Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1081: Which of the following is NOT a DNA virus?

A. Varicella zoster virus
B. Dengue virus (Correct Answer)
C. Hepatitis B virus
D. Parvovirus B19

Explanation: ### Explanation The classification of viruses based on their genetic material is a fundamental topic in medical microbiology. To identify the correct answer, one must distinguish between DNA and RNA viruses. **Why Dengue Virus is the correct answer:** **Dengue virus** belongs to the **Flaviviridae** family. It is a single-stranded, positive-sense **RNA virus**. It is transmitted by the *Aedes aegypti* mosquito and is a leading cause of arboviral illness worldwide. All other options listed are DNA viruses. **Analysis of incorrect options:** * **Varicella-zoster virus (VZV):** A member of the **Herpesviridae** family (Alphaherpesvirinae). It is an enveloped, double-stranded DNA (dsDNA) virus responsible for chickenpox and shingles. * **Hepatitis B virus (HBV):** A member of the **Hepadnaviridae** family. It is a unique partially double-stranded DNA virus that replicates through an RNA intermediate using reverse transcriptase. * **Parvovirus B19:** A member of the **Parvoviridae** family. It is notable for being a **non-enveloped, single-stranded DNA (ssDNA)** virus, causing Erythema infectiosum (Fifth disease). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for DNA Viruses:** "**HHAPPPPy**" – **H**erpes, **H**epadna, **A**deno, **P**apilloma, **P**olyoma, **P**arvo, and **P**ox. * **Exceptions to remember:** Most DNA viruses are double-stranded (except **Parvovirus**, which is ssDNA) and have icosahedral symmetry (except **Poxvirus**, which has complex symmetry and replicates in the cytoplasm). * **Dengue Diagnosis:** NS1 antigen is the marker of choice for early diagnosis (Day 1–5), while IgM ELISA is used after Day 5.

Question 1082: A nursing staff, while inserting an IV line to a severely ill patient with HIV, accidentally sustained a needle-stick injury. Which of the following investigations would be most appropriate for her?

A. P24 antigen capture assay (Correct Answer)
B. ELISA test
C. Western blot
D. Blood culture

Explanation: **Explanation:** The correct answer is **A. P24 antigen capture assay.** **1. Why P24 antigen capture assay is correct:** Following a needle-stick injury, the primary concern is the early detection of HIV infection during the **"window period"** (the time between infection and the development of detectable antibodies). The **p24 antigen** is a structural protein of the HIV capsid that appears in the blood as early as **1–3 weeks** after exposure, significantly earlier than antibodies. Therefore, it is the most appropriate investigation for early diagnosis in an occupational exposure scenario. **2. Why other options are incorrect:** * **B. ELISA test:** Standard ELISA tests detect **anti-HIV antibodies**. These typically take 3–12 weeks to develop (seroconversion). Testing immediately or shortly after a needle-stick injury would yield a false negative. * **C. Western blot:** This is a supplemental test used to **confirm** a positive ELISA by detecting specific antibodies against HIV proteins (gp120, gp41, p24). Like ELISA, it relies on the host's immune response and is not useful in the early window period. * **D. Blood culture:** HIV is an intracellular virus and is not diagnosed via routine blood culture. While viral culture is possible in specialized research labs, it is slow, expensive, and not clinically indicated for post-exposure management. **3. Clinical Pearls for NEET-PG:** * **Window Period:** The time when a person is infected but tests (ELISA) are negative. P24 antigen and **HIV-RNA (PCR)** are the earliest markers. * **Fourth Generation ELISA:** Modern assays (p24 antigen + IgM/IgG antibodies) have shortened the window period significantly. * **Post-Exposure Prophylaxis (PEP):** Must be started as soon as possible, ideally within **2 hours** and no later than **72 hours**. The standard regimen is a 3-drug combination (e.g., Tenofovir + Lamivudine + Dolutegravir) for **28 days**.

Question 1083: Which of the following viruses is a common cause of chronic liver disease?

A. Hepatitis B (Correct Answer)
B. Hepatitis A
C. Hepatitis C
D. Hepatitis E

Explanation: **Explanation:** The development of chronic liver disease (CLD) depends on the ability of a virus to cause a persistent infection (viremia lasting >6 months). Among the options provided, **Hepatitis B Virus (HBV)** is a major global cause of chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). While both HBV and HCV cause chronic disease, HBV is often prioritized in standard textbooks as a primary prototype for chronic viral hepatitis due to its high global prevalence and complex integration into the host genome. **Analysis of Options:** * **Hepatitis B (Correct):** Approximately 5-10% of adults and up to 90% of infected neonates develop chronic infection. It is a DNA virus that can lead to long-term complications like cirrhosis. * **Hepatitis C:** Also a major cause of CLD (with a higher chronicity rate of ~75-85% compared to HBV), but in many standardized exams, HBV is the classic answer unless "most common cause of post-transfusion chronic hepatitis" is specified. * **Hepatitis A & E:** These are transmitted via the **fecal-oral route** and typically cause acute, self-limiting hepatitis. They **do not** cause chronic liver disease (Exception: HEV can cause chronic infection in severely immunocompromised patients, but this is not the rule). **High-Yield Pearls for NEET-PG:** * **Chronicity Risk:** Inversely proportional to age at infection for HBV (highest in neonates). * **Hepatitis D:** Requires HBsAg (HBV) for replication; it can only cause chronic disease in the presence of a chronic HBV state (Superinfection). * **Hepatitis E:** Associated with high mortality (up to 20%) in **pregnant women** due to fulminant hepatic failure. * **Ground Glass Hepatocytes:** Pathognomonic histological finding in chronic Hepatitis B.

Question 1084: Which virus leads to aplastic crisis?

A. Poxvirus
B. Parvovirus B19 (Correct Answer)
C. Hepatitis A
D. Hepatitis B

Explanation: **Explanation:** **Parvovirus B19** is the correct answer because it has a specific tropism for **erythroid progenitor cells**. The virus enters these cells via the **P-antigen** (globoside) receptor and replicates within the nucleus, leading to cell lysis. In healthy individuals, this causes a transient drop in red blood cell production that is clinically silent. However, in patients with high red cell turnover (e.g., **Sickle Cell Anemia, Hereditary Spherocytosis, Thalassemia**), this temporary cessation of erythropoiesis leads to a life-threatening **Aplastic Crisis**, characterized by a sudden drop in hemoglobin and a low reticulocyte count. **Incorrect Options:** * **Poxvirus:** Known for causing skin lesions (e.g., Molluscum contagiosum or Variola). It does not target bone marrow precursors. * **Hepatitis A & B:** While severe viral hepatitis can rarely lead to *aplastic anemia* (pancytopenia) via immune-mediated bone marrow destruction, they do not typically cause the classic "aplastic crisis" (isolated erythroid failure) associated with Parvovirus B19. **High-Yield Clinical Pearls for NEET-PG:** * **Erythema Infectiosum (Fifth Disease):** Parvovirus B19 causes the classic "slapped-cheek" rash in children. * **Hydrops Fetalis:** If a pregnant woman is infected, the virus can cross the placenta, attack fetal RBC precursors, and lead to high-output cardiac failure and fetal death. * **Pure Red Cell Aplasia (PRCA):** In immunocompromised patients, Parvovirus B19 can cause chronic anemia due to persistent infection. * **Diagnosis:** Look for **giant proerythroblasts** with viral inclusion bodies in the bone marrow.

Question 1085: Which virus is the leading cause of bronchiolitis and community-acquired pneumonia in infants?

A. Measles virus
B. Influenza virus
C. Respiratory syncytial virus (Correct Answer)
D. Parainfluenza virus

Explanation: **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.

Question 1086: Viral enterotoxin is detected as a possible mechanism of pathogenesis in which of the following viruses?

A. Adenovirus
B. Rotavirus (Correct Answer)
C. Calicivirus
D. Astrovirus

Explanation: **Explanation:** The correct answer is **Rotavirus**. The hallmark of Rotavirus pathogenesis is the production of a non-structural protein called **NSP4**, which acts as the first identified **viral enterotoxin**. **1. Why Rotavirus is correct:** NSP4 functions similarly to the *Vibrio cholerae* toxin. It triggers a signal transduction pathway that increases intracellular calcium levels. This leads to the secretion of chloride and water into the intestinal lumen, resulting in profuse secretory diarrhea. Additionally, NSP4 stimulates the enteric nervous system, further increasing intestinal motility and secretion. **2. Why the other options are incorrect:** * **Adenovirus (Serotypes 40/41):** These cause viral gastroenteritis primarily through direct destruction of enterocytes (villous atrophy), leading to malabsorption. They do not produce an enterotoxin. * **Calicivirus (e.g., Norovirus):** These are the most common cause of epidemic gastroenteritis. Their mechanism involves blunting of intestinal villi and decreased brush border enzyme activity, not enterotoxin production. * **Astrovirus:** These cause mild diarrhea, mainly in children, via direct epithelial damage and osmotic imbalance. **NEET-PG High-Yield Pearls:** * **NSP4 Protein:** The key virulence factor for Rotavirus; it is a "viral enterotoxin." * **Mechanism:** Secretory diarrhea (via NSP4) + Malabsorptive diarrhea (via villous destruction). * **Diagnosis:** ELISA for Rotavirus antigen in stool or "Wheels-like" appearance on Electron Microscopy. * **Vaccines:** Rotarix (Monovalent) and RotaTeq (Pentavalent) are live-attenuated oral vaccines. * **Most common cause:** Rotavirus is the leading cause of severe dehydrating diarrhea in children worldwide.

Question 1087: Chicken pox is a common disease of childhood. It is caused by which of the following viruses?

A. Cytomegalovirus
B. Rotavirus
C. Varicella-zoster virus (Correct Answer)
D. Adenovirus

Explanation: **Explanation:** **Correct Answer: C. Varicella-zoster virus (VZV)** Chickenpox (Varicella) is the primary infection caused by the **Varicella-zoster virus**, a member of the *Alphaherpesvirinae* subfamily (Human Herpesvirus 3). It is highly contagious and typically presents in children with a characteristic "centripetal" rash—starting on the trunk and spreading to the face and limbs. The lesions appear in "crops" and are pleomorphic, meaning different stages (papules, vesicles, and crusts) are visible simultaneously. After the primary infection, the virus remains latent in the **dorsal root ganglia** and can reactivate later in life as Herpes Zoster (Shingles). **Analysis of Incorrect Options:** * **A. Cytomegalovirus (CMV):** A Betaherpesvirus (HHV-5). It is the most common cause of congenital viral infections and causes "Infectious Mononucleosis-like syndrome" (heterophile antibody negative) in immunocompetent adults. * **B. Rotavirus:** A Reovirus that is the leading cause of severe, dehydrating diarrhea in infants and young children worldwide. It does not cause a vesicular rash. * **C. Adenovirus:** A non-enveloped DNA virus primarily responsible for respiratory tract infections, pharyngoconjunctival fever, and epidemic keratoconjunctivitis (pink eye). **High-Yield Clinical Pearls for NEET-PG:** * **Dew-drop on a rose petal:** Classic description of the clear varicella vesicle on an erythematous base. * **Tzanck Smear:** Microscopic examination shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusion bodies. * **Congenital Varicella Syndrome:** Occurs if the mother is infected in early pregnancy; characterized by limb hypoplasia, scarring of the skin, and microcephaly. * **Vaccine:** Live attenuated strain (**Oka strain**) is used for prevention.

Question 1088: All of the following CSF findings are present in tuberculous meningitis, except:

A. Cob web formation
B. Elevated protein levels
C. Elevated sugar levels (Correct Answer)
D. Decreased chloride levels

Explanation: In **Tuberculous Meningitis (TBM)**, the CSF profile typically reflects a chronic granulomatous inflammatory process. The correct answer is **Elevated sugar levels** because TBM characteristically causes **Hypoglycorrhachia** (decreased CSF glucose). ### Why "Elevated sugar levels" is the correct answer: In bacterial and fungal infections like TBM, the glucose level in the CSF decreases (usually <40 mg/dL or a CSF:Plasma ratio <0.5). This occurs due to the metabolic consumption of glucose by the bacteria (*Mycobacterium tuberculosis*) and the infiltrating leukocytes, as well as impaired glucose transport across the blood-brain barrier. Therefore, elevated sugar is **not** a finding in TBM. ### Explanation of other options: * **Cobweb formation:** This is a classic high-yield finding in TBM. When CSF is left to stand, a delicate fibrin clot (pellicle) forms due to high fibrinogen levels. * **Elevated protein levels:** TBM typically shows significantly high protein (100–500 mg/dL) due to increased permeability of the blood-brain barrier and inflammatory exudates at the base of the brain. * **Decreased chloride levels:** Historically, low chloride (<110 mmol/L) was considered a hallmark of TBM. While less specific than glucose, it remains a classic descriptive finding in medical exams. ### NEET-PG High-Yield Pearls: * **Predominant Cells:** Lymphocytes (Pleocytosis), though neutrophils may be seen in the very early stages. * **Gold Standard Diagnosis:** CSF Culture (Lowenstein-Jensen medium) or BACTEC. * **Rapid Test of Choice:** GeneXpert (NAAT) is now preferred for its high specificity. * **Target Area:** TBM characteristically involves the **basal cisterns** (basal exudates), often leading to cranial nerve palsies (CN VI is most common).

Question 1089: Which of the following statements about Coronaviruses is false?

A. These viruses have club-shaped peplomers on their surface.
B. SARS spreads mainly by inhalation.
C. The SARS virus is highly mutable.
D. It does not spread through coughing, sneezing, or direct contact. (Correct Answer)

Explanation: **Explanation:** Coronaviruses are large, enveloped, positive-sense single-stranded RNA viruses. The correct answer is **Option D** because it is a false statement; Coronaviruses, including SARS-CoV and SARS-CoV-2, primarily spread through respiratory droplets generated by **coughing and sneezing**, as well as through **direct contact** with contaminated surfaces (fomites). **Analysis of Options:** * **Option A (True):** Coronaviruses derive their name from the "halo" or "crown" appearance seen under electron microscopy. This is due to large, **club-shaped peplomers** (Spike proteins) protruding from the envelope. * **Option B (True):** The primary mode of transmission for SARS is the **inhalation** of respiratory droplets. While it can be found in stool and urine, the respiratory route is the most significant for outbreaks. * **Option C (True):** Like most RNA viruses, Coronaviruses have a high mutation rate. Although they possess a "proofreading" enzyme (Exonuclease), they undergo significant **antigenic drift and recombination**, leading to the emergence of new variants and cross-species transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** SARS-CoV and SARS-CoV-2 bind to the **ACE-2 receptor** (Angiotensin-converting enzyme 2) found in the lower respiratory tract. * **Morphology:** They are the largest RNA viruses and possess a **helical symmetry** (unique among most positive-sense RNA viruses). * **Diagnosis:** The gold standard for acute infection is **RT-PCR**. * **Lungs:** Severe cases often present with "Ground Glass Opacities" on HRCT.

Question 1090: Rubeola refers to which of the following diseases?

A. German measles
B. Measles (Correct Answer)
C. Small pox
D. Chicken pox

Explanation: **Explanation:** The term **Rubeola** is the medical synonym for **Measles**, a highly contagious viral infection caused by the *Measles virus* (a member of the Genus *Morbillivirus*, Family *Paramyxoviridae*). It is characterized by the classic triad of the "3 Cs"—Cough, Coryza, and Conjunctivitis—along with the pathognomonic **Koplik spots** on the buccal mucosa. **Analysis of Options:** * **Option A: German Measles** is the synonym for **Rubella**. While the names sound similar, Rubella is caused by a *Togavirus*. It is generally milder than Rubeola but carries a significant risk of Congenital Rubella Syndrome (CRS) if contracted during pregnancy. * **Option C: Smallpox** is caused by the **Variola virus**. It was officially declared eradicated by the WHO in 1980. * **Option D: Chickenpox** is caused by the **Varicella-Zoster Virus (VZV)**, a member of the Herpesvirus family. It is characterized by pleomorphic rashes (appearing in different stages simultaneously). **High-Yield Clinical Pearls for NEET-PG:** * **Koplik Spots:** Small, bluish-white spots on an erythematous base found opposite the lower second molars; they appear *before* the rash. * **Rash Progression:** The maculopapular rash in Measles starts behind the ears (retro-auricular) and spreads cephalocaudally (downward). * **Complications:** The most common complication is Otitis Media; the most common cause of death is Pneumonia (Hecht’s giant cell pneumonia); the most dreaded late complication is **SSPE (Subacute Sclerosing Panencephalitis)**. * **Vitamin A:** Supplementation is recommended in all children with Measles to reduce morbidity and mortality.

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