Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1051: Which of the following is NOT true about varicella?

A. All stages of the rash are seen at one time (Correct Answer)
B. Humans are the only known reservoir
C. Children between 5-10 years old are most commonly affected
D. Patients are infectious 48 hours before the onset of the vesicular rash and until all vesicles are crusted

Explanation: **Explanation** The correct answer is **A**, as the statement "All stages of the rash are seen at one time" is actually a **characteristic feature** of Varicella (Chickenpox), not a false statement. In the context of NEET-PG, this question is often framed to test the distinction between Varicella and Variola (Smallpox). 1. **Why Option A is the correct choice (as a true statement):** Varicella rash appears in successive crops. Because new lesions appear while older ones are healing, the rash is **pleomorphic**, meaning macules, papules, vesicles ("dewdrops on a rose petal"), and crusts are all visible simultaneously in the same anatomical area. In contrast, Smallpox lesions are monomorphic (all at the same stage). 2. **Option B (Humans are the only reservoir):** This is a true statement. There is no animal reservoir for Varicella-Zoster Virus (VZV), which makes it a candidate for theoretical eradication. 3. **Option C (Age group):** This is true. In temperate climates and pre-vaccination eras, chickenpox is primarily a childhood disease, most common in the 5–10 year age group. 4. **Option D (Infectivity):** This is true. The period of communicability extends from **48 hours before** the rash appears until **all vesicles have crusted over** (usually 5 days after onset). **High-Yield Clinical Pearls for NEET-PG:** * **Centripetal Distribution:** Varicella rash is denser on the trunk and sparse on the extremities (opposite of Smallpox). * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions. * **Secondary Infection:** The most common complication in children is secondary bacterial skin infection (Staph/Strep). * **Congenital Varicella Syndrome:** Highest risk if the mother is infected during the first 20 weeks of pregnancy (presents with limb hypoplasia and cicatricial skin scarring).

Question 1052: Which virus family is characterized by a segmented double-stranded RNA genome?

A. Reovirus (Correct Answer)
B. Myxovirus
C. Rabies virus
D. Parvovirus

Explanation: **Explanation:** The correct answer is **A. Reovirus**. **1. Why Reovirus is Correct:** The Reoviridae family (e.g., Rotavirus, Coltivirus) is unique among RNA viruses because it possesses a **segmented, double-stranded RNA (dsRNA)** genome. Most RNA viruses are single-stranded. The genome is typically divided into 10–12 segments, which allows for **genetic reassortment**, similar to the influenza virus. This structural feature is a high-yield fact for competitive exams. **2. Why the Other Options are Incorrect:** * **B. Myxovirus (Orthomyxoviridae):** While these viruses (like Influenza) have segmented genomes, their genetic material is **single-stranded RNA (ssRNA)** of negative polarity, not double-stranded. * **C. Rabies virus (Rhabdoviridae):** This is a bullet-shaped virus containing a **non-segmented, single-stranded negative-sense RNA** genome. * **D. Parvovirus:** This is the smallest DNA virus. It is unique because it contains **single-stranded DNA (ssDNA)**, whereas most DNA viruses are double-stranded. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Rotavirus:** A member of the Reoviridae family, it is the most common cause of severe dehydrating diarrhea in infants and young children worldwide. It has a characteristic **"wheel-like" appearance** under electron microscopy. * **The "REO" Acronym:** Stands for **R**espiratory **E**nteric **O**rphan virus. * **Segmented Viruses Mnemonic (BOAR):** **B**unyavirus (3), **O**rthomyxovirus (8), **A**renavirus (2), and **R**eovirus (10–12). * **Double-stranded RNA:** If a question mentions dsRNA, think Reovirus immediately. If it mentions ssDNA, think Parvovirus B19.

Question 1053: What is the most common cause of acute gastroenteritis?

A. Norovirus (Correct Answer)
B. Rotavirus
C. Salmonella
D. E. coli

Explanation: **Explanation:** **Norovirus (Option A)** is currently the most common cause of acute gastroenteritis (AGE) worldwide across all age groups. While Rotavirus was historically the leading cause in children, the widespread implementation of the Rotavirus vaccine has shifted the epidemiology, making Norovirus the primary pathogen for both sporadic cases and large outbreaks (often associated with cruise ships, schools, and nursing homes). It is highly contagious due to its low infectious dose and resistance to common disinfectants like alcohol. **Why other options are incorrect:** * **Rotavirus (Option B):** Formerly the #1 cause in children under 5 years. It remains a significant cause in unvaccinated populations but has been surpassed by Norovirus in global prevalence. * **Salmonella (Option C):** A common cause of *bacterial* food poisoning (inflammatory diarrhea), but it is less frequent than viral etiologies in the general population. * **E. coli (Option D):** While Enterotoxigenic E. coli (ETEC) is the most common cause of *Traveler’s diarrhea*, it is not the most common cause of general acute gastroenteritis. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** Norovirus belongs to the *Caliciviridae* family (ssRNA, non-enveloped). * **Transmission:** Fecal-oral route; characteristically causes "winter vomiting disease." * **Key Feature:** It is the most common cause of **outbreaks** in closed settings. * **Diagnosis:** RT-PCR is the gold standard for detection in stool samples. * **Resistance:** Norovirus is resistant to alcohol-based hand sanitizers; handwashing with soap and water is essential for prevention.

Question 1054: Which of the following is true about bacteriophages?

A. Can transmit toxins to bacteria.
B. A bacterium that transmits DNA to another bacterium.
C. Causes transformation of bacteria.
D. A virus that invades bacteria. (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. A virus that invades bacteria.** **1. Understanding the Correct Option:** Bacteriophages (or simply "phages") are obligate intracellular **viruses** that specifically infect and replicate within bacteria. They consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat (capsid). Their life cycle involves attaching to specific receptors on the bacterial cell wall and injecting their genetic material to hijack the host's machinery. **2. Analysis of Incorrect Options:** * **Option A:** While bacteriophages *can* transmit toxin genes (a process called **Lysogenic Conversion**), this is a *consequence* of infection rather than the definition of the phage itself. Option D is the fundamental biological definition. * **Option B:** This describes **Conjugation**, where DNA is transferred between bacteria via a sex pilus. A bacteriophage is a virus, not a bacterium. * **Option C:** **Transformation** refers to the uptake of naked DNA from the environment by a competent bacterium. The process involving a bacteriophage is called **Transduction**. **3. NEET-PG High-Yield Clinical Pearls:** * **Lysogenic Conversion:** This is a favorite exam topic. Specific bacterial toxins are encoded by bacteriophages, not the bacterial chromosome. * *Mnemonic (ABCDES):* **A**ntigen (O) of Salmonella, **B**otulinum toxin, **C**holera toxin, **D**iphtheria toxin, **E**rythrogenic toxin (S. pyogenes), **S**higa toxin. * **Transduction:** The process of horizontal gene transfer mediated by phages. * *Generalized:* Occurs during the lytic cycle (any gene). * *Specialized:* Occurs during the lysogenic cycle (specific adjacent genes). * **Therapeutic Use:** Phage therapy is being explored as an alternative to antibiotics for Multi-Drug Resistant (MDR) organisms.

Question 1055: Which of the following is NOT a Flavivirus?

A. Hepatitis C virus (HCV)
B. Chikungunya virus (Correct Answer)
C. Yellow fever virus
D. Japanese encephalitis virus

Explanation: **Explanation:** The correct answer is **Chikungunya virus** because it belongs to the **Togaviridae** family (Genus: *Alphavirus*), not the Flaviviridae family. While it shares clinical similarities with Flaviviruses—such as being an arbovirus transmitted by the *Aedes* mosquito—its genomic structure and replication strategy are distinct. **Analysis of Options:** * **Hepatitis C virus (HCV):** Although not an arbovirus, HCV is a member of the *Flaviviridae* family (Genus: *Hepacivirus*). It is a major cause of chronic liver disease and hepatocellular carcinoma. * **Yellow Fever virus:** This is the prototype virus of the *Flaviviridae* family. It is characterized by Councilman bodies (acidophilic degeneration of hepatocytes) and is transmitted by *Aedes aegypti*. * **Japanese Encephalitis virus (JEV):** A significant member of the *Flaviviridae* family and the leading cause of viral encephalitis in Asia. It is transmitted by *Culex* mosquitoes, with pigs and water birds acting as reservoirs. **High-Yield Clinical Pearls for NEET-PG:** * **Flaviviridae Family:** Includes Dengue, Zika, West Nile, Yellow Fever, JEV, and HCV. All are (+)ssRNA, enveloped, and icosahedral. * **Togaviridae Family:** Includes Chikungunya and Rubella. * **Differentiating Chikungunya vs. Dengue:** Chikungunya is typically associated with severe, debilitating **joint pain (arthralgia)** that can persist for months, whereas Dengue is more likely to cause retro-orbital pain and significant thrombocytopenia. * **Vector Mnemonics:** *Aedes* transmits Dengue, Chikungunya, Zika, and Yellow Fever. *Culex* transmits Japanese Encephalitis and West Nile Virus.

Question 1056: Which of the following is the least common chronic complication of measles?

A. Diarrhoea
B. Pneumonia
C. Otitis media
D. Subacute sclerosing panencephalitis (Correct Answer)

Explanation: **Explanation:** The question asks for the **least common chronic complication** of measles. While measles is known for its acute symptoms, its complications are what lead to significant morbidity and mortality. **Why Subacute Sclerosing Panencephalitis (SSPE) is the correct answer:** SSPE is a progressive, fatal neurodegenerative disease caused by a persistent infection with a defective measles virus. While it is a severe **chronic** complication, it is extremely rare, occurring in approximately **1 in 10,000 to 1 in 100,000** cases of measles. It typically manifests 7–10 years after the initial infection. Because of its very low incidence compared to acute complications, it is the "least common" among the choices provided. **Analysis of Incorrect Options:** * **Diarrhoea:** This is the **most common** complication of measles overall (occurring in about 8% of cases), particularly in malnourished children. * **Pneumonia:** This is the **most common cause of death** associated with measles in children. It can be caused by the measles virus itself (Hecht’s giant cell pneumonia) or secondary bacterial infections. * **Otitis Media:** This is a very frequent bacterial complication, occurring in nearly 7–10% of cases, often leading to permanent hearing loss if untreated. **NEET-PG High-Yield Pearls:** * **Most common complication:** Diarrhoea. * **Most common cause of death:** Pneumonia. * **SSPE Diagnosis:** Look for high titers of anti-measles antibodies in the CSF and serum, and **periodic complexes** on EEG. * **Vitamin A:** Supplementation reduces the severity and mortality of measles complications. * **Koplik spots:** Pathognomonic sign found on the buccal mucosa opposite the lower second molars during the pre-eruptive stage.

Question 1057: Which Human Papillomavirus (HPV) types are considered high-risk?

A. 16 and 18 (Correct Answer)
B. 6 and 11
C. 42 and 44
D. 70 and 72

Explanation: **Explanation:** Human Papillomavirus (HPV) is a double-stranded DNA virus with over 200 genotypes. These are clinically categorized based on their oncogenic potential into "High-risk" and "Low-risk" types. **1. Why Option A is Correct:** **HPV 16 and 18** are the most potent **high-risk (oncogenic)** types. They are responsible for approximately 70% of all cervical cancers worldwide. Their oncogenicity is primarily due to the overexpression of two early proteins: * **E6:** Binds to and degrades the **p53** tumor suppressor protein. * **E7:** Binds to and inactivates the **pRb** (Retinoblastoma) protein. This leads to uncontrolled cell cycle progression and genomic instability. **2. Why Other Options are Incorrect:** * **Option B (6 and 11):** These are **low-risk** types. They are the primary cause of **Condyloma acuminatum** (anogenital warts) and Recurrent Respiratory Papillomatosis (RRP). They rarely progress to malignancy. * **Options C & D:** Types 42, 44, 70, and 72 are generally considered low-risk or of undetermined significance and are not the primary drivers of cervical carcinogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Most common type in Cervical Cancer:** HPV 16 (followed by 18). * **Most common type in Oropharyngeal Cancer:** HPV 16. * **Screening:** The Papanicolaou (Pap) smear looks for **Koilocytes** (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Vaccination:** The **9-valent vaccine (Gardasil 9)** covers types 6, 11, 16, 18, 31, 33, 45, 52, and 58. * **Schiller’s Test:** Used during colposcopy; cancerous areas are **Lugol’s iodine negative** (remain pale/yellow) due to lack of glycogen.

Question 1058: A patient presents with acute symptoms of hepatitis and tests positive for HDV antigen. Given that HDV requires HBV for replication, which of the following sets of serological markers indicates chronic HBV infection with superinfection by HDV?

A. HBsAg+, HBeAg+, Anti-HBc IgM+, Anti-HBc IgG-, Anti-HBs-
B. HBsAg+, HBeAg+, Anti-HBc IgM-, Anti-HBc IgG+, Anti-HBs- (Correct Answer)
C. HBsAg-, HBeAg-, Anti-HBc IgM-, Anti-HBc IgG+, Anti-HBs+
D. HBsAg-, HBeAg-, Anti-HBc IgM-, Anti-HBc IgG-, Anti-HBs+

Explanation: ### Explanation The key to solving this question lies in distinguishing between **HBV/HDV Co-infection** and **HDV Superinfection**. Hepatitis D Virus (HDV) is a defective RNA virus that requires the Hepatitis B Surface Antigen (HBsAg) coat for its assembly and transmission. **1. Why Option B is Correct:** In **HDV Superinfection**, a patient who is already a chronic carrier of HBV (or has chronic hepatitis B) becomes infected with HDV. * **Chronic HBV status** is defined by the presence of **HBsAg** for >6 months and the presence of **Anti-HBc IgG**. * The absence of **Anti-HBc IgM** is crucial here, as IgM indicates an acute HBV infection. * Therefore, the profile **HBsAg+, Anti-HBc IgG+, and Anti-HBc IgM-** confirms a pre-existing chronic HBV state upon which the acute HDV infection has occurred. **2. Analysis of Incorrect Options:** * **Option A:** This profile (Anti-HBc IgM+) indicates an **acute HBV infection**. If HDV markers were also present, this would represent **Co-infection** (simultaneous infection with both viruses), not superinfection. * **Option C:** This indicates a **resolved HBV infection** (HBsAg negative, Anti-HBs positive, and Anti-HBc IgG positive). HDV cannot replicate without active HBsAg production. * **Option D:** This indicates **immunity via vaccination** (only Anti-HBs positive; Anti-HBc is negative as there was no exposure to the viral core). **3. High-Yield Clinical Pearls for NEET-PG:** * **Co-infection:** Usually results in acute hepatitis that resolves; low risk of chronicity. * **Superinfection:** Often leads to severe "flare-up" of hepatitis and carries a very high risk (up to 80%) of progressing to **chronic HDV**, cirrhosis, and liver failure. * **HDV Diagnosis:** Look for HDV-Ag or HDV-RNA in the blood. * **Prevention:** The HBV vaccine is the most effective way to prevent HDV infection in HBV-naive individuals.

Question 1059: What is the causative organism of SARS?

A. H1N1
B. Coronavirus (Correct Answer)
C. Rotavirus
D. RSV

Explanation: **Explanation:** The correct answer is **Coronavirus**. Severe Acute Respiratory Syndrome (SARS) is caused by the **SARS-associated coronavirus (SARS-CoV)**. This is an enveloped, single-stranded, positive-sense RNA virus belonging to the family *Coronaviridae*. It first emerged in 2002–2003 in China, causing a global outbreak characterized by high fever, malaise, and progressive respiratory failure. **Analysis of Options:** * **H1N1 (Option A):** This is a subtype of **Influenza A virus**. It was responsible for the 1918 Spanish Flu and the 2009 Swine Flu pandemic. While it causes respiratory distress, it is genetically distinct from the coronavirus family. * **Rotavirus (Option C):** This is a double-stranded RNA virus and the leading cause of **severe dehydrating diarrhea** in infants and young children worldwide. It does not cause primary respiratory syndromes like SARS. * **RSV (Respiratory Syncytial Virus) (Option D):** A member of the *Pneumoviridae* family, RSV is the most common cause of **bronchiolitis and pneumonia** in infants under one year of age. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** SARS-CoV (and SARS-CoV-2) utilizes the **ACE2 (Angiotensin-Converting Enzyme 2)** receptor to enter host cells. * **Zoonotic Origin:** The natural reservoir for SARS-CoV is the **horseshoe bat**, with the **masked palm civet** serving as the intermediate host. * **Morphology:** Coronaviruses are named for the "crown-like" spikes (S-proteins) on their surface visible under electron microscopy. * **Diagnostic Gold Standard:** Real-time Reverse Transcription-Polymerase Chain Reaction (RT-PCR).

Question 1060: Primary monkey kidney culture are used for diagnostic criteria for which virus?

A. Adenovirus
B. Poliovirus (Correct Answer)
C. HIV
D. Measles

Explanation: **Explanation:** The isolation of viruses in cell culture remains a gold standard in virology. **Poliovirus** (an Enterovirus) has a specific tropism for primate cells due to the presence of the CD155 receptor. **Primary Monkey Kidney (PMK) cells** are the most sensitive substrate for the primary isolation of Poliovirus from clinical samples (like stool or throat swabs). In these cultures, Poliovirus produces a characteristic **Cytopathic Effect (CPE)** consisting of cell rounding, shrinkage, and eventual detachment within 24–72 hours. **Analysis of Options:** * **Adenovirus:** While they can grow in various lines, they are best isolated in **human epithelial cell lines** (e.g., HeLa, HEp-2, or HEK293), where they produce "grape-like clusters" CPE. * **HIV:** Diagnosis is primarily serological (ELISA/Western Blot) or molecular (RT-PCR). For isolation, **stimulated peripheral blood mononuclear cells (PBMCs)** or specific T-cell lines are required, not monkey kidney cells. * **Measles:** The virus is best isolated in **human embryonic kidney** or **primary human amnion cells**. A classic diagnostic feature in culture is the formation of multinucleated giant cells (syncytia). **High-Yield Pearls for NEET-PG:** * **Primary Cultures:** Derived directly from animal/human tissue (e.g., PMK). They can be subcultured only once or twice. * **Continuous Cell Lines:** Derived from cancer cells (e.g., **HeLa** from cervical cancer, **HEp-2** from laryngeal cancer) and can be subcultured indefinitely. * **Diploid Cell Lines:** Derived from embryonic tissue (e.g., **WI-38**, **MRC-5**); used for vaccine production (e.g., RA 27/3 Rubella vaccine). * **Poliovirus CPE:** Rapidly developing, "refractile" round cells.

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