Virology — MCQs
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Which of the following statements best describes subacute sclerosing panencephalitis (SSPE) virus?
Which cells are primarily affected by the Human Immunodeficiency Virus (HIV)?
Which type of hepatitis is typically associated with chronic infection?
Herpangina is commonly caused by which virus?
A 7-year-old girl with sickle cell anemia presents with extreme fatigue and pallor. Her parents report that several classmates had recent rashes and bright red cheeks. On examination, the conjunctiva, gums, and nail beds are pale, and tachycardia is noted. A CBC reveals a 2 g/dL drop in hemoglobin from her last result 3 months ago, with a reticulocyte count of 0.05%. What is the most likely diagnosis?
Which virus can be easily cultured from CSF?
Rotavirus is a double-stranded RNA virus with a double-walled capsid. Which one of the following statements best describes rotavirus?
Mumps most commonly affects which gland?
Rabies virus is best described as which of the following?
Which viral infection always causes clinical disease in human beings?
Virology Indian Medical PG Practice Questions and MCQs
Question 741: Which of the following statements best describes subacute sclerosing panencephalitis (SSPE) virus?
- A. It is a progressive disease involving both white and gray matter. (Correct Answer)
- B. It is a late central nervous system manifestation of mumps.
- C. It is a common event occurring in 1 of 300,000 cases of mumps.
- D. Viral DNA can be demonstrated in brain cells.
Explanation: Subacute Sclerosing Panencephalitis (SSPE) is a rare, chronic, and progressive neurodegenerative disease caused by a persistent infection with a **defective Measles virus** (not mumps). ### **Explanation of Options** * **Option A (Correct):** SSPE is characterized as a **"panencephalitis"** because it involves both the **gray matter** (neuronal cell bodies) and **white matter** (myelinated axons) of the cerebral hemispheres and brainstem. Pathologically, it presents with inflammation, demyelination, and gliosis. * **Option B & C (Incorrect):** SSPE is a late complication of **Measles (Rubeola)**, not Mumps. It typically occurs 5–10 years after the initial measles infection. The incidence is approximately 1 in 10,000 to 1 in 100,000 measles cases (higher if the primary infection occurred before age 2). * **Option D (Incorrect):** The Measles virus is a single-stranded, negative-sense **RNA virus** (Paramyxoviridae family). Therefore, viral **RNA** or viral antigens—not DNA—are demonstrated in brain cells via PCR or immunohistochemistry. ### **High-Yield Clinical Pearls for NEET-PG** * **Pathogenesis:** Caused by a **mutated M protein** (matrix protein) of the measles virus, which prevents the virus from budding, leading to intracellular persistence. * **Diagnosis:** 1. **CSF:** Characterized by **oligoclonal bands** and extremely high titers of anti-measles antibodies (**intrathecal antibody synthesis**). 2. **EEG:** Shows characteristic **periodic, high-voltage slow-wave complexes** (Radermecker complexes). * **Clinical Stages:** Starts with behavioral changes, progressing to **myoclonic jerks** (hallmark), dementia, and eventually vegetative state/death. * **Histology:** **Cowdry Type A** intranuclear inclusion bodies in neurons and glial cells.
Question 742: Which cells are primarily affected by the Human Immunodeficiency Virus (HIV)?
- A. CD4+ T cells (Correct Answer)
- B. CD8 cells
- C. Lymphocytes
- D. Plasma cells
Explanation: **Explanation:** The hallmark of HIV pathogenesis is the selective depletion of **CD4+ T lymphocytes**. HIV primarily targets these cells because its viral envelope glycoprotein, **gp120**, has a high affinity for the **CD4 receptor** molecule. To enter the cell, the virus also requires co-receptors: **CCR5** (predominant in early/macrophage-tropic strains) or **CXCR4** (seen in later/T-cell-tropic strains). The progressive loss of these "helper" cells leads to profound immunosuppression, eventually resulting in AIDS. **Analysis of Options:** * **CD8 cells (B):** These are cytotoxic T cells. While they play a role in the initial immune response against HIV, they lack the CD4 receptor and are not the primary targets for viral entry. * **Lymphocytes (C):** This is a broad category including T cells, B cells, and NK cells. While HIV affects a subset of lymphocytes, "CD4+ T cells" is the more specific and accurate answer. * **Plasma cells (D):** These are terminally differentiated B cells that produce antibodies. They are not directly infected by HIV, although their function is impaired due to the lack of "help" from CD4+ T cells. **High-Yield Clinical Pearls for NEET-PG:** * **The "Window Period":** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **Indicator of Progression:** The **CD4+ T cell count** is the best indicator of immune status and risk for opportunistic infections (e.g., *Pneumocystis jirovecii* occurs when CD4 < 200 cells/mm³). * **Viral Load:** Plasma HIV RNA levels are the best predictor of disease progression and are used to monitor the efficacy of ART. * **Other Targets:** Besides T cells, HIV also infects **monocytes, macrophages, and dendritic cells** (which act as reservoirs) and **microglial cells** in the brain.
Question 743: Which type of hepatitis is typically associated with chronic infection?
- A. Hepatitis C (Correct Answer)
- B. Hepatitis D
- C. Hepatitis A
- D. Hepatitis E
Explanation: **Explanation:** The hallmark of **Hepatitis C Virus (HCV)** is its high propensity for chronicity. Unlike other hepatitis viruses, HCV has a high rate of spontaneous mutation (due to lack of proofreading by its RNA polymerase), allowing it to evade the host immune response. Approximately **75%–85%** of individuals infected with HCV will develop chronic infection, which can lead to liver cirrhosis and hepatocellular carcinoma (HCC) over decades. **Analysis of Options:** * **Hepatitis D (HDV):** While HDV can cause chronic infection, it is a "defective" virus that requires the presence of Hepatitis B (HBV) to replicate. It is not the *typical* or most common representative of chronic viral hepatitis in isolation compared to HCV. * **Hepatitis A (HAV):** This is an enterically transmitted virus (fecal-oral route) that causes **acute hepatitis only**. It never progresses to a chronic state or a carrier state. * **Hepatitis E (HEV):** Similar to HAV, it typically causes acute, self-limiting infection. While chronic HEV can occur in severely immunocompromised patients (e.g., organ transplant recipients), it is not the typical clinical course for the general population. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** HCV is most commonly transmitted via **parenteral routes** (IV drug use, blood transfusions). * **Screening vs. Diagnosis:** Anti-HCV antibodies are used for screening; **HCV-RNA (PCR)** is the gold standard for confirming active/chronic infection. * **Treatment:** Chronic HCV is now highly curable with **Direct-Acting Antivirals (DAAs)** like Sofosbuvir. * **Pregnancy:** Hepatitis E is associated with high mortality (up to 20%) in pregnant women due to fulminant hepatic failure.
Question 744: Herpangina is commonly caused by which virus?
- A. Coxsackie virus B (Correct Answer)
- B. Coxsackie virus A
- C. Echovirus
- D. Poliovirus
Explanation: **Explanation:** **Herpangina** is an acute febrile illness characterized by small vesicular and ulcerative lesions on the posterior oropharynx (tonsillar pillars, soft palate, and uvula). It is primarily caused by **Coxsackievirus Group A** (specifically types A1–A10, A16, and A22). *Note: There appears to be a discrepancy in the provided key. In standard medical microbiology (Jawetz, Harrison, Bailey & Scott), Herpangina is classically associated with **Coxsackievirus Group A**, while Group B is more commonly associated with Pleurodynia and Myocarditis.* **Analysis of Options:** * **Coxsackievirus A (Correct Pathogen):** This is the most common cause of Herpangina and Hand-Foot-Mouth Disease (HFMD). It typically affects children and presents with sudden fever and sore throat. * **Coxsackievirus B:** While it can cause respiratory infections, it is the classic cause of **Bornholm disease (Pleurodynia)**, Myocarditis, and Pericarditis. * **Echovirus:** These can cause aseptic meningitis and non-specific exanthems but are less frequent causes of classic Herpangina. * **Poliovirus:** Primarily causes asymptomatic infection, abortive poliomyelitis, or paralytic disease by affecting the anterior horn cells of the spinal cord. **High-Yield Clinical Pearls for NEET-PG:** * **Herpangina vs. Herpes Stomatitis:** Herpangina lesions are located in the **posterior** pharynx, whereas Gingivostomatitis (HSV-1) typically involves the **anterior** mouth and gums. * **Hand-Foot-Mouth Disease (HFMD):** Most commonly caused by **Coxsackie A16** and **Enterovirus 71**. * **Pleurodynia (Devil’s Grip):** Characterized by paroxysmal thoracic pain, caused by **Coxsackie B**. * **Myocarditis:** Coxsackie B is the most common viral cause of infectious myocarditis.
Question 745: A 7-year-old girl with sickle cell anemia presents with extreme fatigue and pallor. Her parents report that several classmates had recent rashes and bright red cheeks. On examination, the conjunctiva, gums, and nail beds are pale, and tachycardia is noted. A CBC reveals a 2 g/dL drop in hemoglobin from her last result 3 months ago, with a reticulocyte count of 0.05%. What is the most likely diagnosis?
- A. Aplastic crisis from parvovirus B19 infection (Correct Answer)
- B. Pericarditis caused by Coxsackievirus B
- C. Gastroenteritis with bleeding caused by Norovirus
- D. Exacerbated anemia from Colti virus infection
Explanation: **Explanation:** The clinical presentation is a classic case of **Transient Aplastic Crisis (TAC)** triggered by **Parvovirus B19**. In patients with high red cell turnover (like Sickle Cell Anemia), Parvovirus B19 is particularly dangerous because it infects and lyses **erythroid progenitor cells** by binding to the **P-antigen** (globoside). The hallmark of an aplastic crisis is a sudden drop in hemoglobin accompanied by an **inappropriately low reticulocyte count** (<1%), indicating bone marrow failure rather than hemolysis. The mention of "bright red cheeks" in classmates refers to **Erythema Infectiosum (Fifth Disease)**, the common pediatric presentation of Parvovirus B19. **Analysis of Incorrect Options:** * **B. Coxsackievirus B:** While a common cause of viral myocarditis and pericarditis, it does not typically cause bone marrow suppression or aplastic crises. * **C. Norovirus:** This is a leading cause of viral gastroenteritis. While it causes vomiting and diarrhea, it does not target erythroid precursors or cause acute drops in hemoglobin. * **D. Coltivirus:** This is the causative agent of Colorado Tick Fever. While it can cause a mild leukopenia, it is not associated with aplastic crises in sickle cell patients. **NEET-PG High-Yield Pearls:** * **Receptor:** Parvovirus B19 uses the **P-antigen** on RBCs. * **Morphology:** Look for **"Giant Pronormoblasts"** with viral inclusions in the bone marrow. * **Other Manifestations:** Hydrops fetalis (in pregnancy), symmetric polyarthritis (in adults), and "Slapped Cheek" rash. * **Key Lab Finding:** The **reticulocytopenia** is the "clincher" to differentiate aplastic crisis from a sequestration or hemolytic crisis.
Question 746: Which virus can be easily cultured from CSF?
- A. Poliovirus
- B. Coxsackievirus
- C. Echovirus
- D. Mumps virus (Correct Answer)
Explanation: **Explanation:** The correct answer is **Mumps virus**. In the context of viral meningitis, the ability to isolate a virus from the cerebrospinal fluid (CSF) depends on the duration and magnitude of the viral load during the clinical phase. **Why Mumps virus is correct:** Mumps virus is highly neurotropic. In patients presenting with mumps meningitis, the virus is shed in high titers into the CSF. It can be successfully cultured from the CSF in approximately **50–70% of cases** during the first week of symptoms. This makes it one of the most "culture-positive" viruses in clinical virology compared to other common causes of aseptic meningitis. **Why the other options are incorrect:** * **Poliovirus:** While Poliovirus causes significant CNS pathology (anterior horn cell destruction), it is **rarely isolated from the CSF**. Diagnosis is typically made via stool culture or throat swabs, as the virus replicates in the oropharynx and intestines. * **Coxsackievirus & Echovirus:** These are Enteroviruses. While they are the most common causes of viral meningitis, their isolation rate from CSF is significantly lower than that of Mumps (typically <30-40%). They are more easily recovered from throat swabs or fecal samples. **NEET-PG High-Yield Pearls:** * **Most common cause of viral meningitis:** Enteroviruses (Coxsackie and Echo). * **Mumps Meningitis:** Occurs in up to 15% of mumps cases; it is usually benign and self-limiting. * **CSF Findings in Viral Meningitis:** Lymphocytic pleocytosis, normal glucose, and slightly elevated protein. * **Gold Standard for Enterovirus:** Though culture is possible, **RT-PCR** is now the diagnostic method of choice for all viral CNS infections due to higher sensitivity and speed.
Question 747: Rotavirus is a double-stranded RNA virus with a double-walled capsid. Which one of the following statements best describes rotavirus?
- A. There are no related animal viruses
- B. It is a major cause of neonatal diarrhea (Correct Answer)
- C. It is readily cultured from the stool of infected persons
- D. Maternal antibody does not appear to be protective
Explanation: **Explanation:** **Rotavirus** is a member of the *Reoviridae* family, characterized by a segmented, double-stranded RNA genome and a unique wheel-like (rota), triple-layered capsid. **Why Option B is Correct:** Rotavirus is the **most common cause of severe, dehydrating diarrhea** in infants and young children worldwide (typically aged 6 months to 2 years). In the neonatal period, while many infections are asymptomatic due to maternal antibodies, it remains a significant cause of both sporadic cases and outbreaks of neonatal diarrhea in nursery settings. **Analysis of Incorrect Options:** * **Option A:** Rotaviruses are widespread in nature. Many animals (cows, pigs, horses) have their own species-specific rotaviruses. While cross-species transmission is rare, these animal viruses are genetically related to human strains. * **Option C:** Rotavirus is notoriously **difficult to culture** in standard diagnostic laboratories. Diagnosis is typically made using rapid antigen detection (ELISA) or Latex Agglutination from stool samples, or by visualizing "wheel-shaped" particles via Electron Microscopy. * **Option D:** Maternal antibodies (IgG transferred transplacentally and IgA in breast milk) **are protective**. This explains why severe clinical disease is less common in infants under 6 months of age compared to older toddlers. **High-Yield Clinical Pearls for NEET-PG:** * **Genome:** 11 segments of dsRNA (allows for genetic reassortment). * **Pathogenesis:** Produces a viral enterotoxin called **NSP4**, which induces secretion by increasing intracellular calcium. * **Seasonality:** Traditionally peaks in winter months ("Winter diarrhea"). * **Vaccines:** Live attenuated oral vaccines (Rotarix, RotaTeq, and Rotavac) are part of the Universal Immunization Programme (UIP) in India. * **Morphology:** Triple-layered capsid; appears as a "cartwheel" on Electron Microscopy.
Question 748: Mumps most commonly affects which gland?
- A. Parotid gland (Correct Answer)
- B. Submandibular gland
- C. Sublingual gland
- D. Lacrimal gland
Explanation: **Explanation:** Mumps is an acute viral infection caused by the **Mumps virus** (a single-stranded RNA virus belonging to the *Rubulavirus* genus in the *Paramyxoviridae* family). **Why Parotid Gland is correct:** The hallmark of mumps is **nonsuppurative parotitis**. The virus has a specific tropism for glandular epithelium and the central nervous system. The **parotid gland** is the most commonly affected salivary gland, involved in approximately 95% of symptomatic cases. Inflammation leads to painful swelling, typically starting unilaterally and becoming bilateral in 70% of patients. The swelling displaces the earlobe upward and outward, a classic clinical sign. **Why other options are incorrect:** * **Submandibular and Sublingual glands:** While these salivary glands can be involved in mumps (often concurrently with the parotid), isolated involvement is rare. They are significantly less common primary sites compared to the parotid. * **Lacrimal gland:** Inflammation of the lacrimal gland (dacryoadenitis) is not a standard feature of mumps. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Respiratory droplets; patients are most infectious 2 days before to 5 days after the onset of parotitis. * **Diagnosis:** Clinical diagnosis is standard, but **increased serum amylase** (S-type) is a key laboratory finding due to salivary gland inflammation. * **Complications:** * **Orchitis:** Most common complication in post-pubertal males (usually unilateral; rarely leads to sterility). * **Aseptic Meningitis:** Most common extra-glandular manifestation. * **Pancreatitis:** Suggested by epigastric pain and elevated serum lipase. * **Ovarian involvement (Oophoritis):** Seen in ~5% of post-pubertal females. * **Deafness:** Unilateral sensorineural hearing loss (rare but permanent).
Question 749: Rabies virus is best described as which of the following?
- A. Cytotropic
- B. Dermatotropic
- C. Chromophilic
- D. Neurotropic (Correct Answer)
Explanation: **Explanation:** **1. Why Neurotropic is Correct:** The Rabies virus (family *Rhabdoviridae*, genus *Lyssavirus*) is classicially **neurotropic**, meaning it has a specific affinity for nervous tissue. After an animal bite, the virus replicates locally in muscle cells before binding to **Nicotinic Acetylcholine Receptors (nAChR)** at the neuromuscular junction. It then undergoes **retrograde axonal transport** via the dynein motor proteins to reach the Central Nervous System (CNS). Its primary pathology involves the destruction of neurons, leading to the characteristic fatal encephalitis. **2. Why the Other Options are Incorrect:** * **Cytotropic:** This is a general term referring to viruses that have an affinity for specific cells. While technically true for many viruses, it is not the specific descriptive term used for Rabies in medical microbiology. * **Dermatotropic:** These viruses primarily affect the skin (e.g., HPV, Molluscum contagiosum). While Rabies is introduced through the skin via a bite, it does not replicate or cause pathology there. * **Chromophilic:** This term refers to cells or tissues that stain easily with dyes. It is not a standard classification for viral tropism. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Bullet-shaped virus with a lipoprotein envelope and spike-like glycoprotein (G protein) which mediates attachment. * **Diagnosis:** Presence of **Negri Bodies** (intracytoplasmic eosinophilic inclusions) typically found in the **Hippocampus** (Ammon’s horn) and **Cerebellum** (Purkinje cells). * **Incubation Period:** Highly variable; depends on the distance of the bite site from the CNS. * **Prophylaxis:** Post-exposure prophylaxis (PEP) includes wound cleaning, Rabies Immunoglobulin (RIG), and the Modern Cell Culture Vaccine (IDRV/IM). Once clinical symptoms appear, the mortality rate is nearly 100%.
Question 750: Which viral infection always causes clinical disease in human beings?
- A. Rubella
- B. Poliomyelitis
- C. Measles (Correct Answer)
- D. Chicken pox
Explanation: **Explanation:** The correct answer is **Measles**. This question tests the concept of the **Iceberg Phenomenon of Disease**. In most viral infections, a large proportion of cases are subclinical or asymptomatic (the submerged portion of the iceberg). However, Measles is a classic exception where the "iceberg" is entirely above the water. **Why Measles is correct:** Measles virus has a very high secondary attack rate and high pathogenicity. It is characterized by **near-total clinical expression**; almost every susceptible individual infected with the virus will develop clinical symptoms (fever, cough, coryza, conjunctivitis, and the pathognomonic Koplik spots). Subclinical or inapparent infections in measles are extremely rare. **Why other options are incorrect:** * **Poliomyelitis:** This is the classic example of the Iceberg Phenomenon. Over 90-95% of cases are asymptomatic or cause minor flu-like illness (abortive polio), while paralytic polio occurs in less than 1% of infections. * **Rubella:** Up to 25-50% of Rubella infections are subclinical or asymptomatic, making it difficult to track during outbreaks. * **Chickenpox (Varicella):** While highly symptomatic in children, subclinical infections can occur, especially in partially immune individuals or infants with maternal antibodies. **High-Yield Clinical Pearls for NEET-PG:** * **Iceberg Phenomenon:** Absent in Measles, Rabies, and Tetanus (clinical disease is always apparent). * **Koplik Spots:** Appear on the buccal mucosa opposite the lower second molars *before* the rash appears. * **Vitamin A:** Supplementation is mandatory in Measles management to reduce mortality and prevent complications like blindness. * **SSPE (Subacute Sclerosing Panencephalitis):** A rare, delayed, fatal neurological complication of Measles.
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Virus Structure and Classification
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Viral Replication
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Pathogenesis of Viral Infections
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DNA Viruses: Herpesviruses
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DNA Viruses: Poxviruses and Adenoviruses
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Hepatitis Viruses
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RNA Viruses: Orthomyxoviruses
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RNA Viruses: Paramyxoviruses
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Enteroviruses and Rhinoviruses
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Arboviruses
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HIV and Retroviruses
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Oncogenic Viruses
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