Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 931: What is the primary method for diagnosing polio?

A. Detection of poliovirus in stool (Correct Answer)
B. Serology
C. Limb wasting
D. Acute flaccid paralysis (AFP)

Explanation: **Explanation:** The gold standard and primary method for diagnosing poliomyelitis is the **isolation and detection of poliovirus from the stool**. **1. Why Option A is correct:** Poliovirus is an enterovirus that replicates extensively in the Peyer’s patches of the intestine. It is excreted in high concentrations in the feces for several weeks, even after the virus is no longer detectable in the throat or cerebrospinal fluid (CSF). For the Global Polio Eradication Initiative, "adequate stool samples" (two samples collected 24 hours apart within 14 days of paralysis onset) are the definitive diagnostic requirement. **2. Why the other options are incorrect:** * **B. Serology:** While neutralizing antibodies rise after infection, serology is often inconclusive because it cannot easily distinguish between antibodies from natural infection, oral polio vaccine (OPV), or previous exposure. * **C. Limb wasting:** This is a late clinical sequela (atrophy) resulting from the destruction of anterior horn cells. It is a physical finding, not a primary diagnostic tool for acute infection. * **D. Acute Flaccid Paralysis (AFP):** AFP is a **clinical syndrome**, not a diagnostic test. While polio is a leading cause of AFP, other conditions like Guillain-Barré Syndrome (GBS) present similarly. AFP triggers the investigation, but stool viral isolation confirms the diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Specimen of choice:** Stool (highest yield); Throat swabs (only in the first week). * **Cell lines for isolation:** Monkey kidney (PMK) or human diploid (WI-38) cells. * **Most common presentation:** 90–95% of cases are **asymptomatic**. * **Pathology:** Destruction of **Anterior Horn Cells** of the spinal cord (Lower Motor Neuron lesion). * **Surveillance:** India was declared Polio-free in 2014; the last case was reported in January 2011 (Howrah, West Bengal).

Question 932: Which of the following conditions is NOT caused by Respiratory syncytial virus?

A. Common cold in children
B. Coryza in adults
C. Pneumonia in the elderly
D. Acute Respiratory Distress Syndrome (ARDS) (Correct Answer)

Explanation: ### Explanation **Respiratory Syncytial Virus (RSV)** is the most common cause of lower respiratory tract infections (LRTI) in infants and young children worldwide. It belongs to the *Paramyxoviridae* family (Genus: *Orthopneumovirus*). **Why ARDS is the correct answer:** While RSV can cause severe respiratory failure, **Acute Respiratory Distress Syndrome (ARDS)** is a complex clinical syndrome characterized by diffuse alveolar damage and non-cardiogenic pulmonary edema, typically triggered by sepsis, massive trauma, or severe pneumonia (including COVID-19 or Influenza). RSV primarily causes **bronchiolitis** and **interstitial pneumonia** rather than the classic diffuse alveolar hyaline membrane formation seen in ARDS. In the context of NEET-PG, ARDS is not considered a standard clinical manifestation of RSV infection. **Analysis of other options:** * **Common cold in children:** RSV is a leading cause of upper respiratory infections (URI) and the "common cold" in pediatric populations. * **Coryza in adults:** In healthy adults, RSV reinfection is common and usually presents as a self-limiting afebrile URI or "coryza" (nasal congestion, rhinorrhea). * **Pneumonia in the elderly:** RSV is increasingly recognized as a significant cause of severe pneumonia and exacerbation of COPD/CHF in the elderly, with morbidity rates comparable to Influenza. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause** of Bronchiolitis and Pneumonia in infants (<1 year). * **Surface Proteins:** It possesses **G-protein** (attachment) and **F-protein** (fusion), which causes infected cells to fuse, forming **multinucleated giant cells (Syncytia)**—hence the name. * **Lacks Hemagglutinin (H) and Neuraminidase (N)**, unlike other Paramyxoviruses. * **Treatment:** **Ribavirin** (nebulized) is used in severe cases; **Palivizumab** (monoclonal antibody against F-protein) is used for prophylaxis in high-risk premature infants.

Question 933: What is the percentage of fecal-oral transmission of hepatitis A?

A. 5% (Correct Answer)
B. 10%
C. 25%
D. 50%

Explanation: **Explanation:** The correct answer is **5%**. This question refers to the **secondary attack rate (SAR)** or the transmission efficiency within households/close contacts for Hepatitis A Virus (HAV). While the primary route of HAV transmission is fecal-oral (via contaminated food and water), the risk of clinical infection spreading to a susceptible household contact through direct person-to-person fecal-oral contact is approximately **5%**. **Breakdown of Options:** * **Option A (5%):** This is the established secondary attack rate for HAV. Despite the virus being highly stable in the environment, the actual transmission rate among household contacts is relatively low compared to other viral infections, largely due to the short period of peak infectivity (which occurs *before* the onset of jaundice). * **Options B, C, and D:** These percentages (10%, 25%, 50%) overestimate the transmission efficiency. While HAV is highly contagious in outbreak settings (point-source outbreaks), the individual-to-individual transmission rate remains at the lower 5% threshold. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** Picornaviridae; **Genus:** Hepatovirus. * **Incubation Period:** 2–6 weeks (Average 28 days). * **Infectivity:** Maximum during the late incubation period (2 weeks before jaundice) and decreases rapidly after jaundice appears. * **Diagnosis:** IgM anti-HAV is the gold standard for acute infection. IgG anti-HAV indicates past infection or vaccination (conferring lifelong immunity). * **Prognosis:** HAV never causes chronic hepatitis or a carrier state. However, it can rarely cause **Fulminant Hepatic Failure**, especially in patients with pre-existing liver disease. * **Prevention:** Post-exposure prophylaxis (vaccine or immunoglobulin) is effective if given within 14 days of exposure.

Question 934: Which of the following viruses is not a common cause of viral encephalitis?

A. Herpes simplex virus type 2 (Correct Answer)
B. Japanese encephalitis virus
C. Nipah virus
D. Cytomegalovirus

Explanation: The correct answer is **Herpes simplex virus type 2 (HSV-2)**. ### **Explanation** The distinction between HSV-1 and HSV-2 is a high-yield concept in neuro-virology. * **HSV-1** is the most common cause of sporadic, fatal **viral encephalitis** in adults, typically involving the temporal lobes. * **HSV-2**, conversely, is primarily associated with **aseptic meningitis** in adults (Mollaret’s meningitis) and disseminated encephalitis only in **neonates** (acquired during birth). In the context of general viral encephalitis among the adult/pediatric population, HSV-2 is not considered a "common" cause. ### **Analysis of Incorrect Options** * **Japanese Encephalitis Virus (JEV):** This is the most common cause of epidemic viral encephalitis in India. It specifically targets the basal ganglia and thalamus. * **Nipah Virus:** An emerging zoonotic paramyxovirus (reservoir: fruit bats) known for causing outbreaks of severe encephalitis with high mortality rates, particularly in Kerala, India. * **Cytomegalovirus (CMV):** A significant cause of viral encephalitis in immunocompromised individuals (e.g., HIV/AIDS patients), often presenting as ventriculoencephalitis. ### **NEET-PG High-Yield Pearls** 1. **Site Specificity:** HSV-1 encephalitis classically shows a predilection for the **temporal lobes** (look for hemorrhagic necrosis on MRI). 2. **Diagnosis:** **CSF PCR** is the gold standard for diagnosing HSV encephalitis. 3. **Treatment:** Intravenous **Acyclovir** is the drug of choice and should be started empirically if encephalitis is suspected. 4. **India Context:** Always remember JEV for "epidemic" scenarios and Nipah for "outbreak" scenarios in South India.

Question 935: Which of the following drugs acts by blocking reverse transcriptase?

A. Zidovudine (Correct Answer)
B. Acyclovir
C. Amantadine
D. Ribavirin

Explanation: **Explanation:** **Zidovudine (AZT)** is the correct answer because it belongs to the **Nucleoside Reverse Transcriptase Inhibitor (NRTI)** class of antiretroviral drugs. It acts as a thymidine analogue. Once phosphorylated into its active triphosphate form within the cell, it competes with natural nucleotides for incorporation into the viral DNA chain. Because it lacks a 3'-hydroxyl group, it causes **premature chain termination**, effectively blocking the RNA-dependent DNA polymerase (Reverse Transcriptase) enzyme of HIV. **Analysis of Incorrect Options:** * **Acyclovir:** A guanosine analogue used primarily for Herpes Simplex (HSV) and Varicella-Zoster (VZV). It inhibits **viral DNA polymerase**, not reverse transcriptase. It requires activation by viral thymidine kinase. * **Amantadine:** An anti-influenza drug that acts by blocking the **M2 ion channel** protein, preventing the uncoating of the Influenza A virus. It is no longer widely used due to high resistance. * **Ribavirin:** A broad-spectrum antiviral that interferes with **RNA polymerase** and depletes intracellular guanosine triphosphate (GTP) pools. It is commonly used for Hepatitis C and RSV. **High-Yield Clinical Pearls for NEET-PG:** * **Zidovudine Side Effects:** The most characteristic side effect is **bone marrow suppression** (anemia and neutropenia). It is also associated with nail hyperpigmentation and myopathy. * **Pregnancy:** Zidovudine is a key drug used to prevent **vertical transmission** (mother-to-child) of HIV. * **NRTI Mechanism:** All NRTIs (except Tenofovir, which is a Nucleotide) require triple phosphorylation to become active.

Question 936: Which of the following is a member of the Paramyxoviridae family?

A. Retrovirus
B. Poliovirus
C. Parainfluenza virus (Correct Answer)
D. Rabies virus

Explanation: **Explanation:** The **Paramyxoviridae** family consists of large, enveloped, pleomorphic viruses with a non-segmented, negative-sense, single-stranded RNA genome. **Parainfluenza virus** is a classic member of this family, alongside others like Measles (Morbillivirus), Mumps (Rubulavirus), and Respiratory Syncytial Virus (RSV, now often classified under Pneumoviridae). **Analysis of Options:** * **Parainfluenza virus (Correct):** It belongs to the Paramyxoviridae family. It is a leading cause of Croup (laryngotracheobronchitis) in children, characterized by a "barking" cough and the "steeple sign" on X-ray. * **Retrovirus (Incorrect):** These belong to the **Retroviridae** family (e.g., HIV). They are unique for using reverse transcriptase to convert RNA into DNA. * **Poliovirus (Incorrect):** This is a member of the **Picornaviridae** family (genus Enterovirus). It is a small, non-enveloped, positive-sense RNA virus. * **Rabies virus (Incorrect):** This belongs to the **Rhabdoviridae** family. It is easily distinguished by its characteristic bullet-shaped morphology. **High-Yield Clinical Pearls for NEET-PG:** 1. **Surface Spikes:** Paramyxoviruses typically possess two types of glycoprotein spikes: **Hemagglutinin-Neuraminidase (HN)** or H/G proteins (for attachment) and **Fusion (F) protein** (mediates cell-to-cell fusion, leading to syncytia/multinucleated giant cell formation). 2. **Cytoplasmic Inclusions:** Since they replicate in the cytoplasm, they often produce eosinophilic cytoplasmic inclusion bodies (e.g., Warthin-Finkeldey cells in Measles). 3. **Vitamin A:** Supplementation is crucial in managing Measles (a paramyxovirus) to reduce morbidity and mortality.

Question 937: Which of the following viruses does NOT cause diarrhea?

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

Explanation: **Explanation:** The correct answer is **Reovirus**. While the family *Reoviridae* contains several genera that cause gastroenteritis (most notably *Rotavirus*), the genus **Reovirus** (Respiratory Enteric Orphan virus) itself is generally considered non-pathogenic in humans. Despite being isolated from the respiratory and enteric tracts, it is not a recognized cause of clinical diarrhea. **Analysis of Options:** * **Rotavirus (Option A):** The most common cause of severe, dehydrating diarrhea in infants and young children worldwide. It belongs to the *Reoviridae* family and primarily infects the mature enterocytes of the villi in the small intestine. * **Calicivirus (Option B):** This family includes **Norovirus** (the leading cause of epidemic non-bacterial gastroenteritis in all ages) and **Sapovirus**. They are classic causes of "winter vomiting disease" and outbreaks in closed settings like cruise ships or nursing homes. * **Adenovirus (Option D):** Specifically, **Serotypes 40 and 41** (Subgroup F) are known as "Enteric Adenoviruses." They are the second most common viral cause of childhood diarrhea after Rotavirus. **High-Yield NEET-PG Pearls:** * **Rotavirus:** Characterized by a **wheel-like appearance** on electron microscopy. It produces **NSP4**, a viral enterotoxin that induces secretory diarrhea. * **Norovirus:** Associated with a very low infectious dose and resistance to common disinfectants; often linked to **shellfish** consumption or contaminated water. * **Astrovirus:** Another cause of pediatric diarrhea, recognized by its **star-shaped** morphology. * **Reovirus Mnemonic:** "Orphan" virus because it was originally not associated with any known disease.

Question 938: All of the following are viral inclusion bodies except?

A. Guarneri bodies
B. Bollinger bodies
C. Paschen bodies
D. Psammoma bodies (Correct Answer)

Explanation: **Explanation:** The correct answer is **Psammoma bodies** because they are not viral inclusion bodies; rather, they are characteristic **extracellular collections of calcium** (dystrophic calcification). Microscopically, they appear as laminated, concentric whorled structures. They are high-yield markers for specific tumors, most notably **Papillary carcinoma of the thyroid**, **Serous cystadenocarcinoma of the ovary**, and **Meningioma**. **Analysis of Viral Inclusion Bodies (Incorrect Options):** Viral inclusion bodies are nuclear or cytoplasmic aggregates of stainable substances (usually viral proteins or nucleic acids) formed during viral replication. * **Guarneri bodies:** These are eosinophilic, **intracytoplasmic** inclusion bodies found in cells infected with **Variola virus (Smallpox)** or Vaccinia virus. * **Bollinger bodies:** These are large, granular, eosinophilic **intracytoplasmic** inclusions seen in **Fowlpox**. * **Paschen bodies:** These represent the actual **virus particles (virions)** of Variola/Vaccinia when seen under a light microscope using special stains (like Gutstein’s stain). They are considered the smallest visible particles in smallpox. **NEET-PG High-Yield Pearls:** * **Negri bodies:** Intracytoplasmic inclusions in pyramidal cells of the hippocampus/Purkinje cells (Pathognomonic for **Rabies**). * **Owl’s eye appearance:** Large intranuclear inclusions seen in **CMV** (Cytomegalovirus). * **Cowdry Type A:** Intranuclear inclusions seen in **Herpes Simplex Virus (HSV)** and Yellow Fever (Torres bodies). * **Molluscum bodies (Henderson-Patterson bodies):** Large, eosinophilic cytoplasmic inclusions seen in **Molluscum contagiosum**.

Question 939: Which of the following is NOT transmitted by Aedes mosquitoes?

A. Chikungunya
B. Zika
C. Dengue
D. Malaria (Correct Answer)

Explanation: **Explanation:** The correct answer is **Malaria**. This question tests the fundamental knowledge of vector-borne diseases, specifically distinguishing between viral and protozoal transmission cycles. **1. Why Malaria is the Correct Answer:** Malaria is caused by protozoan parasites of the genus *Plasmodium*. It is exclusively transmitted by the bite of an infected **female Anopheles mosquito**, not *Aedes*. The life cycle of the malaria parasite involves a sexual cycle in the Anopheles mosquito (definitive host) and an asexual cycle in humans (intermediate host). **2. Why the other options are incorrect:** * **Chikungunya, Zika, and Dengue** are all viral infections (Arboviruses) primarily transmitted by **Aedes aegypti** and **Aedes albopictus**. * These mosquitoes are "day-biters" and typically breed in clean, stagnant water (e.g., flower pots, discarded tires). **Clinical Pearls for NEET-PG:** * **Aedes Mosquito:** Known as the "Tiger Mosquito" due to white stripes on its body. It is the vector for Dengue, Chikungunya, Zika, Yellow Fever, and Rift Valley Fever. * **Dengue:** Look for "break-bone fever" and retro-orbital pain in clinical vignettes. * **Zika:** High-yield association with **Microcephaly** in newborns and **Guillain-Barré Syndrome** in adults. * **Chikungunya:** Characterized by severe, often persistent, debilitating joint pain (arthritis). * **Malaria Vector:** *Anopheles stephensi* is the primary urban malaria vector in India, while *Anopheles culicifacies* is the major rural vector.

Question 940: Which of the following is always present in a virus?

A. Enzymes
B. Envelope
C. RNA or DNA (Correct Answer)
D. All of the above

Explanation: ### Explanation **Core Concept:** A virus is defined as an obligate intracellular parasite consisting of a genetic core surrounded by a protein coat (capsid). The defining characteristic of all viruses is the presence of a **nucleic acid genome**, which serves as the blueprint for replication. Crucially, a virus contains **either DNA or RNA**, but never both (with very rare exceptions like Mimiviruses, which are not typically tested in this context). **Analysis of Options:** * **C (Correct): RNA or DNA.** This is the essential genetic material required for viral survival and replication within a host cell. Whether it is single-stranded or double-stranded, a genome is a universal component of every virion. * **A (Incorrect): Enzymes.** While some viruses carry specific enzymes necessary for their life cycle (e.g., Reverse Transcriptase in HIV or RNA-dependent RNA polymerase in Influenza), many simple viruses rely entirely on the host cell's enzymatic machinery. * **B (Incorrect): Envelope.** Viruses are classified as either "enveloped" or "naked" (non-enveloped). Many clinically significant viruses, such as Adenovirus, Poliovirus, and Hepatitis A, lack a lipid envelope and consist only of a nucleocapsid. **High-Yield NEET-PG Pearls:** * **Smallest DNA Virus:** Parvovirus (Single-stranded DNA). * **Largest DNA Virus:** Poxvirus (Complex symmetry, replicates in the cytoplasm). * **RNA Virus Exception:** Most RNA viruses are single-stranded, except **Reoviridae** (e.g., Rotavirus), which is double-stranded. * **Naked Viruses:** Remember the mnemonic **"PAPP"** for DNA viruses (Parvo, Adeno, Papova, Polyoma) and **"CPR"** for RNA (Calici, Picorna, Reo). Naked viruses are generally more resistant to environmental disinfectants like alcohol and detergents.

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