Virology Practice Questions

Q: What is antigenic shift?

Results from genetic recombination. ### Explanation **Antigenic Shift** is a sudden, major change in the surface antigens (Hemagglutinin and/or Neuraminidase) of the Influenza virus. **Why Option C is Correct:** Antigenic shift occurs due to **genetic reassortment** (recombination). When two different strains of Influenza A virus infect the same host cell (e.g., in a pig or bird), their segmented RNA genomes mix during assembly. This results in a completely new subtype (e.g., H1N1 shifting to H2N2) to which the human population has little to no immunity. This is the primary driver of **Pandemics**. **Why Other Options are Incorrect:** * **Option A:** Antigenic shift is unpredictable and occurs at irregular, long intervals (typically decades), not every 2–3 years. * **Option B:** Gradual changes over time describe **Antigenic Drift**, which results from point mutations during viral replication. * **Option D:** Antigenic shift occurs **only in Influenza A** because it has a wide host range (humans, birds, swine). Influenza B and C undergo only antigenic drift, as they primarily infect humans, limiting the opportunity for reassortment. **High-Yield Clinical Pearls for NEET-PG:** * **Segmented Genome:** Influenza virus has 8 RNA segments. This segmentation is the structural prerequisite for reassortment/shift. * **Drift vs. Shift:** * **Drift:** Point mutations $\rightarrow$ Epidemics $\rightarrow$ Seen in A and B. * **Shift:** Reassortment $\rightarrow$ Pandemics $\rightarrow$ Seen only in A. * **Mixing Vessel:** Pigs are often called "mixing vessels" because they possess receptors for both avian and human influenza viruses.

Q: Which virus is the leading cause of bronchiolitis and community-acquired pneumonia in infants?

Respiratory syncytial virus. **Explanation:** **Respiratory Syncytial Virus (RSV)** is the most common cause of lower respiratory tract infections (LRTIs), specifically **bronchiolitis** and **pneumonia**, in infants and children under the age of two. The underlying medical concept involves the virus causing inflammation and edema of the small airways (bronchioles), leading to obstruction, wheezing, and air trapping. In infants, the narrow caliber of the airways makes them particularly susceptible to significant clinical distress from this inflammation. **Analysis of Incorrect Options:** * **Measles Virus:** While it can cause Giant Cell Pneumonia (Hecht’s pneumonia), it is primarily a systemic febrile illness characterized by Koplik spots and a maculopapular rash. It is not the leading cause of bronchiolitis. * **Influenza Virus:** Though a major cause of pneumonia across all age groups, it typically presents with high fever, myalgia, and systemic symptoms. It is less frequently associated with the specific clinical syndrome of bronchiolitis compared to RSV. * **Parainfluenza Virus:** This is the leading cause of **Croup (Laryngotracheobronchitis)**, characterized by a "barking" cough and inspiratory stridor, rather than the lower airway wheezing seen in bronchiolitis. **High-Yield Clinical Pearls for NEET-PG:** * **RSV Morphology:** A pleomorphic, enveloped, negative-sense ssRNA virus (Paramyxoviridae family). * **Cytopathology:** Characterized by the formation of **syncytia** (multinucleated giant cells) due to the "F" (fusion) protein. * **Diagnosis:** Rapid antigen detection tests or RT-PCR from nasopharyngeal aspirates. * **Prophylaxis:** **Palivizumab**, a monoclonal antibody against the F protein, is used for high-risk premature infants. * **Seasonality:** Typically peaks during winter months.

Q: An 18-year-old lady presents with severe sore throat, fever, and malaise. She has cervical lymphadenopathy, splenomegaly, and scattered petechiae on the soft palate with enlarged tonsils covered with white exudates. Which of the following investigations is most likely to help guide your management?

Heterophile antibody test. ### Explanation The clinical presentation of **fever, sore throat (exudative pharyngitis), cervical lymphadenopathy, and splenomegaly** in a young adult is the classic triad of **Infectious Mononucleosis (IM)**, primarily caused by the **Epstein-Barr Virus (EBV)**. **1. Why Heterophile Antibody Test is Correct:** The Heterophile antibody test (e.g., **Monospot test**) is the screening investigation of choice. It detects IgM antibodies that agglutinate sheep or horse red blood cells. These antibodies are produced during the acute phase of EBV infection due to polyclonal B-cell activation. In a patient with palatal petechiae and splenomegaly, this test confirms the diagnosis of IM, guiding management toward supportive care and avoidance of contact sports (to prevent splenic rupture). **2. Why Other Options are Incorrect:** * **Fine needle aspiration (FNA):** While lymphadenopathy is present, FNA is unnecessary and typically reserved for suspected malignancy (lymphoma). In IM, nodes are reactive and tender. * **Hepatitis B surface antigen:** While EBV can cause mild hepatitis, the primary symptoms (pharyngitis, tonsillar exudates) are not characteristic of HBV. * **HIV test:** Acute Retroviral Syndrome can mimic IM (mononucleosis-like illness), but the presence of **exudative tonsillitis** and **splenomegaly** strongly favors EBV over HIV. **Clinical Pearls for NEET-PG:** * **Atypical Lymphocytes:** Peripheral smear shows "Downey cells" (activated T-cells/CD8+). * **Ampicillin Rash:** Administration of Ampicillin or Amoxicillin in a patient with IM often triggers a characteristic maculopapular rash. * **Specific Serology:** If the heterophile test is negative but IM is suspected, test for **Anti-VCA (Viral Capsid Antigen) IgM**. * **Complication:** Splenic rupture is a rare but life-threatening complication; patients must avoid heavy lifting for 3–4 weeks.

Q: Varicella zoster virus remains latent in which of the following locations?

Trigeminal ganglion. **Explanation:** The **Varicella-Zoster Virus (VZV)**, a member of the *Alphaherpesvirinae* subfamily (Human Herpesvirus 3), follows a distinct pathogenesis. After the primary infection (Chickenpox), the virus travels via retrograde axonal transport from skin lesions to the **sensory nerve ganglia**, where it establishes lifelong latency. **Why the Trigeminal Ganglion is Correct:** VZV remains latent in the **dorsal root ganglia** (spinal nerves) and **cranial nerve ganglia**, most notably the **trigeminal ganglion**. Upon reactivation—usually due to waning cell-mediated immunity—the virus travels back down the sensory nerve to cause **Herpes Zoster (Shingles)**, characterized by a painful, unilateral vesicular rash restricted to a specific dermatome. **Analysis of Incorrect Options:** * **A & B (Lymphocytes & Monocytes):** These are common latency sites for the *Betaherpesvirinae* (e.g., CMV in monocytes) and *Gammaherpesvirinae* (e.g., EBV in B-lymphocytes). VZV does not persist in hematopoietic cells. * **D (Plasma Cells):** While plasma cells are involved in the immune response, they are not reservoirs for viral latency. **High-Yield Clinical Pearls for NEET-PG:** * **Ramsay Hunt Syndrome:** Reactivation of VZV in the **geniculate ganglion**, leading to facial palsy and ear vesicles. * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions (common to HSV and VZV). * **Post-Herpetic Neuralgia:** The most common complication of Shingles. * **Vaccine:** Live attenuated **Oka strain** is used for prevention.

Q: A patient has an increased antibody titer to delta agent. What would you most likely suspect?

Possible hepatitis B infection. **Explanation:** The **Delta agent** refers to the **Hepatitis D Virus (HDV)**. HDV is a "defective" RNA virus that requires the presence of the **Hepatitis B Virus (HBV)** to replicate. Specifically, HDV uses the Hepatitis B surface antigen (HBsAg) as its outer envelope to package its genome and infect other hepatocytes. Therefore, a positive antibody titer to the delta agent is a definitive marker for a co-infection or super-infection with **Hepatitis B**. **Analysis of Options:** * **Option A (Fifth disease):** Caused by **Parvovirus B19**. It typically presents with a "slapped-cheek" rash in children and is unrelated to the delta agent. * **Option B (Susceptibility to chickenpox):** Chickenpox is caused by the **Varicella-Zoster Virus (VZV)**. Susceptibility is determined by the absence of anti-VZV IgG antibodies, not delta agent titers. * **Option C (SSPE):** Subacute sclerosing panencephalitis is a rare, progressive neurological complication caused by a persistent **Measles virus** infection. Diagnosis involves high titers of measles antibodies in the CSF and serum. **High-Yield Clinical Pearls for NEET-PG:** * **Co-infection:** Simultaneous infection of HBV and HDV. It usually results in acute hepatitis but has a low risk of chronicity. * **Super-infection:** HDV infection in a chronic HBV carrier. This carries a much higher risk of fulminant hepatitis and rapid progression to cirrhosis. * **Prevention:** The Hepatitis B vaccine is protective against HDV because HDV cannot exist without HBV. * **Genome:** HDV has a circular, single-stranded negative-sense RNA genome.

Q: A 2-year-old child attending daycare develops diarrhea and gastroenteritis as a result of adenoviral infection. Which of the following adenoviral serotypes would most likely be responsible for this child's illness?

Type 41. **Explanation:** Adenoviruses are non-enveloped, double-stranded DNA viruses that cause a wide spectrum of clinical syndromes depending on their serotype. **Correct Option: D (Type 41)** Adenoviruses are classified into subgroups A through G. **Subgroup F (Serotypes 40 and 41)** are specifically known as **"Enteric Adenoviruses."** These are the second most common cause of viral gastroenteritis in infants and young children worldwide, following Rotavirus. Unlike other adenoviruses, types 40 and 41 are fastidious (difficult to grow in standard cell cultures) and primarily replicate in the intestinal tract, leading to diarrhea and vomiting. **Incorrect Options:** * **Types 4 and 7 (Options A & B):** These belong to Subgroup E and B, respectively. They are the primary causes of **Acute Respiratory Disease (ARD)**, often seen in military recruits, and can cause pneumonia or conjunctivitis. * **Type 19 (Option C):** This serotype (along with Type 8 and 37) is a classic cause of **Epidemic Keratoconjunctivitis (EKC)**, characterized by severe "pink eye" and corneal involvement. **NEET-PG High-Yield Pearls:** * **Enteric Adenoviruses (40, 41):** Known as "Fastidious Adenoviruses"; they do not typically cause respiratory symptoms. * **Pharyngoconjunctival Fever:** Most commonly caused by **Type 3 and 7**. * **Hemorrhagic Cystitis:** Characterized by hematuria in children, primarily caused by **Types 11 and 21**. * **Structure:** Adenoviruses possess a unique **Penton fiber** that acts as a hemagglutinin and is toxic to human cells.

Question 1

What is antigenic shift?

Accepted Answer

Results from genetic recombination

Answer

Occurs every 2-3 years

Answer

Gradual change over time

Answer

Occurs in all influenza viruses

Question 2

A 6-year-old girl presents with a blotchy, reddish-brown rash on her face, trunk, and proximal extremities that developed over 3 days. Physical examination reveals 0.2-cm to 0.5-cm ulcerated lesions on the oral mucosa and generalized tender lymphadenopathy. A cough with minimal sputum production worsens over the next 3 days. Which of the following viruses is most likely to produce these findings?

Accepted Answer

Rubeola virus

Answer

Epstein-Barr virus

Answer

Mumps virus

Answer

Rubella virus

Question 3

Which of the following is the first stage in the life cycle of a bacteriophage?

Accepted Answer

Lytic cycle

Answer

Lysogenic cycle

Answer

Maturation

Answer

Eclipse phase

Question 4

All of the following are true about HIV except?

Accepted Answer

Mostly spread by heterosexual contact.

Answer

A DNA virus belonging to the retrovirus family.

Answer

Attacks CD4 lymphocytes.

Answer

The CD4:CD8 ratio is reversed.

Question 5

Which virus is the leading cause of bronchiolitis and community-acquired pneumonia in infants?

Accepted Answer

Respiratory syncytial virus

Answer

Measles virus

Answer

Influenza virus

Answer

Parainfluenza virus

Question 6

Which of the following statements about Coronaviruses is false?

Accepted Answer

It does not spread through coughing, sneezing, or direct contact.

Answer

These viruses have club-shaped peplomers on their surface.

Answer

SARS spreads mainly by inhalation.

Answer

The SARS virus is highly mutable.

Question 7

An 18-year-old lady presents with severe sore throat, fever, and malaise. She has cervical lymphadenopathy, splenomegaly, and scattered petechiae on the soft palate with enlarged tonsils covered with white exudates. Which of the following investigations is most likely to help guide your management?

Accepted Answer

Heterophile antibody test

Answer

Fine needle aspiration of a lymph node

Answer

Hepatitis B surface antigen

Answer

HIV test

Question 8

Varicella zoster virus remains latent in which of the following locations?

Accepted Answer

Trigeminal ganglion

Answer

Lymphocytes

Answer

Monocytes

Answer

Plasma cells

Question 9

A patient has an increased antibody titer to delta agent. What would you most likely suspect?

Accepted Answer

Possible hepatitis B infection

Answer

Fifth disease

Answer

Susceptibility to chickenpox

Answer

Possible subacute sclerosing panencephalitis (SSPE)

Question 10

A 2-year-old child attending daycare develops diarrhea and gastroenteritis as a result of adenoviral infection. Which of the following adenoviral serotypes would most likely be responsible for this child's illness?

Accepted Answer

Type 41

Answer

Type 4

Answer

Type 7

Answer

Type 19

Virology — MCQs

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