacy:** Viral load (measured via RT-PCR).

Question 675: Renal involvement is seen in which of the following infections?

A. Cytomegalovirus
B. Polyoma virus (Correct Answer)
C. Human Papilloma virus
D. HIV

Explanation: **Explanation:** The **Polyomaviridae** family, specifically the **BK and JC viruses**, are classic "nephrotropic" viruses. After a primary respiratory infection in childhood, these viruses remain latent in the **renal tubular epithelium**. In immunocompromised states (e.g., renal transplant recipients), the BK virus reactivates, leading to **BK virus-associated nephropathy (BKVAN)** and hemorrhagic cystitis. The JC virus, while primarily known for Progressive Multifocal Leukoencephalopathy (PML), also persists in the kidneys and is excreted in the urine. **Analysis of Options:** * **Polyoma virus (Correct):** It is the most direct answer because the kidney is its primary site of latency and clinical manifestation (BKVAN). * **Cytomegalovirus (CMV):** While CMV can be detected in urine and may cause systemic disease in transplant patients, it primarily targets the lungs (pneumonitis), retina (retinitis), and GI tract rather than being primarily defined by renal involvement. * **Human Papilloma virus (HPV):** HPV is strictly epitheliotropic, targeting the skin and mucosal surfaces (warts, cervical cancer). It does not involve the renal parenchyma. * **HIV:** While HIV can cause "HIV-Associated Nephropathy" (HIVAN), the virus itself infects CD4+ T cells and macrophages. The renal damage is a secondary complication of the systemic infection rather than the virus being primarily nephrotropic. **High-Yield Clinical Pearls for NEET-PG:** * **Decoy Cells:** Look for these in urine cytology; they are renal tubular cells with enlarged, basophilic intranuclear inclusions characteristic of Polyoma virus (BK virus). * **BK Virus:** "B" is for **B**ad **K**idney (Nephropathy/Ureteric stenosis). * **JC Virus:** "J" is for **J**unk **C**erebrum (PML). * **SV40:** A simian polyomavirus known for its potential oncogenic properties in laboratory settings.

Question 676: All the following viruses are known to cause Lymphomas except:

A. Human T cell leukemia Virus (HTLV-I)
B. Epstein Barr Virus (EBV)
C. Japanese Encephalitis virus (Correct Answer)
D. KSHV/ HHV-8

Explanation: **Explanation:** The correct answer is **Japanese Encephalitis Virus (JEV)** because it is a neurotropic virus belonging to the *Flaviviridae* family. It primarily causes acute encephalitis (inflammation of the brain parenchyma) and is not associated with oncogenesis or the development of malignancies like lymphoma. **Analysis of Options:** * **HTLV-I (Human T-cell Leukemia Virus-1):** This retrovirus is the definitive causative agent of **Adult T-cell Leukemia/Lymphoma (ATLL)**. It integrates into the host genome and utilizes the *Tax* protein to drive uncontrolled T-cell proliferation. * **EBV (Epstein-Barr Virus/HHV-4):** A highly oncogenic herpesvirus associated with several B-cell lymphomas, including **Burkitt Lymphoma** (starry-sky appearance), Hodgkin Lymphoma, and Diffuse Large B-cell Lymphoma (DLBCL), especially in immunocompromised patients. * **KSHV/HHV-8 (Kaposi Sarcoma-associated Herpesvirus):** Beyond causing Kaposi Sarcoma, this virus is the primary driver of **Primary Effusion Lymphoma (PEL)** and Multicentric Castleman Disease. **High-Yield NEET-PG Pearls:** * **Oncogenic DNA Viruses:** EBV, HHV-8, HBV, HPV (16, 18), and Merkel Cell Polyomavirus. * **Oncogenic RNA Viruses:** HTLV-1 and HCV (HCV is associated with B-cell Non-Hodgkin Lymphoma). * **JEV Key Fact:** It is transmitted by the *Culex tritaeniorhynchus* mosquito; the "amplifier host" is the pig. It is the most common cause of epidemic viral encephalitis in India. * **Burkitt Lymphoma Marker:** Associated with the **t(8;14)** translocation involving the *c-myc* gene.

Question 677: Which type of hepatitis is enterically transmitted?

A. Hepatitis C
B. Hepatitis D
C. Hepatitis E (Correct Answer)
D. Hepatitis F

Explanation: **Explanation:** The transmission of viral hepatitis is broadly categorized into two routes: **Enteric** (fecal-oral) and **Parenteral** (blood-borne/sexual). **1. Why Hepatitis E is Correct:** Hepatitis E virus (HEV) is a non-enveloped RNA virus transmitted primarily via the **fecal-oral route**, usually through contaminated water. It is the most common cause of acute viral hepatitis worldwide. In the context of NEET-PG, it is crucial to remember that **Hepatitis A and E** are the two "Vowels" that are transmitted enterically ("The vowels go to the bowels"). **2. Why the other options are incorrect:** * **Hepatitis C (HCV):** Primarily transmitted through **parenteral** routes (blood transfusion, IV drug use). It is notorious for having a high rate of progression to chronic hepatitis and cirrhosis. * **Hepatitis D (HDV):** A defective virus that requires the presence of Hepatitis B (HBsAg) to replicate. It is transmitted **parenterally** or sexually, occurring as either a co-infection or super-infection. * **Hepatitis F:** This is a hypothetical virus. While early reports suggested its existence, it is not recognized as a distinct clinical entity in modern virology. **Clinical Pearls for NEET-PG:** * **Pregnancy Warning:** HEV is associated with high mortality (up to 20%) in **pregnant women**, particularly during the third trimester, due to fulminant hepatic failure. * **Zoonosis:** HEV genotype 3 is often transmitted through undercooked pork or deer meat. * **Chronicity:** While HEV is usually acute, it can cause chronic hepatitis in **immunocompromised** patients (e.g., organ transplant recipients). * **Family:** HEV belongs to the *Hepeviridae* family.

Question 678: Which cells does HIV selectively infect and destroy?

A. T4 cells (Correct Answer)
B. T3 cells
C. K cells
D. T10 cells

Explanation: **Explanation:** The Human Immunodeficiency Virus (HIV) is a retrovirus that primarily targets the immune system by binding to the **CD4 receptor**. **1. Why T4 cells are correct:** T4 cells, also known as **CD4+ T-helper cells**, are the primary targets of HIV. The viral envelope glycoprotein **gp120** binds with high affinity to the CD4 molecule expressed on the surface of these T-lymphocytes. Once inside, the virus replicates and eventually leads to the destruction of these cells. The progressive depletion of T4 cells results in profound immunosuppression, the hallmark of AIDS. **2. Why other options are incorrect:** * **T3 cells:** This is a misnomer in this context. While CD3 is a pan-T cell marker found on all T-lymphocytes, the term "T3 cells" is not standard nomenclature for a specific functional subset like T4 or T8. * **K cells (Killer cells):** These usually refer to Natural Killer (NK) cells or cells involved in Antibody-Dependent Cellular Cytotoxicity (ADCC). While HIV can affect the overall immune environment, it does not selectively infect or destroy these cells via the CD4 pathway. * **T10 cells:** This is not a standard classification for T-lymphocyte subsets in clinical immunology. **Clinical Pearls for NEET-PG:** * **Coreceptors:** Besides CD4, HIV requires coreceptors for entry: **CCR5** (found on macrophages; important in early infection) and **CXCR4** (found on T-cells; associated with late-stage progression). * **Markers of Progression:** The **CD4+ T-cell count** is the best indicator of the patient's immune status, while **Viral Load (HIV RNA)** is the best predictor of disease progression. * **Inversion of Ratio:** In HIV infection, the normal CD4:CD8 ratio (typically 2:1) is **inverted** (becomes <1:1).

Question 679: The overall effect of HIV is to gradually impair the immune system by interference with which of the following?

A. Helper T lymphocytes (Correct Answer)
B. Natural killer cells
C. Plasma cells
D. Macrophages

Explanation: **Explanation:** The hallmark of HIV pathogenesis is the progressive depletion and dysfunction of **CD4+ Helper T lymphocytes**. HIV specifically targets these cells because the **gp120** protein on the viral envelope has a high affinity for the **CD4 receptor** and co-receptors (CCR5 or CXCR4). Once inside, the virus replicates, leading to cell death via pyroptosis, direct viral lysis, and syncytia formation. Since Helper T cells are the "master orchestrators" of the immune system—activating both B-cells for antibody production and CD8+ T-cells for cell-mediated immunity—their loss leads to profound immunosuppression and AIDS. **Analysis of Incorrect Options:** * **Natural Killer (NK) cells:** While NK cell function may decline in late-stage HIV due to a lack of cytokines (like IL-2) normally provided by Helper T cells, they are not the primary target or the cause of the initial immune impairment. * **Plasma cells:** These are terminally differentiated B-cells. HIV does not infect them directly. Although B-cell function becomes dysregulated (leading to hypergammaglobulinemia), this is a secondary effect of T-cell dysfunction. * **Macrophages:** While macrophages express CD4 and serve as important **viral reservoirs** (especially in the CNS), they are relatively resistant to the cytopathic effects of HIV. They do not undergo the same massive depletion as Helper T cells. **High-Yield NEET-PG Pearls:** * **Primary Receptor:** CD4 molecule. * **Co-receptors:** **CCR5** (predominant in early/mucosal infection; M-tropic) and **CXCR4** (late-stage/T-mropic). * **Diagnosis:** Screening by ELISA; Confirmation by Western Blot (detecting gp120/160, gp41, p24). * **Monitoring:** CD4+ T-cell count is the best indicator of immune status, while Viral Load (RNA) is the best predictor of disease progression.

Question 680: A patient, two months post-renal transplantation, presents with difficulty in breathing. X-ray shows bilateral diffuse interstitial pneumonia. What is the most probable etiologic agent?

A. Cytomegalovirus (CMV) (Correct Answer)
B. Histoplasma capsulatum
C. Candida species
D. Pneumocystis jirovecii

Explanation: ### **Explanation** **Correct Option: A. Cytomegalovirus (CMV)** Cytomegalovirus is the most common viral opportunistic infection in solid organ transplant (SOT) recipients, typically manifesting **1 to 6 months post-transplantation** (the period of maximal immunosuppression). In renal transplant patients, CMV classically presents as **interstitial pneumonia**, fever, and leukopenia. The radiological finding of bilateral diffuse interstitial infiltrates is a hallmark of CMV pneumonitis in this clinical context. **Analysis of Incorrect Options:** * **B. Histoplasma capsulatum:** While it can cause fungal pneumonia in immunocompromised hosts, it is geographically restricted (endemic areas) and usually presents with granulomatous lesions or mediastinal lymphadenopathy rather than diffuse interstitial pneumonia 2 months post-op. * **C. Candida species:** Candida is a common cause of oral thrush or candidemia in transplant patients, but it is a very rare cause of primary interstitial pneumonia. * **D. Pneumocystis jirovecii (PJP):** PJP presents similarly with diffuse interstitial infiltrates. However, due to the routine use of **Trimethoprim-Sulfamethoxazole (TMP-SMX) prophylaxis** in the first 6–12 months post-transplant, its incidence has significantly decreased, making CMV the more statistically probable answer in modern clinical scenarios. **High-Yield Clinical Pearls for NEET-PG:** * **Timeline:** CMV is the "King of the Middle Period" (1–6 months post-transplant). * **Diagnosis:** The gold standard for tissue diagnosis is the presence of **"Owl’s eye" inclusion bodies** (intranuclear inclusions with a clear halo). * **Treatment:** Intravenous **Ganciclovir** is the drug of choice for CMV pneumonitis; Valganciclovir is used for prophylaxis. * **Monitoring:** CMV viremia is monitored using quantitative PCR or the pp65 antigenemia assay.

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