Virology Practice Questions

Q: Which of the following is NOT included in the picornavirus group?

Hepatitis E virus (HEV). **Explanation:** The **Picornaviridae** family consists of small (pico), non-enveloped, positive-sense single-stranded RNA viruses. **Why Hepatitis E Virus (HEV) is the correct answer:** Hepatitis E virus was previously classified under Picornaviridae due to its similar morphology. However, it is now classified in its own family, **Hepeviridae** (Genus: *Orthohepevirus*). Unlike picornaviruses, HEV has a unique genomic organization and is the only major hepatitis virus that is "quasi-enveloped" in the blood but non-enveloped in feces. **Analysis of Incorrect Options:** * **Poliovirus:** A classic member of the *Enterovirus* genus within the Picornaviridae family. It is the causative agent of paralytic poliomyelitis. * **Foot and Mouth Disease Virus (FMDV):** Belonging to the *Aphthovirus* genus, it is a highly infectious picornavirus affecting cloven-hoofed animals; it is historically significant as the first animal virus discovered. * **Encephalomyocarditis Virus (EMCV):** A member of the *Cardiovirus* genus within Picornaviridae, known for causing encephalitis and myocarditis in a wide range of mammalian hosts. **High-Yield Clinical Pearls for NEET-PG:** * **Picornavirus Mnemonic (PERCH):** **P**olio, **E**cho, **R**hino, **C**oxsackie, and **H**epatitis A. * **Hepatitis E Key Fact:** It is the most common cause of acute viral hepatitis worldwide and carries a high mortality rate (up to 20%) in **pregnant women** due to fulminant hepatic failure. * **Rhinovirus:** The only picornavirus that is **acid-labile** (destroyed by stomach acid), which is why it causes respiratory infections rather than GI disease.

Q: What is the first virological marker following acute Hepatitis B infection?

HBsAg. **Explanation:** **Hepatitis B Surface Antigen (HBsAg)** is the correct answer because it is the **first detectable virological marker** in the serum following an acute infection. It typically appears 2 to 8 weeks before the onset of clinical symptoms (jaundice) and biochemical evidence of liver damage (elevated ALT). Its presence indicates that the individual is infectious. **Analysis of Incorrect Options:** * **IgM Anti-HBc (Option A):** This is the first **antibody** to appear. It is crucial for diagnosing acute infection during the "window period" (when HBsAg has disappeared but Anti-HBs hasn't appeared yet). However, it appears after HBsAg. * **Anti-HBs (Option C):** This antibody appears during the recovery phase after HBsAg disappears. It signifies immunity (either from past infection or vaccination). * **Anti-HBe (Option D):** This antibody appears after the disappearance of HBeAg. It indicates a transition from high infectivity to a low-replicative state. **High-Yield Clinical Pearls for NEET-PG:** * **First marker to appear:** HBsAg. * **First antibody to appear:** IgM Anti-HBc. * **Marker of Infectivity:** HBeAg (indicates active viral replication). * **Window Period Marker:** IgM Anti-HBc is the only positive marker. * **Marker of Vaccination:** Only Anti-HBs is positive (HBsAg and Anti-HBc will be negative). * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months.

Q: Malaise and fatigue with increased "atypical" lymphocytes and a reactive heterophil antibody test is most commonly caused by?

Epstein-Barr virus. **Explanation:** The clinical presentation of malaise, fatigue, and fever, combined with the presence of **atypical lymphocytes** (Downey cells) and a **positive heterophil antibody test** (Monospot test), is the classic triad for **Infectious Mononucleosis (IM)**, most commonly caused by the **Epstein-Barr Virus (EBV)**. 1. **Why EBV is correct:** EBV infects B-lymphocytes via the CD21 receptor. In response, the body produces cytotoxic T-cells (CD8+) to control the infection; these activated T-cells appear as "atypical lymphocytes" on a peripheral smear. The virus also induces polyclonal B-cell activation, leading to the production of **heterophil antibodies** (antibodies that agglutinate sheep or horse RBCs), which is the diagnostic hallmark of EBV-induced IM. 2. **Why other options are incorrect:** * **Toxoplasma:** Can cause a mononucleosis-like syndrome but is **heterophil-negative**. * **Borrelia burgdorferi:** The causative agent of Lyme disease, typically presenting with erythema migrans (bull’s eye rash), arthritis, or neurological symptoms, not heterophil-positive IM. * **Parvovirus (B19):** Causes Erythema Infectiosum (Fifth disease) characterized by a "slapped-cheek" rash or aplastic crisis in patients with hemolytic anemia. **High-Yield NEET-PG Pearls:** * **Paul-Bunnell Test:** The specific heterophil antibody test used for EBV diagnosis. * **CMV:** The most common cause of **heterophil-negative** mononucleosis. * **Ampicillin Rash:** Patients with EBV-IM who are mistakenly treated with Ampicillin or Amoxicillin often develop a characteristic maculopapular rash. * **Atypical Lymphocytes:** These are NOT infected B-cells; they are **reactive T-cells** (CD8+).

Q: Antigenic drift and antigenic shift are characteristic features of which virus?

Influenza A virus. **Explanation:** The correct answer is **Influenza A virus**. This virus belongs to the Orthomyxoviridae family and possesses a **segmented RNA genome** (8 segments), which is the structural basis for its unique genetic variations: 1. **Antigenic Drift:** These are **point mutations** in the genes coding for Hemagglutinin (HA) and Neuraminidase (NA). This occurs in both Influenza A and B, leading to seasonal epidemics and necessitating the annual update of the flu vaccine. 2. **Antigenic Shift:** This is a major change involving **genetic reassortment** between different strains (e.g., human and avian) infecting the same cell. This only occurs in **Influenza A** because it infects multiple species (birds, pigs, humans). This results in a new subtype, leading to **pandemics**. **Analysis of Incorrect Options:** * **Swine flu virus (H1N1):** While H1N1 undergoes these processes, it is a specific *subtype* of Influenza A. In medical exams, the broader category "Influenza A" is the standard answer as it encompasses all subtypes capable of shifting. * **Rotavirus:** Although it has a segmented genome (11 segments) and can undergo reassortment, the specific terms "antigenic drift/shift" are classically reserved for Influenza nomenclature in clinical virology. * **Herpes virus:** This is a DNA virus. DNA viruses have proofreading mechanisms and do not undergo rapid antigenic variation or reassortment like segmented RNA viruses. **High-Yield Clinical Pearls for NEET-PG:** * **Pandemics** are caused by **Shift**; **Epidemics** are caused by **Drift**. * Influenza **B** only undergoes **Drift** (no animal reservoir). * The site of Influenza virus replication is unique: it is an RNA virus that replicates in the **nucleus**. * **Amantadine** inhibits the M2 ion channel; **Oseltamivir** inhibits Neuraminidase.

Q: Which statement is incorrect regarding the hepatitis B virus?

It is transmitted via the fecal-oral route.. ### Explanation **1. Why Option B is the correct (incorrect statement):** Hepatitis B Virus (HBV) is **not** transmitted via the fecal-oral route. It is primarily transmitted through parenteral routes (blood transfusion, contaminated needles), sexual contact, and vertical transmission (mother to child). Fecal-oral transmission is characteristic of **Hepatitis A and E** ("The vowels hit the bowels"). **2. Analysis of other options:** * **Option A (DNA Virus):** HBV is a member of the *Hepadnaviridae* family. It is the only DNA virus among the major hepatitis viruses (A, B, C, D, and E are all RNA viruses). * **Option C (Perinatal transmission):** This is a major route of transmission, especially in endemic areas. If a mother is HBeAg positive, the risk of transmission to the neonate is as high as 90%. * **Option D (Reverse Transcriptase):** HBV has a unique replication cycle. Its genome is partially double-stranded DNA (dsDNA). It uses an enzyme called **RNA-dependent DNA polymerase (Reverse Transcriptase)** to transcribe its genomic DNA from an intermediate RNA template (pre-genome). **3. High-Yield Clinical Pearls for NEET-PG:** * **Structure:** HBV is a 42 nm particle known as the **Dane particle**. * **Serology Marker of Infectivity:** The presence of **HBeAg** indicates high viral replication and high infectivity. * **Window Period:** The interval when HBsAg has disappeared but Anti-HBs has not yet appeared. During this time, **Anti-HBc IgM** is the only diagnostic marker. * **Ground Glass Hepatocytes:** The characteristic histopathological finding in chronic Hepatitis B due to the accumulation of HBsAg in the endoplasmic reticulum.

Q: Which of the following Hepatitis B virus antigens/antibodies does NOT circulate in the blood?

HBcAg (Hepatitis B core antigen). **Explanation:** The correct answer is **HBcAg (Hepatitis B core antigen)**. **Why HBcAg is the correct answer:** HBcAg is the internal nucleocapsid protein of the Hepatitis B virus. In the bloodstream, the core antigen is entirely sequestered within the outer lipid envelope (HBsAg). Because it is "hidden" inside the complete virion (Dane particle), it does not circulate freely in the serum and cannot be detected by standard diagnostic assays. To visualize HBcAg, one would typically need to perform an immunohistochemical stain on a liver biopsy specimen, where it is found within the nuclei of infected hepatocytes. **Analysis of Incorrect Options:** * **HBsAg (Option D):** This is the surface envelope protein. It is produced in massive excess by hepatocytes and circulates freely in the blood as spherical or tubular particles. It is the first marker to appear in acute infection. * **HBeAg (Option C):** This is a soluble protein secreted by infected cells. It circulates in the blood and serves as a marker of high viral replication and infectivity. * **Anti-HBc (Option B):** These are antibodies (IgM or IgG) produced by the host against the core antigen. They circulate in the blood and are crucial for diagnosis (e.g., IgM anti-HBc is the only marker positive during the "window period"). **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The interval between the disappearance of HBsAg and the appearance of Anti-HBs. During this time, **IgM Anti-HBc** is the most reliable diagnostic marker. * **HBeAg vs. Anti-HBe:** Presence of HBeAg indicates high infectivity; seroconversion to Anti-HBe indicates lower infectivity. * **Pre-core Mutants:** These are HBV strains that do not produce HBeAg despite high viral loads (HBV DNA positive).

Q: Which of the following statements about Dengue fever is incorrect?

It has an incubation period of 2-3 weeks.. ### Explanation **1. Why Option B is the Correct Answer (Incorrect Statement):** The incubation period of Dengue fever is typically **3 to 14 days** (average 4–7 days), not 2–3 weeks. In clinical virology, an incubation period exceeding 14 days is rare for most arboviral infections. Identifying the correct timeline is crucial for epidemiological tracking and diagnosing returning travelers. **2. Analysis of Other Options:** * **Option A:** Dengue is primarily transmitted by the **Aedes aegypti** mosquito (the principal vector) and occasionally by *Aedes albopictus*. These are "day-biters" that breed in stagnant clean water. * **Option C:** The Dengue virus (DENV) belongs to the genus **Flavivirus** and family *Flaviviridae*. It is a single-stranded, positive-sense RNA virus with four distinct serotypes (DEN-1 to DEN-4). * **Option D:** Dengue is classically known as **"Break-bone fever"** due to the characteristic severe myalgia, arthralgia, and retro-orbital pain associated with the febrile phase. **3. NEET-PG High-Yield Pearls:** * **Diagnosis:** **NS1 Antigen** is the marker of choice for the first 1–5 days. **IgM ELISA** is used after day 5. * **Pathogenesis:** Severe forms like Dengue Hemorrhagic Fever (DHF) occur due to **Antibody-Dependent Enhancement (ADE)**, usually during a secondary infection with a different serotype. * **Tourniquet Test:** A positive test (≥10 petechiae per square inch) indicates capillary fragility, a hallmark of DHF. * **Hematology:** Characterized by **leukopenia** and **thrombocytopenia**. A rising hematocrit (>20% increase) is a critical sign of plasma leakage.

Q: Which virus is noted for such a high incidence of antigenic drift that more than one antigenic variant can be isolated from infected individuals?

HIV. ### Explanation The correct answer is **HIV (Human Immunodeficiency Virus)**. **Why HIV is correct:** The hallmark of HIV is its extreme genetic diversity, driven by the error-prone nature of the **Reverse Transcriptase** enzyme, which lacks 3' to 5' exonuclease (proofreading) activity. This leads to a high rate of point mutations during replication. Consequently, HIV undergoes such rapid **antigenic drift** that it exists within a single patient as a collection of closely related but distinct genetic variants known as **quasispecies**. This allows the virus to constantly evade the host’s immune response and complicates vaccine development. **Why other options are incorrect:** * **Influenza Virus:** While famous for antigenic drift (causing seasonal epidemics) and shift (causing pandemics), the variants typically emerge at a population level over time. It does not usually produce multiple distinct antigenic variants within a single host simultaneously to the extent HIV does. * **Adenovirus & Herpesvirus:** These are **DNA viruses**. DNA polymerases generally have proofreading mechanisms, making these viruses genetically stable compared to RNA viruses. They do not exhibit significant antigenic drift. **High-Yield Clinical Pearls for NEET-PG:** * **Quasispecies:** This term specifically refers to the diverse pool of HIV variants within one individual. * **Reverse Transcriptase:** The highest mutation rate among all known biological entities ($10^{-4}$ to $10^{-5}$ mutations per base pair per cycle). * **Influenza Antigenic Shift:** Due to the **segmented genome** (8 segments), allowing for genetic reassortment. * **HIV Tropism:** Determined by the **gp120** protein binding to CD4 receptors and co-receptors (CCR5 or CXCR4).

Question 1

Which of the following is NOT included in the picornavirus group?

Accepted Answer

Hepatitis E virus (HEV)

Answer

Encephalomyocarditis virus

Answer

Foot and mouth disease virus

Answer

Poliovirus

Question 2

What is the first virological marker following acute Hepatitis B infection?

Accepted Answer

HBsAg

Answer

IgM Anti-HBc

Answer

Anti-HBs

Answer

Anti-HBe

Question 3

Malaise and fatigue with increased "atypical" lymphocytes and a reactive heterophil antibody test is most commonly caused by?

Accepted Answer

Epstein-Barr virus

Answer

Toxoplasma

Answer

Borrelia burgdorferi

Answer

Parvovirus

Question 4

Antigenic drift and antigenic shift are characteristic features of which virus?

Accepted Answer

Influenza A virus

Answer

Swine flu virus

Answer

Rotavirus

Answer

Herpes virus

Question 5

Which statement is incorrect regarding the hepatitis B virus?

Accepted Answer

It is transmitted via the fecal-oral route.

Answer

It is a DNA virus.

Answer

It can be transmitted from mother to child (perinatal transmission).

Answer

It contains reverse transcriptase.

Question 6

Which of the following Hepatitis B virus antigens/antibodies does NOT circulate in the blood?

Accepted Answer

HBcAg (Hepatitis B core antigen)

Answer

Anti-HBc (Antibody to Hepatitis B core antigen)

Answer

HBeAg (Hepatitis B e antigen)

Answer

HBsAg (Hepatitis B surface antigen)

Question 7

Which virus remains dormant but can be reactivated?

Accepted Answer

Herpes zoster

Answer

Herpes simplex

Answer

Epstein-Barr virus

Answer

Cytomegalovirus

Question 8

Which of the following statements about Dengue fever is incorrect?

Accepted Answer

It has an incubation period of 2-3 weeks.

Answer

It is spread by the vector Aedes aegypti.

Answer

It is caused by a Flavivirus.

Answer

It characteristically causes severe myalgia.

Question 9

Which virus is noted for such a high incidence of antigenic drift that more than one antigenic variant can be isolated from infected individuals?

Accepted Answer

HIV

Answer

Adenovirus

Answer

Herpesvirus

Answer

Influenza Virus

Question 10

Which of the following statements about poliovirus is incorrect?

Accepted Answer

Type I is responsible for vaccine-associated paralytic poliomyelitis

Answer

Type I is responsible for most epidemics

Answer

Type I is very difficult to eliminate

Answer

Type I is most commonly associated with paralysis

Virology — MCQs

Virology — MCQs

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