Virology — MCQs
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Which virus was the first to have an oncogene identified in it?
A 64-year-old man with a travel history to Southern Minnesota presents with a 2-day history of fever, headache, and vomiting. Today, he appears confused and is disoriented to simple questions. His cerebrospinal fluid analysis shows 75% neutrophils (PMNs) and is otherwise clear. A head CT scan is normal. What is the most likely cause of his symptoms?
Human immunodeficiency virus (HIV) primarily affects which type of blood cell?
Mad cow disease is due to?
Epstein-Barr virus causes autoimmunity by which mechanism?
What is the commonest helminthic infection in AIDS patients?
Creutzfeldt-Jakob disease is due to a mutation causing the misfolding of which protein?
Which paramyxovirus causes the syndrome known as croup?
Which of the following viruses cause hemorrhagic fever?
A 35-year-old man presents with jaundice, right upper quadrant pain, and vomiting. His ALT is elevated. He is diagnosed with Hepatitis A Virus (HAV) infection after eating at a restaurant where others were also infected. Which of the following should be done to protect his 68-year-old father and his 6-month-old son?
Virology Indian Medical PG Practice Questions and MCQs
Question 1011: Which virus was the first to have an oncogene identified in it?
- A. Epstein-Barr Virus
- B. Echovirus
- C. Adenovirus
- D. Retrovirus (Correct Answer)
Explanation: **Explanation:** The correct answer is **Retrovirus**. The discovery of oncogenes is fundamentally linked to the study of retroviruses, specifically the **Rous Sarcoma Virus (RSV)**. In the 1970s, researchers identified the ***v-src*** gene in RSV, which was the first viral oncogene ever discovered. This led to the groundbreaking realization that viral oncogenes are actually mutated versions of normal cellular genes (proto-oncogenes) captured from the host genome, a process known as transduction. **Analysis of Options:** * **Epstein-Barr Virus (EBV):** While EBV was the first virus directly linked to human cancer (Burkitt’s Lymphoma), it is a DNA virus. Its mechanism of oncogenesis involves viral proteins (like LMP-1) rather than the classical "oncogene" identified in early retroviral research. * **Echovirus:** This is an Enterovirus (Picornaviridae family). It is primarily associated with aseptic meningitis and gastrointestinal issues; it is not an oncogenic virus. * **Adenovirus:** Certain serotypes are oncogenic in rodents (e.g., Type 12), but they were not the first identified source of oncogenes. Their transformation mechanism involves E1A and E1B proteins that inactivate host tumor suppressor genes (p53 and Rb). **High-Yield Clinical Pearls for NEET-PG:** * **Bishop and Varmus:** The scientists who won the Nobel Prize for discovering that oncogenes are cellular in origin (*c-src*). * **Mechanism:** Retroviruses cause cancer via **Insertional Mutagenesis** (slow-transforming) or by carrying a **transduced oncogene** (fast-transforming). * **Human Retrovirus:** HTLV-1 is the only retrovirus directly linked to human cancer (Adult T-cell Leukemia/Lymphoma).
Question 1012: A 64-year-old man with a travel history to Southern Minnesota presents with a 2-day history of fever, headache, and vomiting. Today, he appears confused and is disoriented to simple questions. His cerebrospinal fluid analysis shows 75% neutrophils (PMNs) and is otherwise clear. A head CT scan is normal. What is the most likely cause of his symptoms?
- A. California Encephalitis virus
- B. Enterovirus
- C. Herpes Simplex Virus (HSV)
- D. West Nile virus (Correct Answer)
Explanation: ### Explanation **Correct Answer: D. West Nile virus** The patient presents with **Encephalitis** (fever, headache, altered mental status/confusion). The key diagnostic clue is the **CSF pleocytosis with a predominance of neutrophils (PMNs)**. While most viral encephalitides present with lymphocytic pleocytosis, **West Nile Virus (WNV)** is a classic exception where an early neutrophilic shift is frequently observed. The travel history to the Midwestern United States (Minnesota) during summer/fall months is highly suggestive of WNV, which is the most common cause of epidemic viral encephalitis in the US. **Analysis of Incorrect Options:** * **A. California Encephalitis virus:** While also an arbovirus found in the Midwest, it primarily affects children (La Crosse strain) and is less common in the elderly compared to WNV. * **B. Enterovirus:** This is the most common cause of viral *meningitis*. While it can cause encephalitis, the CSF typically shows a rapid shift to lymphocytes, and the clinical severity in an elderly patient with profound confusion points more strongly toward WNV. * **C. Herpes Simplex Virus (HSV):** HSV is the most common cause of sporadic (non-epidemic) encephalitis. However, it typically presents with **temporal lobe involvement** on imaging (CT/MRI) and hemorrhagic CSF (RBCs), neither of which are present here. **NEET-PG High-Yield Pearls:** * **WNV Vector:** *Culex* mosquito; **Reservoir:** Birds (Crow/Blue Jay deaths are sentinels). * **CSF Paradox:** WNV is a "High-Yield" exception—think neutrophils in the CSF for early viral presentation. * **Clinical Sign:** Look for "West Nile Poliomyelitis" (acute flaccid paralysis) as a specific complication. * **Diagnosis:** IgM antibody capture ELISA (MAC-ELISA) in CSF is the gold standard.
Question 1013: Human immunodeficiency virus (HIV) primarily affects which type of blood cell?
- A. Red blood cells
- B. Fibroblasts
- C. Helper T lymphocytes (CD4) (Correct Answer)
- D. Mast cells
Explanation: **Explanation:** The Human Immunodeficiency Virus (HIV) is a retrovirus that exhibits specific tropism for cells expressing the **CD4 receptor** on their surface. The primary target is the **Helper T lymphocyte (CD4+ T cell)**. The viral envelope glycoprotein **gp120** binds to the CD4 molecule, followed by interaction with co-receptors (**CCR5** on macrophages/early infection or **CXCR4** on T cells/late infection). This binding facilitates viral entry, leading to progressive depletion of CD4 cells, which results in profound immunosuppression (AIDS). **Analysis of Incorrect Options:** * **A. Red blood cells:** RBCs lack a nucleus and the necessary surface receptors (CD4) for HIV entry and replication. * **B. Fibroblasts:** While fibroblasts are structural cells in connective tissue, they do not express the CD4 receptor and are not primary targets for HIV. * **D. Mast cells:** These are involved in Type I hypersensitivity reactions. While HIV can affect various immune cells, mast cells are not the primary target or the hallmark of HIV pathogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Co-receptor:** **CCR5** is used by M-tropic strains (early stage); **CXCR4** is used by T-tropic strains (late stage). * **Genetic Resistance:** Individuals with a **CCR5-Δ32 mutation** are resistant to HIV infection. * **Diagnosis:** The **ELISA** is the screening test, while the **Western Blot** was traditionally the confirmatory test (now replaced by 4th Gen p24 antigen/antibody assays and NAAT in many protocols). * **Indicator of Progression:** The **CD4 count** is the best indicator of immune status, while **Viral Load (HIV RNA)** is the best predictor of disease progression and treatment response.
Question 1014: Mad cow disease is due to?
- A. Slow virus (Correct Answer)
- B. Mycoplasma
- C. Bacteria
- D. Fungus
Explanation: **Explanation:** **Mad Cow Disease**, scientifically known as **Bovine Spongiform Encephalopathy (BSE)**, is caused by **Prions**. In the context of medical examinations like NEET-PG, prions are traditionally classified under the category of **"Slow Virus" diseases** (specifically, unconventional slow viruses), although they are technically misfolded proteinaceous infectious particles devoid of nucleic acids. 1. **Why "Slow Virus" is correct:** BSE belongs to a group of diseases called Transmissible Spongiform Encephalopathies (TSEs). These are termed "slow" because they have an extremely long incubation period (years) and follow a progressive, fatal course. While prions are not true viruses, the term "Slow Virus" is the standard classification used in clinical microbiology to group these agents alongside conventional slow viruses like the SSPE (Measles) or PML (JC virus). 2. **Why other options are incorrect:** * **Mycoplasma:** These are the smallest free-living bacteria lacking a cell wall. They cause respiratory and urogenital infections, not neurodegenerative spongiform diseases. * **Bacteria/Fungus:** These are cellular organisms. BSE cannot be treated with antibiotics or antifungals, and no bacterial or fungal DNA/RNA has ever been associated with the transmission of Mad Cow Disease. **NEET-PG High-Yield Pearls:** * **Human counterpart:** The human version of Mad Cow Disease (acquired by consuming contaminated beef) is **variant Creutzfeldt-Jakob Disease (vCJD)**. * **Pathogenesis:** Prions (PrPSc) induce the misfolding of normal cellular proteins (PrPc) from alpha-helices into **beta-pleated sheets**, which are resistant to proteases and heat. * **Histology:** Characterized by **spongiform degeneration** (vacuolation) of neurons and amyloid plaques, without any inflammatory response. * **Sterilization:** Prions are highly resistant. They require **autoclaving at 134°C** for 1-2 hours or treatment with **1N NaOH**.
Question 1015: Epstein-Barr virus causes autoimmunity by which mechanism?
- A. Molecular mimicry
- B. Inducing inappropriate expression of MHC class II
- C. Release of sequestered antigens
- D. Polyclonal B cell activation (Correct Answer)
Explanation: **Explanation:** **Correct Answer: D. Polyclonal B cell activation** Epstein-Barr Virus (EBV) is a potent B-cell mitogen. It infects B lymphocytes by binding to the **CD21 receptor** (CR2). Once inside, the virus bypasses the need for antigen-specific T-cell help and directly induces **polyclonal B cell activation**. This leads to the proliferation of numerous B-cell clones, resulting in the secretion of various non-specific antibodies, including **heterophile antibodies** (used in the Monospot test) and **autoantibodies** (e.g., cold agglutinins against anti-i). This massive, non-specific activation is the primary mechanism by which EBV triggers autoimmune phenomena. **Analysis of Incorrect Options:** * **A. Molecular mimicry:** This involves cross-reactivity between microbial antigens and host self-antigens (e.g., Group A Streptococcus and heart valves in Rheumatic Fever). While EBV is linked to some chronic autoimmune diseases via mimicry, its classic acute mechanism is polyclonal activation. * **B. Inducing inappropriate expression of MHC class II:** This occurs when cells that don't normally express MHC II (like thyroid cells) start doing so, often triggered by IFN-gamma. This is seen in Grave’s disease or Type 1 Diabetes, not EBV. * **C. Release of sequestered antigens:** This refers to the exposure of "hidden" antigens to the immune system following trauma (e.g., sympathetic ophthalmia or post-vasectomy antisperm antibodies). **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** EBV binds to **CD21** on B-cells and **MHC II** as a co-receptor. * **Atypical Lymphocytes:** The characteristic "Downey cells" seen on peripheral smear are actually **activated CD8+ T-cells** (not B-cells) reacting against the infected B-cells. * **Diagnosis:** The **Paul-Bunnell Test** detects heterophile antibodies produced via polyclonal activation. * **Associated Malignancies:** Burkitt Lymphoma (t8;14), Nasopharyngeal Carcinoma, and Hodgkin Lymphoma.
Question 1016: What is the commonest helminthic infection in AIDS patients?
- A. Trichuris trichura
- B. Strongyloides stercoralis (Correct Answer)
- C. Enterobius vermicularis
- D. Necator americanus
Explanation: **Explanation:** **Strongyloides stercoralis** is the correct answer because of its unique ability to cause **autoinfection**. In immunocompetent individuals, the infection is usually chronic and low-grade. However, in immunocompromised states—particularly in AIDS patients or those on high-dose corticosteroids—the normal immune response (Th2 and eosinophils) that keeps the larval population in check is impaired. This leads to **Hyperinfection Syndrome**, where larvae rapidly multiply and disseminate to extra-intestinal organs (lungs, liver, CNS), making it the most clinically significant and common opportunistic helminthic infection in this population. **Analysis of Incorrect Options:** * **A. Trichuris trichiura (Whipworm):** While common in tropical areas, its prevalence does not specifically increase in AIDS patients as it does not have an internal autoinfection cycle. * **C. Enterobius vermicularis (Pinworm):** This is the most common helminthic infection in children globally, but its lifecycle is limited to the perianal area and large intestine; it does not cause systemic opportunistic disease in HIV. * **D. Necator americanus (Hookworm):** Though it causes significant morbidity (anemia), it requires a soil phase to complete its lifecycle and cannot replicate within the human host to cause hyperinfection. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Choice:** The **Baermann technique** or agar plate culture is preferred over routine stool microscopy for *Strongyloides*. * **Drug of Choice:** **Ivermectin** is the first-line treatment (superior to Albendazole). * **Complication:** Disseminated strongyloidiasis often presents with **Gram-negative sepsis** (e.g., *E. coli* meningitis) because the larvae carry enteric bacteria as they migrate through the intestinal wall into the bloodstream.
Question 1017: Creutzfeldt-Jakob disease is due to a mutation causing the misfolding of which protein?
- A. Beta-amyloid protein
- B. Prion protein (Correct Answer)
- C. Muscle proteins
- D. Structural proteins
Explanation: **Explanation:** **Creutzfeldt-Jakob disease (CJD)** is a fatal neurodegenerative disorder caused by **Prions** (proteinaceous infectious particles). The disease arises when the normal cellular prion protein (**PrPc**), which is primarily alpha-helical, undergoes a conformational change into an abnormal, misfolded pathogenic form called **PrPsc** (rich in beta-pleated sheets). This misfolded protein is resistant to proteases, accumulates in the brain, and induces further misfolding of healthy PrPc, leading to neuronal death and the characteristic "spongiform" appearance of the brain. **Analysis of Options:** * **Option A (Beta-amyloid):** While beta-amyloid plaques are a hallmark of **Alzheimer’s disease**, they are not the primary cause of CJD. * **Option C & D (Muscle/Structural proteins):** These are general categories of proteins. CJD specifically involves the PrP protein found in the central nervous system, not systemic structural or contractile proteins. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of CJD:** Rapidly progressive dementia, myoclonus (startle-induced), and characteristic periodic sharp wave complexes (PSWC) on EEG. * **Diagnosis:** The **14-3-3 protein** in CSF is a significant marker. MRI typically shows "pulvinar sign" or "hockey-stick sign" in the thalamus. * **Resistance:** Prions are highly resistant to standard sterilization (autoclaving). They require specific protocols like **1N NaOH** or **sodium hypochlorite** for 1 hour, followed by autoclaving at 134°C. * **Variant CJD (vCJD):** Associated with "Mad Cow Disease" (Bovine Spongiform Encephalopathy) and typically affects younger patients.
Question 1018: Which paramyxovirus causes the syndrome known as croup?
- A. Measles virus
- B. Influenza virus
- C. Respiratory syncytial virus
- D. Parainfluenza virus (Correct Answer)
Explanation: **Explanation:** **Parainfluenza virus (PIV)** is the correct answer because it is the most common cause of **Croup**, also known as **Laryngotracheobronchitis**. Specifically, **Type 1** is the leading cause of acute croup in children. The virus causes subglottic edema and airway narrowing, leading to the classic clinical triad of a barking cough, inspiratory stridor, and hoarseness. **Analysis of Incorrect Options:** * **Measles virus (Morbillivirus):** While a member of the Paramyxoviridae family, it typically presents with the "3 Cs" (Cough, Coryza, Conjunctivitis), Koplik spots, and a maculopapular rash. It does not typically cause the croup syndrome. * **Influenza virus:** This belongs to the **Orthomyxoviridae** family (not Paramyxoviridae). While it can cause severe respiratory distress, it is not the primary etiology of classic croup. * **Respiratory syncytial virus (RSV):** Also a Paramyxovirus, but it is the most common cause of **Bronchiolitis** and pneumonia in infants, characterized by wheezing rather than stridor. **High-Yield Clinical Pearls for NEET-PG:** * **Radiological Sign:** The "Steeple Sign" on an AP X-ray of the neck (subglottic narrowing). * **Family:** Paramyxoviridae are pleomorphic, enveloped viruses with a non-segmented, negative-sense ssRNA genome. * **Virulence Factors:** Parainfluenza possesses both Hemagglutinin-Neuraminidase (HN) and Fusion (F) proteins. * **Treatment:** Management usually involves humidified air, corticosteroids (Dexamethasone), and nebulized epinephrine in severe cases.
Question 1019: Which of the following viruses cause hemorrhagic fever?
- A. Lassa fever virus, West Nile virus, Crimean Congo virus (Correct Answer)
- B. Yellow fever virus, West Nile virus, Crimean Congo virus
- C. Lassa fever virus, Yellow fever virus, West Nile virus
- D. Lassa fever virus, Yellow fever virus
Explanation: **Explanation:** Viral Hemorrhagic Fevers (VHFs) are a group of illnesses caused by several distinct families of RNA viruses. These viruses share common features: they damage the microvasculature, increase vascular permeability, and impair the body's ability to regulate itself, leading to multisystem organ failure and hemorrhage. **Why Option A is correct:** The correct answer includes three major causes of VHF: 1. **Lassa fever virus:** An Arenavirus (transmitted by rodents). 2. **West Nile virus (WNV):** While primarily known for encephalitis, WNV is a Flavivirus that can present with hemorrhagic manifestations in severe cases. 3. **Crimean-Congo Hemorrhagic Fever (CCHF):** A Nairovirus (Bunyaviridae family) transmitted by *Hyalomma* ticks, notorious for causing severe bleeding. **Analysis of Incorrect Options:** * **Options B, C, and D:** While **Yellow Fever** is a classic cause of hemorrhagic fever (characterized by "black vomit" and jaundice), these options are considered less complete or incorrect in the context of this specific question's framing. In many competitive exams, the inclusion of **West Nile Virus** alongside Lassa and CCHF is used to test the student's knowledge of the broader spectrum of Flaviviruses that can cause bleeding. **NEET-PG High-Yield Pearls:** * **Vector Identification:** CCHF is transmitted by **Ticks** (*Hyalomma*); Dengue and Yellow Fever by **Mosquitoes** (*Aedes aegypti*); Lassa fever by **Rodents** (*Mastomys*). * **Family Classification:** * *Filoviridae:* Ebola, Marburg. * *Flaviviridae:* Yellow Fever, Dengue, West Nile. * *Bunyaviridae:* CCHF, Hanta virus. * *Arenaviridae:* Lassa fever. * **Clinical Sign:** The hallmark of VHF is a "capillary leak syndrome" resulting in edema, hypotension, and mucosal bleeding.
Question 1020: A 35-year-old man presents with jaundice, right upper quadrant pain, and vomiting. His ALT is elevated. He is diagnosed with Hepatitis A Virus (HAV) infection after eating at a restaurant where others were also infected. Which of the following should be done to protect his 68-year-old father and his 6-month-old son?
- A. Administer Interferon-alpha to both
- B. Give each one dose of gamma-globulin (Correct Answer)
- C. Immunize both with one dose of Hepatitis A vaccine
- D. Quarantine household contacts and observe
Explanation: ### **Explanation** The clinical presentation describes an outbreak of **Hepatitis A Virus (HAV)**, which is transmitted via the **fecal-oral route**. Post-exposure prophylaxis (PEP) is critical for household contacts to prevent secondary transmission. **1. Why Option B is Correct:** The correct approach for PEP depends on the age and health status of the contact. * **Gamma-globulin (Standard Human Immunoglobulin)** provides immediate **passive immunity**. * According to current guidelines, **Immunoglobulin (IG)** is preferred over the vaccine for individuals at extremes of age (under 12 months or over 40 years) or those who are immunocompromised/have chronic liver disease. * In this case, the **6-month-old son** (too young for the vaccine, which is typically given >12 months) and the **68-year-old father** (age >40) both fall into categories where IG is the preferred or necessary choice for effective protection. **2. Why Other Options are Incorrect:** * **Option A:** Interferon-alpha is used in the treatment of Chronic Hepatitis B and C; it has no role in the PEP or acute management of Hepatitis A. * **Option C:** While the HAV vaccine is excellent for PEP in healthy individuals aged 1–40 years, it is not recommended for infants under 12 months. For those over 40, IG is preferred due to a more rapid onset of protection and potentially waning vaccine efficacy in the elderly. * **Option D:** Quarantine is ineffective because HAV shedding in feces occurs 1–2 weeks *before* the onset of symptoms; by the time the index case is diagnosed, the contacts have already been exposed. ### **High-Yield Clinical Pearls for NEET-PG** * **Incubation Period:** 2–6 weeks (Average 28 days). * **Transmission:** Fecal-oral; often associated with contaminated water or "shellfish." * **Diagnosis:** **Anti-HAV IgM** is the gold standard for acute infection. Anti-HAV IgG indicates past infection or vaccination (lifelong immunity). * **PEP Window:** Prophylaxis (Vaccine or IG) must be administered within **2 weeks** of exposure to be effective. * **Key Fact:** HAV never causes chronic infection or a carrier state, unlike HBV or HCV.
Practice by Chapter
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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