Virology Practice Questions

Q: A rise in the anti-HBc immunoglobulin in a patient indicates which of the following?

Acute infection. **Explanation:** The detection of **anti-HBc (Antibody to Hepatitis B core antigen)** is a critical marker in the serological diagnosis of Hepatitis B. 1. **Why Acute Infection is Correct:** Anti-HBc is the first antibody to appear after HBsAg. During an **acute infection**, the body produces **IgM anti-HBc**. This is the only reliable marker during the "Window Period"—the gap where HBsAg has disappeared but anti-HBs has not yet appeared. A rise in these titers signifies active viral replication and the host's primary immune response. 2. **Why Other Options are Incorrect:** * **Carrier State:** Defined by the persistence of HBsAg for >6 months. While anti-HBc (IgG type) is present, it does not "rise" acutely; rather, it remains stable. * **Prodromal Phase:** In this early stage, HBsAg and HBeAg are typically the only detectable markers. Anti-HBc usually appears only after the onset of clinical symptoms or biochemical evidence of liver injury (elevated ALT). * **Convalescence:** This phase is characterized by the disappearance of HBsAg and the appearance of **anti-HBs** (protective antibody). While IgG anti-HBc persists, it is the rise of anti-HBs that defines recovery. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period Marker:** IgM anti-HBc is the "sole marker" of acute HBV infection during the window period. * **IgM vs. IgG:** IgM anti-HBc indicates **acute** infection; IgG anti-HBc indicates **past** exposure or chronic infection. * **Vaccination vs. Natural Infection:** Vaccinated individuals are **Anti-HBs positive** but **Anti-HBc negative** (since vaccines contain only the surface antigen). Natural infection results in positivity for both.

Q: Hepatitis A virus can be inactivated by which of the following methods?

Boiling at 120°C for 1 minute. **Explanation:** Hepatitis A Virus (HAV) is a non-enveloped, single-stranded RNA virus belonging to the *Picornaviridae* family. Its lack of a lipid envelope makes it remarkably stable and resistant to many common physical and chemical agents. **1. Why Option A is Correct:** HAV is highly heat-resistant compared to other viruses. While it can survive at 60°C for an hour, it is effectively inactivated by high temperatures. **Boiling at 100°C–120°C for at least 1 minute** (or autoclaving) is a reliable method to denature the viral capsid and render the virus non-infectious. This is a critical point for preventing fecal-oral transmission via contaminated water or food. **2. Why Incorrect Options are Wrong:** * **Ether and Chloroform (Options B & C):** These are organic solvents that act by dissolving the lipid envelope of viruses. Because HAV is a **non-enveloped virus**, it is inherently resistant to lipid solvents like ether, chloroform, and alcohols. * **Iodine (Option D):** While iodine is a potent antiseptic, HAV shows significant resistance to standard concentrations of many disinfectants. Effective chemical inactivation usually requires specific concentrations of chlorine (sodium hypochlorite), formalin, or glutaraldehyde. **High-Yield Clinical Pearls for NEET-PG:** * **Resistance Profile:** HAV is resistant to low pH (pH 1), allowing it to survive the gastric acid barrier. * **Chlorination:** In water treatment, HAV is inactivated by free residual chlorine (0.5–1.5 mg/L) after 30 minutes of contact. * **Comparison:** Unlike Hepatitis B (HBV) or C (HCV), which are enveloped and susceptible to organic solvents, HAV and HEV (both fecal-oral) are non-enveloped and environmentally hardy. * **Inactivation Summary:** Formalin (0.3% at 37°C for 72 hours) and UV radiation are also effective against HAV.

Q: Which test is used for the diagnosis of HIV infection during the window period?

p24 antigen. **Explanation:** The **window period** in HIV infection is the interval between the initial infection and the production of detectable antibodies (usually 3–4 weeks). During this phase, standard antibody tests (ELISA) will yield a false negative result. **Why p24 antigen is the correct answer:** The **p24 antigen** is a structural protein of the HIV capsid. It is the first marker to appear in the blood, becoming detectable as early as **10–14 days** after infection, well before seroconversion (antibody production). Modern 4th-generation ELISA tests combine p24 antigen detection with antibody testing to significantly shorten the window period. **Analysis of Incorrect Options:** * **p18 antigen:** This is a matrix protein of HIV-1. While it is a structural component, it is not used as a primary diagnostic marker for early infection because it does not reach detectable levels as reliably or as early as p24. * **gp120 and gp41:** These are envelope glycoproteins. While they are highly immunogenic and used in **Western Blot** to confirm HIV infection by detecting the *antibodies* formed against them, the antigens themselves are not typically measured for early diagnosis during the window period. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest Marker:** HIV-RNA (detected by NAT/PCR) is the very first marker (detectable at ~10 days), followed by p24 antigen. * **Best Screening Test:** 4th Generation ELISA (p24 Ag + Ab combo). * **Confirmatory Test:** Western Blot (detects antibodies to gp41, gp120, and p24). * **Monitoring Progress:** CD4+ T-cell count is used to monitor immune status. * **Monitoring Treatment:** Viral load (HIV-RNA) is the best predictor of treatment efficacy and disease progression.

Q: Which virus reactivation is known to involve the eye?

Herpes zoster. **Explanation:** The correct answer is **Herpes zoster (Option A)**. **1. Why Herpes Zoster is Correct:** Herpes zoster is caused by the reactivation of the **Varicella-Zoster Virus (VZV)**, which remains latent in the sensory ganglia (like the trigeminal ganglion) after a primary chickenpox infection. When it reactivates along the **Ophthalmic division (V1) of the Trigeminal nerve**, it causes **Herpes Zoster Ophthalmicus (HZO)**. This typically presents with a painful vesicular rash in a dermatomal distribution and can lead to keratitis, uveitis, and secondary glaucoma. **2. Why other options are incorrect:** * **Cytomegalovirus (CMV):** While CMV causes retinitis (especially in HIV/AIDS patients with CD4 <50), it is generally considered an **opportunistic infection** or a manifestation of primary/persistent infection in the immunocompromised, rather than a classic "reactivation" syndrome defined by dermatomal or neural involvement like VZV. * **Epstein-Barr Virus (EBV):** EBV is primarily associated with infectious mononucleosis, Burkitt lymphoma, and nasopharyngeal carcinoma. It rarely involves the eye. * **Enterovirus 70:** This virus is a major cause of **Acute Hemorrhagic Conjunctivitis (AHC)**. However, this is an **acute primary infection** (often occurring in epidemics), not a reactivation of a latent virus. **3. NEET-PG High-Yield Pearls:** * **Hutchinson’s Sign:** Vesicles on the tip or side of the nose indicate involvement of the nasociliary branch of the trigeminal nerve and are highly predictive of ocular involvement in Herpes Zoster. * **Dendritic Ulcers:** While both HSV and VZV cause them, VZV ulcers are "pseudodendrites" (smaller, lack terminal bulbs, and are poorly stained with fluorescein) compared to the true dendrites of HSV. * **Treatment:** Oral Acyclovir, Valacyclovir, or Famciclovir started within 72 hours of rash onset.

Q: A microbiologist working on influenza virus in a lab observes reversal of hemagglutination. What is this phenomenon called?

Elution. ### Explanation **1. Why Elution is the Correct Answer:** The influenza virus possesses two major surface glycoproteins: **Hemagglutinin (HA)** and **Neuraminidase (NA)**. * **Hemagglutination:** Initially, the HA spikes bind to sialic acid receptors on Red Blood Cells (RBCs), forming a lattice (clumping). * **Elution:** Upon incubation at 37°C, the **Neuraminidase (NA)** enzyme acts as a "receptor-destroying enzyme." It cleaves the sialic acid bonds, releasing the virus from the RBC surface. This reversal of clumping, where the virus detaches and the RBCs settle to the bottom of the tube, is known as **Elution**. **2. Why Other Options are Incorrect:** * **A. Hemolysis:** This refers to the rupture of RBCs with the release of hemoglobin. While some viruses (like Mumps) can cause hemolysis, the reversal of clumping specifically describes elution. * **C. Complement Fixation:** This is an immunological test used to detect specific antibodies or antigens using the complement system. It is not a property of viral surface enzymes. * **D. Precipitation:** This occurs when a soluble antigen reacts with a soluble antibody to form an insoluble complex. Hemagglutination involves particulate antigens (cells), not soluble ones. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Neuraminidase Inhibitors:** Drugs like **Oseltamivir** and **Zanamivir** work by inhibiting the NA enzyme, thereby preventing the elution/release of new virions from host cells. * **Antigenic Drift vs. Shift:** Drift involves point mutations in HA/NA (epidemics); Shift involves genetic reassortment (pandemics). * **H1N1:** The "swine flu" strain is a classic example of antigenic shift. * **Diagnosis:** The Hemagglutination Inhibition (HI) test is the gold standard for detecting antibodies against influenza.

Q: HTLV-II has been implicated in the etiology of which condition?

Hairy cell leukemia. **Explanation:** **Human T-cell Lymphotropic Virus type II (HTLV-II)** is a retrovirus closely related to HTLV-I. While HTLV-I is the definitive causative agent of Adult T-cell Leukemia/Lymphoma (ATLL), **HTLV-II** has been specifically isolated from and implicated in the etiology of **Hairy Cell Leukemia (HCL)**, particularly certain atypical variants. Although the primary driver of HCL is the **BRAF V600E mutation**, the association with HTLV-II remains a classic high-yield association in viral oncogenesis. **Analysis of Incorrect Options:** * **B. AIDS:** This is caused by the Human Immunodeficiency Virus (HIV-1 and HIV-2), which targets CD4+ T-cells, leading to profound immunosuppression. * **C. Adult T-cell Lymphoma (ATLL):** This is caused by **HTLV-I**, not HTLV-II. HTLV-I is also associated with Tropical Spastic Paraparesis (TSP). * **D. Zinc deficiency:** This is a nutritional disorder leading to acrodermatitis enteropathica, impaired wound healing, and immune dysfunction; it has no viral etiology. **High-Yield Clinical Pearls for NEET-PG:** * **Hairy Cell Leukemia (HCL):** A B-cell neoplasm characterized by "hairy" cytoplasmic projections [1]. * **Key Marker:** **TRAP positive** (Tartrate-Resistant Acid Phosphatase). * **Immunophenotype:** CD11c, CD25, CD103, and Annexin A1 (most specific). * **Clinical Feature:** Massive splenomegaly and **"Dry tap"** on bone marrow aspiration due to increased reticulin fibrosis [1]. * **Genetic Hallmark:** **BRAF V600E** mutation is present in nearly 100% of classic HCL cases. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 612.

Q: A 32-year-old unvaccinated woman presented with fever, headache, malaise, and ear pain along with parotid gland swelling. A week later, her fever resolved, but she developed pelvic pain and tenderness. Which virus is the likely causative agent?

Mumps virus. ### Explanation **Correct Option: B. Mumps virus** The clinical presentation of fever, malaise, and **parotid gland swelling** (parotitis) is a classic manifestation of the Mumps virus. The subsequent development of pelvic pain and tenderness in a female patient indicates **oophoritis** (inflammation of the ovaries), which is a known complication of Mumps in post-pubertal females. In males, the equivalent complication is epididymo-orchitis. **Analysis of Incorrect Options:** * **A. Cytomegalovirus (CMV):** While CMV can cause sialadenitis (salivary gland inflammation) in immunocompromised patients, it typically presents as mononucleosis-like syndrome or congenital infections. It does not characteristically cause oophoritis. * **C. Rabies virus:** This neurotropic virus presents with hydrophobia, aerophobia, and encephalopathy following an animal bite. It does not involve the parotid glands or ovaries. * **D. Respiratory syncytial virus (RSV):** RSV is a leading cause of bronchiolitis and pneumonia in infants. It does not cause systemic involvement of the salivary glands or reproductive organs. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** Paramyxoviridae; **Genus:** Rubulavirus. * **Transmission:** Respiratory droplets. * **Most Common Complication:** Aseptic meningitis (often asymptomatic). * **Most Common Extra-salivary Site:** Orchitis (usually unilateral; rarely leads to sterility). * **Other Complications:** Pancreatitis (look for elevated serum amylase), sensorineural hearing loss (usually permanent), and myocarditis. * **Prevention:** Live attenuated vaccine (Jeryl Lynn strain) administered as part of the MMR vaccine.

Q: RSV causes all EXCEPT:

ARDS. Respiratory Syncytial Virus (RSV) is the most common cause of lower respiratory tract infections (LRTI) in infants and young children worldwide. **Explanation of the Correct Answer:** **Option B (ARDS)** is the correct answer because RSV typically causes localized respiratory disease rather than Acute Respiratory Distress Syndrome (ARDS). While severe RSV can lead to respiratory failure requiring mechanical ventilation, ARDS is a specific clinical syndrome characterized by diffuse alveolar damage and non-cardiogenic pulmonary edema, usually triggered by sepsis, trauma, or severe pneumonia (like COVID-19 or Influenza). RSV's primary pathology is focused on the bronchioles (bronchiolitis). **Explanation of Incorrect Options:** * **Option A & D (Coryza/Common Cold):** In older children and healthy adults, RSV most commonly presents as a mild upper respiratory tract infection (URTI) manifesting as coryza (nasal congestion, sneezing, sore throat) and the common cold. * **Option C (Bronchitis/Bronchiolitis):** RSV is the leading cause of **bronchiolitis** and can also cause bronchitis and pneumonia in infants. It leads to inflammation, mucus plugging, and narrowing of the small airways. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Cause:** RSV is the #1 cause of **Bronchiolitis** and **Pneumonia** in children under 1 year of age. * **Surface Proteins:** It possesses **G-protein** (for attachment) and **F-protein** (for fusion and entry). It lacks Hemagglutinin (H) and Neuraminidase (N), unlike other Paramyxoviruses. * **Cytopathology:** It induces the formation of **multinucleated giant cells (Syncytia)** via the F-protein. * **Prophylaxis:** **Palivizumab** (a monoclonal antibody against the F-protein) is used for high-risk preterm infants. * **Treatment:** **Ribavirin** (aerosolized) may be used in severe, hospitalized cases.

Q: Conjunctivitis is caused by all EXCEPT:

CMV. **Explanation:** The correct answer is **CMV (Cytomegalovirus)**. While CMV is a significant ocular pathogen, it primarily affects the **posterior segment** of the eye, causing **retinitis** (especially in immunocompromised patients like those with HIV/AIDS). It does not typically cause conjunctivitis. **Analysis of Options:** * **Adenovirus:** This is the **most common cause** of viral conjunctivitis. It presents as Pharyngoconjunctival Fever (Serotypes 3, 7) or Epidemic Keratoconjunctivitis (Serotypes 8, 19, 37), the latter being highly contagious and associated with subepithelial corneal infiltrates. * **Enterovirus 70 & Coxsackievirus A24:** These are the classic causative agents of **Acute Hemorrhagic Conjunctivitis (AHC)**. AHC is characterized by rapid onset, eyelid swelling, and prominent subconjunctival hemorrhages. These viruses belong to the Picornaviridae family and are known for causing large-scale outbreaks. **High-Yield Clinical Pearls for NEET-PG:** 1. **Adenovirus:** Look for "follicular conjunctivitis" and preauricular lymphadenopathy in clinical vignettes. 2. **CMV Retinitis:** Classically described as a **"Pizza-pie appearance"** or "Cottage cheese and ketchup" fundus due to retinal necrosis and hemorrhage. 3. **Herpes Simplex Virus (HSV):** A common cause of dendritic keratitis (corneal involvement), but can also cause follicular conjunctivitis. 4. **Chlamydia trachomatis:** Serotypes A, B, Ba, and C cause Trachoma (leading cause of infectious blindness), while D-K cause inclusion conjunctivitis.

Question 1

A rise in the anti-HBc immunoglobulin in a patient indicates which of the following?

Accepted Answer

Acute infection

Answer

Carrier state

Answer

Prodromal phase

Answer

Convalescence

Question 2

Hepatitis A virus can be inactivated by which of the following methods?

Accepted Answer

Boiling at 120°C for 1 minute

Answer

Ether

Answer

Chloroform

Answer

Iodine

Question 3

A 6-month-old baby presents with a 5-day history of fever, cough, and cold. Which of the following statements is false regarding the likely causative virus in this scenario?

Accepted Answer

It is the most important cause of bronchiolitis.

Answer

The cytopathic effect is syncytium formation.

Answer

Ribavirin is the drug of choice.

Answer

It causes upper respiratory tract infection.

Question 4

Which test is used for the diagnosis of HIV infection during the window period?

Accepted Answer

p24 antigen

Answer

p18 antigen

Answer

gp120 antigen

Answer

gp41 antigen

Question 5

Which virus reactivation is known to involve the eye?

Accepted Answer

Herpes zoster

Answer

Cytomegalovirus (CMV)

Answer

Epstein-Barr Virus (EBV)

Answer

Enterovirus 70

Question 6

A microbiologist working on influenza virus in a lab observes reversal of hemagglutination. What is this phenomenon called?

Accepted Answer

Elution

Answer

Hemolysis

Answer

Complement fixation

Answer

Precipitation

Question 7

HTLV-II has been implicated in the etiology of which condition?

Accepted Answer

Hairy cell leukemia

Answer

AIDS

Answer

Adult T-cell lymphoma

Answer

Zinc deficiency

Question 8

A 32-year-old unvaccinated woman presented with fever, headache, malaise, and ear pain along with parotid gland swelling. A week later, her fever resolved, but she developed pelvic pain and tenderness. Which virus is the likely causative agent?

Accepted Answer

Mumps virus

Answer

Cytomegalovirus

Answer

Rabies virus

Answer

Respiratory syncytial virus

Question 9

RSV causes all EXCEPT:

Accepted Answer

ARDS

Answer

Coryza in kids

Answer

Bronchitis

Answer

Common cold

Question 10

Conjunctivitis is caused by all EXCEPT:

Accepted Answer

CMV

Answer

Enterovirus 70

Answer

Coxsackievirus A 24

Answer

Adenovirus

Virology — MCQs

Virology — MCQs

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