Virology — MCQs
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An outbreak of diarrhea occurred among elderly patients in an assisted care facility, which had been repeatedly cited by the public health department for poor hygiene practices. The agent that caused the infections had a star-like morphology in electron micrographs. Enzyme immunoassay (EIA) tests for several agents of viral gastroenteritis were negative. Which virus was most likely responsible for this outbreak?
Polio virus infection can result in all of the following except?
What is the most common complication of rubella?
Hepatitis A virus is best diagnosed by which of the following methods?
Genital warts (condyloma acuminata) are most commonly caused by which of the following serotypes of HPV?
Which is an unenveloped ssRNA virus?
Australia antigen is associated with which of the following?
Which of the following is the ideal culture medium for pox virus?
Burkitt's lymphoma is characterized by elevated "early antigen" tests with a restricted pattern of fluorescence. This disease is caused by which of the following agents?
Epstein Barr virus is associated with all EXCEPT?
Virology Indian Medical PG Practice Questions and MCQs
Question 121: An outbreak of diarrhea occurred among elderly patients in an assisted care facility, which had been repeatedly cited by the public health department for poor hygiene practices. The agent that caused the infections had a star-like morphology in electron micrographs. Enzyme immunoassay (EIA) tests for several agents of viral gastroenteritis were negative. Which virus was most likely responsible for this outbreak?
- A. Adenovirus 40/41
- B. Astrovirus (Correct Answer)
- C. Hepatitis A virus (HAV)
- D. Norovirus
Explanation: ### Explanation **Correct Answer: B. Astrovirus** The diagnosis is based on the classic morphological description and the clinical context. 1. **Morphology:** The term "Astrovirus" is derived from the Greek word *astron* (star). Under electron microscopy (EM), these viruses exhibit a characteristic **5- or 6-pointed star-like appearance**. 2. **Clinical Context:** While Astroviruses are a common cause of pediatric diarrhea, they are notorious for causing outbreaks in **elderly populations** and institutionalized settings (nursing homes/assisted care) due to waning immunity and poor hygiene. 3. **Diagnostic Clue:** The question mentions that EIA tests for "several agents" were negative. While EIA exists for Astrovirus, it is less commonly included in standard rapid panels compared to Rotavirus or Adenovirus, often requiring EM or RT-PCR for definitive diagnosis in outbreak settings. **Analysis of Incorrect Options:** * **A. Adenovirus 40/41:** These are the enteric serotypes. On EM, they show a typical **icosahedral** shape with fibers (spikes), not a star shape. * **C. Hepatitis A:** While transmitted via the fecal-oral route, HAV causes hepatitis (jaundice, elevated ALT/AST), not a primary diarrheal outbreak. * **D. Norovirus:** This is the most common cause of adult gastroenteritis outbreaks (often on cruise ships). However, on EM, Noroviruses have a **"cup-shaped"** depression (Calicivirus family) or a "ragged" surface, not a distinct star shape. **NEET-PG High-Yield Pearls:** * **Astrovirus:** Star-shaped; (+)ssRNA, non-enveloped; causes outbreaks in children and the elderly. * **Rotavirus:** Wheel-like appearance (*Rota* = wheel); most common cause of severe diarrhea in infants worldwide. * **Norovirus:** Most common cause of viral gastroenteritis outbreaks in all ages; associated with cruise ships and raw shellfish. * **Sapovirus:** Also a Calicivirus; shows a "Star of David" configuration on EM (often confused with Astrovirus, but Astrovirus is the classic "star" answer in exams).
Question 122: Polio virus infection can result in all of the following except?
- A. Anterior horn cell damage
- B. Autonomic involvement
- C. Respiratory involvement
- D. Paralysis in more than 70% of cases (Correct Answer)
Explanation: **Explanation:** The correct answer is **D (Paralysis in more than 70% of cases)** because Poliovirus infection is characterized by a high rate of subclinical or asymptomatic infections. In reality, **paralytic polio occurs in less than 1%** of all infected individuals. **Breakdown of Clinical Outcomes:** * **Inapparent/Asymptomatic (90–95%):** Most common outcome. * **Abortive Polio/Minor Illness (4–8%):** Non-specific febrile illness. * **Non-paralytic Polio/Aseptic Meningitis (1–2%):** Meningeal signs without paralysis. * **Paralytic Polio (<1%):** The rarest but most severe form. **Why other options are incorrect:** * **Option A:** Poliovirus has a specific tropism for the **Anterior Horn Cells** of the spinal cord. Destruction of these lower motor neurons leads to the characteristic flaccid paralysis. * **Option B:** While primarily affecting motor neurons, severe cases (especially bulbar polio) can involve the **autonomic nervous system**, leading to blood pressure fluctuations and tachycardia. * **Option C:** **Respiratory involvement** is a major complication caused by either paralysis of the intercostal muscles and diaphragm (spinal polio) or damage to the respiratory centers in the medulla (bulbar polio). **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route (most common). * **Specimen of choice:** Stool (virus is excreted for weeks). * **Type of Paralysis:** Asymmetrical, descending, **Flaccid** paralysis with preserved sensory functions. * **Post-Polio Syndrome:** Occurs decades later due to the death of over-exerted surviving neurons. * **Vaccines:** Salk (IPV - Killed) and Sabin (OPV - Live attenuated). Sabin is superior for inducing **local intestinal immunity (IgA)**.
Question 123: What is the most common complication of rubella?
- A. Polyarthritis (Correct Answer)
- B. Encephalitis
- C. Orchitis
- D. Thrombocytopenia
Explanation: **Explanation:** **Rubella (German Measles)** is a viral infection caused by the Rubivirus (Togaviridae family). While generally a mild illness in children, it presents differently in adults, particularly females. **Why Polyarthritis is correct:** Arthralgia and **polyarthritis** are the most common complications of Rubella, occurring in up to 70% of adult females. It typically involves the small joints of the hands (PIP, MCP), wrists, and knees. The pathogenesis is thought to be immune-mediated (deposition of immune complexes) rather than direct viral invasion. It usually appears shortly after the rash and is self-limiting, resolving within a few weeks without permanent joint damage. **Why the other options are incorrect:** * **Encephalitis:** This is a rare but serious complication (1 in 6,000 cases). It is much less common than joint involvement. * **Orchitis:** This is a classic complication of **Mumps**, not Rubella. * **Thrombocytopenia:** Post-infectious thrombocytopenic purpura can occur (1 in 3,000 cases), but it is significantly rarer than polyarthritis. **NEET-PG High-Yield Pearls:** * **Incubation Period:** 14–21 days. * **Forchheimer Spots:** Small, red petechiae on the soft palate (seen in 20% of cases; not pathognomonic). * **Lymphadenopathy:** Post-auricular and sub-occipital lymphadenopathy is a hallmark clinical feature. * **Congenital Rubella Syndrome (CRS):** The most serious consequence if contracted during the first trimester. The classic triad includes **Cataract, Sensorineural deafness, and PDA (Patent Ductus Arteriosus).** * **Gregg’s Triad:** Another name for the CRS triad.
Question 124: Hepatitis A virus is best diagnosed by which of the following methods?
- A. IgM antibodies in serum (Correct Answer)
- B. Isolation from stool
- C. Culture from blood
- D. Isolation from bile
Explanation: **Explanation:** The diagnosis of acute Hepatitis A Virus (HAV) infection relies primarily on serology because the clinical symptoms usually coincide with the peak of the immune response rather than the peak of viral shedding. **Why Option A is Correct:** The detection of **IgM anti-HAV antibodies** in serum is the gold standard for diagnosing acute infection. These antibodies appear early in the course of the disease (usually at the onset of symptoms and jaundice), remain detectable for 3 to 6 months, and are highly sensitive and specific. IgG anti-HAV, conversely, indicates past infection or immunity. **Why Other Options are Incorrect:** * **B. Isolation from stool:** While HAV is shed in feces, viral shedding is maximal *before* the onset of symptoms (during the late incubation period). By the time a patient presents with jaundice, fecal shedding has significantly declined, making stool isolation unreliable for routine diagnosis. * **C & D. Culture from blood/bile:** HAV is rarely isolated from blood (viremia is transient and short-lived) or bile in clinical practice. Furthermore, HAV is notoriously difficult to grow in conventional cell cultures, making viral isolation impractical for diagnostic purposes. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route (most common). * **Incubation Period:** 2–6 weeks (Average: 28 days). * **Prognosis:** HAV never causes chronic hepatitis or a carrier state. It is usually self-limiting but can rarely cause fulminant hepatic failure. * **Vaccination:** Killed vaccine is available; it is recommended for travelers to endemic areas and patients with chronic liver disease. * **Post-exposure Prophylaxis:** Single dose of HAV vaccine or Immunoglobulin (IG) within 2 weeks of exposure.
Question 125: Genital warts (condyloma acuminata) are most commonly caused by which of the following serotypes of HPV?
- A. HPV 6 (Correct Answer)
- B. HPV 16
- C. HPV 18
- D. HPV 33
Explanation: **Explanation:** Human Papillomavirus (HPV) is a double-stranded DNA virus with over 100 serotypes, categorized based on their oncogenic potential. **1. Why HPV 6 is correct:** HPV serotypes **6 and 11** are classified as **"Low-risk" HPV**. They are responsible for approximately 90% of cases of **Condyloma acuminata** (anogenital warts). These lesions are benign epithelial proliferations and rarely progress to malignancy. HPV 6 is the most frequently isolated strain in these clinical presentations. **2. Why the other options are incorrect:** * **HPV 16 & 18 (Options B and C):** These are **"High-risk" HPV** types. They are strongly associated with intraepithelial neoplasia and are the primary causes of **Cervical Cancer**, as well as oropharyngeal, anal, and vulvar cancers. HPV 16 is the most common high-risk type worldwide. * **HPV 33 (Option D):** This is also a high-risk serotype associated with cervical dysplasia and carcinoma, but it is less common than types 16 and 18 and does not typically cause benign genital warts. **Clinical Pearls for NEET-PG:** * **Low-risk (Warts):** HPV 6, 11 (also cause Recurrent Respiratory Papillomatosis). * **High-risk (Cancer):** HPV 16, 18, 31, 33, 45. * **Skin Warts (Verruca vulgaris):** HPV 1, 2, 3, 4. * **Koilocytes:** The hallmark cytological finding in HPV infection (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Vaccination:** The quadrivalent vaccine (Gardasil) targets types 6, 11, 16, and 18.
Question 126: Which is an unenveloped ssRNA virus?
- A. Hepatitis B virus (HBV)
- B. Hepatitis E virus (HEV) (Correct Answer)
- C. Hepatitis C virus (HCV)
- D. None of the above
Explanation: ### Explanation The correct answer is **Hepatitis E virus (HEV)**. To master Hepatitis viruses for NEET-PG, it is essential to categorize them based on their genomic structure and the presence of an envelope. **1. Why Hepatitis E is correct:** Hepatitis E is a **non-enveloped (naked)** virus with a **single-stranded, positive-sense RNA (ssRNA)** genome. It belongs to the *Hepeviridae* family. Because it lacks a lipid envelope, it is stable in the environment and resistant to bile, allowing it to be transmitted via the **fecal-oral route**. **2. Analysis of Incorrect Options:** * **Hepatitis B virus (HBV):** This is the only DNA hepatitis virus. It is a **double-stranded DNA (dsDNA)** virus and is **enveloped**. * **Hepatitis C virus (HCV):** While HCV is an **ssRNA** virus (Flaviviridae), it is **enveloped**. The presence of an envelope makes it fragile, necessitating transmission through blood and body fluids (parenteral) rather than the fecal-oral route. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Envelopes:** Remember **"Vowels are Bowels."** Hepatitis **A** and **E** are transmitted via the fecal-oral route and are **non-enveloped** (naked). All others (B, C, D) are enveloped. * **Mnemonic for Genome:** All Hepatitis viruses are **RNA**, except for Hepatitis **B** (DNA). * **HEV in Pregnancy:** HEV infection is associated with high mortality (up to 20%) in pregnant women due to fulminant hepatic failure. * **Zoonosis:** HEV genotype 3 is commonly associated with the consumption of undercooked pork.
Question 127: Australia antigen is associated with which of the following?
- A. Hepatitis B surface antigen in acute hepatitis (Correct Answer)
- B. AIDS
- C. Chronic leukemia
- D. Basal cell carcinoma
Explanation: **Explanation:** **Australia Antigen (HBsAg)** is the surface antigen of the Hepatitis B virus (HBV). It was first discovered by **Baruch Blumberg** in 1965 in the serum of an Australian Aborigine, which led to its name. 1. **Why Option A is correct:** The Australia antigen is synonymous with **HBsAg**. It is the first serological marker to appear in the blood after HBV infection (appearing even before the onset of clinical symptoms). Its presence indicates that the individual is infectious, whether the infection is acute or chronic. In **acute hepatitis B**, it typically disappears within 4–6 months; persistence beyond 6 months defines a chronic carrier state. 2. **Why the other options are incorrect:** * **B. AIDS:** Caused by the Human Immunodeficiency Virus (HIV). While HBV and HIV share similar transmission routes (blood-borne, sexual), Australia antigen is specific to HBV. * **C. Chronic Leukemia:** There is no diagnostic association between Australia antigen and leukemia. However, patients with leukemia are often immunocompromised and may be at higher risk for HBV if they receive multiple blood transfusions. * **D. Basal Cell Carcinoma:** This is a skin malignancy primarily linked to UV radiation exposure, not viral antigens. **High-Yield Clinical Pearls for NEET-PG:** * **Dane Particle:** The complete infectious virion of HBV (42 nm). * **Window Period:** The interval during which HBsAg has disappeared but Anti-HBs has not yet appeared. The only marker present during this time is **Anti-HBc IgM**. * **Screening:** HBsAg is the primary marker used for screening blood donors to prevent transfusion-associated hepatitis. * **Ground-glass Hepatocytes:** The characteristic histological finding in chronic HBV infection due to the accumulation of HBsAg in the endoplasmic reticulum.
Question 128: Which of the following is the ideal culture medium for pox virus?
- A. Cell culture
- B. Chorio-allantoic membrane
- C. Hela cell line (Correct Answer)
- D. Organ culture
Explanation: **Explanation:** The **Poxviruses** (including Variola and Vaccinia) are the largest and most complex viruses. While they can be grown in various systems, the **HeLa cell line** is considered an ideal and highly efficient medium for their cultivation in modern laboratory settings. **Why HeLa cell line is correct:** Poxviruses have a unique replication cycle; unlike most DNA viruses, they replicate entirely within the **host cell cytoplasm**. Continuous cell lines like **HeLa** (derived from cervical cancer cells) provide a stable, rapidly dividing environment that supports high-titer viral replication. They are preferred for studying viral entry, protein synthesis, and morphogenesis due to their consistency and ease of maintenance compared to primary tissues. **Analysis of other options:** * **Chorio-allantoic membrane (CAM):** Historically, this was the standard method for Poxvirus cultivation. Variola produces small, white, non-necrotic pocks, while Vaccinia produces large, necrotic pocks. While still used for differentiation, it has been largely superseded by cell cultures for routine propagation. * **Cell culture (General):** While technically true, "HeLa cell line" is a more specific and "ideal" answer in the context of standardized virology examinations. * **Organ culture:** This involves growing viruses in intact organ slices (e.g., tracheal rings). It is specialized and rarely used for Poxviruses, which grow readily in simpler systems. **High-Yield NEET-PG Pearls:** * **Guarnieri Bodies:** These are eosinophilic intracytoplasmic inclusion bodies seen in cells infected with Variola/Vaccinia. * **Replication:** Poxvirus is the only DNA virus that replicates in the **cytoplasm** because it carries its own DNA-dependent RNA polymerase. * **Morphology:** Described as "brick-shaped" under electron microscopy.
Question 129: Burkitt's lymphoma is characterized by elevated "early antigen" tests with a restricted pattern of fluorescence. This disease is caused by which of the following agents?
- A. Cytomegalovirus
- B. Borrelia burgdorferi
- C. Epstein-Barr virus (Correct Answer)
- D. Lymphogranuloma venereum
Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, a member of the Gammaherpesvirinae family (HHV-4), is the causative agent of Burkitt’s lymphoma. The diagnosis often relies on serological markers. In EBV-infected cells, the **Early Antigen (EA)** is produced during the lytic cycle. * **Restricted pattern (EA-R):** Fluorescence is restricted to the cytoplasm. This pattern is highly characteristic of **Burkitt’s lymphoma**. * **Diffuse pattern (EA-D):** Fluorescence is seen in both the nucleus and cytoplasm, typically associated with **Infectious Mononucleosis** and **Nasopharyngeal Carcinoma**. **Analysis of Incorrect Options:** * **A. Cytomegalovirus (CMV):** While a herpesvirus (HHV-5), it is associated with "Owl’s eye" intranuclear inclusions and infectious mononucleosis-like syndrome (heterophile negative), not Burkitt’s lymphoma. * **B. Borrelia burgdorferi:** This is a spirochete causing Lyme disease, characterized by Erythema chronicum migrans, not viral oncogenesis. * **D. Lymphogranuloma venereum (LGV):** Caused by *Chlamydia trachomatis* (serotypes L1-L3), it presents with genital ulcers and painful inguinal lymphadenopathy (Groove sign). **High-Yield Clinical Pearls for NEET-PG:** * **Translocation:** Burkitt’s lymphoma is classically associated with **t(8;14)**, involving the **c-myc** oncogene. * **Histology:** Shows a characteristic **"Starry-sky appearance"** (macrophages containing apoptotic debris amidst a sea of neoplastic B-cells). * **Other EBV Associations:** Oral Hairy Leukoplakia (in HIV), Hodgkin’s Lymphoma (Mixed cellularity type), and Duncan’s syndrome (X-linked lymphoproliferative disorder). * **Receptor:** EBV binds to B-cells via the **CD21** receptor (CR2).
Question 130: Epstein Barr virus is associated with all EXCEPT?
- A. Hodgkin's disease
- B. Burkitt's lymphoma
- C. Nasopharyngeal carcinoma
- D. Laryngeal carcinoma (Correct Answer)
Explanation: **Explanation:** The correct answer is **D. Laryngeal carcinoma**. Epstein-Barr Virus (EBV), also known as Human Herpesvirus 4 (HHV-4), is a potent oncogenic virus with a strong tropism for B-lymphocytes and epithelial cells. While EBV is implicated in several head and neck malignancies, **Laryngeal carcinoma** is primarily associated with risk factors like chronic smoking, alcohol consumption, and Human Papillomavirus (HPV) types 16 and 18, rather than EBV. **Analysis of Options:** * **A. Hodgkin’s Disease:** EBV is found in approximately 40-50% of Hodgkin’s cases, particularly the Mixed Cellularity subtype. The virus expresses LMP-1 (Latent Membrane Protein), which mimics CD40 signaling to drive B-cell proliferation. * **B. Burkitt’s Lymphoma:** This is the classic association, especially the **Endemic (African)** form, where EBV is found in nearly 100% of cases. It involves the characteristic t(8;14) translocation of the c-myc oncogene. * **C. Nasopharyngeal Carcinoma:** This is strongly linked to EBV, particularly the undifferentiated type (Type III). It is highly prevalent in Southern China and is characterized by elevated titers of IgA antibodies against EBV viral capsid antigen (VCA). **High-Yield Clinical Pearls for NEET-PG:** * **Other EBV Associations:** Infectious Mononucleosis (Glandular fever), Oral Hairy Leukoplakia (in HIV patients), and Gastric Carcinoma (approx. 10%). * **Diagnostic Marker:** Heterophile antibodies (Monospot Test) are positive in Infectious Mononucleosis but negative in other EBV-related malignancies. * **Receptor:** EBV enters B-cells via the **CD21** receptor (also the receptor for C3d complement component). * **Atypical Lymphocytes:** Known as **Downey cells**, these are actually activated T-cells (CD8+) reacting against the EBV-infected B-cells.
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Virus Structure and Classification
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Viral Replication
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Pathogenesis of Viral Infections
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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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HIV and Retroviruses
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Oncogenic Viruses
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