Virology — MCQs
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Which of the following is true about Rotavirus?
Progressive multifocal leukoencephalopathy (PML) is caused by which of the following viruses?
An 18-month-old child developed acute gastroenteritis with fever and watery diarrhea that lasted 10 days. She had been vaccinated against rotavirus at 2 and 4 months of age as recommended. Eight days later, both of her brothers, ages 3 and 6, developed acute gastroenteritis. Which of the following tests would most likely reveal the etiologic agent of their gastroenteritis?
All of the following statements about Lambda phage are true, EXCEPT:
What is the epidemiological marker of Hepatitis B?
All the following are modes of transmission of rabies, EXCEPT:
The HIV virus can be destroyed in vitro by which of the following methods?
Which of the following is an HIV gene?
What is the incubation period of rubella?
Epstein-Barr virus (EBV) primarily infects which type of cell?
Virology Indian Medical PG Practice Questions and MCQs
Question 841: Which of the following is true about Rotavirus?
- A. Commonly affects children (Correct Answer)
- B. Double stranded DNA virus
- C. Can be grown easily on cell culture
- D. Egg shell appearance under electron microscope
Explanation: **Explanation:** **Rotavirus** is the most common cause of severe, dehydrating diarrhea in infants and young children worldwide (typically aged 6 months to 2 years). It belongs to the *Reoviridae* family. 1. **Why Option A is correct:** Rotavirus primarily targets the mature enterocytes of the villi in the small intestine. Due to the lack of pre-existing immunity and the specific pathophysiology of the NSP4 enterotoxin, **children** are the most susceptible population. By age 5, nearly every child has been infected at least once. 2. **Why other options are incorrect:** * **Option B:** Rotavirus is a **Double-stranded RNA (dsRNA)** virus, not DNA. It is characterized by a segmented genome (11 segments), which allows for genetic reassortment. * **Option C:** Rotavirus is notoriously **difficult to grow** in standard cell cultures. It requires the addition of proteolytic enzymes like trypsin to the medium to enhance infectivity and viral replication. * **Option D:** Under an electron microscope, Rotavirus has a characteristic **"Wheel-like" appearance** (derived from the Latin *Rota*, meaning wheel), with a distinct inner and outer capsid rim and radiating spokes. "Egg-shell appearance" is not a recognized description for this virus. **High-Yield Clinical Pearls for NEET-PG:** * **NSP4 Protein:** Acts as a viral enterotoxin that induces calcium-dependent chloride secretion, leading to secretory diarrhea. * **Diagnosis:** Latex agglutination or ELISA for detecting VP6 antigen in stools. * **Vaccines:** Live attenuated oral vaccines (Rotarix, RotaTeq, and the indigenous Rotavac) are part of the Universal Immunization Programme (UIP) in India. * **Seasonality:** More common in winter months (winter diarrhea).
Question 842: Progressive multifocal leukoencephalopathy (PML) is caused by which of the following viruses?
- A. Cytomegalovirus (CMV)
- B. Papovavirus (Correct Answer)
- C. Human Immunodeficiency Virus (HIV)
- D. Poliovirus
Explanation: **Explanation:** **Correct Option: B. Papovavirus** Progressive Multifocal Leukoencephalopathy (PML) is a demyelinating disease of the Central Nervous System caused by the **JC virus** (John Cunningham virus). The JC virus belongs to the **Polyomavirus** family. Historically, the families *Papillomaviridae* and *Polyomaviridae* were grouped together under the name **Papovavirus** (PA-pilloma, PO-lyoma, VA-cuolating virus). In PML, the JC virus infects and destroys **oligodendrocytes** (the cells responsible for myelin production in the CNS), leading to multifocal areas of demyelination. This typically occurs in severely immunocompromised patients, such as those with AIDS or those on monoclonal antibody therapies (e.g., Natalizumab). **Incorrect Options:** * **A. Cytomegalovirus (CMV):** While CMV is a common opportunistic infection in HIV patients, it typically causes retinitis, esophagitis, or encephalitis (periventricular calcifications), not PML. * **C. Human Immunodeficiency Virus (HIV):** HIV is the most common *predisposing factor* for PML due to immunosuppression, but the direct causative agent of the demyelination is the JC virus. HIV itself causes HIV-associated dementia (HAD). * **D. Poliovirus:** This is an enterovirus that targets the **anterior horn cells** of the spinal cord, leading to lower motor neuron paralysis, not white matter demyelination. **High-Yield Clinical Pearls for NEET-PG:** * **JC Virus:** "Junction of Gray and White matter" – PML typically involves the subcortical white matter. * **MRI Finding:** Classic "scalloped" appearance of hyperintense lesions on T2/FLAIR images without mass effect or enhancement. * **Diagnosis:** Detection of JC virus DNA in CSF via PCR or brain biopsy showing enlarged nuclei with viral inclusions in oligodendrocytes. * **Association:** Strongly linked to **Natalizumab** (used in Multiple Sclerosis) and **Rituximab**.
Question 843: An 18-month-old child developed acute gastroenteritis with fever and watery diarrhea that lasted 10 days. She had been vaccinated against rotavirus at 2 and 4 months of age as recommended. Eight days later, both of her brothers, ages 3 and 6, developed acute gastroenteritis. Which of the following tests would most likely reveal the etiologic agent of their gastroenteritis?
- A. Culture for Norovirus
- B. DFA for enterovirus on intestinal biopsy
- C. EIA for adenovirus 40/41 (Correct Answer)
- D. EM examination of stool for astrovirus
Explanation: **Explanation:** The clinical presentation of prolonged watery diarrhea (10 days) in a child already vaccinated against Rotavirus, followed by secondary cases in older siblings, strongly points towards **Enteric Adenoviruses (Serotypes 40 and 41)**. **1. Why Option C is Correct:** * **Duration:** While Rotavirus and Norovirus typically cause diarrhea lasting 3–7 days, Adenovirus gastroenteritis is notorious for a longer duration, often persisting for **8–12 days**. * **Vaccination Status:** The child was vaccinated against Rotavirus, making it a less likely culprit. * **Diagnosis:** Enzyme Immunoassay (EIA) or Latex Agglutination are the standard, rapid diagnostic methods used to detect Adenovirus 40/41 antigens directly from stool samples. **2. Why Other Options are Incorrect:** * **Option A:** Norovirus is the most common cause of viral gastroenteritis outbreaks, but it **cannot be routinely cultured** in clinical settings. Diagnosis is typically via RT-PCR. * **Option B:** Enteroviruses (like Polio or Coxsackie) primarily cause systemic or respiratory illness; they are shed in the stool but are **not** common causes of primary gastroenteritis. Biopsy is unnecessarily invasive. * **Option D:** While Electron Microscopy (EM) can identify Astrovirus (star-shaped), it is a labor-intensive, expensive tool not used for routine diagnosis. Astrovirus usually causes milder, shorter-lived symptoms. **Clinical Pearls for NEET-PG:** * **Adenovirus 40/41:** Belongs to Subgenus F. It is the second most common cause of infantile viral diarrhea after Rotavirus. * **Key Differentiator:** If the question mentions diarrhea lasting **>7 days** in a vaccinated child, think Adenovirus. * **Norovirus:** Associated with "Cruise ships," "Institutional outbreaks," and "projectile vomiting." It is the #1 cause of gastroenteritis in all ages. * **Rotavirus:** Characterized by "Wheels" (Rota) on EM; most common in children <2 years.
Question 844: All of the following statements about Lambda phage are true, EXCEPT:
- A. In the lysogenic phase, it integrates with the host chromosome and remains dormant.
- B. In the lytic phase, it replicates and produces new phage particles.
- C. Both the lytic and lysogenic phases occur simultaneously. (Correct Answer)
- D. In the lytic phase, it causes host cell lysis and releases progeny virus particles.
Explanation: **Explanation** Lambda phage is the classic example of a **temperate bacteriophage**, capable of two distinct life cycles: the **Lytic cycle** and the **Lysogenic cycle**. The decision between these two pathways is governed by a genetic "switch" (primarily the competition between *cI* repressor and *Cro* proteins). **1. Why Option C is the correct answer (The "Except" statement):** The lytic and lysogenic cycles are **mutually exclusive** processes within a single host cell. Once the phage DNA enters the bacterium, it either integrates into the host genome (Lysogeny) or immediately hijacks the cellular machinery to replicate (Lysis). They cannot occur simultaneously because the molecular signals required for one (e.g., *cI* protein for lysogeny) actively inhibit the genes required for the other. **2. Analysis of other options:** * **Option A:** True. In lysogeny, the phage DNA integrates into the *E. coli* chromosome at a specific site (*attB*) and is called a **prophage**. It remains dormant and replicates along with the host DNA. * **Option B & D:** True. The lytic phase is the productive/virulent stage. The phage replicates its genome, synthesizes capsids, assembles new virions, and eventually induces cell lysis via enzymes (holins/endolysins) to release progeny. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Lysogenic Conversion:** This is a high-yield clinical concept where a non-pathogenic bacterium acquires virulence factors via a temperate phage. Examples include **Diphtheria toxin** (*Corynebacterium diphtheriae*), **Cholera toxin**, **Shiga toxin**, and **Erythrogenic toxin** (GAS). * **Induction:** A lysogenic phage can switch to the lytic cycle if the host cell undergoes stress (e.g., UV light exposure), damaging the *cI* repressor. * **Transduction:** Lambda phage is associated with **Specialized Transduction**, where only specific genes adjacent to the integration site are transferred.
Question 845: What is the epidemiological marker of Hepatitis B?
- A. HBsAg (Correct Answer)
- B. Anti-HBs
- C. Anti-HBc
- D. HBeAg
Explanation: ### Explanation **Hepatitis B Surface Antigen (HBsAg)** is the correct answer because it is the first serological marker to appear in the blood after infection (even before symptoms or biochemical changes). In epidemiological studies, HBsAg is used to determine the **prevalence** of HBV in a population and to identify both acute and chronic carriers. Its presence for more than 6 months defines a chronic carrier state. **Analysis of Incorrect Options:** * **Anti-HBs (HBsAb):** This antibody indicates **immunity** to HBV, either through successful vaccination or recovery from a natural infection. It is not used as a marker for active disease prevalence. * **Anti-HBc (HBcAb):** This is a marker of **exposure**. IgM anti-HBc indicates recent/acute infection (and is the only marker positive during the "window period"), while IgG anti-HBc indicates past exposure. * **HBeAg:** This is a marker of **active viral replication and high infectivity**. While clinically significant for assessing the risk of transmission, it is not the primary epidemiological tool for screening populations. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The interval when HBsAg disappears but Anti-HBs has not yet appeared. **IgM anti-HBc** is the diagnostic marker here. * **Screening:** HBsAg is the standard marker for screening blood donors. * **Vaccine Response:** A person vaccinated against HBV will be **Anti-HBs positive** but **Anti-HBc negative** (since the vaccine contains only the surface antigen). * **Infectivity:** HBeAg and HBV-DNA levels are the best indicators of a patient's level of infectivity.
Question 846: All the following are modes of transmission of rabies, EXCEPT:
- A. Person to person transmission
- B. Aerosol
- C. Ingestion of products made from infected animals (Correct Answer)
- D. Licks
Explanation: **Explanation:** The correct answer is **C (Ingestion of products made from infected animals)**. Rabies virus is highly labile and is inactivated by gastric acid and digestive enzymes. Therefore, the consumption of cooked meat or pasteurized milk from a rabid animal does not transmit the disease. While raw milk consumption is theoretically discouraged, there are no documented cases of human rabies resulting from ingestion. **Analysis of Options:** * **Licks (Option D):** This is a common mode of transmission. If the saliva of a rabid animal comes into contact with pre-existing cuts, abrasions, or intact mucous membranes (eyes, mouth), the virus can enter the peripheral nerves. * **Aerosol (Option B):** This is a rare but documented route. It occurs in specific high-viral-load environments, such as laboratory accidents or among cave explorers (spelunkers) exposed to high concentrations of aerosolized bat droppings/secretions. * **Person to person (Option A):** While extremely rare, this is a recognized mode of transmission. It primarily occurs through **corneal or solid organ transplants** from undiagnosed infected donors. Although saliva contains the virus, no cases of transmission via biting between humans have been definitively proven. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Usually 1–3 months (highly variable depending on the site of the bite; shorter if closer to the CNS). * **Pathognomonic Feature:** **Negri bodies** (intracytoplasmic eosinophilic inclusions) found in the hippocampus (Ammon’s horn) and cerebellum (Purkinje cells). * **Classification:** Rabies is a **Lyssavirus** (Rhabdoviridae family) with a characteristic **bullet-shaped** morphology. * **Post-Exposure Prophylaxis (PEP):** Includes wound washing (most critical step), Rabies Vaccine (Day 0, 3, 7, 14, 28), and Rabies Immunoglobulin (RIG) for Category III bites.
Question 847: The HIV virus can be destroyed in vitro by which of the following methods?
- A. Boiling
- B. Ethanol
- C. Cidex
- D. All of the above (Correct Answer)
Explanation: **Explanation:** The Human Immunodeficiency Virus (HIV) is an **enveloped RNA virus**. In virology, the presence of a lipid envelope makes a virus highly susceptible to environmental factors and chemical disinfectants, as the disruption of this lipid bilayer renders the virus non-infectious. * **Boiling (Heat):** HIV is thermolabile. It is inactivated by heating at 56°C for 30 minutes. Standard boiling (100°C) destroys the virus almost instantaneously. * **Ethanol:** Alcohols (70% ethyl alcohol or isopropyl alcohol) act by dissolving the lipid envelope and denaturing structural proteins. HIV is rapidly inactivated by standard clinical concentrations of ethanol. * **Cidex (Glutaraldehyde):** This is a high-level disinfectant used for heat-sensitive medical equipment. A 2% glutaraldehyde solution effectively kills HIV by alkylating protein and nucleic acid groups. **Why "All of the above" is correct:** Because HIV is an enveloped virus, it lacks the environmental stability of non-enveloped viruses (like Hepatitis A or Polio). It is easily neutralized by heat, common alcohols, and standard hospital disinfectants. **High-Yield Clinical Pearls for NEET-PG:** 1. **Preferred Disinfectant for Spills:** For blood or body fluid spills contaminated with HIV, **Sodium Hypochlorite (1% freshly prepared solution)** is the agent of choice. 2. **Resistance:** HIV is resistant to ionizing radiation and ultraviolet light, but highly sensitive to pH changes (pH <1 or >13). 3. **Housekeeping:** Standard household bleach, 70% alcohol, and 2% glutaraldehyde are all effective for surface and instrument decontamination.
Question 848: Which of the following is an HIV gene?
- A. Gp73
- B. P24
- C. GP120 (Correct Answer)
- D. Gp5
Explanation: **Explanation:** The HIV genome consists of three structural genes: **gag, pol, and env**. The **env (envelope) gene** encodes a precursor protein, **gp160**, which is cleaved by host proteases into two subunits: **gp120** (surface glycoprotein) and **gp41** (transmembrane glycoprotein). **Why GP120 is correct:** GP120 is the surface spikes of the virus. It is responsible for the initial attachment of HIV to the host cell by binding to the **CD4 receptor** and co-receptors (CCR5 or CXCR4). Since it is encoded directly by the viral *env* gene, it is a primary HIV gene product. **Analysis of Incorrect Options:** * **P24 (Option B):** While p24 is a vital HIV protein (the nucleocapsid/core protein), it is a **protein product** of the *gag* gene, not the gene itself. However, in the context of this question, GP120 is the most specific "envelope gene" product often tested. *Note: If the question asks for the earliest marker of infection, p24 is the correct answer.* * **Gp73 (Option A):** This is a Golgi membrane protein often used as a serum marker for hepatocellular carcinoma; it is not related to HIV. * **Gp5 (Option D):** This is typically associated with the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), not human pathogens. **High-Yield Clinical Pearls for NEET-PG:** 1. **gp120:** Responsible for **tropism** and attachment (CD4 binding). It shows high antigenic variation. 2. **gp41:** Responsible for **fusion** and internalisation. The drug **Enfuvirtide** inhibits this. 3. **p24:** The earliest detectable serological marker (Window period) and used in 4th generation ELISA. 4. **pol gene:** Encodes essential enzymes: Reverse Transcriptase, Integrase, and Protease.
Question 849: What is the incubation period of rubella?
- A. 18-72 hours
- B. 2-3 weeks (Correct Answer)
- C. 1-3 months
- D. More than 1 year
Explanation: **Explanation:** The correct answer is **B. 2-3 weeks**. Rubella (German Measles) is caused by the Rubella virus, a member of the *Togaviridae* family [1]. The incubation period typically ranges from **14 to 21 days**, with an average of 18 days. During this period, the virus replicates in the nasopharynx and regional lymph nodes, followed by viremia and subsequent spread to the skin and other organs. **Analysis of Options:** * **Option A (18-72 hours):** This is characteristic of respiratory viruses with localized infections, such as Influenza or Common Cold (Rhinovirus), which have very short incubation periods. * **Option C (1-3 months):** This is typical for Hepatitis B, Hepatitis C, or Rabies (depending on the bite site). Rubella presents much faster than this. * **Option D (More than 1 year):** This is seen in "slow virus" infections like Subacute Sclerosing Panencephalitis (SSPE) or Prion diseases (Kuru, CJD). **High-Yield Clinical Pearls for NEET-PG:** * **Triad of Congenital Rubella Syndrome (CRS):** Sensorineural deafness (most common), Cataracts, and Patent Ductus Arteriosus (PDA) [1]. * **Forchheimer Spots:** Small, red petechiae on the soft palate (also seen in Scarlet fever). * **Infectivity:** Patients are most infectious from 7 days before to 7 days after the onset of the rash. * **Diagnosis:** IgM antibodies are the gold standard for acute infection; RT-PCR can be used for prenatal diagnosis via amniotic fluid. * **Vaccination:** Live attenuated **RA 27/3 strain** is used (part of the MMR vaccine). It is contraindicated in pregnancy. * **Clinical Stages:** Symptoms often include a prodromal phase of mild fever followed by a three-day maculopapular rash spreading from the face downwards [2].
Question 850: Epstein-Barr virus (EBV) primarily infects which type of cell?
- A. T-cells
- B. Monocytes
- C. B-cells (Correct Answer)
- D. Eosinophils
Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), has a specific tropism for **B-lymphocytes**. The virus gains entry into these cells by binding its viral envelope glycoprotein (gp350/220) to the **CD21 receptor** (also known as CR2 or the C3d complement receptor) located on the surface of B-cells. Once inside, EBV establishes a latent infection, leading to B-cell proliferation and immortalization. **Analysis of Options:** * **B-cells (Correct):** As mentioned, CD21 is the primary receptor for EBV. This interaction is the hallmark of EBV pathogenesis, leading to Infectious Mononucleosis and various B-cell malignancies. * **T-cells:** While EBV can rarely infect T-cells (leading to specific T-cell lymphomas), they are not the primary target. However, the characteristic "Atypical Lymphocytes" (Downey cells) seen on a blood smear in EBV infection are actually **activated CD8+ T-cells** reacting against the infected B-cells. * **Monocytes & Eosinophils:** These cells do not possess the CD21 receptor and are not the primary site of EBV infection or latency. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** EBV binds to **CD21** on B-cells and **MHC Class II** as a co-receptor. * **Diagnosis:** Heterophile antibody test (**Monospot test**) is the gold standard for screening. * **Associated Malignancies:** Burkitt Lymphoma (t[8;14]), Nasopharyngeal Carcinoma, Hodgkin Lymphoma, and Oral Hairy Leukoplakia (in HIV). * **Morphology:** Look for **Downey cells** (Atypical lymphocytes with abundant cytoplasm indenting around RBCs).
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