Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 871: Which of the following statements regarding HIV infection is true?

A. Following needle stick injury, infectivity is reduced by the administration of nucleoside analogues. (Correct Answer)
B. CD4 counts are the best predictors of disease progression.
C. Infected T cells survive for a month in infected patients.
D. In the latent phase, HIV has minimal replication.

Explanation: **Explanation:** **1. Why Option A is Correct:** Post-exposure prophylaxis (PEP) is highly effective in reducing the risk of HIV transmission following a needle-stick injury. The standard regimen involves the administration of antiretroviral drugs, primarily **Nucleoside Reverse Transcriptase Inhibitors (NRTIs)** like Tenofovir and Emtricitabine, often combined with an Integrase Inhibitor. These drugs prevent the viral RNA from being reverse-transcribed into DNA, thereby halting the establishment of a permanent infection if started within 72 hours. **2. Why the Other Options are Incorrect:** * **Option B:** While CD4 counts indicate the current immune status and risk for opportunistic infections, **Plasma Viral Load (HIV RNA levels)** is the best predictor of the rate of disease progression and the risk of transmission. * **Option C:** Productively infected T cells have a very short half-life, typically surviving only **1.5 to 2 days**. The rapid turnover of these cells is a hallmark of the high replicative state of the virus. * **Option D:** The term "clinical latency" is a misnomer regarding viral activity. Even when the patient is asymptomatic, there is **persistent, active viral replication** occurring primarily within the lymphoid organs. It is not a state of viral "quiescence." **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **Best Screening Test:** ELISA (4th generation assays detect both p24 antigen and antibodies). * **Confirmatory Test:** Western Blot (historically) or HIV-1/HIV-2 differentiation immunoassays. * **PEP Timing:** Must be started as soon as possible, ideally within **2 hours**, and no later than **72 hours**. The duration of PEP is **28 days**.

Question 872: What is the term for the virus that causes rabies in humans?

A. Wild virus
B. Street virus (Correct Answer)
C. Fixed virus
D. All of the above

Explanation: **Explanation:** The classification of the Rabies virus into "Street" and "Fixed" strains is a fundamental concept in virology, primarily based on their source and biological behavior. **1. Why "Street Virus" is correct:** The term **Street virus** refers to the rabies virus as it exists in nature, isolated from naturally infected animals (like dogs, bats, or cats) or humans. It is characterized by a long and variable incubation period (usually 1–3 months) and the consistent production of **Negri bodies** (intracytoplasmic inclusion bodies) in the brain tissue. This is the strain responsible for causing clinical rabies in humans. **2. Why the other options are incorrect:** * **Fixed Virus (Option C):** This is a street virus that has been modified by serial passage through the brains of laboratory animals (usually rabbits). This process "fixes" the incubation period to a short, predictable duration (4–6 days). Crucially, fixed viruses are **not** found in nature, do not produce Negri bodies, and are used primarily for vaccine production. * **Wild Virus (Option A):** While "wild" is a general term used for viruses found in nature (like wild-type Polio), it is not the specific technical nomenclature used in Rabies virology to differentiate between natural and laboratory strains. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic for rabies; most commonly found in the **Hippocampus (Ammon’s horn)** and **Cerebellum (Purkinje cells)**. They are absent in infections caused by the Fixed virus. * **Genome:** Negative-sense, single-stranded RNA (ssRNA), bullet-shaped symmetry (Rhabdoviridae). * **Prophylaxis:** Post-exposure prophylaxis (PEP) includes wound cleaning, Rabies vaccine (Active), and Rabies Immunoglobulin (Passive). * **Antigenicity:** Both Street and Fixed viruses share the same surface G-protein antigens, which is why vaccines made from fixed strains protect against street virus exposure.

Question 873: Giant cell (Hecht's) pneumonia is due to which of the following?

A. Cytomegalovirus (CMV)
B. Measles virus (Correct Answer)
C. Malaria parasite
D. Pneumocystis carinii

Explanation: **Explanation:** **Giant cell pneumonia (Hecht’s pneumonia)** is a severe, often fatal interstitial pneumonia caused by the **Measles virus** (Rubeola). It typically occurs in immunocompromised individuals (e.g., those with leukemia, HIV, or severe malnutrition) who fail to develop the characteristic maculopapular rash due to impaired T-cell mediated immunity. 1. **Why Measles is correct:** The hallmark of Measles infection is the formation of **Warthin-Finkeldey giant cells**—large multinucleated cells with eosinophilic intranuclear and intracytoplasmic inclusion bodies. In the lungs, these cells lead to progressive alveolar damage, known as Hecht’s pneumonia. 2. **Why other options are incorrect:** * **CMV:** Causes interstitial pneumonia in transplant recipients, characterized by "Owl’s eye" intranuclear inclusions, but not Hecht’s giant cell pneumonia. * **Malaria:** Can cause Acute Respiratory Distress Syndrome (ARDS) in severe cases (especially *P. falciparum*), but does not produce giant cell pathology. * **Pneumocystis carinii (jirovecii):** Causes PCP pneumonia in HIV patients, characterized by a "crushed ping-pong ball" appearance on silver stain and "foamy" alveolar exudates, not multinucleated giant cells. **High-Yield Clinical Pearls for NEET-PG:** * **Warthin-Finkeldey cells:** Pathognomonic for Measles; found in lymphoid tissue and lungs. * **Koplik’s spots:** Small white spots on buccal mucosa (opposite lower 2nd molars); the earliest clinical sign of Measles. * **Vitamin A:** Supplementation reduces morbidity and mortality in children with Measles. * **SSPE (Subacute Sclerosing Panencephalitis):** A late neurological complication caused by a persistent mutant measles virus.

Question 874: Which of the following is true about the rash of chickenpox?

A. Centripetal (Correct Answer)
B. Deep seated
C. Affects palm
D. Slow to evolve

Explanation: The rash of **Chickenpox (Varicella-Zoster Virus)** is a classic high-yield topic in NEET-PG. Understanding its distribution and evolution is key to differentiating it from Smallpox. ### 1. Why "Centripetal" is Correct The distribution of chickenpox is **centripetal**, meaning the rash is most dense on the trunk and becomes more sparse towards the extremities (periphery). It typically begins on the trunk and spreads to the face and limbs. This is the opposite of Smallpox, which is centrifugal (denser on the face and limbs). ### 2. Why the Other Options are Incorrect * **Deep seated:** Chickenpox lesions are **superficial** and involve only the epidermis. They are often described as "dewdrops on a rose petal." In contrast, Smallpox lesions are deep-seated and firm. * **Affects palm:** Chickenpox characteristically **spares the palms and soles**. If a rash involves the palms and soles, clinicians should consider Smallpox, Syphilis, or Hand-Foot-Mouth Disease. * **Slow to evolve:** The evolution of chickenpox is **rapid**. Lesions progress from macule to papule to vesicle to scab within hours. This leads to **pleomorphism**, where different stages of the rash (vesicles, pustules, and scabs) are seen simultaneously in the same area. ### 3. Clinical Pearls for NEET-PG * **Pleomorphism:** This is the hallmark of Chickenpox (all stages of rash present at once). * **Starry Sky Appearance:** A descriptive term for the pleomorphic rash. * **Infectivity:** Patients are infectious from 48 hours before the rash appears until all vesicles have crusted over. * **Secondary Infection:** The most common complication in children is secondary bacterial infection (usually *Staph. aureus*). * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusion bodies.

Question 875: Which of the following viruses has negative-sense RNA?

A. Rabies (Correct Answer)
B. Reovirus
C. Coronavirus
D. Calicivirus

Explanation: **Explanation:** The classification of RNA viruses based on their genomic polarity is a high-yield topic for NEET-PG. RNA viruses are categorized as **Positive-sense (+ssRNA)**, which can be directly translated into proteins by host ribosomes, or **Negative-sense (-ssRNA)**, which must first be transcribed into positive-sense mRNA by a viral RNA-dependent RNA polymerase (RdRp). **Correct Answer: A. Rabies** Rabies virus belongs to the **Rhabdoviridae** family. All Rhabdoviruses possess a single-stranded, negative-sense RNA genome. Because the genome cannot be directly translated, the virion must carry its own RdRp enzyme to initiate the infection cycle within the host cell. **Incorrect Options:** * **B. Reovirus:** These are unique because they possess **double-stranded RNA (dsRNA)**. They are the only medically important dsRNA viruses (e.g., Rotavirus). * **C. Coronavirus:** These are **positive-sense (+ssRNA)** viruses. They have the largest genomes among RNA viruses and are enveloped with a helical nucleocapsid. * **D. Calicivirus:** These are **positive-sense (+ssRNA)**, non-enveloped viruses (e.g., Norovirus). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Negative-sense RNA viruses:** "**P**aired **O**ld **B**unny **F**ights **R**eally **A**musing **M**onsters" (**P**aramyxo, **O**rthomyxo, **B**unya, **F**ilo, **R**habdo, **A**rena, **M**yxo). * **Rabies Key Features:** Bullet-shaped morphology, Negri bodies (intracytoplasmic inclusions in Hippocampus/Purkinje cells), and centripetal spread via retrograde axonal transport. * All negative-sense RNA viruses are **enveloped** and carry their own **RNA polymerase**.

Question 876: The antibody class specific for infectious mononucleosis is:

A. IgA
B. IgD
C. IgM (Correct Answer)
D. IgG

Explanation: **Explanation:** Infectious Mononucleosis (IM) is primarily caused by the **Epstein-Barr Virus (EBV)**. The diagnosis relies on the detection of two types of antibodies: **Heterophile antibodies** and **EBV-specific antibodies**. **Why IgM is the correct answer:** The hallmark of an acute/primary infection is the presence of **IgM antibodies**. Specifically, **VCA-IgM (Viral Capsid Antigen IgM)** appears early in the infection, peaks within 4–8 weeks, and usually disappears within 3 months. Additionally, the **Monospot test** detects heterophile antibodies, which are also of the **IgM class**. These antibodies cause agglutination of non-human (sheep, horse, or bovine) red blood cells, a classic diagnostic feature of IM. **Analysis of Incorrect Options:** * **IgA:** Primarily involved in mucosal immunity. While EBV replicates in the oropharynx, IgA is not the standard diagnostic marker for acute IM. * **IgD:** Found in trace amounts in serum and functions mainly as a B-cell receptor; it has no diagnostic role in viral infections. * **IgG:** **VCA-IgG** appears shortly after IgM but persists for life, indicating past infection or immunity. It is not specific for an *acute* primary episode of IM. **High-Yield Clinical Pearls for NEET-PG:** * **Atypical Lymphocytes (Downey Cells):** These are activated T-cells (CD8+) seen on a peripheral smear, not B-cells. * **Paul-Bunnell Test:** A classic heterophile antibody test using sheep RBCs. * **EBNA (EBV Nuclear Antigen):** Antibodies to EBNA appear only after the acute phase (3–4 months) and signify convalescence. * **Ampicillin Rash:** Patients with IM often develop a maculopapular rash if treated with Ampicillin or Amoxicillin.

Question 877: Guarnieri's body is seen in which of the following conditions?

A. Chickenpox
B. Smallpox (Correct Answer)
C. Rubella
D. Measles

Explanation: **Explanation:** **Guarnieri bodies** are the hallmark histopathological finding in **Smallpox** (Variola virus) and Vaccinia virus infections. These are **intracytoplasmic, eosinophilic inclusion bodies** that represent "viral factories" where DNA replication and assembly occur. Since Poxviruses are unique among DNA viruses because they replicate entirely within the cytoplasm rather than the nucleus, they leave these distinct cytoplasmic imprints. **Analysis of Options:** * **Smallpox (Correct):** Guarnieri bodies are specific to the Poxvirus family. They are found in the epithelial cells of the skin in Smallpox patients. * **Chickenpox (Incorrect):** Caused by the Varicella-Zoster Virus (a Herpesvirus). It produces **Cowdry Type A** inclusion bodies, which are **intranuclear** and eosinophilic, often associated with multinucleated giant cells (Tzanck cells). * **Rubella (Incorrect):** A Togavirus that typically does not produce characteristic diagnostic inclusion bodies like Pox or Herpes viruses. * **Measles (Incorrect):** Caused by a Paramyxovirus. It is characterized by **Warthin-Finkeldey giant cells** and produces both **intracytoplasmic and intranuclear** inclusion bodies (Cowdry type A). **High-Yield NEET-PG Pearls:** * **Poxvirus:** Largest DNA virus; replicates in the **cytoplasm** (exception to the rule). * **Molluscum Contagiosum:** Another Poxvirus that shows **Henderson-Patterson bodies** (large, eosinophilic cytoplasmic inclusions). * **Negri Bodies:** Intracytoplasmic inclusions seen in **Rabies** (Hippocampus/Purkinje cells). * **Owl’s Eye Appearance:** Intranuclear inclusions seen in **CMV**. * **Torres Bodies:** Acidophilic cytoplasmic inclusions seen in **Yellow Fever**.

Question 878: Which of the following viruses has double-stranded nucleic acid in its genome?

A. Orthomyxoviruses and Parvoviruses
B. Poxviruses and Parvoviruses
C. Poxviruses and Reoviruses (Correct Answer)
D. Orthomyxoviruses and Reoviruses

Explanation: ### Explanation The classification of viruses based on their genomic structure is a high-yield topic for NEET-PG. Most DNA viruses are double-stranded (dsDNA), while most RNA viruses are single-stranded (ssRNA). However, there are notable exceptions that are frequently tested. **1. Why Option C is Correct:** * **Poxviruses:** These are the largest and most complex **dsDNA** viruses. Unlike most DNA viruses that replicate in the nucleus, Poxviruses replicate in the cytoplasm because they carry their own DNA-dependent RNA polymerase. * **Reoviruses:** This family (including *Rotavirus*) is the primary exception to the rule for RNA viruses, as they possess a **segmented dsRNA** genome. **2. Why Other Options are Incorrect:** * **Parvoviruses (Options A & B):** These are the smallest DNA viruses and are unique because they have a **ssDNA** genome (the "exception" to the dsDNA rule for DNA viruses). * **Orthomyxoviruses (Options A & D):** This family (including *Influenza*) consists of **ssRNA** viruses with a segmented genome. **3. High-Yield Clinical Pearls for NEET-PG:** * **DNA Exceptions:** All DNA viruses are dsDNA **except Parvoviridae** (ssDNA). All DNA viruses are icosahedral **except Poxviridae** (complex/brick-shaped). * **RNA Exceptions:** All RNA viruses are ssRNA **except Reoviridae** (dsRNA). * **Segmented Genomes:** Remember the mnemonic **BOAR** (Bunyavirus, Orthomyxovirus, Arenavirus, Reovirus). These viruses can undergo genetic reassortment, leading to antigenic shifts. * **Replication Site:** All DNA viruses replicate in the nucleus **except Poxvirus**. All RNA viruses replicate in the cytoplasm **except Influenza and Retroviruses**.

Question 879: The SA 14-14-2 strain is used in the preparation of which vaccine?

A. JE vaccine (Correct Answer)
B. Typhoid vaccine
C. Influenza vaccine
D. HPV vaccine

Explanation: **Explanation:** The **SA 14-14-2 strain** is a live-attenuated virus strain used globally for the production of the **Japanese Encephalitis (JE) vaccine**. Originally developed in China by passing the wild-type SA 14 strain through primary hamster kidney cells, it is now the most widely used JE vaccine in endemic regions, including India (under the Universal Immunization Programme). **Analysis of Options:** * **A. JE vaccine (Correct):** The SA 14-14-2 is a live-attenuated vaccine. Other JE vaccines include the inactivated mouse brain-derived (Nakayama strain) and the cell culture-derived inactivated vaccine (JENVAC using the Indian Kolar strain). * **B. Typhoid vaccine:** Common strains used for typhoid vaccines include **Ty21a** (oral live-attenuated) and the **Vi capsular polysaccharide** (injectable). * **C. Influenza vaccine:** These vaccines typically use strains recommended annually by the WHO (e.g., H1N1, H3N2, and Type B strains). Live-attenuated versions (LAIV) use cold-adapted, temperature-sensitive master donor viruses. * **D. HPV vaccine:** These are subunit vaccines made of **L1 virus-like particles (VLPs)**. Common brands include Gardasil (quadrivalent/nonavalent) and Cervarix (bivalent). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** JE is transmitted by the *Culex tritaeniorhynchus* mosquito (breeds in rice fields). * **Reservoir:** Pigs (amplifier hosts) and water birds (Ardeid birds). * **Diagnosis:** IgM Capture ELISA (MAC-ELISA) of CSF or serum is the gold standard. * **Vaccination Schedule:** Under India’s UIP, two doses are given at 9 months and 16–24 months of age.

Question 880: What is the primary pharmacological action of Flupiine?

A. Local Anesthetic
B. Analgesic (Correct Answer)
C. Anxiolytic
D. Antihypertensive

Explanation: **Explanation:** **Flupirtine** (often misspelled as Flupiine in some question banks) is a unique, centrally acting non-opioid **analgesic**. Its primary pharmacological action is categorized as a **Selective Neuronal Potassium Channel Opener (SNEPCO)**. 1. **Why the correct answer is right:** Flupirtine works by opening G-protein-coupled inwardly rectifying potassium channels. This leads to an efflux of potassium ions, causing hyperpolarization of the postsynaptic membrane. This stabilizes the resting membrane potential and inhibits the activation of NMDA receptors, effectively "shunting" neuronal excitability. This mechanism provides potent analgesia without the typical side effects associated with opioids (respiratory depression) or NSAIDs (gastric ulcers). 2. **Why the incorrect options are wrong:** * **Local Anesthetic:** These drugs (e.g., Lidocaine) primarily act by blocking voltage-gated sodium channels to prevent nerve impulse conduction, which is not the mechanism of Flupirtine. * **Anxiolytic:** While Flupirtine has muscle-relaxant properties due to its action on the spinal cord, it is not classified as an anxiolytic (like Benzodiazepines), which target GABA-A receptors. * **Antihypertensive:** Flupirtine does not have a significant effect on vascular smooth muscle or the autonomic nervous system to lower blood pressure. **High-Yield Clinical Pearls for NEET-PG:** * **Dual Action:** It acts as both an analgesic and a muscle relaxant. * **NMDA Antagonism:** It is an indirect NMDA receptor antagonist, making it useful in chronic pain and preventing "wind-up" phenomena. * **Safety Note:** A critical high-yield fact is that Flupirtine has been withdrawn in many regions (including the EU) due to its association with **drug-induced liver injury (hepatotoxicity)**. * **Note on Subject:** While the question is categorized under Virology here, Flupirtine is strictly a **Pharmacology** topic. Ensure you do not confuse it with antiviral drugs like Flumadine (Rimantadine).

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