Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 331: The Hella cell line belongs to which category of cell culture?

A. Primary cell culture
B. Diploid cell strains
C. Continuous cell line (Correct Answer)
D. Tissue culture

Explanation: **Explanation:** The **HeLa cell line** is the most famous example of a **Continuous cell line** (also known as immortalized or established cell lines). These are derived from cancer cells or by transforming normal cells with oncogenic viruses or chemicals. 1. **Why "Continuous cell line" is correct:** Continuous cell lines are characterized by their ability to undergo **infinite subcultures** (immortality). HeLa cells were originally derived from a cervical carcinoma biopsy of a patient named Henrietta Lacks in 1951. Because they are malignant in nature, they have lost contact inhibition and can be maintained indefinitely in vitro, making them ideal for large-scale virus vaccine production and research. 2. **Why other options are incorrect:** * **Primary cell culture:** These are normal cells taken directly from an animal/human organ (e.g., Monkey kidney cells). They can only be subcultured once or twice before dying. * **Diploid cell strains:** These are cells that maintain a normal chromosome complement and can be subcultured about 50 times before undergoing senescence (e.g., WI-38, MRC-5). * **Tissue culture:** This is a broad, generic term encompassing all types of cell, organ, and protoplast cultures; it is not a specific category of cell line longevity. **High-Yield Facts for NEET-PG:** * **HeLa Cells:** Derived from Human Cervical Adenocarcinoma. * **Other Continuous Lines:** **HEp-2** (Human Epithelioma of Larynx), **Vero** (Vervet Monkey Kidney), **BHK-21** (Baby Hamster Kidney). * **Diploid Strains:** Used for producing human vaccines (e.g., Rabies, Rubella) because they are non-oncogenic. * **Cytopathic Effect (CPE):** The structural changes in host cells caused by viral invasion, often visualized using these cell lines.

Question 332: Mumps is caused by which type of virus?

A. Orthomyxovirus
B. Paramyxovirus (Correct Answer)
C. Rhinovirus
D. Epstein-Barr virus

Explanation: **Explanation:** **Mumps** is caused by the Mumps virus, which belongs to the genus *Rubulavirus* within the **Paramyxoviridae** family. These are pleomorphic, enveloped viruses containing a single-stranded, negative-sense RNA genome. The virus is primarily known for its tropism for glandular tissue (especially the parotid glands) and the central nervous system. **Analysis of Options:** * **Paramyxovirus (Correct):** This family includes Mumps, Measles (Morbilivirus), and Parainfluenza viruses. They possess a characteristic helical nucleocapsid and an envelope containing Hemagglutinin-Neuraminidase (HN) and Fusion (F) proteins. * **Orthomyxovirus (Incorrect):** This family includes the Influenza viruses. While similar to paramyxoviruses, they have a **segmented** genome, which allows for antigenic shift. * **Rhinovirus (Incorrect):** A member of the Picornaviridae family, these are small, non-enveloped RNA viruses and are the most common cause of the "common cold." * **Epstein-Barr virus (Incorrect):** A DNA virus belonging to the Herpesviridae family, primarily responsible for Infectious Mononucleosis. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by painful, usually bilateral, **parotid swelling**. * **Complications:** The most common complication in post-pubertal males is **orchitis** (usually unilateral, rarely leads to sterility). In females, **oophoritis** can occur. It is also a leading cause of **aseptic meningitis** and **acute pancreatitis**. * **Diagnosis:** Elevated serum **amylase** is a classic biochemical marker (due to parotitis or pancreatitis). * **Prevention:** Live attenuated vaccine (Jeryl Lynn strain) administered as part of the **MMR vaccine**.

Question 333: An AIDS patient is presenting with watery diarrhea. What could be the causative organism?

A. Candida
B. Vibrio cholerae
C. ETEC (Enterotoxigenic Escherichia coli)
D. Cryptosporidia (Correct Answer)

Explanation: **Explanation:** In an immunocompromised patient, particularly those with AIDS (CD4 count <200 cells/mm³), the most common cause of chronic, severe, watery diarrhea is **Cryptosporidium parvum**. **1. Why Cryptosporidia is correct:** Cryptosporidium is an acid-fast protozoan that infects the intestinal epithelium. While it causes self-limiting diarrhea in healthy individuals, it leads to life-threatening, voluminous, non-bloody watery diarrhea in AIDS patients due to the lack of T-cell mediated immunity. Diagnosis is typically made using **Modified Acid-Fast staining** (Kinyoun stain), which reveals bright red oocysts. **2. Why other options are incorrect:** * **Candida:** While common in AIDS (oral thrush, esophagitis), it rarely causes primary watery diarrhea. It is more associated with mucosal infections. * **Vibrio cholerae:** Causes "rice-water" stools through a toxin-mediated mechanism, but it is an acute epidemic infection and not specifically associated with the chronic immunosuppression of AIDS. * **ETEC:** A common cause of Traveler’s diarrhea. Like Cholera, it causes acute watery diarrhea but is not a characteristic opportunistic infection defining the clinical course of an AIDS patient. **Clinical Pearls for NEET-PG:** * **Other AIDS-related Diarrhea:** If CD4 <50, consider **Microsporidia** (very small spores) or **MAC (Mycobacterium avium complex)**. * **Staining:** Cryptosporidium, Isospora, and Cyclospora are all **Acid-Fast**. Cryptosporidium is the smallest (4-6 µm). * **Treatment:** In AIDS patients, the primary treatment is **HAART** (to boost CD4 count); Nitazoxanide has limited efficacy in severe immunosuppression.

Question 334: What is the characteristic pathological manifestation in Rabies?

A. Ventriculitis
B. Brainstem encephalitis (Correct Answer)
C. Basal ganglia affection
D. Meningitis

Explanation: **Explanation:** **1. Why Brainstem Encephalitis is Correct:** Rabies is caused by a neurotropic Rhabdovirus. After entering the peripheral nerves, the virus travels via retrograde axonal transport to the Central Nervous System (CNS). While the virus eventually involves the entire brain, its hallmark pathological manifestation is **encephalitis with a predilection for the brainstem, limbic system, and hippocampus.** The involvement of the brainstem (specifically the cranial nerve nuclei) explains the classic clinical symptoms of hydrophobia and aerophobia, which result from violent, involuntary spasms of the diaphragmatic, accessory respiratory, and pharyngeal muscles. **2. Why the Other Options are Incorrect:** * **Ventriculitis:** This refers to inflammation of the ventricular system, typically seen in bacterial meningitis or as a complication of neurosurgery/shunts. It is not a primary feature of Rabies. * **Basal Ganglia Affection:** While some viruses (like Japanese Encephalitis) specifically target the basal ganglia and thalamus, Rabies primarily targets the brainstem and hippocampus. * **Meningitis:** Rabies is a parenchymal disease (encephalitis). While mild meningeal irritation may occur, the core pathology is neuronal destruction and viral replication within the gray matter, not the meninges. **3. High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** The pathognomonic microscopic finding. These are eosinophilic, intracytoplasmic inclusion bodies found most commonly in the **Purkinje cells of the cerebellum** and **Pyramidal cells of the Hippocampus (Ammon’s horn).** * **Incubation Period:** Highly variable (usually 1–3 months), depending on the distance of the bite site from the CNS. * **Street Virus vs. Fixed Virus:** "Street virus" is the naturally occurring strain; "Fixed virus" is used for vaccine production (Pasteur). * **Diagnosis:** Post-mortem detection of Negri bodies or Antemortem detection via skin biopsy (nuchal area) for viral antigen.

Question 335: Which of the following microorganisms commonly shows antigenic drift in its pathogenicity?

A. Cholera
B. Diphtheria
C. Influenza virus (Correct Answer)
D. Plague

Explanation: **Explanation:** The correct answer is **C. Influenza virus**. **1. Why Influenza Virus is Correct:** Antigenic drift refers to the gradual accumulation of **point mutations** in the genes encoding surface glycoproteins, specifically **Hemagglutinin (HA)** and **Neuraminidase (NA)**. Because the viral RNA polymerase lacks proofreading capability, these minor genetic changes occur frequently. This results in altered viral strains that can partially evade the host’s preexisting immune system, necessitating the annual update of the influenza vaccine. This phenomenon occurs in Influenza types A, B, and C. **2. Why Other Options are Incorrect:** * **A, B, and D (Cholera, Diphtheria, and Plague):** These are bacterial pathogens (*Vibrio cholerae, Corynebacterium diphtheriae,* and *Yersinia pestis*). Unlike RNA viruses, bacteria have more stable genomes with DNA repair mechanisms. While they can undergo genetic variation (e.g., horizontal gene transfer or strain variation), they do not exhibit "antigenic drift," which is a specific virological term describing the mechanism of seasonal epidemic variation in viruses. **3. NEET-PG High-Yield Pearls:** * **Antigenic Drift:** Minor change (point mutations); causes **epidemics**; seen in Influenza A and B. * **Antigenic Shift:** Major change (genetic **reassortment** of segments); causes **pandemics**; seen **only in Influenza A** because it has a broad host range (humans, birds, pigs). * **Segmented Genome:** Influenza is an Orthomyxovirus with 8 RNA segments (Type A and B), which is the structural prerequisite for antigenic shift. * **Vaccine Strain Selection:** The WHO Global Influenza Surveillance and Response System monitors "drift" to decide the composition of the next season's quadrivalent vaccine.

Question 336: Hepatitis E infection spreads by which route?

A. Feco-oral route (Correct Answer)
B. Parenteral
C. Blood transfusion
D. Rectal

Explanation: **Explanation:** Hepatitis E Virus (HEV) is a non-enveloped, single-stranded RNA virus belonging to the *Hepeviridae* family. The primary mode of transmission for HEV (specifically genotypes 1 and 2) is the **feco-oral route**, typically through the consumption of contaminated water. This mirrors the transmission pattern of Hepatitis A Virus (HAV). * **Why Option A is correct:** HEV is excreted in the feces of infected individuals. In areas with poor sanitation, the virus enters the water supply, leading to large-scale waterborne outbreaks. * **Why Options B and C are incorrect:** While rare instances of parenteral transmission (blood transfusion) have been documented for HEV, they are not the primary or characteristic route of spread. Parenteral and blood-borne transmission are the hallmark routes for Hepatitis B, C, and D. * **Why Option D is incorrect:** Rectal transmission is not a recognized primary epidemiological route for HEV; it is specifically associated with waterborne ingestion. **High-Yield Clinical Pearls for NEET-PG:** * **Pregnancy Risk:** HEV is notorious for causing high mortality (up to 20%) in pregnant women, particularly during the third trimester, due to Fulminant Hepatic Failure. * **Zoonosis:** HEV genotypes 3 and 4 are zoonotic, often transmitted via undercooked pork or deer meat. * **Chronicity:** HEV is generally acute and self-limiting; however, chronic infection can occur in immunocompromised individuals (e.g., organ transplant recipients). * **Mnemonic:** Remember **"Vowels (A and E) hit the Bowel"** to recall that Hepatitis A and E are transmitted via the feco-oral route.

Question 337: Which of the following diseases shows centrifugal spread of rash?

A. Dengue
B. Smallpox (Correct Answer)
C. Rocky Mountain spotted fever
D. Erythema multiforme

Explanation: **Explanation:** The distribution of a rash is a high-yield clinical marker in virology. **Smallpox (Variola virus)** is characterized by a **centrifugal spread**, meaning the lesions are most dense on the distal extremities (palms and soles) and the face, with fewer lesions on the trunk. This is the opposite of Chickenpox (Varicella), which shows a centripetal distribution (concentrated on the trunk). In Smallpox, the rash also progresses synchronously (all lesions are at the same stage of development). **Analysis of Incorrect Options:** * **Dengue:** Typically presents with a "white islands in a sea of red" appearance—a generalized maculopapular rash that may have petechiae, but it does not follow a specific centrifugal pattern. * **Rocky Mountain Spotted Fever (RMSF):** While the rash begins on the wrists and ankles and spreads inward (centripetal), it is a rickettsial disease, not primarily classified by the same viral distribution terminology as Smallpox. * **Erythema Multiforme:** Characterized by "target" or "bulls-eye" lesions. While it often involves the extremities, it is an immune-mediated reaction rather than a classic infectious centrifugal exanthem. **High-Yield Clinical Pearls for NEET-PG:** * **Smallpox vs. Chickenpox:** Smallpox is **Centrifugal** (Extremities > Trunk) and **Synchronous**. Chickenpox is **Centripetal** (Trunk > Extremities), **Asynchronous** (pleomorphic), and spares the palms and soles. * **Deep-seated lesions:** Smallpox vesicles are firm, umbilicated, and deep-seated, whereas Varicella vesicles are superficial ("dewdrops on a rose petal"). * **Eradication:** Smallpox was officially declared eradicated by the WHO on May 8, 1980.

Question 338: What is the usual causative agent of infection in renal transplant patients?

A. Cytomegalovirus (CMV) (Correct Answer)
B. Human Immunodeficiency Virus (HIV)
C. Herpes Simplex Virus
D. Salmonella species

Explanation: **Explanation:** **Cytomegalovirus (CMV)** is the most common clinically significant viral pathogen in renal transplant recipients, typically manifesting within the first 1 to 6 months post-transplantation. The primary medical concept involves the **reactivation of latent virus** (sequestered in monocytes and macrophages) or transmission via the donor organ during a period of intense therapeutic immunosuppression. CMV is a major cause of morbidity, leading to "CMV syndrome" (fever, malaise, leucopenia) or tissue-invasive diseases like pneumonitis, hepatitis, and colitis. **Analysis of Incorrect Options:** * **HIV (Option B):** While HIV-positive patients can undergo transplants, HIV is not a "usual" causative agent of post-transplant infection; rather, it is a pre-existing condition or a rare transfusion/transplant-acquired risk. * **Herpes Simplex Virus (Option C):** HSV reactivation is common (causing mucocutaneous lesions), but it occurs less frequently and with less systemic severity than CMV in the modern era of prophylaxis. * **Salmonella species (Option D):** While transplant patients are at risk for intracellular bacterial infections, *Salmonella* is far less common than viral opportunistic infections like CMV. **NEET-PG High-Yield Pearls:** * **Timing:** CMV typically appears in the "middle period" (1–6 months) post-transplant. * **Diagnosis:** The gold standard for monitoring is **Quantitative PCR** for CMV DNA. Histopathology shows characteristic **"Owl’s eye" intranuclear inclusions**. * **Treatment:** **Valganciclovir** (prophylaxis/mild disease) and **Ganciclovir** (treatment of choice for active infection). * **Other Viral Risks:** **BK Virus** is another high-yield pathogen specifically linked to **ureteric stenosis and nephropathy** in renal transplants.

Question 339: A 33-year-old male with AIDS and a history of shingles develops a severe, multifocal encephalitis. Therapy is instituted with acyclovir, but the man dies on the fourth day of his hospital admission. Which of the following viruses is the most likely cause of his encephalitis?

A. Cytomegalovirus
B. Herpes simplex type I
C. Herpes simplex type II
D. Herpes zoster-varicella (Correct Answer)

Explanation: **Explanation:** The correct answer is **Herpes zoster-varicella (VZV)**. This diagnosis is clinically supported by the patient’s history of shingles (reactivation of VZV) and his immunocompromised state (AIDS). In HIV-positive patients, VZV can cause a severe, multifocal, and often fatal encephalitis or vasculopathy. While **Acyclovir** is the treatment of choice, mortality remains high in advanced immunosuppression if therapy is delayed. **Analysis of Options:** * **Cytomegalovirus (CMV):** While CMV is a common cause of encephalitis in AIDS (typically when CD4 <50), it usually presents as a subacute periventricular encephalitis or ventriculitis rather than a multifocal pattern following a history of shingles. * **Herpes simplex type I (HSV-1):** This is the most common cause of sporadic fatal encephalitis in the general population, typically localized to the **temporal lobes**. It does not specifically correlate with a prior history of shingles. * **Herpes simplex type II (HSV-2):** In adults, HSV-2 is more commonly associated with **aseptic meningitis** rather than severe multifocal encephalitis, though it can cause encephalitis in neonates. **Clinical Pearls for NEET-PG:** * **VZV Encephalitis:** Look for the triad of **HIV/Immunosuppression + History of dermatomal rash (shingles) + Neurological deficit.** * **Imaging:** VZV often shows multifocal small and large infarcts (vasculopathy) at the gray-white matter junction. * **HSV-1 Key Fact:** Characterized by hemorrhagic necrosis of the temporal lobes and "Cowdry Type A" intranuclear inclusion bodies. * **Treatment:** High-dose intravenous Acyclovir is the gold standard for both HSV and VZV encephalitis.

Question 340: During pre-operative investigations, a man was found to have positive serological results for HIV. Which of the following is a highly specific test for HIV antibodies in this patient?

A. ELISA
B. Southern blot
C. Northern blot
D. Western blot (Correct Answer)

Explanation: **Explanation:** The diagnosis of HIV infection traditionally follows a two-step algorithm: a highly sensitive screening test followed by a **highly specific confirmatory test**. **1. Why Western Blot is correct:** Western blot is the "gold standard" confirmatory test for HIV antibodies. It involves the separation of specific HIV proteins (antigens) by electrophoresis, which are then reacted with the patient's serum. It is considered highly specific because it detects antibodies against multiple specific viral components, such as **gp120/160, gp41 (envelope), and p24 (gag)**. A positive result requires the presence of antibodies against at least two or three of these specific bands, virtually eliminating false positives. **2. Why other options are incorrect:** * **ELISA (Enzyme-Linked Immunosorbent Assay):** This is the standard **screening test**. While it is highly sensitive (to ensure no cases are missed), it has a lower specificity than Western blot and can yield false positives in conditions like autoimmune diseases or recent vaccinations. * **Southern blot:** This technique is used to detect specific **DNA** sequences. It is not used for routine HIV antibody testing. * **Northern blot:** This technique is used to detect specific **RNA** sequences. While HIV is an RNA virus, Northern blot is a research tool and not a clinical diagnostic test for HIV antibodies. **Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 3–12 weeks). * **Screening vs. Confirmation:** Screening = ELISA (High Sensitivity); Confirmation = Western Blot (High Specificity). * **Diagnosis in Infants:** In infants <18 months (due to maternal IgG), the test of choice is **PCR (DNA PCR)** to detect the proviral DNA, not antibody tests. * **Current Protocol:** Many modern labs now use the **4th Generation p24 Antigen-Antibody Immunoassay** followed by HIV-1/HIV-2 differentiation assays, often bypassing the traditional Western blot.

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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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Virology — MCQs

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