Virology Practice Questions

Q: Which marker indicates active Hepatitis B Virus (HBV) infection?

HBsAg. ### Explanation **Hepatitis B Surface Antigen (HBsAg)** is the hallmark of active infection. It is the first serological marker to appear in the blood (usually 2–6 weeks after exposure) and its presence indicates that the virus is currently replicating in the host. If HBsAg persists for more than 6 months, the infection is classified as **chronic**. #### Analysis of Options: * **A. HBsAg (Correct):** It is the primary screening tool. Its presence signifies an active (acute or chronic) infection. * **B. HBcAg (Hepatitis B Core Antigen):** This is a particulate antigen found inside the hepatocyte. It is **not secreted into the blood** and therefore cannot be detected by routine serum assays. * **C. IgM anti-HBsAg:** This is not a standard clinical marker. Protective antibodies against the surface antigen are typically of the IgG class. * **D. IgG anti-HBsAg:** This indicates **immunity** to HBV. It appears after recovery from a natural infection or following successful vaccination. It is never present during the active phase of the disease. #### NEET-PG High-Yield Pearls: 1. **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs. During this gap, **IgM anti-HBc** is the only diagnostic marker present. 2. **Infectivity Marker:** **HBeAg** (Envelope antigen) indicates high viral replication and high infectivity. 3. **Vaccination vs. Natural Infection:** * **Vaccinated:** Only Anti-HBs positive. * **Recovered from Natural Infection:** Both Anti-HBs and Anti-HBc (IgG) positive. 4. **HBV DNA:** The most sensitive marker for monitoring viral load and response to antiviral therapy.

Q: In a child immunized for hepatitis B, which marker indicates seroconversion?

Anti HBs. ### Explanation **Correct Answer: C. Anti HBs** **1. Why Anti-HBs is the Correct Answer:** The Hepatitis B vaccine contains only the **Hepatitis B surface Antigen (HBsAg)**, which is a recombinant protein. When a child is immunized, their immune system recognizes this surface protein and produces specific antibodies against it, known as **Anti-HBs (Hepatitis B surface antibody)**. * **Seroconversion** is defined by the appearance of these antibodies in the serum. * A protective level is generally considered to be **≥10 mIU/mL**. * Since the vaccine does not contain the viral core or the whole virus, the body *only* produces antibodies against the surface component. **2. Why the Other Options are Incorrect:** * **A. HBsAg:** This is the actual viral surface antigen. Its presence in the blood indicates an **active infection** (acute or chronic), not immunity from vaccination. * **B. Anti-HBc IgM:** These are antibodies against the Hepatitis B **core** antigen. They appear during **acute infection** or a flare-up of chronic infection. Because the vaccine lacks the core antigen, these antibodies are never produced by vaccination. * **D. Anti-HBc IgG:** These indicate a **past or chronic infection**. Like IgM, these are directed against the core antigen. Their absence in a person with positive Anti-HBs confirms that the immunity is due to **vaccination** rather than a prior natural infection. **3. NEET-PG High-Yield Pearls:** * **Vaccine-induced immunity:** Anti-HBs (+), Anti-HBc (-), HBsAg (-). * **Natural infection immunity:** Anti-HBs (+), Anti-HBc (+) [IgG], HBsAg (-). * **Window Period:** Both HBsAg and Anti-HBs are negative; **Anti-HBc IgM** is the only marker present. * **Chronic Infection:** HBsAg persists for >6 months. * **Hepatitis B Vaccine Schedule:** 0, 1, and 6 months (standard) or 6, 10, 14 weeks (under National Immunization Schedule in India).

Q: Which gene encodes the HTLV tax protein?

pX. **Explanation:** Human T-cell Lymphotropic Virus (HTLV-1) is a complex retrovirus. Unlike simple retroviruses, it contains a unique **pX region** located at the 3' end of its genome, which is essential for its oncogenic potential. **1. Why pX is correct:** The **pX region** encodes several non-structural regulatory proteins, most notably **Tax** and **Rex**. * **Tax protein** is a potent transcriptional activator. It upregulates the expression of cellular genes involved in T-cell proliferation (like IL-2 and IL-2 receptors) and inactivates tumor suppressor genes (like p53). This leads to the immortalization of T-cells, eventually causing **Adult T-cell Leukemia/Lymphoma (ATL)**. **2. Why other options are incorrect:** * **Gag (Group-specific antigen):** Encodes the internal structural proteins of the virus, such as the capsid (p24), nucleocapsid, and matrix proteins. * **Pol (Polymerase):** Encodes essential viral enzymes, including Reverse Transcriptase, Integrase, and Protease. * **Env (Envelope):** Encodes the surface glycoproteins (gp46) and transmembrane proteins (gp21) responsible for viral attachment and entry. **Clinical Pearls for NEET-PG:** * **HTLV-1 Association:** Strongly linked to **Adult T-cell Leukemia/Lymphoma (ATL)** (characterized by "flower cells" on peripheral smear) and **Tropical Spastic Paraparesis (TSP)** (a demyelinating disease). * **Transmission:** Similar to HIV (Blood, Sexual contact, and Breastfeeding). * **Tax Protein:** It is the primary oncogenic driver; it induces genomic instability and inhibits DNA repair. * **Rex Protein:** Regulates viral mRNA splicing and export from the nucleus.

Q: Which of the following viruses causes hemolysis of red blood cells?

Human parvovirus B19. **Explanation:** **Human Parvovirus B19** is the correct answer because of its unique tropism for erythroid progenitor cells. The virus binds to the **P-antigen** (globoside) on the surface of red blood cells and their precursors. Once inside, it replicates in the nucleus of rapidly dividing erythroblasts, leading to direct cytotoxicity and **lysis (hemolysis)** of the cells. In healthy individuals, this causes a transient drop in hemoglobin; however, in patients with high RBC turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis), it can trigger a life-threatening **Aplastic Crisis**. **Analysis of Incorrect Options:** * **Rubella:** A Togavirus that causes German Measles. While it can cause thrombocytopenia or vascular complications (congenital rubella syndrome), it does not directly infect or lyse RBCs. * **Measles:** A Paramyxovirus characterized by Koplik spots and a maculopapular rash. It primarily infects respiratory epithelium and immune cells (via CD150/SLAM), not erythroid cells. * **Dengue Virus:** A Flavivirus that causes "breakbone fever." Its primary hematological impact is **thrombocytopenia** (low platelets) and plasma leakage due to increased vascular permeability, rather than direct hemolysis of RBCs. **High-Yield Clinical Pearls for NEET-PG:** * **Erythema Infectiosum (Fifth Disease):** Characterized by the classic "slapped-cheek" rash in children. * **Hydrops Fetalis:** If a pregnant woman is infected, the virus crosses the placenta, lyses fetal RBCs, leading to severe anemia, high-output heart failure, and fetal edema. * **Receptor:** The P-antigen is the essential cellular receptor; individuals lacking this antigen are naturally resistant to B19 infection.

Q: What is the most common viral antigen used for the diagnosis of HIV?

P24. The diagnosis of HIV relies on detecting specific viral components, primarily the **p24 antigen**. This protein forms the **inner viral capsid** (core) that surrounds the RNA genome. **Why p24 is the correct answer:** The p24 antigen is the most abundant viral protein produced during early infection. It is detectable in the blood approximately **1 to 3 weeks** after exposure, appearing even before the development of host antibodies (the "window period"). Modern **4th Generation ELISA** tests (p24 antigen + HIV-1/2 antibodies) utilize this to significantly reduce the diagnostic window, making it the gold standard for early screening. **Analysis of Incorrect Options:** * **B. p17:** This is the **matrix protein** located between the viral envelope and the capsid. While essential for viral assembly, it is not the primary target for diagnostic assays. * **C. p7:** This is a **nucleocapsid protein** that directly binds to the viral RNA. It is much smaller and less immunogenic than p24. * **D. p14:** This is not a standard structural protein of HIV. (Note: HIV accessory proteins include Tat, Rev, Nef, Vif, Vpu, and Vpr). **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies [1]. p24 detection narrows this period. * **Gag Gene:** Encodes the structural proteins **p24 (capsid)**, **p17 (matrix)**, and **p7/p9 (nucleocapsid)**. * **Env Gene:** Encodes **gp120** (attachment to CD4) and **gp41** (fusion/transmembrane). * **Pol Gene:** Encodes essential enzymes: Reverse Transcriptase, Integrase, and Protease. * **Western Blot:** Historically used for confirmation, it specifically looks for antibodies against p24, gp41, and gp120/160.

Q: Which of the following viruses is not an enveloped virus but contains double-stranded RNA?

Reovirus. ### Explanation The correct answer is **Reovirus**. This question tests your knowledge of viral structure, specifically the classification of genomes and envelopes. **1. Why Reovirus is correct:** The **Reoviridae** family (which includes Rotavirus and Coltivirus) is unique because it is one of the few virus families that possesses a **double-stranded RNA (dsRNA)** genome. Structurally, Reoviruses are **non-enveloped** (naked) and exhibit a characteristic double-layered icosahedral capsid. A high-yield mnemonic for dsRNA is: *"A **Double**-stranded **R**eovirus **R**aces"* (dsRNA = Reovirus). **2. Why the other options are incorrect:** * **Adenovirus (Option A):** While it is a non-enveloped (naked) virus, its genome consists of **double-stranded DNA (dsDNA)**, not RNA. It is a common cause of conjunctivitis and pharyngitis. * **Cytomegalovirus (Option C):** CMV belongs to the Herpesviridae family. These are **enveloped** viruses with a **dsDNA** genome. * **Hepatitis B Virus (Option D):** HBV is an **enveloped** virus. Its genome is unique—**partially double-stranded circular DNA**—and it uses reverse transcriptase during replication. **3. High-Yield Clinical Pearls for NEET-PG:** * **Rotavirus:** The most common cause of severe diarrhea in infants and children worldwide. It has a **segmented genome** (11 segments), allowing for genetic reassortment. * **Naked Viruses:** Remember the mnemonic **PAPP H**elp **C**alculate **R**eality (**P**apilloma, **A**deno, **P**arvo, **P**olyoma, **H**epna, **C**alici, **R**eo). These are generally more resistant to environmental heat and detergents. * **RNA Genomes:** Almost all RNA viruses are single-stranded (ssRNA) *except* for Reoviridae.

Question 1

Which marker indicates active Hepatitis B Virus (HBV) infection?

Accepted Answer

HBsAg

Answer

HBcAg

Answer

IgM anti-HBsAg

Answer

IgG anti-HBsAg

Question 2

The human immunodeficiency virus (HIV) can be isolated from which of the following body fluids or sources, except?

Accepted Answer

Skin scraping

Answer

Semen

Answer

Saliva

Answer

Blood transfusion

Question 3

In a child immunized for hepatitis B, which marker indicates seroconversion?

Accepted Answer

Anti HBs

Answer

HBs Ag

Answer

Anti HBc IgM

Answer

Anti HBc IgG

Question 4

Which gene encodes the HTLV tax protein?

Accepted Answer

pX

Answer

Gag

Answer

Pol

Answer

Env

Question 5

Which of the following infections typically manifests initially as an infection of the limbic regions of the brain in children?

Accepted Answer

Rabies

Answer

Enterovirus

Answer

Epstein-Barr virus

Answer

Cytomegalovirus

Question 6

Which of the following is NOT true about Parvovirus B-19?

Accepted Answer

Approximately 10% of infections spread by transplacental route.

Answer

Parvovirus B19 exclusively infects humans.

Answer

It is a DNA virus.

Answer

It affects erythroid progenitors, but individuals who totally lack Blood Group P antigen are resistant to infection.

Question 7

Which of the following viruses causes hemolysis of red blood cells?

Accepted Answer

Human parvovirus B19

Answer

Rubella

Answer

Measles

Answer

Dengue virus

Question 8

What is the most common viral antigen used for the diagnosis of HIV?

Accepted Answer

P24

Answer

P17

Answer

P7

Answer

P14

Question 9

Which of the following viruses is not an enveloped virus but contains double-stranded RNA?

Accepted Answer

Reovirus

Answer

Adenovirus

Answer

Cytomegalovirus (CMV)

Answer

Hepatitis B virus

Question 10

An outbreak of diarrhea occurred among elderly patients in an assisted care facility, which had been repeatedly cited by the public health department for poor hygiene practices. The agent that caused the infections had a star-like morphology in electron micrographs. Enzyme immunoassay (EIA) tests for several agents of viral gastroenteritis were negative. Which virus was most likely responsible for this outbreak?

Accepted Answer

Astrovirus

Answer

Adenovirus 40/41

Answer

Hepatitis A virus (HAV)

Answer

Norovirus

Virology — MCQs

Virology — MCQs

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