Virology Practice Questions

Q: A 24-year-old male presented with a lesion on his genitalia after multiple sexual encounters. Which human papillomavirus type is the causative agent?

HPV 6, 11. **Explanation:** The clinical presentation of a genital lesion (typically **Condyloma acuminatum** or anogenital warts) following sexual contact is most commonly caused by **Human Papillomavirus (HPV) types 6 and 11**. These are classified as **"low-risk" HPV types** because they are associated with benign proliferative lesions rather than invasive squamous cell carcinoma. * **Option A (Correct):** HPV 6 and 11 are responsible for over 90% of cases of genital warts and are also the primary cause of recurrent respiratory papillomatosis. * **Option B (Incorrect):** HPV 16 and 18 are **"high-risk"** oncogenic types. They are the leading cause of cervical cancer, oropharyngeal cancer, and other anogenital malignancies (anal, penile, vulvar). They typically cause flat, subclinical lesions rather than overt warts. * **Options C & D (Incorrect):** HPV types 31, 33, 35, and 45 are also categorized as high-risk types. While they contribute to cervical dysplasia and neoplasia, they are less prevalent than types 16 and 18 and do not typically present as common genital warts. **NEET-PG High-Yield Pearls:** * **Koilocytes:** The hallmark histological finding of HPV infection (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Oncoproteins:** HPV E6 inhibits the **p53** tumor suppressor protein; HPV E7 inhibits the **pRb** (Retinoblastoma) protein. * **Vaccination:** The Quadrivalent vaccine (Gardasil) covers types 6, 11, 16, and 18, providing protection against both warts and cervical cancer. * **Diagnosis:** Usually clinical; confirmed by acetic acid test (acetowhitening) or biopsy if diagnosis is uncertain.

Q: 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?

Anti-HBs antibodies. ### 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.

Q: Which of the following is characteristic of Dengue hemorrhagic fever?

Most common in previously affected patients. ### 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.

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

High viral titres with low CD4 count. **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.

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

Rotaviruses. **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).

Q: 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

cause severe respiratory illness. **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)**.

Q: Which of the following is NOT a marker of the active replicative phase of chronic hepatitis B?

Anti-HBc. **Explanation:** To identify the replicative phase of Chronic Hepatitis B, we look for markers that signify active viral multiplication and the resulting liver injury. **Why Anti-HBc is the correct answer:** **Anti-HBc (Antibody to Hepatitis B core antigen)** is a marker of **exposure**, not replication. It appears shortly after the onset of infection and persists for life. In chronic infection, **Total Anti-HBc** (primarily IgG) remains positive regardless of whether the virus is actively replicating or in a latent/inactive state. Therefore, it cannot differentiate between the active replicative phase and the inactive carrier state. **Why the other options are markers of replication:** * **HBV DNA:** This is the most sensitive and quantitative marker of viral load. High levels directly indicate active viral replication. * **HBV DNA Polymerase:** This enzyme is required for the synthesis of viral DNA; its presence in the serum correlates directly with active viral multiplication. * **AST & ALT:** These liver transaminases are markers of hepatocellular injury. During the active replicative phase (specifically the "Immune Clearance" phase), the host’s immune system attacks infected hepatocytes, leading to elevated AST and ALT levels. **High-Yield Clinical Pearls for NEET-PG:** * **HBeAg:** The classic serological marker for high infectivity and active replication. Its disappearance and the appearance of **Anti-HBe** (seroconversion) usually signal a transition to the inactive state. * **Window Period:** The interval where HBsAg and Anti-HBs are both negative; **IgM Anti-HBc** is the sole diagnostic marker during this phase. * **HBsAg:** Persistence for **>6 months** defines chronic infection. * **Pre-core Mutants:** Patients may have high HBV DNA but be HBeAg negative; these cases still represent active replication.

Q: Recurrent herpes simplex infection occurs due to:

Latent virus in the nerve ganglia. ### Explanation **Correct Answer: C. Latent virus in the nerve ganglia** **Mechanism of Latency and Recurrence:** Herpes Simplex Virus (HSV-1 and HSV-2) exhibits a unique life cycle characterized by **latency**. During the primary infection, the virus replicates in the mucoepithelial cells. From there, it travels via **retrograde axonal transport** along sensory nerve fibers to the sensory nerve ganglia. * **HSV-1** typically remains latent in the **Trigeminal ganglion**. * **HSV-2** typically remains latent in the **Sacral ganglia**. In these ganglia, the viral genome persists in an episomal form without killing the host cell. Upon triggers like stress, UV light, fever, or immunosuppression, the virus undergoes **reactivation**, travels via **anterograde transport** back down the nerve to the skin/mucosa, and causes recurrent lesions (e.g., Herpes Labialis). **Why other options are incorrect:** * **Option A & B:** The virus does not remain latent in the oral mucosa or the skin. While these are the sites of active replication and clinical manifestation, the virus is cleared from these peripheral tissues by the immune system. It only survives long-term by "hiding" in the immunologically privileged site of the nervous system. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Gold Standard:** Viral Culture (though PCR is now more sensitive). * **Tzanck Smear:** Shows **Multinucleated Giant Cells** and **Cowdry Type A** intranuclear inclusion bodies (characteristic but not specific for HSV). * **Drug of Choice:** Acyclovir (inhibits viral DNA polymerase). * **HSV-1** is the most common cause of **Sporadic Viral Encephalitis** (affects the temporal lobe). * **HSV-2** is a common cause of **Aseptic Meningitis**.

Q: Which of the following causes a fatal encephalitis for which a vaccine is available?

Rabies. **Explanation:** **Rabies virus** (Option A) is the correct answer because it causes an acute, progressive, and almost invariably fatal encephalitis once clinical symptoms appear. It is a Rhabdovirus transmitted typically via the saliva of an infected animal. Crucially, it is a vaccine-preventable disease. Both pre-exposure prophylaxis (for high-risk individuals) and post-exposure prophylaxis (PEP) are highly effective if administered before the onset of symptoms. **Analysis of Incorrect Options:** * **Rhinovirus (Option B):** The primary cause of the common cold. It is restricted to the upper respiratory tract and does not cause encephalitis. There is no vaccine due to the high number of serotypes. * **Cytomegalovirus (Option C):** While CMV can cause encephalitis in immunocompromised patients (e.g., AIDS), it is not "invariably fatal" in the general population. Currently, there is no commercially available vaccine for CMV. * **Respiratory Syncytial Virus (Option D):** A major cause of bronchiolitis and pneumonia in infants. It does not typically cause encephalitis, and while vaccines have recently been approved for specific populations (older adults/maternal use), it does not fit the "fatal encephalitis" profile. **High-Yield NEET-PG Pearls:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusions found in pyramidal cells of the hippocampus and Purkinje cells of the cerebellum. * **Mechanism:** The virus binds to **Nicotinic Acetylcholine Receptors (nAChR)** at the neuromuscular junction and travels via retrograde axonal transport to the CNS. * **Vaccine Type:** Modern rabies vaccines (e.g., PCECV, HDCV) are **inactivated/killed** vaccines. * **Hydrophobia:** Characteristic symptom due to painful spasms of the laryngeal and pharyngeal muscles when attempting to swallow.

Question 1

A 24-year-old male presented with a lesion on his genitalia after multiple sexual encounters. Which human papillomavirus type is the causative agent?

Accepted Answer

HPV 6, 11

Answer

HPV 16, 18

Answer

HPV 31, 33

Answer

HPV 35, 45

Question 2

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?

Accepted Answer

Anti-HBs antibodies

Answer

HBeAg

Answer

HBV DNA

Answer

HBV DNA polymerase

Question 3

Which of the following is characteristic of Dengue hemorrhagic fever?

Accepted Answer

Most common in previously affected patients

Answer

DHF-2 is the most common cause

Answer

Associated with immunosuppression

Answer

Incubation period is 7-14 days

Question 4

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

Accepted Answer

High viral titres with low CD4 count

Answer

Low viral titres with low CD4 count

Answer

Low viral titres with high CD4 count

Answer

High viral titres with high CD4 count

Question 5

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

Accepted Answer

Rotaviruses

Answer

Picornaviruses

Answer

Togaviruses

Answer

Paramyxoviruses

Question 6

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

Accepted Answer

cause severe respiratory illness

Answer

cause the common cold

Answer

infect intestinal cells

Answer

cause neurological disorders

Question 7

Which of the following is NOT a marker of the active replicative phase of chronic hepatitis B?

Accepted Answer

Anti-HBc

Answer

HBV DNA

Answer

HBV DNA polymerase

Answer

AST & ALT

Question 8

Recurrent herpes simplex infection occurs due to:

Accepted Answer

Latent virus in the nerve ganglia

Answer

Virus residing in the oral mucosa

Answer

Latent virus in the skin supplying the affected area

Answer

None of the above

Question 9

Which of the following causes a fatal encephalitis for which a vaccine is available?

Accepted Answer

Rabies

Answer

Rhinovirus

Answer

Cytomegalovirus

Answer

Respiratory syncytial virus

Question 10

What is a characteristic of chickenpox?

Accepted Answer

It may be severe in a newborn infected by the mother in late pregnancy.

Answer

It is commonly seen in a congenital form.

Answer

It affects the limbs more than the trunk.

Answer

It may cause pneumonitis.

Virology — MCQs

Virology — MCQs

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