Virology Practice Questions

Q: Epstein-Barr virus (EBV) is associated with which of the following conditions, except?

Anal carcinoma. **Explanation:** The correct answer is **Anal carcinoma** because it is primarily associated with **Human Papillomavirus (HPV)**, specifically high-risk types 16 and 18, rather than the Epstein-Barr Virus (EBV). **Why the other options are associated with EBV:** * **Nasopharyngeal Carcinoma:** EBV has a strong oncogenic association with the undifferentiated type of nasopharyngeal carcinoma, particularly prevalent in Southern China and SE Asia. It involves the expression of viral proteins like LMP-1 in epithelial cells. * **Carcinoma of the Tonsil:** While many oropharyngeal cancers are HPV-related, EBV is also linked to certain epithelial malignancies of the Waldeyer’s ring (including the tonsils), often following a similar pathogenic pathway to nasopharyngeal carcinoma. * **Infectious Mononucleosis (Glandular Fever):** This is the classic acute clinical manifestation of primary EBV infection, characterized by the triad of fever, pharyngitis, and lymphadenopathy, with the presence of atypical lymphocytes (Downey cells) on peripheral smear. **High-Yield Clinical Pearls for NEET-PG:** * **EBV Receptor:** It binds to the **CD21** molecule (CR2) on B-lymphocytes. * **Other EBV Associations:** Burkitt Lymphoma (starry-sky appearance), Hodgkin Lymphoma (Mixed cellularity subtype), Oral Hairy Leukoplakia (in HIV patients), and Post-transplant lymphoproliferative disorder (PTLD). * **Diagnosis:** The **Paul-Bunnell Test** (detecting heterophile antibodies) is the classic screening test for Infectious Mononucleosis. * **Mnemonic for HPV:** HPV is associated with "Below the belt" cancers (Cervical, Anal, Vulvar, Penile) and Oropharyngeal squamous cell carcinoma.

Q: What is the primary receptor through which M-tropic HIV strains bind?

CCR5. **Explanation:** The entry of HIV into host cells is a multi-step process involving the viral envelope glycoprotein **gp120**. This protein first binds to the **CD4 receptor** on T-cells or macrophages, causing a conformational change that allows gp120 to interact with a specific **chemokine co-receptor**. 1. **Why CCR5 is correct:** M-tropic (Macrophage-tropic) strains, also known as **R5 strains**, utilize the **CCR5** co-receptor. These strains are typically responsible for the initial infection and are found in the early stages of the disease. They primarily infect macrophages, monocytes, and memory T-cells. 2. **Why CXCR4 is incorrect:** T-tropic (T-cell-tropic) strains, or **X4 strains**, utilize the **CXCR4** co-receptor. These strains emerge in the later stages of HIV infection, show a preference for naïve T-cells, and are associated with a rapid decline in CD4 counts and progression to AIDS. 3. **Why CXCR5 is incorrect:** CXCR5 is a chemokine receptor primarily involved in B-cell homing to lymph nodes; it does not serve as a primary co-receptor for HIV entry. **High-Yield Clinical Pearls for NEET-PG:** * **Maraviroc:** A CCR5 antagonist (entry inhibitor) used in HIV treatment; it is ineffective against X4 (T-tropic) strains. * **Genetic Resistance:** Individuals with a homozygous **CCR5-Δ32 mutation** (a 32-base pair deletion) are virtually resistant to infection by M-tropic HIV-1. * **Coreceptor Switch:** The progression of HIV often involves a "phenotypic switch" where the virus evolves from using CCR5 (M-tropic) to CXCR4 (T-tropic). * **gp41:** While gp120 handles attachment, **gp41** is responsible for the actual fusion of the viral envelope with the host cell membrane.

Q: A sexually active woman presents for a routine gynecologic exam with a Pap smear report indicating cervical intraepithelial neoplasia. In situ hybridization reveals the presence of human papillomavirus (HPV) type 16 genomes within the neoplastic cells. Which of the following processes is required for HPV to cause cancer development?

Integration of the viral genome. **Explanation:** The progression of Human Papillomavirus (HPV) infection to cervical carcinoma is fundamentally dependent on the **integration of the viral genome** into the host cell DNA. 1. **Why Option A is correct:** In benign lesions (warts), the HPV genome exists as an episome (circular, extrachromosomal). However, in malignant lesions, the viral DNA integrates into the host genome. This integration typically occurs at the **E1/E2 open reading frame**, leading to the **disruption of the E2 gene**. Since the E2 gene normally functions as a negative regulator (repressor) of the **E6 and E7 oncogenes**, its loss leads to the uncontrolled overexpression of E6 and E7. * **E6** binds to and degrades the **p53** tumor suppressor protein. * **E7** binds to and inactivates the **pRb** (Retinoblastoma) protein. The loss of these "molecular brakes" leads to unrestricted cell cycle progression and genomic instability. 2. **Why the other options are incorrect:** * **Option B:** Loss of E6 and E7 would prevent oncogenesis, as these are the primary drivers of malignancy. * **Option C:** While mutations occur in many cancers, the specific oncogenic transformation by HPV is driven by gene expression changes following integration, not random viral mutations. * **Option D:** Viral replication (the production of new virions) occurs in the superficial layers of the epithelium and usually leads to cell death (lysis), which is contrary to the immortalization required for cancer. **High-Yield Clinical Pearls for NEET-PG:** * **High-risk HPV types:** 16 and 18 (associated with ~70% of cervical cancers). * **Low-risk HPV types:** 6 and 11 (associated with Condyloma acuminatum). * **Koilocytosis:** The hallmark cytological finding on Pap smear (perinuclear halo with wrinkled "raisinoid" nuclei). * **Vaccine:** Gardasil-9 covers types 6, 11, 16, 18, 31, 33, 45, 52, and 58.

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.

Question 1

Epstein-Barr virus (EBV) is associated with which of the following conditions, except?

Accepted Answer

Anal carcinoma

Answer

Carcinoma of the tonsil

Answer

Nasopharyngeal carcinoma

Answer

Infectious mononucleosis

Question 2

What is the primary receptor through which M-tropic HIV strains bind?

Accepted Answer

CCR5

Answer

CXCR4

Answer

CXCR5

Answer

Any of the above

Question 3

A sexually active woman presents for a routine gynecologic exam with a Pap smear report indicating cervical intraepithelial neoplasia. In situ hybridization reveals the presence of human papillomavirus (HPV) type 16 genomes within the neoplastic cells. Which of the following processes is required for HPV to cause cancer development?

Accepted Answer

Integration of the viral genome

Answer

Loss of HPV E6 and E7 genes

Answer

Mutation of the virus

Answer

Viral replication

Question 4

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

Accepted Answer

HBsAg

Answer

HBcAg

Answer

IgM anti-HBsAg

Answer

IgG anti-HBsAg

Question 5

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 6

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 7

Which gene encodes the HTLV tax protein?

Accepted Answer

pX

Answer

Gag

Answer

Pol

Answer

Env

Question 8

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 9

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 10

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

Accepted Answer

Human parvovirus B19

Answer

Rubella

Answer

Measles

Answer

Dengue virus

Virology — MCQs

Virology — MCQs

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