Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 351: Trans-placental spread is least associated with which of the following pathogens?

A. Hepatitis B virus
B. Rubella virus
C. Herpes Simplex virus (Correct Answer)
D. Human Immunodeficiency Virus

Explanation: **Explanation:** The core concept tested here is the **mode of vertical transmission**. Vertical transmission can occur via three routes: **in utero** (trans-placental), **intrapartum** (during delivery through the birth canal), or **postpartum** (breastfeeding). **Why Herpes Simplex Virus (HSV) is the correct answer:** While HSV is a major cause of neonatal infection, it is **least associated with trans-placental spread**. Approximately **85-90%** of neonatal HSV cases are acquired **intrapartum** due to direct contact with infected maternal vaginal secretions during labor. Trans-placental (congenital) HSV is rare, occurring in only about 5% of cases, usually following a primary maternal infection during early pregnancy. **Analysis of Incorrect Options:** * **Rubella Virus:** A classic member of the **ToRCH** group. It primarily spreads **trans-placentally**, leading to Congenital Rubella Syndrome (cataracts, PDA, sensorineural deafness), especially if the mother is infected in the first trimester. * **Hepatitis B Virus (HBV):** While HBV is frequently transmitted at the time of delivery (peripartum), it is well-documented to cross the placenta, especially if the mother has high viral loads or is HBeAg positive. * **Human Immunodeficiency Virus (HIV):** HIV can be transmitted across the placenta throughout pregnancy, though the risk is highest during labor and delivery or through breastfeeding. **High-Yield Clinical Pearls for NEET-PG:** * **ToRCH Complex:** Toxoplasmosis, Other (Syphilis, Parvovirus B19, VZV), Rubella, CMV, and HSV. * **HSV Transmission:** Most common during the second stage of labor. If active genital lesions are present at the time of labor, a **Cesarean section** is indicated to prevent neonatal infection. * **CMV:** The most common cause of congenital (trans-placental) viral infection worldwide. * **Hepatitis B:** Neonates born to HBsAg+ mothers must receive both the **HBV vaccine and HBIG** within 12 hours of birth.

Question 352: Which serological marker best diagnoses a recent Hepatitis B infection?

A. Hepatitis B surface antigen (HBsAg)
B. IgG anti-Hepatitis B e antibody
C. Anti-Hepatitis B surface antibody
D. IgM anti-Hepatitis B core antibody (Correct Answer)

Explanation: ### Explanation **Correct Option: D. IgM anti-Hepatitis B core antibody (IgM anti-HBc)** **Why it is correct:** IgM anti-HBc is the hallmark of **acute or recent** Hepatitis B infection (typically within the first 6 months). Its clinical significance is paramount during the **"Window Period"**—the interval where HBsAg has disappeared but Anti-HBs has not yet appeared. During this gap, IgM anti-HBc may be the **only** detectable serological marker of a recent infection. **Analysis of Incorrect Options:** * **A. HBsAg:** While it is the first marker to appear and indicates active infection, it does not distinguish between acute and chronic states. It can remain positive for decades in chronic carriers. * **B. IgG anti-HBe:** This antibody indicates reduced viral replication and low infectivity. It appears later in the course of infection and is not a primary tool for diagnosing a *recent* acute event. * **C. Anti-HBs:** This antibody signifies **immunity**, either through recovery from a natural infection or via vaccination. It appears only after the infection has resolved. **NEET-PG High-Yield Pearls:** 1. **Window Period Marker:** IgM anti-HBc is the diagnostic marker of choice when HBsAg and Anti-HBs are both negative. 2. **Vaccination vs. Natural Infection:** * **Vaccinated:** Only Anti-HBs is positive. * **Prior Natural Infection:** Both Anti-HBs and IgG anti-HBc are positive. 3. **Chronic Infection:** Defined by the persistence of HBsAg for >6 months. 4. **HBeAg:** Indicates high viral load and high infectivity ("e" for envelope/excess replication).

Question 353: Sharps, syringes, and needles used for patients whose HIV test results are not known, should be immersed in which of the following solutions for disinfection?

A. 1% Povidone-iodine solution (Correct Answer)
B. Boiling water
C. 1% solution of sodium hypochlorite
D. 10% solution of Dettol

Explanation: **Explanation:** The management of biomedical waste and disinfection of sharps is a critical component of hospital infection control. According to standard protocols for handling equipment potentially contaminated with blood-borne pathogens like HIV, HBV, or HCV, chemical disinfection is required before final disposal. **1. Why 1% Povidone-iodine is correct:** Povidone-iodine is an iodophor that acts as a potent oxidizing agent, disrupting microbial protein synthesis and cell membranes. For sharps, syringes, and needles—especially when the HIV status is unknown—immersion in **1% Povidone-iodine** for at least 30 minutes is a recommended practice for bedside disinfection to reduce the viral load before the sharps are transported to the central waste management area. **2. Analysis of Incorrect Options:** * **Boiling water (B):** Boiling is a method of disinfection, not sterilization. It does not reliably kill bacterial spores and is impractical/unsafe for the immediate bedside containment of contaminated needles. * **1% Sodium hypochlorite (C):** While hypochlorite is the gold standard for disinfecting **blood spills** on surfaces, it is highly corrosive to metal. Prolonged immersion of needles and sharps in hypochlorite can damage the metal and create hazardous fumes. * **10% Dettol (D):** Dettol (Chloroxylenol) is an antiseptic used for skin and environmental surfaces. It is less effective against blood-borne viruses compared to iodophors or chlorine-based compounds. **High-Yield Clinical Pearls for NEET-PG:** * **Blood Spills:** Use 1% Sodium Hypochlorite for small spills and 10% for large spills (leave for 20–30 mins). * **Needle Stick Injury (NSI):** The first step is to wash the area with soap and water. Do not scrub or use antiseptics like bleach. * **HIV Survival:** HIV is a fragile virus; it is inactivated by heat (56°C for 30 mins) and standard disinfectants (70% ethanol, glutaraldehyde, and iodine). * **BMW Management:** Sharps must always be disposed of in **White, translucent, puncture-proof containers.**

Question 354: Which virus is implicated in Burkitt's lymphoma?

A. EBV (Correct Answer)
B. HTLV
C. HPV
D. HHV8

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is the primary etiological agent implicated in **Burkitt’s Lymphoma**. The virus infects B-lymphocytes via the **CD21 receptor**. The oncogenic mechanism involves a characteristic chromosomal translocation, most commonly **t(8;14)**, which leads to the overexpression of the **c-myc proto-oncogene**, resulting in uncontrolled B-cell proliferation. **Analysis of Options:** * **A. EBV (Correct):** Strongly associated with the endemic (African) form of Burkitt’s lymphoma (found in 100% of cases) and to a lesser extent with sporadic and HIV-associated forms. * **B. HTLV (Human T-cell Lymphotropic Virus):** Specifically associated with **Adult T-cell Leukemia/Lymphoma (ATLL)**, not B-cell lymphomas. * **C. HPV (Human Papillomavirus):** Implicated in squamous cell carcinomas, primarily **Cervical Cancer** (Types 16, 18) and oropharyngeal cancers. * **D. HHV8 (KSHV):** Associated with **Kaposi Sarcoma** and Primary Effusion Lymphoma, typically in immunocompromised patients. **High-Yield Clinical Pearls for NEET-PG:** * **Histology:** Burkitt’s lymphoma classically shows a **"Starry Sky" appearance** (tingible body macrophages against a background of dark neoplastic B-cells). * **Other EBV Associations:** Infectious Mononucleosis (Heterophile positive), Nasopharyngeal Carcinoma, Oral Hairy Leukoplakia (in HIV), and Hodgkin’s Lymphoma (Mixed cellularity type). * **Diagnosis:** EBV is detected via the Monospot test (Paul-Bunnell test) or by identifying EBNA (EBV Nuclear Antigen).

Question 355: The Dane particle is the?

A. HBV (Correct Answer)
B. IgG anti HAV
C. Delta Virus
D. HBC Ag

Explanation: **Explanation:** The **Dane particle** is the complete, infectious virion of the **Hepatitis B Virus (HBV)**. First identified by DS Dane in 1970 via electron microscopy, it is a spherical structure measuring approximately **42 nm** in diameter. It consists of an inner nucleocapsid core (containing HBcAg, the DNA genome, and DNA polymerase) surrounded by an outer lipoprotein envelope containing the surface antigen (HBsAg). **Analysis of Options:** * **Option A (HBV):** Correct. The 42 nm Dane particle represents the intact, double-shelled virus capable of replication. It is found in the serum along with smaller (22 nm) spherical and tubular forms, which are non-infectious surpluses of HBsAg. * **Option B (IgG anti-HAV):** Incorrect. This is a host antibody indicating past infection or immunity to Hepatitis A; it is not a viral particle. * **Option C (Delta Virus):** Incorrect. This refers to Hepatitis D (HDV), a defective RNA virus that requires the HBsAg coat from HBV to replicate but is not called the Dane particle. * **Option D (HBcAg):** Incorrect. This is the Hepatitis B core antigen, which is a component *inside* the Dane particle, not the particle itself. **High-Yield NEET-PG Pearls:** * **Genome:** HBV is the only DNA virus among the Hepatitis viruses (partially double-stranded circular DNA). * **Morphology:** Under EM, HBV shows three forms: Dane particles (infectious), spherical forms, and filamentous forms (both non-infectious HBsAg). * **Serology:** HBsAg is the first marker to appear in blood; Anti-HBs indicates immunity. * **DNA Polymerase:** HBV possesses reverse transcriptase activity during its replication cycle.

Question 356: Which viruses commonly cause gastroenteritis?

A. Rotavirus
B. Norwalk virus
C. Adenovirus
D. All of the above (Correct Answer)

Explanation: Viral gastroenteritis is a leading cause of severe diarrhea and dehydration worldwide. The correct answer is **D (All of the above)** because Rotavirus, Norwalk virus (Norovirus), and specific serotypes of Adenovirus are the primary etiologic agents of viral diarrhea. ### **Detailed Explanation:** 1. **Rotavirus (Option A):** A Reovirus (dsRNA, segmented) that is the **most common cause of severe diarrhea in infants and young children** worldwide. It primarily affects the duodenum and jejunum, leading to malabsorption and osmotic diarrhea. 2. **Norwalk virus / Norovirus (Option B):** A Calicivirus (ssRNA) known as the **most common cause of gastroenteritis outbreaks** across all age groups. It is frequently associated with "cruise ship diarrhea," schools, and nursing homes due to its low infectious dose and environmental stability. 3. **Adenovirus (Option C):** While most Adenoviruses cause respiratory infections, **Serotypes 40 and 41** (Enteric Adenoviruses) are significant causes of infantile gastroenteritis. Unlike others, these are non-enveloped DNA viruses. ### **High-Yield Clinical Pearls for NEET-PG:** * **Rotavirus:** Characterized by a "wheel-like" appearance on electron microscopy. The **NSP4 enterotoxin** is responsible for inducing secretory diarrhea. * **Norovirus:** Currently the leading cause of viral gastroenteritis globally since the introduction of the Rotavirus vaccine. * **Astrovirus:** Another important cause, identified by its "star-shaped" morphology. * **Mechanism:** Most of these viruses cause blunting of the intestinal villi, leading to a decrease in absorptive surface area and transient lactose intolerance.

Question 357: Break bone fever is caused by which of the following viruses?

A. Variola
B. Coxsackie
C. Dengue (Correct Answer)
D. Adenovirus

Explanation: **Explanation:** **Dengue virus** is the correct answer. It is a single-stranded RNA virus belonging to the **Flaviviridae** family, transmitted primarily by the *Aedes aegypti* mosquito. It is clinically referred to as **"Break-bone fever"** because patients often experience excruciating joint and muscle pain (myalgia and arthralgia) that feels as though their bones are breaking. **Analysis of Incorrect Options:** * **Variola:** This is the causative agent of **Smallpox**. It is a DNA virus (Poxviridae) characterized by a centrifugal rash and umbilicated pustules, not severe bone pain. * **Coxsackie:** A member of the Picornaviridae family. Coxsackie A typically causes **Hand-Foot-and-Mouth Disease** or Herpangina, while Coxsackie B is a common cause of **Myocarditis** and Pleurodynia (Bornholm disease). * **Adenovirus:** A non-enveloped DNA virus primarily associated with **Pharyngoconjunctival fever**, epidemic keratoconjunctivitis, and hemorrhagic cystitis. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (Day biter; breeds in clean stagnant water). * **Serotypes:** There are 4 serotypes (DEN 1-4). Infection with one provides lifelong immunity to that specific serotype but increases the risk of **Dengue Hemorrhagic Fever (DHF)** upon secondary infection with a different serotype due to **Antibody-Dependent Enhancement (ADE)**. * **Diagnosis:** * Day 1–5: **NS1 Antigen** (Best early marker). * After Day 5: **IgM/IgG ELISA**. * **Hallmark Lab Finding:** Thrombocytopenia (low platelet count) and hemoconcentration (increased hematocrit). * **Tourniquet Test:** Used as a bedside screening tool for capillary fragility in DHF.

Question 358: Which of the following is characteristic only of viruses?

A. They are intracellular organisms
B. They affect the production of interferon and are sensitive to it. (Correct Answer)
C. They reproduce by binary fission
D. They can be grown on inanimate media

Explanation: ### Explanation **Correct Option: B (They affect the production of interferon and are sensitive to it)** Viruses are unique because they are **obligate intracellular parasites** that lack their own metabolic machinery. When a virus infects a host cell, the presence of viral double-stranded RNA (dsRNA) or other viral components triggers the host cell to produce **Interferons (IFN-α and IFN-β)**. These interferons do not kill the virus directly but induce an "antiviral state" in neighboring cells by inhibiting viral protein synthesis and degrading viral RNA. This specific interaction—inducing and being inhibited by interferons—is a hallmark characteristic of viruses not shared by bacteria or other microorganisms. **Why Other Options are Incorrect:** * **A. They are intracellular organisms:** While viruses are intracellular, this is not *exclusive* to them. Several bacteria (e.g., *Chlamydia*, *Rickettsia*, *Mycobacterium leprae*) and protozoa (e.g., *Plasmodium*, *Leishmania*) are also obligate or facultative intracellular organisms. * **C. They reproduce by binary fission:** Viruses do not undergo binary fission. They replicate through a complex process of **disjunction and assembly**, where individual components (nucleic acids and proteins) are synthesized separately and then assembled into virions. Bacteria and some protozoa reproduce via binary fission. * **D. They can be grown on inanimate media:** Viruses require **living cells** (cell cultures, embryonated eggs, or animal inoculation) to replicate because they depend on the host's ribosomes and enzymes. Only bacteria and fungi can typically be grown on inanimate/artificial media like agar. **High-Yield NEET-PG Pearls:** * **Interferon-gamma (IFN-γ):** Produced by T-cells and NK cells; primarily involved in immune regulation rather than direct antiviral activity. * **Eclipse Period:** The phase in viral replication where the infectious virus cannot be detected inside the host cell. * **Prions:** Smaller than viruses, consist only of proteins, and lack nucleic acids—important to distinguish from viruses in exams.

Question 359: Which staining method is useful for the antemortem diagnosis of rabies?

A. Sellers stain
B. Macchiavello stain
C. Giemsa stain
D. Direct fluorescent antibody stain (Correct Answer)

Explanation: **Explanation:** The **Direct Fluorescent Antibody (DFA) test** is the gold standard for rabies diagnosis. It detects rabies virus antigens in clinical specimens. For **antemortem diagnosis**, the specimen of choice is a **full-thickness skin biopsy from the nape of the neck** (containing hair follicles and cutaneous nerves). DFA is preferred due to its high sensitivity and specificity, allowing for rapid detection before death. **Analysis of Options:** * **Sellers Stain (Option A):** This is used to visualize **Negri bodies** (intracytoplasmic inclusion bodies). While characteristic of rabies, Negri bodies are only present in about 70-80% of cases and are typically identified in **postmortem** brain tissue (Ammon’s horn). * **Macchiavello Stain (Option B):** This stain is historically used to identify **Rickettsiae** and **Chlamydia** (inclusion bodies), not the rabies virus. * **Giemsa Stain (Option C):** This is a versatile hematological stain used for malaria parasites, *Chlamydia*, and *Borrelia*, but it is not specific or diagnostic for rabies. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** DFA is the most reliable test for both antemortem (skin biopsy) and postmortem (brain tissue) diagnosis. * **Negri Bodies:** These are pathognomonic for rabies but their absence does *not* rule out the disease. * **Specimen for Antemortem Diagnosis:** Skin biopsy from the nape of the neck, saliva (for RT-PCR), and CSF. * **Prophylaxis:** Rabies is 100% fatal once symptoms appear, making post-exposure prophylaxis (PEP) with wound cleaning, vaccine, and RIG (if indicated) critical.

Question 360: What is the primary treatment for Herpes zoster?

A. Zidovudine
B. Ganciclovir (Correct Answer)
C. Ribavirin
D. Nevirapine

Explanation: **Explanation:** **Correct Answer: B. Ganciclovir** The primary treatment for infections caused by the Herpesviridae family involves DNA polymerase inhibitors. While **Acyclovir** is typically the first-line treatment for Herpes zoster (Varicella-Zoster Virus), among the options provided, **Ganciclovir** is the only drug belonging to the same class of guanosine analogs. Ganciclovir works by inhibiting viral DNA polymerase, effectively halting viral replication. In clinical practice, while Ganciclovir is more commonly associated with Cytomegalovirus (CMV), it possesses significant activity against VZV and is the most appropriate choice among the listed antivirals. **Analysis of Incorrect Options:** * **A. Zidovudine (AZT):** A Nucleoside Reverse Transcriptase Inhibitor (NRTI) used exclusively in the treatment of HIV/AIDS. It has no efficacy against DNA viruses like VZV. * **C. Ribavirin:** A guanosine analog used primarily for Hepatitis C (in combination with interferon) and Respiratory Syncytial Virus (RSV). It is not indicated for Herpes zoster. * **D. Nevirapine:** A Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI) used in the management of HIV-1. It does not inhibit DNA polymerase. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Oral **Acyclovir**, Valacyclovir, or Famciclovir are preferred for Herpes zoster to reduce the duration of viral shedding and the risk of **Post-Herpetic Neuralgia (PHN)**. * **Mechanism:** Acyclovir/Ganciclovir require initial phosphorylation by viral **thymidine kinase** (absent in host cells), ensuring selective toxicity. * **Clinical Sign:** Look for "Dew drops on a rose petal" appearance (vesicles on an erythematous base) following a dermatomal distribution. * **Tzanck Smear:** Characteristically shows **Multinucleated Giant Cells** and Cowdry Type A inclusion bodies.

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Virology — MCQs

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