Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 441: Which among the following is the only hepatitis virus that can be cultured?

A. Hepatitis A virus (HAV) (Correct Answer)
B. Hepatitis B virus (HBV)
C. Hepatitis D virus (HDV)
D. Hepatitis C virus (HCV)

Explanation: ### Explanation **Correct Option: A. Hepatitis A virus (HAV)** Hepatitis A virus (HAV) is unique among the primary hepatitis viruses because it is the **only one that can be routinely grown in cell culture**. It can be propagated in various human and primate cell lines (e.g., fetal rhesus monkey kidney cells). However, it is important to note that HAV is fastidious; it grows slowly, does not produce a cytopathic effect (CPE) in most primary isolates, and requires adaptation to the culture medium. This property was historically significant for the development of the inactivated HAV vaccine. **Why other options are incorrect:** * **Hepatitis B virus (HBV):** HBV cannot be grown in standard cell cultures. Research relies on transfected cell lines or "humanized" mouse models because the virus requires highly specific hepatocyte differentiation to replicate. * **Hepatitis D virus (HDV):** As a defective virus, HDV requires the presence of HBV (specifically HBsAg) to replicate and assemble. It cannot be cultured independently. * **Hepatitis C virus (HCV):** For decades, HCV could not be cultured. While specific laboratory strains (like JFH-1) can now be grown in specialized Huh7 cell lines for research, it is not considered "culturable" in the traditional diagnostic or general sense compared to HAV. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** HAV belongs to *Picornaviridae* (Genus: *Hepatovirus*). * **Genome:** All hepatitis viruses are RNA viruses except **HBV**, which is a DNA virus. * **Transmission:** HAV and HEV are transmitted via the **fecal-oral route**, while HBV, HCV, and HDV are parenteral. * **Chronicity:** HAV and HEV (except in pregnancy/immunocompromised) do **not** cause chronic infection. * **Fulminant Hepatitis:** HEV has the highest mortality rate in pregnant women (up to 20%).

Question 442: A patient presented with acute onset of jaundice and raised aminotransferases. Preliminary serology showed HBsAg positivity. On further testing, which of the following is least likely to be found in this patient?

A. HBeAg
B. Anti-HBs antibodies (Correct Answer)
C. HBV DNA
D. HBV DNA polymerase

Explanation: ### Explanation The patient presents with acute hepatitis and is **HBsAg positive**, indicating an active Hepatitis B virus (HBV) infection. **Why Anti-HBs is the correct answer:** Anti-HBs (Hepatitis B surface antibody) is a **neutralizing antibody** that appears only after HBsAg has been cleared from the blood. Its presence signifies either recovery from a natural infection or successful immunization. In an acute infection where HBsAg is still detectable, Anti-HBs will be absent. The period between the disappearance of HBsAg and the appearance of Anti-HBs is known as the **"Window Period,"** during which only Anti-HBc IgM is typically detectable. **Analysis of Incorrect Options:** * **HBeAg:** This is a marker of active viral replication and high infectivity. It is commonly found in the early stages of acute hepatitis B alongside HBsAg. * **HBV DNA:** This is the most sensitive marker of viral replication. It appears very early in the infection, often before HBsAg, and remains positive during the acute phase. * **HBV DNA Polymerase:** As an enzyme required for viral replication, its presence correlates with the presence of HBV DNA and HBeAg during active infection. **Clinical Pearls for NEET-PG:** * **First marker to appear:** HBsAg (even before symptoms or rise in ALT). * **Marker of infectivity:** HBeAg. * **Marker of "Window Period":** Anti-HBc IgM. * **Marker of immunity:** Anti-HBs. * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months.

Question 443: The rash of chickenpox typically begins from which area of the body?

A. Leg
B. Hand
C. Genitalia
D. Face (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Face** **Medical Concept:** Chickenpox, caused by the **Varicella-Zoster Virus (VZV)**, is characterized by a classic centripetal rash. The eruption typically begins on the **face** or the **trunk** and then spreads peripherally to the extremities. The hallmark of the chickenpox rash is its rapid progression from macules to papules, then to "dew-drop on a rose petal" vesicles, and finally crusting. A key diagnostic feature is **pleomorphism**, where lesions in all different stages of development are present simultaneously in the same anatomical area. **Analysis of Incorrect Options:** * **A & B (Leg and Hand):** These represent the distal extremities. In chickenpox, the rash is **centripetal**, meaning it is most dense on the trunk and face, sparing the distal extremities (palms and soles are rarely involved). In contrast, Smallpox presents with a **centrifugal** distribution, starting on the face/hands and involving the palms and soles. * **C (Genitalia):** While lesions can occasionally appear on mucous membranes (including the genital mucosa) as the disease progresses, it is never the primary site of onset. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 10–21 days (Average 14–16 days). * **Infectivity:** 1–2 days *before* the rash appears until all vesicles have crusted over. * **Secondary Attack Rate:** Very high (~90%). * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusion bodies (also seen in HSV). * **Complications:** Secondary bacterial skin infections (most common in children) and Varicella pneumonia (most common/severe in adults). * **Congenital Varicella Syndrome:** Characterized by cicatricial skin scarring, limb hypoplasia, and chorioretinitis if the mother is infected in early pregnancy.

Question 444: What is the method for the rapid diagnosis of rabies in a living rabid dog?

A. Fluorescent antibody test (Correct Answer)
B. Corneal impression
C. Inoculation in mice
D. None of the above

Explanation: ### Explanation The gold standard for the rapid diagnosis of rabies in both animals and humans is the **Direct Fluorescent Antibody (DFA) test**. **1. Why Option A is Correct:** The DFA test detects rabies virus antigens in brain tissue or other infected tissues. In a living animal or human, it can be performed on a **full-thickness skin biopsy** (usually from the nape of the neck), where the virus is detected within the cutaneous nerves surrounding hair follicles. It is highly sensitive (98-100%), specific, and provides results within a few hours, making it the preferred rapid diagnostic tool. **2. Why Other Options are Incorrect:** * **Option B (Corneal Impression):** While this was historically used to detect viral antigens in corneal epithelial cells, it is no longer recommended due to its **low sensitivity** and high rate of false negatives. * **Option C (Inoculation in mice):** This is a biological test (Mouse Inoculation Test) used to isolate the virus. While definitive, it is **not rapid**, taking 5 to 21 days for the mice to show symptoms or die. It is generally reserved for confirming results from other tests. **3. NEET-PG Clinical Pearls:** * **Negri Bodies:** These are pathognomonic intracytoplasmic inclusion bodies found in the neurons (Hippocampus/Cerebellum). However, they are only seen in 70-80% of cases and are usually a **post-mortem** finding. * **Antemortem Diagnosis in Humans:** Requires a combination of samples: Saliva (RT-PCR), Serum/CSF (Antibody testing), and Skin biopsy (DFA). * **Post-Exposure Prophylaxis (PEP):** Once clinical symptoms appear, rabies is virtually 100% fatal. Therefore, diagnosis in the biting animal is crucial for deciding the course of PEP for the victim.

Question 445: Which of the following is characteristic of Dengue hemorrhagic fever?

A. Most common in previously affected patients (Correct Answer)
B. DHF-2 is the most common cause
C. Associated with immunosuppression
D. Incubation period is 7-14 days

Explanation: ### Explanation The correct answer is **A: Most common in previously affected patients.** This phenomenon is explained by the **Immunological Theory of Halstead (Antibody-Dependent Enhancement - ADE)**. When a patient is infected with a different serotype of the Dengue virus (DENV 1-4) for the second time, the pre-existing non-neutralizing antibodies from the primary infection bind to the new virus. Instead of neutralizing it, these antibodies facilitate the entry of the virus into macrophages and monocytes via Fc receptors. This leads to an exaggerated immune response, a "cytokine storm," increased vascular permeability, and the clinical manifestations of Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). #### Analysis of Incorrect Options: * **B. DHF-2 is the most common cause:** This is factually incorrect. While DENV-2 is frequently associated with severe outbreaks and DHF, any of the four serotypes can cause DHF upon secondary infection. * **C. Associated with immunosuppression:** DHF is actually a result of an **overactive immune system** (hyper-immune response), not immunosuppression. The pathology is driven by excessive T-cell activation and cytokine release. * **D. Incubation period is 7-14 days:** The typical incubation period for Dengue is **3 to 14 days** (average 5–7 days). While 14 is the upper limit, it is not the standard characteristic range used to define the disease. #### NEET-PG High-Yield Pearls: * **Vector:** *Aedes aegypti* (Daytime biter, breeds in artificial collections of clean water). * **Hemorrhagic Marker:** Positive **Tourniquet test** (presence of >20 petechiae per square inch). * **Lab Diagnosis:** NS1 Antigen (Day 1-5), IgM/IgG ELISA (after Day 5). * **Critical Period:** Occurs during the **defervescence phase** (when fever subsides), usually between days 3–7 of illness. This is when plasma leakage and shock are most likely to occur.

Question 446: Full blown Immunodeficiency syndrome is characterized by which of the following?

A. High viral titres with low CD4 count (Correct Answer)
B. Low viral titres with low CD4 count
C. Low viral titres with high CD4 count
D. High viral titres with high CD4 count

Explanation: **Explanation:** The progression of HIV infection to **Full-blown AIDS (Stage 3)** is defined by the critical failure of the cell-mediated immune system. 1. **Why Option A is correct:** In the final stage of the disease, the virus has successfully exhausted the host's immune defenses. The **CD4+ T-lymphocyte count drops below 200 cells/mm³** (or <14%), which is the hallmark of immunodeficiency. Simultaneously, because the immune system can no longer suppress viral replication, the **viral load (HIV RNA titres) surges** significantly. This high viremia facilitates the development of life-threatening opportunistic infections and malignancies. 2. **Why other options are incorrect:** * **Option B & C:** Low viral titres are typically seen during the "Clinical Latency" phase or in "Elite Controllers," where the immune system or ART (Antiretroviral Therapy) keeps the virus in check. * **Option D:** High viral titres with high CD4 counts are characteristic of the **Acute HIV Syndrome** (initial infection), where the virus replicates rapidly before the immune system mounts a response, but the CD4 pool has not yet been depleted. **High-Yield Clinical Pearls for NEET-PG:** * **Normal CD4/CD8 Ratio:** 2:1. In AIDS, this ratio is **inverted** (<1:1). * **Indicator of Prognosis:** Viral load (HIV RNA) is the best predictor of disease progression. * **Indicator of Immune Status:** CD4+ T-cell count is the best indicator of current immune competence and risk for opportunistic infections. * **Pneumocystis jirovecii:** The most common opportunistic infection when CD4 falls below 200 cells/mm³.

Question 447: Which of the following statements regarding Varicella-Zoster Virus (VZV) is incorrect?

A. VZV causes chickenpox and herpes zoster.
B. Chickenpox represents the primary VZV infection.
C. Herpes zoster represents a recurrent VZV infection. (Correct Answer)
D. VZV can establish latent infection in the trigeminal ganglion.

Explanation: The correct answer is **C** because it contains a subtle but important terminological error. In virology, **Herpes zoster (shingles)** is defined as a **reactivation** of the latent virus, not a "recurrent" infection. While the terms are often used interchangeably in common parlance, "recurrent" typically implies re-infection or repeated clinical episodes, whereas "reactivation" specifically describes a latent virus emerging from sensory ganglia due to waning cell-mediated immunity. **Explanation of Options:** * **Option A (Correct statement):** VZV is a member of the *Alphaherpesvirinae* subfamily. It is unique among herpesviruses for causing two distinct clinical syndromes: Varicella (chickenpox) and Herpes Zoster (shingles). * **Option B (Correct statement):** Chickenpox is the primary infection occurring in seronegative individuals (usually children), characterized by a generalized pruritic vesicular rash. * **Option D (Correct statement):** After the primary infection, VZV travels retrograde along sensory axons to establish lifelong **latency** in the dorsal root ganglia or cranial nerve ganglia, most commonly the **trigeminal ganglion** (leading to herpes zoster ophthalmicus) or thoracic ganglia. **High-Yield NEET-PG Pearls:** * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions (seen in VZV, HSV-1, and HSV-2). * **Congenital Varicella Syndrome:** Occurs if the mother is infected during the first 20 weeks of pregnancy; characterized by limb hypoplasia, scarring, and microcephaly. * **Ramsay Hunt Syndrome:** Reactivation involving the geniculate ganglion (CN VII), causing facial palsy and vesicles in the external auditory canal. * **Vaccine:** Live attenuated **Oka strain** is used for both chickenpox and shingles prevention.

Question 448: Which of the following microbes is the most common cause of gastroenteritis in children?

A. Rotaviruses (Correct Answer)
B. Picornaviruses
C. Togaviruses
D. Paramyxoviruses

Explanation: **Explanation:** **1. Why Rotavirus is Correct:** Rotavirus (a member of the *Reoviridae* family) is the **most common cause of severe dehydrating diarrhea** in infants and young children worldwide. It primarily affects the 6-month to 2-year age group. The virus infects the mature enterocytes of the villi in the small intestine, leading to malabsorption and osmotic diarrhea. Its characteristic "wheel-like" appearance under electron microscopy (Latin: *Rota* = wheel) is a classic diagnostic feature. **2. Analysis of Incorrect Options:** * **Picornaviruses:** This family includes Poliovirus, Rhinovirus, and Hepatitis A. While some (like Coxsackieviruses) can cause systemic illness, they are not the primary cause of pediatric gastroenteritis. * **Togaviruses:** This family includes Rubella and Alpha viruses (like Chikungunya). These typically present with rashes, fever, or arthralgia, not primary gastroenteritis. * **Paramyxoviruses:** This family includes Measles, Mumps, and RSV. These are primarily respiratory pathogens or cause systemic infections with parotitis; they do not cause diarrheal disease. **3. NEET-PG High-Yield Pearls:** * **Mechanism:** Rotavirus produces a viral enterotoxin called **NSP4**, which induces secretion by increasing intracellular calcium. * **Seasonality:** In temperate climates, it is more common in **winter** ("Winter diarrhea"). * **Vaccines:** Two major live-attenuated oral vaccines are used: **Rotarix** (monovalent) and **RotaTeq** (pentavalent). In India, **Rotavac** is part of the National Immunization Schedule. * **Diagnosis:** The gold standard for rapid diagnosis is **ELISA** for detecting VP6 antigen in stools. * **Note:** While Rotavirus is the most common in children, **Norovirus** is the most common cause of viral gastroenteritis outbreaks across all age groups (epidemic diarrhea).

Question 449: Coronaviruses are recognized by club-shaped surface projections that are 20 nm long and resemble solar coronas. These viruses are characterized by their ability to

A. cause the common cold
B. cause severe respiratory illness (Correct Answer)
C. infect intestinal cells
D. cause neurological disorders

Explanation: **Explanation:** Coronaviruses are large, enveloped, positive-sense single-stranded RNA (+ssRNA) viruses. Their name is derived from the characteristic **club-shaped surface projections** (S-proteins) that create a "halo" or solar corona appearance under electron microscopy. **Why Option B is Correct:** While coronaviruses have historically been associated with mild disease, they are clinically significant for their ability to cause **severe respiratory illness**. This was highlighted by the outbreaks of **SARS-CoV** (2003), **MERS-CoV** (2012), and the **SARS-CoV-2** (COVID-19) pandemic. These viruses infect the lower respiratory tract, leading to severe pneumonia, Acute Respiratory Distress Syndrome (ARDS), and multi-organ failure. **Analysis of Incorrect Options:** * **Option A:** While coronaviruses are the second most common cause of the **common cold** (after Rhinoviruses), the question asks for the defining clinical characteristic that distinguishes their medical importance in a postgraduate context. "Severe respiratory illness" is the more definitive clinical hallmark of the pathogenic strains. * **Option C:** Some coronaviruses (like certain animal strains) can infect intestinal cells causing diarrhea, but this is not the primary clinical manifestation in humans compared to respiratory distress. * **Option D:** Neurological symptoms (like anosmia or encephalopathy) can occur as complications, but they are secondary to the primary respiratory pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Genome:** Largest genome among RNA viruses (~30 kb). * **Receptor Binding:** SARS-CoV and SARS-CoV-2 bind to **ACE-2 receptors**, while MERS-CoV binds to **DPP-4 (CD26)**. * **Morphology:** Helical nucleocapsid (unique for a positive-sense RNA virus). * **Replication:** Occurs in the cytoplasm; they acquire their envelope by budding through the **ER-Golgi intermediate compartment (ERGIC)**.

Question 450: A 30-year-old patient presented with a 10-day history of jaundice. His liver function tests showed bilirubin of 10 mg/dl, SGOT/SGPT - 1100/1450, and serum alkaline phosphatase - 240 IU. He was positive for HBsAg. What is the confirmatory test to establish acute hepatitis B infection?

A. IgM anti-HBc antibody (Correct Answer)
B. HBe Ag
C. HBV DNA by PCR
D. Anti-HBc antibody

Explanation: **Explanation:** The diagnosis of **Acute Hepatitis B** is established by the presence of **HBsAg** and **IgM anti-HBc**. In this clinical scenario (jaundice, significantly elevated transaminases >1000 IU/L, and HBsAg positivity), the goal is to differentiate an acute infection from a chronic carrier state. 1. **Why IgM anti-HBc is correct:** This is the **first antibody to appear** and is a specific marker of acute infection. It is particularly crucial during the **"Window Period"** (the gap between the disappearance of HBsAg and the appearance of Anti-HBs), where it may be the only detectable marker of a recent infection. 2. **Why other options are incorrect:** * **HBeAg:** Indicates high viral replication and infectivity, but does not distinguish between acute and chronic phases. * **HBV DNA by PCR:** A quantitative marker used to assess viral load and monitor treatment response; it is not the primary diagnostic tool for defining "acute" status. * **Anti-HBc antibody (Total):** This includes both IgM and IgG. Since IgG persists for life, a total anti-HBc test cannot differentiate between a new infection and a past/chronic infection. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period Marker:** IgM anti-HBc. * **Marker of Infectivity:** HBeAg. * **Marker of Recovery/Immunity:** Anti-HBs. * **Chronic Infection:** Defined by HBsAg persistence for >6 months. * **First Marker to appear:** HBsAg (appears even before symptoms or transaminase rise).

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Virology — MCQs

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