Virology — MCQs

Infection with hepatitis D virus (HDV) can occur simultaneously with infection with hepatitis B virus (HBV) or in a carrier of hepatitis B virus because HDV is a defective virus that requires HBV for its replicative function. What serologic test can be used to determine whether a patient with HDV is an HBV carrier?

Q417Easy

What is the most common cause of sporadic encephalitis?

Q418Medium

Hantavirus is an emerging pathogen that is best described by which of the following statements?

Q419Easy

Influenza is caused by which type of virus?

Q420Easy

What is true about a bacteriophage?

Virology Indian Medical PG Practice Questions and MCQs

Question 411: What culture media is used for the cultivation of HSV?

A. Chocolate agar
B. Robertson's cooked-meat broth
C. Chorioallantoic membrane (Correct Answer)
D. Sabouraud's agar

Explanation: **Explanation:** **1. Why Chorioallantoic Membrane (CAM) is correct:** Herpes Simplex Virus (HSV) is an obligate intracellular parasite, meaning it cannot grow on artificial, non-living media. It requires living cells for replication. The **Chorioallantoic Membrane (CAM)** of an embryonated chicken egg is a classic method for cultivating several DNA viruses. When HSV is inoculated onto the CAM, it produces characteristic macroscopic lesions called **pocks**. The morphology of these pocks can help differentiate between HSV-1 (small pocks) and HSV-2 (large pocks). **2. Why the other options are incorrect:** * **A. Chocolate agar:** This is an enriched non-selective medium used for fastidious bacteria like *Neisseria* and *Haemophilus influenzae*. It contains lysed red blood cells but no living cells. * **B. Robertson's cooked-meat (RCM) broth:** This is an anaerobic culture medium used primarily for the cultivation of *Clostridium* species. * **C. Sabouraud's agar (SDA):** This is a selective medium used for the cultivation of fungi (yeasts and molds). **3. High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for HSV:** While CAM is used historically, **Cell Culture** (e.g., Human embryonic lung fibroblasts or Vero cells) is the modern gold standard. HSV produces a characteristic "ballooning" cytopathic effect (CPE). * **Tzanck Smear:** A rapid bedside test showing **multinucleated giant cells** with Cowdry Type A intranuclear inclusion bodies (Lipschutz bodies). * **Drug of Choice:** Acyclovir is the mainstay of treatment for HSV infections. * **Pock-forming viruses:** Besides HSV, Poxviruses (like Variola and Vaccinia) also produce pocks on CAM.

Question 412: Herpangina is caused by which virus?

A. Enterovirus (Correct Answer)
B. Rhinoviruses
C. Myxovirus
D. Rabies virus

Explanation: **Explanation:** **Herpangina** is a common febrile illness characterized by small, painful vesicular or ulcerative lesions on the posterior oropharynx (soft palate, tonsils, and uvula). **1. Why Enterovirus is correct:** Herpangina is primarily caused by **Coxsackievirus Group A** (specifically types A1–A10, A12, and A22), which belongs to the **Enterovirus** genus within the *Picornaviridae* family. These viruses are transmitted via the fecal-oral route or respiratory droplets. While Coxsackie A is the most common cause, other enteroviruses like Coxsackie B and Enterovirus 71 can also be implicated. **2. Why the other options are incorrect:** * **Rhinoviruses:** These are the most common cause of the "common cold" (upper respiratory tract infections). They typically cause rhinorrhea and nasal congestion rather than vesicular oropharyngeal lesions. * **Myxovirus:** This group includes Orthomyxoviruses (Influenza) and Paramyxoviruses (Measles, Mumps). These present with systemic respiratory symptoms or specific glandular swelling, not the localized posterior pharyngeal ulcers seen in Herpangina. * **Rabies virus:** A rhabdovirus that causes fatal encephalitis. Clinical features include hydrophobia, aerophobia, and spasms, but not vesicular pharyngitis. **Clinical Pearls for NEET-PG:** * **Herpangina vs. Hand-Foot-Mouth Disease (HFMD):** Both are caused by Coxsackie A (usually A16 for HFMD). The key difference is the distribution: Herpangina is limited to the **posterior** pharynx, while HFMD involves the anterior mouth, palms, and soles. * **Herpetic Gingivostomatitis:** Caused by HSV-1; unlike Herpangina, it typically involves the **anterior** mouth (gingiva and buccal mucosa) and presents with high fever and lymphadenopathy. * **Seasonality:** Enteroviral infections typically peak during summer and autumn months.

Question 413: Rapid progression of disease with full-blown manifestation in AIDS occurs when the T4 cell count falls below which value?

A. 1000/microliter
B. 500/microliter
C. 200/microliter (Correct Answer)
D. 50/microliter

Explanation: ### Explanation The progression of HIV infection to **AIDS (Acquired Immunodeficiency Syndrome)** is clinically and immunologically defined by the depletion of CD4+ T-lymphocytes (T4 cells). **1. Why Option C is Correct:** According to the CDC classification, a diagnosis of AIDS is made when the **CD4+ T-cell count falls below 200 cells/μL** (or a CD4 percentage of total lymphocytes <14%). At this critical threshold, the immune system is severely compromised, leading to the "full-blown" manifestation of the disease characterized by life-threatening **opportunistic infections** (e.g., *Pneumocystis jirovecii* pneumonia) and AIDS-defining malignancies (e.g., Kaposi sarcoma). **2. Analysis of Incorrect Options:** * **Option A (1000/μL):** This is within the normal range for a healthy adult (500–1500 cells/μL). * **Option B (500/μL):** Between 200–500 cells/μL, patients are in the "Intermediate Stage." While they may show symptoms like lymphadenopathy or oral thrush, they do not yet meet the criteria for AIDS. * **Option D (50/μL):** This represents **Advanced HIV infection**. At this level, patients are at risk for specific "late-stage" infections such as *Mycobacterium avium complex* (MAC) and Cytomegalovirus (CMV) retinitis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **Best Predictor of Progression:** CD4+ T-cell count. * **Best Predictor of Treatment Response:** Viral load (HIV RNA levels). * **Prophylaxis Thresholds:** * Start prophylaxis for *Pneumocystis jirovecii* when CD4 < 200. * Start prophylaxis for *Toxoplasma gondii* when CD4 < 100. * Start prophylaxis for *MAC* when CD4 < 50.

Question 414: Which of the following viral infections is NOT typically transmitted from human to human?

A. SARS
B. Japanese B encephalitis (Correct Answer)
C. Bird's flu
D. Poliomyelitis

Explanation: ### Explanation The correct answer is **Japanese B encephalitis (JEV)**. **1. Why Japanese B Encephalitis is the correct answer:** Japanese Encephalitis is a **zoonotic viral infection** caused by a Flavivirus. It follows a complex transmission cycle involving **Culex mosquitoes** (primarily *Culex tritaeniorhynchus*) as the vector, and **pigs or water birds** as the natural reservoirs/amplifying hosts. Humans are considered **"dead-end hosts"** because the level of viremia in human blood is typically insufficient to infect a biting mosquito. Therefore, direct human-to-human transmission does not occur. **2. Why the other options are incorrect:** * **SARS (Severe Acute Respiratory Syndrome):** Caused by a coronavirus, it is highly contagious and spreads primarily through respiratory droplets and direct contact between humans. * **Bird’s Flu (Avian Influenza, e.g., H5N1):** While primarily a disease of birds, limited and non-sustained human-to-human transmission has been documented, especially among close family contacts. * **Poliomyelitis:** This is an exclusively human pathogen. It is transmitted via the **fecal-oral route** (and occasionally respiratory droplets) from one person to another. **3. NEET-PG High-Yield Pearls:** * **Vector for JEV:** *Culex tritaeniorhynchus* (breeds in stagnant water/rice fields). * **Amplifying Host:** Pigs (they develop high-level viremia without getting sick). * **Dead-end Hosts:** Humans and Horses. * **Vaccine:** Live attenuated (SA-14-14-2) and Inactivated (Jenvac) vaccines are available. * **Other "Dead-end" infections:** Rabies, West Nile Virus, and Hydatid disease (Echinococcosis).

Question 415: Infection with which of the following agents is particularly dangerous for anemic patients?

A. Adenovirus
B. Cytomegalovirus
C. Herpes simplex virus
D. Parvovirus (Correct Answer)

Explanation: **Explanation:** **1. Why Parvovirus B19 is the Correct Answer:** Parvovirus B19 is uniquely dangerous for anemic patients because it has a specific tropism for **erythroid progenitor cells**. The virus enters these cells via the **P-antigen** (globoside) receptor and replicates within them, leading to direct cytotoxicity and the temporary cessation of erythropoiesis. In healthy individuals, this brief pause in red blood cell (RBC) production is clinically silent. However, in patients with high RBC turnover (e.g., **Sickle Cell Anemia, Hereditary Spherocytosis, Thalassemia**), the bone marrow cannot compensate for the loss. This results in a life-threatening **Aplastic Crisis**, characterized by a sudden drop in hemoglobin and a dangerously low reticulocyte count. **2. Why Other Options are Incorrect:** * **Adenovirus:** Primarily causes respiratory infections, conjunctivitis (pink eye), and hemorrhagic cystitis. It does not target erythroid precursors. * **Cytomegalovirus (CMV):** A member of the Herpesviridae family, it typically causes infectious mononucleosis-like symptoms or severe systemic disease in immunocompromised hosts (retinitis, colitis), but not selective bone marrow suppression of RBCs. * **Herpes Simplex Virus (HSV):** Primarily associated with mucocutaneous lesions (cold sores, genital herpes) and encephalitis; it does not impact erythropoiesis. **3. NEET-PG High-Yield Clinical Pearls:** * **Erythema Infectiosum (Fifth Disease):** Classic presentation in children featuring a "slapped-cheek" rash. * **Hydrops Fetalis:** If a pregnant woman is infected, the virus can cross the placenta, causing severe fetal anemia, high-output cardiac failure, and fetal death. * **Diagnosis:** Look for **"Giant Pronormoblasts"** in the bone marrow and a **low reticulocyte count** (distinguishes aplastic crisis from hemolytic crisis). * **Receptor:** P-antigen (individuals lacking P-antigen are resistant to Parvovirus B19).

Question 416: Infection with hepatitis D virus (HDV) can occur simultaneously with infection with hepatitis B virus (HBV) or in a carrier of hepatitis B virus because HDV is a defective virus that requires HBV for its replicative function. What serologic test can be used to determine whether a patient with HDV is an HBV carrier?

A. Anti-HBe
B. Anti-HDV IgM (Correct Answer)
C. Anti-HBc IgM
D. HBsAg quantification

Explanation: **Explanation:** The key to distinguishing between **HDV Co-infection** (simultaneous infection with HBV and HDV) and **HDV Super-infection** (HDV infection in a chronic HBV carrier) lies in the serologic markers of Hepatitis B. 1. **Why Anti-HBc IgM is the differentiator:** * In **Co-infection**, the patient is experiencing an acute infection of both viruses. Therefore, markers of acute HBV infection will be present, specifically **Anti-HBc IgM**. * In **Super-infection**, the patient is already a chronic HBV carrier. Therefore, they will test positive for **Anti-HBc IgG**, but **negative for Anti-HBc IgM**. * *Note on the provided answer:* While the question marks Anti-HDV IgM as correct, in standard clinical practice, **Anti-HBc IgM** is the definitive marker used to determine if the HBV component is acute (co-infection) or chronic (super-infection). However, if the question implies identifying the *acute HDV event* itself, Anti-HDV IgM confirms active HDV replication. 2. **Analysis of Incorrect Options:** * **Anti-HBe (A):** This indicates low viral infectivity/seroconversion in HBV; it does not differentiate between acute or chronic HBV status in the context of HDV. * **Anti-HDV IgM (B):** This marker indicates an acute/active HDV infection but does not provide information about the duration of the underlying HBV infection. * **HBsAg quantification (D):** While HBsAg must be present for HDV to exist, its quantity does not reliably distinguish between a new co-infection and a carrier state. **High-Yield Clinical Pearls for NEET-PG:** * **HDV** is a defective RNA virus (Deltavirus) that requires the **HBsAg coat** for assembly and transmission. * **Co-infection:** Usually results in acute hepatitis; low risk of chronicity (<5%). * **Super-infection:** Often leads to severe "flare-ups" of hepatitis and has a very high risk of progressing to **chronic HDV/HBV** and cirrhosis (up to 80%). * **Diagnosis Tip:** If you see **Anti-HBc IgM negative + HBsAg positive + HDV markers positive**, think **Super-infection**.

Question 417: What is the most common cause of sporadic encephalitis?

A. EBV
B. HSV (Correct Answer)
C. Poliovirus
D. CMV

Explanation: **Explanation:** **Herpes Simplex Virus (HSV)**, specifically **HSV-1**, is the most common cause of sporadic (non-epidemic) fatal encephalitis worldwide. The underlying medical concept involves the virus's neurotropic nature; it typically reaches the brain via retrograde axonal transport along the trigeminal nerve or olfactory bulb. A hallmark of HSV encephalitis is its predilection for the **temporal lobes**, leading to hemorrhagic necrosis. **Analysis of Options:** * **HSV (Correct):** Responsible for nearly 90% of adult cases of sporadic viral encephalitis. It presents with acute onset fever, headache, seizures, and focal neurological deficits (aphasia or behavioral changes due to temporal lobe involvement). * **EBV (Incorrect):** While EBV can cause neurological complications like meningitis or Guillain-Barré syndrome, it is a rare cause of isolated encephalitis. * **Poliovirus (Incorrect):** This is an enterovirus that primarily targets the anterior horn cells of the spinal cord, leading to asymmetric flaccid paralysis (Poliomyelitis) rather than encephalitis. * **CMV (Incorrect):** CMV encephalitis is typically seen in immunocompromised individuals (e.g., AIDS patients) and neonates (congenital CMV), rather than as a cause of sporadic encephalitis in the general population. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** PCR of Cerebrospinal Fluid (CSF) for HSV DNA. * **Imaging:** MRI is the modality of choice, showing hyperintensity in the **temporal lobes** and orbital-frontal regions. * **EEG Finding:** Periodic Lateralized Epileptiform Discharges (PLEDs). * **Treatment:** Immediate IV **Acyclovir** (do not wait for PCR results if clinical suspicion is high).

Question 418: Hantavirus is an emerging pathogen that is best described by which of the following statements?

A. Influenza-like symptoms are followed rapidly by acute respiratory failure (Correct Answer)
B. Hemolysis is common in infected patients
C. It is acquired by inhalation of aerosols of the urine and feces of infected rodents
D. Transmission from human to human is common

Explanation: ### Explanation **1. Why the correct answer is right:** Hantavirus (specifically the Sin Nombre virus) is the causative agent of **Hantavirus Pulmonary Syndrome (HPS)**. The pathophysiology involves a "cytokine storm" that leads to increased capillary permeability, primarily in the lungs. Clinically, patients present with a prodrome of fever and myalgia (influenza-like symptoms) which progresses rapidly (often within 24–48 hours) to non-cardiogenic pulmonary edema and acute respiratory failure. **2. Why the incorrect options are wrong:** * **Option B:** While Hantaviruses can cause Hemorrhagic Fever with Renal Syndrome (HFRS) in Europe and Asia, **hemolysis** (destruction of RBCs) is not a hallmark feature. The primary hematological findings are thrombocytopenia and hemoconcentration. * **Option C:** This statement is actually **factually correct** regarding the transmission of Hantavirus. However, in the context of many standardized medical exams (including NEET-PG style questions), if a question asks for the "best description" of a pathogen's clinical impact or "emerging" nature, the **clinical presentation (Option A)** is often prioritized as the defining characteristic over the route of transmission. *Note: In some versions of this question, Option C is considered a secondary correct fact, but Option A defines the "emerging" clinical threat.* * **Option D:** Human-to-human transmission is **extremely rare** (documented only for the Andes virus in South America). The primary reservoir is the deer mouse (*Peromyscus maniculatus*). **3. High-Yield Clinical Pearls for NEET-PG:** * **Family:** *Bunyaviridae* (Segmented, negative-sense RNA virus). * **Vector:** Rodents (Deer mouse); transmission via inhalation of dried excreta (aerosolization). * **Triad of HPS:** Fever/Myalgia, rapid onset respiratory distress, and "Immunoblasts" on peripheral smear. * **Key Lab Finding:** Thrombocytopenia and elevated hematocrit (due to plasma leakage). * **Treatment:** Primarily supportive; Ribavirin is used for HFRS but has limited efficacy in HPS.

Question 419: Influenza is caused by which type of virus?

A. Type A (Correct Answer)
B. Type B
C. Type C
D. Type D

Explanation: **Explanation:** Influenza viruses belong to the family **Orthomyxoviridae** and are classified into types A, B, C, and D based on their core proteins (nucleoprotein and matrix protein). **Why Type A is the correct answer:** While Types A, B, and C all cause human disease, **Influenza Type A** is the most significant pathogen. It is the only type capable of causing **pandemics** because it undergoes both **antigenic drift** (minor mutations) and **antigenic shift** (major genetic reassortment). It has a wide host range, infecting humans, birds, and pigs, which facilitates the emergence of novel strains. **Analysis of Incorrect Options:** * **Type B:** This type primarily infects humans and is a common cause of seasonal epidemics. However, it does not cause pandemics because it does not undergo antigenic shift (it lacks an animal reservoir). * **Type C:** This type causes only mild respiratory illness or sporadic cases and does not cause epidemics or pandemics. * **Type D:** This type primarily affects cattle and is not known to cause illness in humans. **High-Yield NEET-PG Clinical Pearls:** * **Genome:** Segmented, single-stranded, negative-sense RNA. Type A and B have **8 segments**, while Type C has **7 segments**. * **Antigenic Shift:** Reassortment of segments between different strains (e.g., human and avian) in a single host (e.g., a pig). This leads to pandemics. * **Antigenic Drift:** Point mutations in Hemagglutinin (HA) and Neuraminidase (NA) leading to seasonal epidemics. * **Drug of Choice:** Oseltamivir (Neuraminidase inhibitor) is effective against both Type A and B. * **Gold Standard Diagnosis:** Viral culture or RT-PCR.

Question 420: What is true about a bacteriophage?

A. It is a virus.
B. It causes transduction.
C. It causes lysis of bacteria.
D. All of the above. (Correct Answer)

Explanation: ### Explanation A **bacteriophage** (or "phage") is a virus that specifically infects and replicates within bacteria. This question tests the fundamental understanding of viral life cycles and their role in bacterial genetics. * **Option A (It is a virus):** Bacteriophages are obligate intracellular parasites consisting of a nucleic acid core (DNA or RNA) surrounded by a protein coat (capsid). They are the most abundant biological entities on Earth. * **Option B (It causes transduction):** Transduction is the process by which foreign DNA is introduced into a cell by a virus. During the assembly of new phages, fragments of bacterial host DNA may be accidentally packaged into the viral capsid. When this phage infects a new bacterium, it transfers the previous host's genetic material, leading to genetic recombination. * **Option C (It causes lysis of bacteria):** In the **lytic cycle**, the bacteriophage replicates rapidly and produces enzymes (like endolysins) that rupture the bacterial cell wall to release progeny virions, resulting in the death of the host cell. **Conclusion:** Since all three statements accurately describe the nature and function of bacteriophages, **Option D** is the correct answer. --- ### High-Yield Clinical Pearls for NEET-PG * **Lysogenic Conversion:** Some phages integrate their DNA into the bacterial chromosome (prophage). This can grant the bacteria new virulence factors. * *Classic Examples:* **Diphtheria toxin** (*C. diphtheriae*), **Cholera toxin** (*V. cholerae*), **Botulinum toxin**, and **Shiga toxin** are all encoded by bacteriophages. * **Phage Typing:** Used in epidemiology to identify specific strains of bacteria (e.g., *Staphylococcus aureus* or *Salmonella Typhi*) based on their susceptibility to different bacteriophages. * **Generalized vs. Specialized Transduction:** * *Generalized:* Occurs during the lytic cycle; any part of the bacterial genome can be transferred. * *Specialized:* Occurs during the lysogenic cycle; only specific genes adjacent to the prophage insertion site are transferred.

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Virology — MCQs

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