Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 661: Which marker indicates active replication of the Hepatitis B virus?

A. HBV DNA polymerase (Correct Answer)
B. IgG anti-HBc
C. Hepatitis B core antigen (HBcAg)
D. Antibody to Hepatitis B surface antigen (Anti-HBsAg)

Explanation: **Explanation:** The presence of **HBV DNA polymerase** is a direct indicator of active viral replication. As Hepatitis B is a DNA virus, this enzyme is essential for synthesizing new viral DNA within the host cell. Its detection in the serum correlates strongly with high viral loads and high infectivity. **Analysis of Options:** * **HBV DNA polymerase (Correct):** Along with **HBeAg** and **HBV DNA** (measured via PCR), this marker signifies that the virus is actively multiplying. * **IgG anti-HBc:** This indicates a past or chronic infection. It is not a marker of replication but rather a sign of prior exposure to the core antigen. (Note: *IgM* anti-HBc is the marker for acute infection). * **HBcAg (Hepatitis B core antigen):** This is an intracellular antigen found within hepatocytes. It is **not secreted into the blood** and therefore cannot be used as a routine serum marker for replication. * **Anti-HBsAg:** This antibody appears after the disappearance of HBsAg. it indicates **immunity** (either from recovery or vaccination) and the termination of the carrier state. **High-Yield Clinical Pearls for NEET-PG:** * **Best indicator of infectivity:** HBV DNA (Quantitative PCR). * **Marker of "Window Period":** IgM anti-HBc (when both HBsAg and Anti-HBs are negative). * **First marker to appear:** HBsAg (indicates infection, not necessarily replication). * **Marker of reduced infectivity:** Anti-HBe (seroconversion from HBeAg to Anti-HBe).

Question 662: Hepatitis B surface antigen (HBsAg) carrier state is not associated with which of the following conditions?

A. Down's syndrome
B. Chronic renal failure
C. Polyarteritis nodosa (PAN)
D. Infectious mononucleosis (Correct Answer)

Explanation: ### Explanation The **HBsAg carrier state** is defined by the persistence of Hepatitis B surface antigen in the blood for more than 6 months. This state is more likely to occur in individuals with an impaired immune response or specific systemic associations. **Why Infectious Mononucleosis is the correct answer:** Infectious Mononucleosis is caused by the **Epstein-Barr Virus (EBV)**. While EBV can cause mild, transient hepatitis (elevated liver enzymes), it is an acute, self-limiting infection in immunocompetent hosts. It does not predispose a patient to a chronic carrier state of the Hepatitis B virus. There is no pathophysiological link between EBV infection and the inability to clear HBsAg. **Analysis of Incorrect Options:** * **Down’s Syndrome:** Individuals with Down’s syndrome often have associated immune deficiencies (T-cell dysfunction). Historically, institutionalization and frequent medical procedures in this population increased exposure, while their impaired immunity led to a higher rate of chronic HBsAg carriage. * **Chronic Renal Failure (CRF):** Patients with CRF, especially those on hemodialysis, are in a state of relative immunosuppression. Their immune systems often fail to mount an adequate response to clear the virus, leading to a high frequency of the carrier state. * **Polyarteritis Nodosa (PAN):** This is a systemic necrotizing vasculitis. Approximately 10–30% of PAN cases are associated with chronic Hepatitis B. In these cases, HBsAg-antibody immune complexes deposit in vessel walls, leading to inflammation. Thus, PAN is strongly associated with the HBsAg carrier state. **High-Yield Clinical Pearls for NEET-PG:** * **Risk of Chronicity:** The risk of becoming a carrier is inversely proportional to age at infection (90% in neonates vs. <5% in adults). * **PAN Association:** "Hepatitis B" is the classic viral association for Polyarteritis Nodosa (Type III Hypersensitivity). * **Carrier Definition:** Requires HBsAg positivity on two occasions at least 6 months apart. * **Other Carrier Associations:** Lepromatous leprosy, Leukemia, and patients on immunosuppressive therapy.

Question 663: A nursing student has just completed her hepatitis B vaccine series. Assuming she has no prior exposure to hepatitis B, what laboratory finding would you expect?

A. Positive test for hepatitis B surface antigen
B. Antibody against hepatitis B surface antigen (anti-HBs) alone (Correct Answer)
C. Antibody against hepatitis B core antigen (anti-HBc)
D. Antibody against both hepatitis B surface and core antigen

Explanation: ### Explanation **1. Why Option B is Correct:** The Hepatitis B vaccine is a **recombinant subunit vaccine** containing only the **Hepatitis B surface antigen (HBsAg)**. When administered, the body’s immune system recognizes this protein and produces protective antibodies against it, known as **anti-HBs**. Since the vaccine does not contain the viral core or the intact virus, the individual will only develop antibodies to the surface component. A finding of anti-HBs alone (≥10 mIU/mL) indicates successful immunization and protection. **2. Why Other Options are Incorrect:** * **Option A (HBsAg):** This indicates an **active infection** (either acute or chronic). The vaccine uses a non-infectious recombinant protein that does not cause HBsAg to persist in the blood. * **Option C (Anti-HBc):** The core antigen (HBcAg) is located inside the intact virion and is not present in the vaccine. Therefore, **anti-HBc is a marker of natural infection** (past or present). Its absence confirms the person has never been naturally infected. * **Option D (Both anti-HBs and anti-HBc):** This pattern is seen in individuals who have **recovered from a natural Hepatitis B infection**. They develop immunity to both the surface and the core components of the virus. **3. NEET-PG High-Yield Pearls:** * **Window Period:** The period where HBsAg disappears but anti-HBs hasn't appeared yet. The only positive marker here is **IgM anti-HBc**. * **HBeAg:** Indicates high viral replication and high infectivity (**"e" for Envelope/Extremely infectious**). * **Vaccine Non-responders:** Individuals who do not develop anti-HBs after two full series of vaccinations. * **Recombinant Technology:** The HBV vaccine is produced by inserting the HBsAg gene into **Saccharomyces cerevisiae** (yeast).

Question 664: Which of the following is a diploid cell strain?

A. Rhesus monkey kidney cell culture
B. HeLa
C. Human embryonic lung cell strain (Correct Answer)
D. McCoy

Explanation: Cell cultures in virology are classified into three types based on their origin, chromosomal constitution, and lifespan. **Explanation of the Correct Answer:** **Option C (Human embryonic lung cell strain)** is the correct answer. **Diploid cell strains** are derived from primary cultures (usually fetal tissue) and consist of cells that maintain the normal diploid number of chromosomes. They can be subcultured for a limited number of generations (usually 50 passages) before undergoing senescence. Examples include **WI-38** and **MRC-5**, both derived from human embryonic lung tissue. They are highly significant in vaccine production (e.g., Rubella, Rabies, and Varicella vaccines). **Explanation of Incorrect Options:** * **A. Rhesus monkey kidney cell culture:** This is a **Primary cell culture**. These are derived directly from animal or human organs. They are the most sensitive for primary virus isolation but cannot be subcultured beyond 1–2 times. * **B. HeLa:** This is a **Continuous (Immortal) cell line**. Derived from a human cervical cancer, these cells have an aneuploid chromosome number and can be subcultured indefinitely. * **C. McCoy:** This is also a **Continuous cell line**. It is famously used for the cultivation of *Chlamydia trachomatis*. **High-Yield Facts for NEET-PG:** * **Primary Cultures:** Best for primary isolation (e.g., Monkey kidney for Myxoviruses). * **Diploid Strains:** Used for vaccine manufacture because they are non-oncogenic. * **Continuous Lines:** Derived from tumors or transformed cells (e.g., HeLa, HEp-2, Vero, BHK-21). * **Cytopathic Effect (CPE):** The structural changes in host cells caused by viral invasion, used for identification in these cultures.

Question 665: Which of the following serological markers is used for epidemiologic studies of Hepatitis B?

A. HBe Ag
B. HBc Ag
C. HBs Ag
D. Anti HBc (Correct Answer)

Explanation: **Explanation** The correct answer is **Anti-HBc (Antibody to Hepatitis B core antigen)**. **1. Why Anti-HBc is the correct answer:** In epidemiological studies, the goal is to determine the **total number of people who have ever been infected** with Hepatitis B (prevalence). Anti-HBc is the most reliable marker for this because it appears shortly after the onset of infection and **persists for life**, regardless of whether the patient recovers or becomes a chronic carrier. Unlike other markers, it does not appear after vaccination; therefore, its presence specifically indicates a natural infection (past or present). **2. Why the other options are incorrect:** * **HBeAg:** This is a marker of **active viral replication** and high infectivity. It is used to assess the degree of infectiousness, not for broad epidemiological prevalence. * **HBcAg:** This is a particulate antigen found inside the hepatocyte. It is **not detectable in the serum** under normal conditions and therefore cannot be used as a serological marker. * **HBsAg:** This is the first marker to appear and indicates **current infection** (acute or chronic). However, it disappears upon recovery. Using HBsAg alone would miss individuals who have cleared the virus, thus underestimating the total disease burden in a population. **3. NEET-PG High-Yield Pearls:** * **Window Period:** The period where HBsAg has disappeared but Anti-HBs has not yet appeared. During this time, **Anti-HBc IgM** is the only diagnostic marker. * **Vaccination vs. Natural Infection:** * **Vaccinated:** Only Anti-HBs is positive. * **Natural Infection (Recovered):** Both Anti-HBs and Anti-HBc (IgG) are positive. * **Anti-HBc IgM:** Indicates acute infection. * **Anti-HBc IgG:** Indicates past or chronic infection.

Question 666: A 15-year-old girl presents with symptoms suggestive of rabies. Which clinical sample is most suitable for confirming the diagnosis?

A. Serum for anti-rabies IgG antibody
B. Corneal impression smear for immunofluorescence stain (Correct Answer)
C. Cerebrospinal fluid sample for viral culture
D. Giemsa stain on smear prepared from salivary secretions

Explanation: ### Explanation The diagnosis of rabies in a living patient (antemortem) relies on detecting the virus or its components, as clinical symptoms are often non-specific initially. **Why Option B is Correct:** The **Corneal Impression Smear** is a classic antemortem diagnostic method. It involves collecting epithelial cells from the cornea and using **Direct Fluorescent Antibody (DFA)** testing to detect rabies viral antigens. Since the rabies virus travels via axoplasmic flow through cranial nerves to reach highly innervated areas like the cornea and salivary glands, the antigen can be identified here even before death. **Analysis of Incorrect Options:** * **Option A:** Serum antibodies (IgG) are generally not useful for early diagnosis because they appear very late in the clinical course. Furthermore, they cannot distinguish between a current infection and a previous vaccination. * **Option C:** Viral culture from CSF is technically difficult, time-consuming, and has a very low sensitivity. Rabies virus is rarely isolated from CSF during the clinical phase. * **Option D:** While saliva is used for diagnosis, it is tested via **RT-PCR** (to detect viral RNA) or viral isolation, not Giemsa stain. Giemsa stain is used for identifying Negri bodies in brain tissue, but this is a **post-mortem** finding. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard (Post-mortem):** Detection of **Negri bodies** (intracytoplasmic eosinophilic inclusions) in the hippocampus (Ammon’s horn) or cerebellum. * **Most Sensitive Antemortem Test:** **RT-PCR** of saliva or a **nuchal skin biopsy** (hair follicles contain high concentrations of the virus). * **Pathogenesis:** The virus binds to **Nicotinic Acetylcholine Receptors (nAchR)** at the neuromuscular junction. * **Incubation Period:** Usually 1–3 months; depends on the distance of the bite site from the CNS.

Question 667: Prions consist of which of the following?

A. DNA and RNA
B. DNA, RNA, and protein
C. RNA and protein
D. Only proteins (Correct Answer)

Explanation: **Explanation:** **1. Why "Only proteins" is correct:** Prions (Proteinaceous Infectious Particles) are unique pathogens that lack any form of nucleic acid (DNA or RNA). They are composed entirely of an abnormally folded isoform of a host-encoded glycoprotein called **PrP (Prion Protein)**. The normal cellular protein (**PrPc**) is converted into the infectious, protease-resistant form (**PrPsc**) through a conformational change (from alpha-helices to beta-pleated sheets). This misfolded protein acts as a template, inducing other normal proteins to misfold, leading to neurodegeneration. **2. Why other options are incorrect:** * **Options A, B, and C:** These are incorrect because the defining characteristic of prions is the **absence of nucleic acids**. Unlike viruses (which contain DNA or RNA), bacteria, or fungi, prions are not inactivated by treatments that destroy nucleic acids (such as UV radiation, nucleases, or formalin). They are only inactivated by treatments that denature proteins (e.g., autoclaving at 134°C, 1N NaOH, or sodium hypochlorite). **3. High-Yield Clinical Pearls for NEET-PG:** * **Pathology:** Characterized by "spongiform" changes (vacuolation of neurons), astrocytosis, and neuronal loss without an inflammatory response. * **Human Diseases:** * **Kuru:** Associated with ritualistic cannibalism. * **Creutzfeldt-Jakob Disease (CJD):** Most common human prion disease (presents with rapidly progressive dementia and myoclonus). * **Variant CJD (vCJD):** Linked to Bovine Spongiform Encephalopathy (Mad Cow Disease). * **Fatal Familial Insomnia:** Characterized by severe sleep disturbances. * **Resistance:** Prions are highly resistant to standard sterilization methods. The recommended disinfection involves **1N NaOH for 1 hour** followed by **autoclaving at 134°C**.

Question 668: Which of the following is the next most common cause of blood transfusion-related hepatitis after hepatitis B?

A. Hepatitis A
B. Epstein-Barr hepatitis
C. Hepatitis C (Correct Answer)
D. Hepatitis D

Explanation: ### Explanation **Correct Option: C. Hepatitis C** The primary cause of post-transfusion hepatitis (PTH) globally is **Hepatitis B Virus (HBV)**, largely due to the "window period" where HBsAg is undetectable despite infectivity. **Hepatitis C Virus (HCV)** is the **second most common cause**. Before the introduction of mandatory blood screening for HCV in the 1990s, it was actually the leading cause of "Non-A, Non-B" post-transfusion hepatitis. While modern nucleic acid testing (NAT) has significantly reduced the risk, HCV remains a significant concern due to its high rate of chronicity (75–85%) following acute infection. **Analysis of Incorrect Options:** * **A. Hepatitis A:** This virus is transmitted via the **fecal-oral route**. It has a very brief viremic phase and does not lead to a chronic carrier state, making transfusion-related transmission extremely rare. * **B. Epstein-Barr Virus (EBV):** While EBV can cause hepatitis as part of infectious mononucleosis and can be transmitted via blood, it is a rare cause of clinically significant post-transfusion hepatitis compared to hepatotropic viruses. * **D. Hepatitis D:** HDV is a defective virus that requires the presence of **HBsAg** (HBV co-infection or superinfection) to replicate. While it is blood-borne, it is categorized as a complication of HBV rather than a standalone second-most common cause. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of PTH:** Hepatitis B (due to the window period). * **Most common cause of PTH in the 1980s:** Hepatitis C (formerly Non-A, Non-B). * **Screening:** Mandatory screening for blood donors in India includes HIV, HBV (HBsAg), HCV, Syphilis, and Malaria. * **Risk Reduction:** The use of **Nucleic Acid Testing (NAT)** has drastically reduced the "window period" for HCV from ~70 days to only 3–5 days.

Question 669: Examples of prion diseases include:

A. Creutzfeldt-Jakob disease (Correct Answer)
B. Subacute sclerosing panencephalitis
C. Alzheimer's disease
D. None of the above

Explanation: **Explanation:** **Prion diseases** (Transmissible Spongiform Encephalopathies) are caused by **prions**, which are infectious, misfolded proteins ($PrP^{Sc}$) that lack nucleic acids. They induce the misfolding of normal cellular proteins ($PrP^C$) into a pathological beta-sheet conformation, leading to neuronal loss and a "spongiform" appearance of the brain. * **Creutzfeldt-Jakob Disease (CJD):** This is the most common human prion disease. It is characterized by rapidly progressive dementia, myoclonus, and ataxia. It can occur sporadically (85%), via genetic mutation, or through iatrogenic transmission (e.g., contaminated corneal grafts or growth hormone). **Analysis of Incorrect Options:** * **Subacute Sclerosing Panencephalitis (SSPE):** This is a chronic, progressive neurodegenerative disease caused by a **persistent infection with a mutant Measles virus**, not a prion. It typically occurs years after an initial measles infection. * **Alzheimer’s Disease:** While Alzheimer’s involves protein misfolding (Amyloid-beta and Tau), it is classified as a **neurodegenerative amyloidosis**, not a transmissible prion disease. **High-Yield Clinical Pearls for NEET-PG:** * **Kuru:** A prion disease associated with ritualistic cannibalism in Papua New Guinea. * **Variant CJD (vCJD):** Linked to the consumption of beef infected with Bovine Spongiform Encephalopathy ("Mad Cow Disease"). * **Diagnosis:** Look for **14-3-3 protein** in CSF and "periodic sharp wave complexes" on EEG. * **Resistance:** Prions are highly resistant to standard sterilization (autoclaving). They require **1N NaOH or 5% Sodium Hypochlorite** for inactivation.

Question 670: Which of the following viruses has NOT been associated with oncogenesis?

A. Human Papilloma Viruses
B. Epstein Barr virus
C. Human T cell leukemia virus
D. Varicella Zoster virus (Correct Answer)

Explanation: **Explanation:** The association between viruses and cancer is termed **viral oncogenesis**. This occurs when a virus introduces oncogenes into a host cell or disrupts host tumor-suppressor genes (like p53 or Rb), leading to uncontrolled cell proliferation [2]. **Why Varicella Zoster Virus (VZV) is the correct answer:** VZV (Human Herpesvirus 3) is the causative agent of **Chickenpox** and **Herpes Zoster (Shingles)** [1]. Unlike other members of the Herpesviridae family (like EBV or HHV-8), VZV is not associated with malignancy [3]. It establishes latency in the dorsal root ganglia but does not possess the molecular machinery to transform host cells into a cancerous state [1]. **Analysis of Incorrect Options:** * **Human Papilloma Virus (HPV):** High-risk types (16, 18) produce E6 and E7 oncoproteins which inhibit p53 and Rb proteins, respectively, leading to **Cervical and Oropharyngeal carcinoma** [2], [4]. * **Epstein-Barr Virus (EBV):** Known as the first human virus associated with cancer. It is linked to **Burkitt lymphoma**, Nasopharyngeal carcinoma, and Hodgkin lymphoma. * **Human T-cell Leukemia Virus (HTLV-1):** A retrovirus that causes **Adult T-cell Leukemia/Lymphoma (ATLL)** by producing the *Tax* protein, which stimulates cell proliferation [4]. **High-Yield Clinical Pearls for NEET-PG:** * **DNA Oncogenic Viruses:** HPV, EBV, HBV, HHV-8 (Kaposi Sarcoma), and Merkel Cell Polyomavirus [3]. * **RNA Oncogenic Viruses:** HTLV-1 and Hepatitis C Virus (HCV) [4]. * **Key Mechanism:** Most DNA oncoviruses integrate into the host genome or exist as episomes [4], whereas HCV (an RNA virus) causes cancer primarily through chronic inflammation and hepatocyte regeneration.

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