Virology Practice Questions

Q: What is the commonly used screening test for Human Immunodeficiency Virus?

ELISA test. **Explanation:** The diagnosis of HIV infection follows a specific algorithm consisting of a highly sensitive screening test followed by a highly specific confirmatory test. **1. Why ELISA is the Correct Answer:** The **ELISA (Enzyme-Linked Immunosorbent Assay)** is the standard screening test for HIV. It is designed to have **high sensitivity**, ensuring that almost all infected individuals are identified. Modern 4th-generation ELISA kits (p24 antigen + IgM/IgG antibodies) have significantly reduced the "window period," allowing for earlier detection of the virus. **2. Analysis of Incorrect Options:** * **VDRL (Venereal Disease Research Laboratory) test:** This is a non-specific screening test for **Syphilis** (Treponema pallidum), detecting reagin antibodies. * **Weil-Felix test:** A heterophile agglutination test used for the diagnosis of **Rickettsial infections** (based on cross-reactivity with Proteus antigens). * **Western blot test:** While used for HIV, it is a **confirmatory test**, not a screening test. It has high specificity as it detects antibodies against specific viral proteins (gp120, gp41, p24). *Note: Current WHO/NACO guidelines have shifted towards using multiple rapid ELISA/EIA tests for confirmation instead of Western Blot in many settings.* **Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **Best Initial Test:** 4th Gen ELISA (p24 Ag + Ab). * **Gold Standard for Diagnosis in Infants (<18 months):** PCR (DNA PCR) to detect viral nucleic acid, as maternal IgG antibodies can cause false positives in ELISA. * **Monitoring Treatment:** **Viral Load (RNA PCR)** is the best indicator of prognosis and response to HAART.

Q: Which marker indicates infectivity of Hepatitis B?

HBeAg. ### Explanation **Hepatitis B markers** are a high-yield topic for NEET-PG, as they differentiate between infection stages, immunity, and viral replication. **Why HBeAg is the correct answer:** **HBeAg (Hepatitis B e-antigen)** is a soluble protein derived from the precore/core region. It is a qualitative marker of **active viral replication**. Its presence in the serum correlates with high levels of HBV DNA and a high count of Dane particles (complete virions). Therefore, it is the primary indicator of **high infectivity** and a high risk of transmission (e.g., vertical transmission from mother to child). **Analysis of Incorrect Options:** * **A. HBsAg (Surface Antigen):** This is the first marker to appear. It indicates that the patient is **infected** (acute or chronic), but it does not specifically quantify the level of replication or infectivity. * **C. Anti-HBs (Surface Antibody):** This antibody indicates **immunity** and recovery. It appears after the disappearance of HBsAg or following successful vaccination. * **D. Anti-HBc (Core Antibody):** This is a marker of **exposure** to the actual virus (not found in vaccinated individuals). IgM anti-HBc indicates acute infection (and is the only marker positive during the "window period"), while IgG anti-HBc indicates past or chronic infection. **Clinical Pearls for NEET-PG:** 1. **Best marker of infectivity:** HBV DNA (quantitative) > HBeAg (qualitative). 2. **Window Period marker:** Anti-HBc IgM. 3. **Marker of Vaccination:** Anti-HBs positive; all other markers (HBsAg, Anti-HBc) are negative. 4. **Precore Mutants:** In some cases, HBeAg is negative but HBV DNA is high; this indicates a mutation in the precore region, yet the patient remains highly infectious.

Q: What is the term for the symmetric protein shell that encases the nucleic acid core of a virus?

Capsid. ### Explanation **Correct Answer: B. Capsid** **1. Why it is correct:** The **capsid** is the protective, symmetric protein shell that surrounds and stabilizes the viral genome (DNA or RNA). Together with the nucleic acid, it forms the **nucleocapsid**. Capsids are composed of repeating protein subunits called capsomeres. Their primary functions are to protect the viral genome from environmental degradation (like nucleases) and to facilitate attachment to host cell receptors in non-enveloped viruses. **2. Why the other options are incorrect:** * **A. Capsomere:** These are the individual morphological subunits that aggregate to form the capsid. While they make up the shell, the term for the entire structure itself is the capsid. * **C. Basidiomycetes:** This is a taxonomic class of **Fungi** (e.g., mushrooms, puffballs) characterized by spores produced on a basidium. It is unrelated to viral structure. * **D. Fungi imperfecti (Deuteromycetes):** This is an older classification for fungi that lack a known sexual cycle. Like option C, this belongs to the field of Mycology, not Virology. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Symmetry:** Viral capsids generally exhibit two types of symmetry: **Icosahedral** (e.g., Adenovirus, Herpesvirus) or **Helical** (e.g., Influenza, Rabies). * **Enveloped vs. Non-enveloped:** Viruses lacking an outer lipid envelope are called "naked" viruses. These are typically more resistant to heat, acids, and detergents (e.g., Hepatitis A, Poliovirus). * **Function:** In naked viruses, the capsid contains the **VAPs (Viral Attachment Proteins)**. In enveloped viruses, these proteins are located on the lipid envelope. * **Composition:** Capsids are always proteinaceous, whereas the envelope is derived from host cell membranes (lipids and glycoproteins).

Q: Reverse transcriptase polymerase chain reactions can aid in the diagnosis of all of the following viral infections except?

Adenovirus. **Explanation:** The fundamental principle behind this question lies in the type of nucleic acid present in the virus. **Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)** is a laboratory technique used to amplify **RNA** sequences. It involves two steps: first, the enzyme reverse transcriptase converts RNA into complementary DNA (cDNA), which is then amplified using standard PCR. 1. **Why Adenovirus is the correct answer:** **Adenovirus** is a **double-stranded DNA (dsDNA) virus**. Since its genome is already DNA, it does not require the reverse transcription step. Diagnosis of Adenovirus is typically performed using standard **PCR**, viral culture, or antigen detection. 2. **Why the other options are incorrect:** * **Astrovirus:** These are positive-sense, single-stranded RNA (+ssRNA) viruses. * **Rotavirus:** These are double-stranded RNA (dsRNA) viruses (Reoviridae family). * **Poliovirus:** These are +ssRNA viruses (Picornaviridae family). Because Astrovirus, Rotavirus, and Poliovirus all possess **RNA genomes**, RT-PCR is the gold-standard molecular method for their detection and quantification. **High-Yield Clinical Pearls for NEET-PG:** * **DNA Viruses:** Most are dsDNA (except Parvoviridae, which is ssDNA). Remember the mnemonic "HHAPPPy" (Herpes, Hepadna, Adeno, Papova, Pox, Parvo). * **RNA Viruses:** Most are ssRNA (except Reoviridae/Rotavirus, which is dsRNA). * **RT-PCR vs. PCR:** Use RT-PCR for RNA viruses (HIV, HCV, SARS-CoV-2, Influenza) and standard PCR for DNA viruses (HBV, HSV, CMV). * **Adenovirus:** Common cause of pharyngoconjunctival fever, hemorrhagic cystitis, and epidemic keratoconjunctivitis (Pink eye).

Q: Which of the following statements about Dengue fever is incorrect?

It has an incubation period of 2-3 weeks.. ### Explanation **1. Why Option B is the Correct Answer (Incorrect Statement):** The incubation period of Dengue fever is typically **3 to 14 days** (average 4–7 days), not 2–3 weeks. In clinical virology, an incubation period exceeding 14 days is rare for most arboviral infections. Identifying the correct timeline is crucial for epidemiological tracking and diagnosing returning travelers. **2. Analysis of Other Options:** * **Option A:** Dengue is primarily transmitted by the **Aedes aegypti** mosquito (the principal vector) and occasionally by *Aedes albopictus*. These are "day-biters" that breed in stagnant clean water. * **Option C:** The Dengue virus (DENV) belongs to the genus **Flavivirus** and family *Flaviviridae*. It is a single-stranded, positive-sense RNA virus with four distinct serotypes (DEN-1 to DEN-4). * **Option D:** Dengue is classically known as **"Break-bone fever"** due to the characteristic severe myalgia, arthralgia, and retro-orbital pain associated with the febrile phase. **3. NEET-PG High-Yield Pearls:** * **Diagnosis:** **NS1 Antigen** is the marker of choice for the first 1–5 days. **IgM ELISA** is used after day 5. * **Pathogenesis:** Severe forms like Dengue Hemorrhagic Fever (DHF) occur due to **Antibody-Dependent Enhancement (ADE)**, usually during a secondary infection with a different serotype. * **Tourniquet Test:** A positive test (≥10 petechiae per square inch) indicates capillary fragility, a hallmark of DHF. * **Hematology:** Characterized by **leukopenia** and **thrombocytopenia**. A rising hematocrit (>20% increase) is a critical sign of plasma leakage.

Q: Which virus is noted for such a high incidence of antigenic drift that more than one antigenic variant can be isolated from infected individuals?

HIV. ### Explanation The correct answer is **HIV (Human Immunodeficiency Virus)**. **Why HIV is correct:** The hallmark of HIV is its extreme genetic diversity, driven by the error-prone nature of the **Reverse Transcriptase** enzyme, which lacks 3' to 5' exonuclease (proofreading) activity. This leads to a high rate of point mutations during replication. Consequently, HIV undergoes such rapid **antigenic drift** that it exists within a single patient as a collection of closely related but distinct genetic variants known as **quasispecies**. This allows the virus to constantly evade the host’s immune response and complicates vaccine development. **Why other options are incorrect:** * **Influenza Virus:** While famous for antigenic drift (causing seasonal epidemics) and shift (causing pandemics), the variants typically emerge at a population level over time. It does not usually produce multiple distinct antigenic variants within a single host simultaneously to the extent HIV does. * **Adenovirus & Herpesvirus:** These are **DNA viruses**. DNA polymerases generally have proofreading mechanisms, making these viruses genetically stable compared to RNA viruses. They do not exhibit significant antigenic drift. **High-Yield Clinical Pearls for NEET-PG:** * **Quasispecies:** This term specifically refers to the diverse pool of HIV variants within one individual. * **Reverse Transcriptase:** The highest mutation rate among all known biological entities ($10^{-4}$ to $10^{-5}$ mutations per base pair per cycle). * **Influenza Antigenic Shift:** Due to the **segmented genome** (8 segments), allowing for genetic reassortment. * **HIV Tropism:** Determined by the **gp120** protein binding to CD4 receptors and co-receptors (CCR5 or CXCR4).

Q: What is the characteristic feature of a retrovirus?

Reverse transcriptase. **Explanation:** The hallmark of a **Retrovirus** (such as HIV or HTLV) is the presence of the enzyme **Reverse Transcriptase (RNA-dependent DNA polymerase)**. Unlike most organisms that follow the central dogma of biology (DNA → RNA → Protein), retroviruses have an RNA genome. Upon entering a host cell, they use Reverse Transcriptase to transcribe their single-stranded RNA into double-stranded DNA. This viral DNA is then integrated into the host cell's genome by the enzyme *integrase*, allowing the virus to replicate using the host's cellular machinery. **Analysis of Incorrect Options:** * **A. Ribonuclease:** While retroviruses possess RNase H activity (which degrades the RNA strand from the RNA-DNA hybrid during replication), it is a component of the reverse transcriptase complex rather than the defining characteristic of the virus family. * **C. DNA polymerase:** While reverse transcriptase functions as a polymerase, "DNA polymerase" usually refers to DNA-dependent DNA polymerase (found in humans and DNA viruses), which uses a DNA template to make DNA. * **D. Restriction endonuclease:** These are enzymes found in bacteria used to cleave DNA at specific sequences as a defense mechanism against bacteriophages. They are not found in retroviruses. **High-Yield Clinical Pearls for NEET-PG:** * **Genome:** Retroviruses are the only viruses that are **diploid** (contain two identical copies of ssRNA). * **Replication:** They replicate in the **nucleus** (unlike most RNA viruses which replicate in the cytoplasm). * **Key Genes:** * *gag*: Codes for structural proteins (p24, p17). * *pol*: Codes for Reverse Transcriptase, Integrase, and Protease. * *env*: Codes for envelope glycoproteins (gp120 for attachment, gp41 for fusion).

Question 1

What is the commonly used screening test for Human Immunodeficiency Virus?

Accepted Answer

ELISA test

Answer

VDRL test

Answer

Weil-Felix test

Answer

Western blot test

Question 2

Which marker indicates infectivity of Hepatitis B?

Accepted Answer

HBeAg

Answer

HBsAg

Answer

Anti HBs

Answer

Anti HBc

Question 3

Which virus remains dormant but can be reactivated?

Accepted Answer

Herpes zoster

Answer

Herpes simplex

Answer

Epstein-Barr virus

Answer

Cytomegalovirus

Question 4

Which of the following statements about Hepatitis C is true?

Accepted Answer

Hepatitis C is the most common indication for liver transplant.

Answer

Hepatitis C is a DNA virus.

Answer

Hepatitis C does not cause liver cancer.

Answer

Hepatitis C causes coinfection with hepatitis B.

Question 5

What is the term for the symmetric protein shell that encases the nucleic acid core of a virus?

Accepted Answer

Capsid

Answer

Capsomere

Answer

Basidiomycetes

Answer

Fungi imperfecti

Question 6

Reverse transcriptase polymerase chain reactions can aid in the diagnosis of all of the following viral infections except?

Accepted Answer

Adenovirus

Answer

Astrovirus

Answer

Rotavirus

Answer

Poliovirus

Question 7

Which of the following statements about Dengue fever is incorrect?

Accepted Answer

It has an incubation period of 2-3 weeks.

Answer

It is spread by the vector Aedes aegypti.

Answer

It is caused by a Flavivirus.

Answer

It characteristically causes severe myalgia.

Question 8

Which virus is noted for such a high incidence of antigenic drift that more than one antigenic variant can be isolated from infected individuals?

Accepted Answer

HIV

Answer

Adenovirus

Answer

Herpesvirus

Answer

Influenza Virus

Question 9

What is the characteristic feature of a retrovirus?

Accepted Answer

Reverse transcriptase

Answer

Ribonuclease

Answer

DNA polymerase

Answer

Restriction endonuclease

Question 10

Which of the following statements about poliovirus is incorrect?

Accepted Answer

Type I is responsible for vaccine-associated paralytic poliomyelitis

Answer

Type I is responsible for most epidemics

Answer

Type I is very difficult to eliminate

Answer

Type I is most commonly associated with paralysis

Virology — MCQs

Virology — MCQs

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