Virology Practice Questions

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).

Q: Herpangina is commonly caused by which virus?

Coxsackie virus B. **Explanation:** **Herpangina** is an acute febrile illness characterized by small vesicular and ulcerative lesions on the posterior oropharynx (tonsillar pillars, soft palate, and uvula). It is primarily caused by **Coxsackievirus Group A** (specifically types A1–A10, A16, and A22). *Note: There appears to be a discrepancy in the provided key. In standard medical microbiology (Jawetz, Harrison, Bailey & Scott), Herpangina is classically associated with **Coxsackievirus Group A**, while Group B is more commonly associated with Pleurodynia and Myocarditis.* **Analysis of Options:** * **Coxsackievirus A (Correct Pathogen):** This is the most common cause of Herpangina and Hand-Foot-Mouth Disease (HFMD). It typically affects children and presents with sudden fever and sore throat. * **Coxsackievirus B:** While it can cause respiratory infections, it is the classic cause of **Bornholm disease (Pleurodynia)**, Myocarditis, and Pericarditis. * **Echovirus:** These can cause aseptic meningitis and non-specific exanthems but are less frequent causes of classic Herpangina. * **Poliovirus:** Primarily causes asymptomatic infection, abortive poliomyelitis, or paralytic disease by affecting the anterior horn cells of the spinal cord. **High-Yield Clinical Pearls for NEET-PG:** * **Herpangina vs. Herpes Stomatitis:** Herpangina lesions are located in the **posterior** pharynx, whereas Gingivostomatitis (HSV-1) typically involves the **anterior** mouth and gums. * **Hand-Foot-Mouth Disease (HFMD):** Most commonly caused by **Coxsackie A16** and **Enterovirus 71**. * **Pleurodynia (Devil’s Grip):** Characterized by paroxysmal thoracic pain, caused by **Coxsackie B**. * **Myocarditis:** Coxsackie B is the most common viral cause of infectious myocarditis.

Q: Which virus can be easily cultured from CSF?

Mumps virus. **Explanation:** The correct answer is **Mumps virus**. In the context of viral meningitis, the ability to isolate a virus from the cerebrospinal fluid (CSF) depends on the duration and magnitude of the viral load during the clinical phase. **Why Mumps virus is correct:** Mumps virus is highly neurotropic. In patients presenting with mumps meningitis, the virus is shed in high titers into the CSF. It can be successfully cultured from the CSF in approximately **50–70% of cases** during the first week of symptoms. This makes it one of the most "culture-positive" viruses in clinical virology compared to other common causes of aseptic meningitis. **Why the other options are incorrect:** * **Poliovirus:** While Poliovirus causes significant CNS pathology (anterior horn cell destruction), it is **rarely isolated from the CSF**. Diagnosis is typically made via stool culture or throat swabs, as the virus replicates in the oropharynx and intestines. * **Coxsackievirus & Echovirus:** These are Enteroviruses. While they are the most common causes of viral meningitis, their isolation rate from CSF is significantly lower than that of Mumps (typically <30-40%). They are more easily recovered from throat swabs or fecal samples. **NEET-PG High-Yield Pearls:** * **Most common cause of viral meningitis:** Enteroviruses (Coxsackie and Echo). * **Mumps Meningitis:** Occurs in up to 15% of mumps cases; it is usually benign and self-limiting. * **CSF Findings in Viral Meningitis:** Lymphocytic pleocytosis, normal glucose, and slightly elevated protein. * **Gold Standard for Enterovirus:** Though culture is possible, **RT-PCR** is now the diagnostic method of choice for all viral CNS infections due to higher sensitivity and speed.

Question 1

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 2

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 3

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 4

Which virus remains dormant but can be reactivated?

Accepted Answer

Herpes zoster

Answer

Herpes simplex

Answer

Epstein-Barr virus

Answer

Cytomegalovirus

Question 5

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 6

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 7

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

Question 8

Which of the following statements best describes subacute sclerosing panencephalitis (SSPE) virus?

Accepted Answer

It is a progressive disease involving both white and gray matter.

Answer

It is a late central nervous system manifestation of mumps.

Answer

It is a common event occurring in 1 of 300,000 cases of mumps.

Answer

Viral DNA can be demonstrated in brain cells.

Question 9

Herpangina is commonly caused by which virus?

Accepted Answer

Coxsackie virus B

Answer

Coxsackie virus A

Answer

Echovirus

Answer

Poliovirus

Question 10

Which virus can be easily cultured from CSF?

Accepted Answer

Mumps virus

Answer

Poliovirus

Answer

Coxsackievirus

Answer

Echovirus

Virology — MCQs

Virology — MCQs

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