Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 91: What is the emerging organism responsible for causing Pyelonephritis in Renal Allografts?

A. Polyoma virus (Correct Answer)
B. Herpes virus
C. Hepatitis B virus
D. Rota virus

Explanation: ### Explanation **Correct Answer: A. Polyoma virus** The **Polyoma virus**, specifically the **BK virus (BKV)**, is a significant cause of graft dysfunction in renal transplant recipients. After primary infection (usually in childhood), the virus remains latent in the renal tubular epithelium. In the setting of potent immunosuppression following a renal allograft, the virus undergoes **reactivation**. This leads to **BK Virus-Associated Nephropathy (BKVAN)**, which clinically presents as tubulointerstitial nephritis or "Polyoma virus pyelonephritis." Histologically, it is characterized by intranuclear inclusion bodies (Cowdry type A) and can mimic graft rejection. **Why other options are incorrect:** * **B. Herpes virus:** While Cytomegalovirus (CMV), a member of the Herpes family, is the most common viral infection post-transplant, it typically causes systemic symptoms (fever, leukopenia) or specific organ involvement like pneumonitis or colitis, rather than primary pyelonephritis. * **C. Hepatitis B virus:** HBV primarily affects the liver. While it can cause glomerulonephritis (like Membranous Nephropathy) via immune complex deposition, it does not cause infectious pyelonephritis in allografts. * **D. Rota virus:** This is a primary cause of severe dehydrating diarrhea in children and does not have a tropism for the renal parenchyma or allografts. **High-Yield Clinical Pearls for NEET-PG:** * **Decoy Cells:** The presence of renal tubular epithelial cells with enlarged, "ground-glass" intranuclear inclusions in the **urine cytology** is a key screening marker for BK virus. * **JC Virus:** Another Polyoma virus; while BK affects the **B**ody (**K**idney), JC affects the **J**unction (**C**NS), causing Progressive Multifocal Leukoencephalopathy (PML). * **Diagnosis:** The gold standard for BKVAN is a **renal biopsy** showing viral cytopathic changes and positive SV40 immunohistochemical staining. * **Management:** The primary treatment strategy is the **reduction of immunosuppressive therapy**.

Question 92: Shingles is caused by which virus?

A. Varicella-zoster virus (VZV) (Correct Answer)
B. Herpes simplex virus (HSV)
C. Cytomegalovirus (CMV)
D. Enterovirus 70

Explanation: **Explanation:** **Shingles (Herpes Zoster)** is caused by the **Varicella-zoster virus (VZV)**, which is Human Herpesvirus 3 (HHV-3). The pathogenesis involves two distinct clinical phases: 1. **Primary Infection:** Causes **Varicella (Chickenpox)**, characterized by a generalized vesicular rash. 2. **Latency and Reactivation:** Following the primary infection, the virus remains latent in the **dorsal root ganglia** or cranial nerve ganglia. When cell-mediated immunity declines (due to age, stress, or immunosuppression), the virus reactivates and travels down the sensory nerve to cause **Shingles**, a painful, unilateral vesicular eruption localized to a specific **dermatome**. **Analysis of Incorrect Options:** * **Herpes simplex virus (HSV):** HSV-1 typically causes orolabial lesions (cold sores), while HSV-2 causes genital herpes. They do not cause shingles. * **Cytomegalovirus (CMV):** Also known as HHV-5, it commonly causes infectious mononucleosis-like syndrome or severe retinitis/colitis in immunocompromised patients (e.g., AIDS). * **Enterovirus 70:** This is a major cause of **Acute Hemorrhagic Conjunctivitis (AHC)**, not vesicular skin eruptions. **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 (seen in both VZV and HSV). * **Complication:** The most common chronic complication of Shingles is **Post-herpetic Neuralgia (PHN)**. * **Hutchinson’s Sign:** Vesicles on the tip of the nose indicating involvement of the ophthalmic division of the Trigeminal nerve (Herpes Zoster Ophthalmicus). * **Ramsay Hunt Syndrome:** Reactivation in the geniculate ganglion affecting CN VII and VIII.

Question 93: Epstein-Barr virus (EBV) is associated with which of the following conditions, except?

A. Carcinoma of the tonsil
B. Nasopharyngeal carcinoma
C. Anal carcinoma (Correct Answer)
D. Infectious mononucleosis

Explanation: **Explanation:** The correct answer is **Anal carcinoma** because it is primarily associated with **Human Papillomavirus (HPV)**, specifically high-risk types 16 and 18, rather than the Epstein-Barr Virus (EBV). **Why the other options are associated with EBV:** * **Nasopharyngeal Carcinoma:** EBV has a strong oncogenic association with the undifferentiated type of nasopharyngeal carcinoma, particularly prevalent in Southern China and SE Asia. It involves the expression of viral proteins like LMP-1 in epithelial cells. * **Carcinoma of the Tonsil:** While many oropharyngeal cancers are HPV-related, EBV is also linked to certain epithelial malignancies of the Waldeyer’s ring (including the tonsils), often following a similar pathogenic pathway to nasopharyngeal carcinoma. * **Infectious Mononucleosis (Glandular Fever):** This is the classic acute clinical manifestation of primary EBV infection, characterized by the triad of fever, pharyngitis, and lymphadenopathy, with the presence of atypical lymphocytes (Downey cells) on peripheral smear. **High-Yield Clinical Pearls for NEET-PG:** * **EBV Receptor:** It binds to the **CD21** molecule (CR2) on B-lymphocytes. * **Other EBV Associations:** Burkitt Lymphoma (starry-sky appearance), Hodgkin Lymphoma (Mixed cellularity subtype), Oral Hairy Leukoplakia (in HIV patients), and Post-transplant lymphoproliferative disorder (PTLD). * **Diagnosis:** The **Paul-Bunnell Test** (detecting heterophile antibodies) is the classic screening test for Infectious Mononucleosis. * **Mnemonic for HPV:** HPV is associated with "Below the belt" cancers (Cervical, Anal, Vulvar, Penile) and Oropharyngeal squamous cell carcinoma.

Question 94: What is the primary receptor through which M-tropic HIV strains bind?

A. CCR5 (Correct Answer)
B. CXCR4
C. CXCR5
D. Any of the above

Explanation: **Explanation:** The entry of HIV into host cells is a multi-step process involving the viral envelope glycoprotein **gp120**. This protein first binds to the **CD4 receptor** on T-cells or macrophages, causing a conformational change that allows gp120 to interact with a specific **chemokine co-receptor**. 1. **Why CCR5 is correct:** M-tropic (Macrophage-tropic) strains, also known as **R5 strains**, utilize the **CCR5** co-receptor. These strains are typically responsible for the initial infection and are found in the early stages of the disease. They primarily infect macrophages, monocytes, and memory T-cells. 2. **Why CXCR4 is incorrect:** T-tropic (T-cell-tropic) strains, or **X4 strains**, utilize the **CXCR4** co-receptor. These strains emerge in the later stages of HIV infection, show a preference for naïve T-cells, and are associated with a rapid decline in CD4 counts and progression to AIDS. 3. **Why CXCR5 is incorrect:** CXCR5 is a chemokine receptor primarily involved in B-cell homing to lymph nodes; it does not serve as a primary co-receptor for HIV entry. **High-Yield Clinical Pearls for NEET-PG:** * **Maraviroc:** A CCR5 antagonist (entry inhibitor) used in HIV treatment; it is ineffective against X4 (T-tropic) strains. * **Genetic Resistance:** Individuals with a homozygous **CCR5-Δ32 mutation** (a 32-base pair deletion) are virtually resistant to infection by M-tropic HIV-1. * **Coreceptor Switch:** The progression of HIV often involves a "phenotypic switch" where the virus evolves from using CCR5 (M-tropic) to CXCR4 (T-tropic). * **gp41:** While gp120 handles attachment, **gp41** is responsible for the actual fusion of the viral envelope with the host cell membrane.

Question 95: What is used to prevent maternal to child transmission of HIV?

A. Nevirapine (Correct Answer)
B. Lamivudine
C. Didanosine
D. Abacavir

Explanation: **Explanation:** The prevention of mother-to-child transmission (PMTCT) of HIV is a critical high-yield topic for NEET-PG. **Why Nevirapine is the correct answer:** Nevirapine is a **Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)**. It is historically the drug of choice for PMTCT because it has a long half-life, excellent placental transfer, and rapid onset of action. Under the classic WHO and National AIDS Control Organisation (NACO) guidelines (specifically the "Option B" and "Option B+" protocols), a single dose of Nevirapine given to the mother at the onset of labor and to the neonate within 72 hours of birth significantly reduces the risk of vertical transmission. **Analysis of Incorrect Options:** * **Lamivudine (3TC), Didanosine (ddI), and Abacavir (ABC):** These are all **Nucleoside Reverse Transcriptase Inhibitors (NRTIs)**. While these drugs are components of Highly Active Antiretroviral Therapy (HAART) regimens used to treat HIV-positive pregnant women, they are not used as a standalone single-dose intervention for PMTCT in the same way Nevirapine has been traditionally utilized in resource-limited settings. **Clinical Pearls for NEET-PG:** * **Current Protocol:** While single-dose Nevirapine was the standard, current NACO guidelines recommend **Life-long ART** (usually TLE regimen: Tenofovir + Lamivudine + Efavirenz) for all pregnant and breastfeeding women regardless of CD4 count. * **Infant Prophylaxis:** Infants born to HIV-positive mothers should receive daily Nevirapine prophylaxis for at least **6 weeks**. * **Mechanism:** NNRTIs like Nevirapine bind directly to the HIV-1 reverse transcriptase enzyme, causing a conformational change that inhibits its activity. * **Side Effect:** A major side effect of Nevirapine to remember is **Stevens-Johnson Syndrome (SJS)** and hepatotoxicity.

Question 96: Diagnosis of Dengue fever can be made earliest by?

A. Viral culture
B. NS-1 antigen detection (Correct Answer)
C. IgG antibody detection
D. Nucleic acid test

Explanation: **Explanation:** The diagnosis of Dengue fever depends on the timing of the clinical presentation. The correct answer is **NS-1 antigen detection** because it is the earliest detectable marker in the blood. **1. Why NS-1 Antigen is correct:** Non-Structural protein 1 (NS1) is a highly conserved glycoprotein secreted by the Dengue virus during its replication. It becomes detectable in the serum as early as **Day 1 of fever** (even before the onset of symptoms) and typically remains positive until Day 9. Its high sensitivity in the early acute phase makes it the gold standard for early diagnosis in clinical practice. **2. Why other options are incorrect:** * **Viral culture:** While highly specific, it is technically demanding, expensive, and takes several days to weeks to yield results. It is used for research, not for early clinical diagnosis. * **IgG antibody detection:** IgG appears late (after 10–14 days) in primary infections. It is a marker of past infection or secondary infection, not early acute diagnosis. * **Nucleic acid test (RT-PCR):** While RT-PCR is highly sensitive and can detect the virus as early as NS1, it is not the "earliest" practical choice compared to NS1 in most settings due to cost, complexity, and a shorter detection window (viremia often drops after Day 5). In many standardized exams, NS1 is favored as the primary early diagnostic tool. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** NS1 (Day 1–9), IgM (Day 5 onwards), IgG (Day 10–14 in primary; Day 2 in secondary). * **Serology:** A four-fold rise in IgG titers is diagnostic of a recent infection. * **Vector:** *Aedes aegypti* (Day biter; breeds in artificial collections of clean water). * **Tourniquet Test:** Used as a clinical indicator of capillary fragility in Dengue Hemorrhagic Fever (DHF).

Question 97: What is the most common cause of the common cold/coryza?

A. Influenza virus
B. Respiratory Syncytial virus
C. Adenovirus (Correct Answer)
D. Enterovirus 70

Explanation: **Explanation:** The **common cold (coryza)** is an acute, self-limiting viral infection of the upper respiratory tract. While **Rhinoviruses** are globally the most frequent cause of the common cold, among the options provided, **Adenovirus** is the most appropriate answer. Adenoviruses are a major cause of upper respiratory tract infections, particularly in children and military recruits, often presenting as pharyngitis, coryza, and conjunctivitis. **Analysis of Options:** * **Adenovirus (Correct):** It is a non-enveloped DNA virus known for causing a wide spectrum of respiratory illnesses. It is a frequent cause of the common cold and is specifically associated with **Pharyngoconjunctival fever**. * **Influenza virus:** Primarily causes "the flu," a more severe systemic illness characterized by high fever, myalgia, and significant malaise, rather than simple coryza. * **Respiratory Syncytial Virus (RSV):** While it can cause cold-like symptoms in adults, it is the leading cause of **bronchiolitis and pneumonia** in infants and young children. * **Enterovirus 70:** This specific serotype is primarily associated with **Acute Hemorrhagic Conjunctivitis (AHC)**, not respiratory infections. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause overall:** Rhinoviruses (30-50%). * **Second most common:** Coronaviruses (excluding COVID-19 pandemic strains). * **Adenovirus Serotypes:** Types 1, 2, 5, and 6 cause common cold; Types 3, 7, and 14 cause pharyngoconjunctival fever; Types 40 and 41 cause gastroenteritis. * **Military association:** Adenovirus types 4 and 7 are notorious for outbreaks in military barracks (prevented by a live oral vaccine in some countries).

Question 98: Which of the following viruses has a double-stranded RNA genome?

A. Reovirus (Correct Answer)
B. Rhabdovirus
C. Parvovirus
D. Retrovirus

Explanation: **Explanation:** The correct answer is **Reovirus**. In virology, the nature of the viral genome (DNA vs. RNA and single-stranded vs. double-stranded) is a high-yield classification for competitive exams. **1. Why Reovirus is Correct:** Most RNA viruses are single-stranded (ssRNA). **Reoviruses** (including Rotavirus and Coltivirus) are the notable exception, possessing a **segmented, double-stranded RNA (dsRNA)** genome. This unique structure requires the virus to carry its own RNA-dependent RNA polymerase to transcribe mRNA from the negative strand of the dsRNA. **2. Analysis of Incorrect Options:** * **Rhabdovirus (e.g., Rabies):** These are negative-sense, single-stranded RNA (-ssRNA) viruses. They are characterized by their bullet-shaped morphology. * **Parvovirus (e.g., B19):** This is the "exception" in the DNA family. While most DNA viruses are double-stranded, Parvovirus is a **single-stranded DNA (ssDNA)** virus. * **Retrovirus (e.g., HIV):** These contain two identical copies of **positive-sense, single-stranded RNA (+ssRNA)**. They are unique because they use reverse transcriptase to convert RNA into DNA. **3. NEET-PG High-Yield Pearls:** * **Mnemonic for dsRNA:** "REO" stands for **R**espiratory **E**nteric **O**rphan. * **Rotavirus:** A member of the Reoviridae family, it is the most common cause of severe diarrhea in infants and young children worldwide. It has **11 segments** in its genome. * **Segmented Viruses:** Remember **BOAR** (Bunyavirus, Orthomyxovirus, Arenavirus, Reovirus). Reovirus is the only one in this group that is double-stranded. * **Double-stranded RNA** is a potent inducer of **Interferon** production in the host cell.

Question 99: The dengue fever virus belongs to which family?

A. Flavivirus (Correct Answer)
B. Echovirus
C. Enterovirus
D. Orthomyxovirus

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. The family Flaviviridae also includes other clinically significant viruses such as Yellow Fever, West Nile, Zika, and Hepatitis C viruses. **Analysis of Options:** * **A. Flavivirus (Correct):** Dengue virus has four distinct serotypes (DEN-1 to DEN-4). Infection with one serotype provides lifelong immunity to that specific type but increases the risk of severe disease (Dengue Hemorrhagic Fever) upon secondary infection with a different serotype due to **Antibody-Dependent Enhancement (ADE)**. * **B. & C. Echovirus and Enterovirus:** These belong to the **Picornaviridae** family. They are small, non-enveloped RNA viruses typically transmitted via the fecal-oral route, causing conditions like aseptic meningitis, myocarditis, or hand-foot-and-mouth disease. * **D. Orthomyxovirus:** This family includes the **Influenza viruses**. These are enveloped, segmented, negative-sense RNA viruses characterized by surface glycoproteins Hemagglutinin (H) and Neuraminidase (N). **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 (Day 1–5). IgM/IgG ELISA is used after Day 5. * **Tourniquet Test:** A positive test (≥10-20 petechiae per square inch) indicates capillary fragility. * **Characteristic Triad:** High fever, retro-orbital pain, and severe backache ("Break-bone fever").

Question 100: A 14-year-old boy presents with a sore throat, fever, enlarged lymph nodes, pharyngeal inflammation, splenomegaly, and severe fatigue. How is the causative agent best confirmed?

A. A positive Tzanck smear
B. IgM heterophile antibodies (Correct Answer)
C. Koilocytotic cells
D. PCR for Enterovirus

Explanation: ### Explanation The clinical presentation of fever, sore throat (pharyngitis), lymphadenopathy, splenomegaly, and fatigue in a teenager is classic for **Infectious Mononucleosis (IM)**, most commonly caused by **Epstein-Barr Virus (EBV)**. **Why Option B is Correct:** The diagnosis of IM is best confirmed by detecting **heterophile antibodies** (IgM). These are non-specific antibodies that agglutinate sheep or horse red blood cells (the basis of the **Monospot test**). In a patient with the characteristic triad of fever, pharyngitis, and lymphadenopathy, a positive heterophile antibody test is highly diagnostic. If the Monospot is negative but suspicion remains high, EBV-specific serology (e.g., anti-VCA IgM) is the next step. **Why Other Options are Incorrect:** * **A. Tzanck smear:** Used to identify multinucleated giant cells in infections caused by HSV-1, HSV-2, or VZV (Varicella-Zoster). It is not used for EBV. * **C. Koilocytotic cells:** These are hallmark histological findings of **Human Papillomavirus (HPV)** infection, characterized by perinuclear halos and nuclear wrinkling. * **D. PCR for Enterovirus:** Enteroviruses (like Coxsackievirus) can cause herpangina or hand-foot-mouth disease, but they do not typically cause significant splenomegaly or positive heterophile antibodies. **High-Yield Clinical Pearls for NEET-PG:** * **Hematology:** Look for **atypical lymphocytes** (Downey cells) on a peripheral smear—these are activated T-cells (CD8+) reacting against infected B-cells. * **The "Ampicillin Rash":** If a patient with IM is mistakenly treated with Ampicillin or Amoxicillin for suspected strep throat, they often develop a characteristic maculopapular rash. * **Complications:** Splenic rupture is a rare but serious complication; patients must avoid contact sports for 3–4 weeks. * **Receptor:** EBV enters B-cells via the **CD21** receptor (CR2).

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Virology — MCQs

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