Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 161: Measles belongs to which virus family?

A. Togavirus
B. Paramyxovirus (Correct Answer)
C. Arbovirus
D. None of the above

Explanation: **Explanation:** Measles (Rubeola) is caused by the **Measles virus**, which is a member of the **Genus Morbillivirus** within the **Paramyxoviridae** family. These are pleomorphic, enveloped viruses containing a linear, non-segmented, negative-sense single-stranded RNA (ssRNA). A key characteristic of this family is the presence of Hemagglutinin (H) and Fusion (F) proteins, though the Measles virus notably lacks Neuraminidase activity. **Analysis of Options:** * **Option A (Togavirus):** This family includes the Rubella virus (German Measles). While the names are similar, Rubella is a positive-sense ssRNA virus and belongs to the genus *Rubivirus*. * **Option B (Paramyxovirus):** Correct. This family also includes Mumps, Parainfluenza, and Respiratory Syncytial Virus (RSV). * **Option C (Arbovirus):** This is an ecological classification (Arthropod-borne) rather than a taxonomic family. Measles is transmitted via respiratory droplets, not insect vectors. **High-Yield Clinical Pearls for NEET-PG:** * **Koplik Spots:** Pathognomonic bluish-white spots on an erythematous base found on the buccal mucosa (opposite lower 2nd molars) during the prodromal stage. * **Warthin-Finkeldey Cells:** Multinucleated giant cells with eosinophilic inclusion bodies found in lymphoid tissue, characteristic of Measles. * **Complications:** The most common complication is **Otitis Media**; the most common cause of death is **Pneumonia** (Hecht’s giant cell pneumonia); the most dreaded late-onset neurological complication is **SSPE** (Subacute Sclerosing Panencephalitis). * **Vitamin A:** Supplementation is recommended to reduce morbidity and mortality in children.

Question 162: Epstein-Barr virus causes all the following except?

A. Infectious mononucleosis
B. Measles (Correct Answer)
C. Nasopharyngeal carcinoma
D. Non-Hodgkin lymphoma

Explanation: **Explanation:** The correct answer is **Measles**, as it is caused by the **Measles virus** (a member of the *Paramyxoviridae* family, genus *Morbillivirus*), not the Epstein-Barr Virus (EBV). EBV, also known as Human Herpesvirus 4 (HHV-4), is a DNA virus belonging to the *Gammaherpesvirinae* subfamily. It is primarily known for its tropism for B-lymphocytes and epithelial cells. **Analysis of Options:** * **Infectious Mononucleosis (Option A):** This is the most common clinical manifestation of primary EBV infection, characterized by the triad of fever, pharyngitis, and lymphadenopathy. It is associated with "atypical lymphocytes" (Downey cells) on peripheral smear. * **Nasopharyngeal Carcinoma (Option C):** EBV is strongly associated with the undifferentiated type of this malignancy, particularly in Southern China and Southeast Asia. It involves the oncogenic transformation of nasopharyngeal epithelial cells. * **Non-Hodgkin Lymphoma (Option D):** EBV is a major oncogenic driver for several B-cell lymphomas, including **Burkitt lymphoma** (starry-sky appearance), Hodgkin lymphoma, and various Non-Hodgkin Lymphomas (NHL) in immunocompromised patients (e.g., CNS lymphoma in AIDS). **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** EBV enters B-cells via the **CD21** receptor (also the receptor for C3d complement component). * **Diagnosis:** The **Paul-Bunnell Test** (detecting heterophile antibodies) is the classic screening test for Infectious Mononucleosis. * **Other Associations:** Oral Hairy Leukoplakia (in HIV patients) and Gastric Carcinoma. * **Distinction:** Measles is characterized by **Koplik spots** and a maculopapular rash, which are clinically distinct from EBV-related pathologies.

Question 163: The 'bowl of spaghetti' appearance is characteristic of which of the following?

A. Ebola virions (Correct Answer)
B. Adenovirus
C. Marburg Viruses
D. Poliovirus

Explanation: **Explanation:** The characteristic **'bowl of spaghetti'** appearance refers to the unique morphology of **Ebola virions** when viewed under an electron microscope. Ebola belongs to the **Filoviridae** family (from the Latin *filum*, meaning thread). These viruses are pleomorphic, appearing as long, filamentous, non-segmented forms that can be straight, curved, or coiled into "6-shaped," "U-shaped," or circular configurations. When multiple long, intertwined filaments are present in a sample, they resemble a bowl of spaghetti. **Analysis of Options:** * **Ebola Virions (Correct):** As members of the Filoviridae family, their elongated, thread-like structure (up to 14,000 nm in length) creates the classic "spaghetti" or "shepherd’s crook" appearance. * **Adenovirus:** These are non-enveloped, **icosahedral** viruses with fibers protruding from the vertices (pentons), giving them a "space satellite" or "soccer ball" appearance. * **Marburg Virus:** While also a Filovirus, Marburg typically presents as shorter filaments or distinct "6-shaped" structures. While morphologically similar to Ebola, the specific descriptive term 'bowl of spaghetti' is most classically associated with Ebola in standardized medical literature. * **Poliovirus:** A member of the Picornaviridae family, it is a very small (approx. 30 nm), simple **icosahedral** virus. **High-Yield NEET-PG Pearls:** * **Filoviridae Characteristics:** Negative-sense ssRNA, enveloped, helical nucleocapsid. * **Transmission:** Direct contact with infected blood, secretions, or organs (often via fruit bats as natural reservoirs). * **Diagnosis:** Gold standard for early detection is **RT-PCR**. Electron microscopy is used for structural identification. * **Other "Shapes":** * **Rabies:** Bullet-shaped. * **Poxvirus:** Brick-shaped. * **Rotavirus:** Wheel-like (*Rota* = wheel).

Question 164: Which of the following allows binding of HIV to CD4 cells?

A. gp 120 (Correct Answer)
B. gp 41
C. Proteins formed by expression of gag gene
D. CCR5

Explanation: The human immunodeficiency virus (HIV) is an enveloped RNA virus that targets the immune system by specifically binding to CD4+ T lymphocytes and macrophages. ### **Explanation of the Correct Answer** **Option A (gp 120)** is correct because it is the surface envelope glycoprotein responsible for the **initial attachment** of the virus to the host cell. The gp 120 molecule has a high affinity for the **CD4 receptor**. Once gp 120 binds to CD4, it undergoes a conformational change that allows it to interact with co-receptors (CCR5 or CXCR4). ### **Analysis of Incorrect Options** * **Option B (gp 41):** This is the transmembrane envelope glycoprotein. Its primary role is **fusion** of the viral envelope with the host cell membrane, occurring *after* gp 120 has anchored the virus. * **Option C (gag gene proteins):** The *gag* gene encodes structural proteins of the viral core, such as **p24** (capsid), p17 (matrix), and p7/p9 (nucleocapsid). These are internal proteins and do not mediate initial binding. * **Option D (CCR5):** This is a **co-receptor** found on the host cell (macrophages). While essential for entry, it is not the molecule on the virus that "allows binding to CD4"; rather, it is the secondary docking site after CD4 binding has occurred. ### **High-Yield Clinical Pearls for NEET-PG** * **The "Docking" vs. "Fusion" Rule:** Remember **gp 120 for Attachment/Docking** and **gp 41 for Fusion**. * **Gene Products:** * *env* gene $\rightarrow$ gp 160 (cleaved into gp 120 and gp 41). * *pol* gene $\rightarrow$ Reverse transcriptase, Integrase, and Protease. * **Tropism:** M-tropic strains use **CCR5** (predominant in early infection), while T-tropic strains use **CXCR4** (associated with progression to AIDS). * **Maraviroc** is a drug that acts as a CCR5 antagonist, preventing the gp 120-co-receptor interaction.

Question 165: Which of the following is NOT true about the dengue virus?

A. It belongs to the Flaviviridae family.
B. DEN 4 is the most common serotype in India. (Correct Answer)
C. The main vectors are Aedes aegypti and Aedes albopictus.
D. The virus has positive-sense RNA.

Explanation: **Explanation:** **1. Why Option B is the correct answer (The False Statement):** While all four serotypes (DEN 1–4) circulate in India, **DEN 2** has historically been the most common and dominant serotype associated with severe outbreaks and Dengue Hemorrhagic Fever (DHF). Recent epidemiological shifts have shown a rise in DEN 1 and DEN 3 in certain regions, but **DEN 4** remains the least common serotype in the Indian subcontinent. **2. Analysis of Incorrect Options (True Statements):** * **Option A:** Dengue virus is a member of the genus *Flavivirus* within the **Flaviviridae** family. * **Option C:** The primary vector is ***Aedes aegypti*** (the "Tiger mosquito," a day-biter that breeds in artificial collections of clean water). ***Aedes albopictus*** is the secondary vector. * **Option D:** The virus possesses a **single-stranded, positive-sense RNA** genome, which is enveloped and icosahedral in symmetry. **3. Clinical Pearls for NEET-PG:** * **Antibody-Dependent Enhancement (ADE):** This occurs when a person is infected with a different serotype for the second time. Non-neutralizing antibodies from the first infection facilitate viral entry into macrophages, leading to a massive cytokine storm and **Dengue Hemorrhagic Fever (DHF)** or **Dengue Shock Syndrome (DSS)**. * **Diagnosis:** * **NS1 Antigen:** Best marker for early diagnosis (Day 1–5). * **IgM ELISA:** Appears after Day 5 (indicates current/recent infection). * **IgG ELISA:** Indicates past infection or secondary infection if titers are very high. * **Tourniquet Test:** A positive test (≥10 petechiae per square inch) is a clinical indicator of capillary fragility in DHF.

Question 166: Hand, foot, and mouth disease is typically caused by which of the following viruses?

A. Parvovirus B6
B. Parvovirus B19
C. Coxsackievirus A16 (Correct Answer)
D. Coxsackievirus A19

Explanation: **Explanation:** **Hand, Foot, and Mouth Disease (HFMD)** is a common viral illness, primarily affecting infants and children. It is characterized by a mild fever followed by a vesicular eruption on the palms of the hands, soles of the feet, and painful ulcerations in the oral cavity (stomatitis). **1. Why Coxsackievirus A16 is Correct:** HFMD is most commonly caused by viruses belonging to the **Picornaviridae** family, specifically the **Enterovirus** genus. **Coxsackievirus A16 (CVA16)** is the most frequent causative agent worldwide. Another significant cause is **Enterovirus 71 (EV71)**, which is noteworthy because it is often associated with more severe neurological complications like aseptic meningitis or encephalitis. **2. Why the Other Options are Incorrect:** * **Parvovirus B19 (Option B):** This virus causes **Erythema Infectiosum (Fifth Disease)**, characterized by the classic "slapped-cheek" rash and a lace-like reticular rash on the body. It is also associated with aplastic crisis in patients with hemolytic anemias. * **Parvovirus B6 (Option A):** This is not a recognized human pathogen in the context of common exanthematous diseases. * **Coxsackievirus A19 (Option D):** While many Coxsackie A serotypes exist, A19 is not a primary or typical cause of HFMD. **Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route and respiratory droplets. * **Herpangina:** Also caused by Coxsackie A viruses, but presents with fever and painful throat vesicles *without* the skin rash on hands and feet. * **Complications:** While usually self-limiting, watch for EV71 strains in Southeast Asia which carry a higher risk of pulmonary edema and neurological involvement. * **Seasonality:** Peak incidence occurs in summer and early autumn.

Question 167: A hospital worker is found to be positive for hepatitis B surface antigen. Subsequent tests reveal the presence of HBeAg as well. Which of the following best describes the worker?

A. Has a biologic false-positive test for hepatitis B
B. Is highly contagious (Correct Answer)
C. Is less contagious
D. Is not contagious

Explanation: **Explanation:** The presence of **HBeAg (Hepatitis B e-antigen)** is the hallmark of active viral replication and high infectivity. In this scenario, the hospital worker is positive for both HBsAg (indicating current infection) and HBeAg, which signifies a high viral load in the blood and body fluids. **1. Why Option B is Correct:** HBeAg is a soluble protein derived from the precore/core gene. It is secreted into the serum only when the virus is actively replicating. Therefore, its presence serves as a surrogate marker for high levels of HBV DNA. Individuals who are HBeAg-positive are considered **highly contagious** and pose a significant risk of transmission via needle-stick injuries or mucosal exposure. **2. Why Other Options are Incorrect:** * **Option A:** A biologic false-positive is unlikely when multiple specific markers (HBsAg and HBeAg) are detected. These are definitive viral proteins. * **Option C & D:** If the worker were HBeAg-negative and **Anti-HBe positive**, they would be considered "less contagious" (lower viral replication). No HBsAg-positive individual is considered "not contagious" unless the virus is completely cleared (HBsAg becomes negative). **NEET-PG High-Yield Pearls:** * **HBsAg:** First marker to appear; indicates the person is infected (Acute or Chronic). * **HBeAg:** Indicates **high infectivity** and active replication. * **Anti-HBe:** Indicates the "window of resolution" or low infectivity state. * **Anti-HBc (IgM):** The best marker for diagnosing acute infection during the **"Window Period"** (when HBsAg and Anti-HBs are both negative). * **Anti-HBs:** Indicates immunity (via recovery or vaccination). Note: Vaccinated individuals are Anti-HBs positive but **Anti-HBc negative**.

Question 168: A patient with HIV presents with diarrhea and acid-fast bacilli (AFB) positive in stool. What is the most likely causative organism?

A. Mycobacterium avium intracellulare (Correct Answer)
B. Mycobacterium tuberculosis
C. Mycobacterium leprae
D. Mycoplasma

Explanation: ### Explanation **Correct Option: A. Mycobacterium avium intracellulare (MAC)** In the context of HIV/AIDS, the presence of **acid-fast bacilli (AFB)** in a stool sample from a patient with chronic diarrhea is a classic presentation of **Disseminated Mycobacterium avium Complex (MAC)**. * **Pathophysiology:** MAC is an opportunistic infection that typically occurs when the **CD4 count falls below 50 cells/mm³**. Unlike *M. tuberculosis*, which is primarily respiratory, MAC in advanced AIDS often involves the gastrointestinal tract and the reticuloendothelial system, leading to malabsorption and diarrhea. * **Microscopy:** MAC organisms are strongly acid-fast. Finding them in stool (Modified Ziehl-Neelsen stain) is a high-yield diagnostic marker for gastrointestinal involvement in immunocompromised hosts. **Why other options are incorrect:** * **B. Mycobacterium tuberculosis:** While *M. tuberculosis* is common in HIV patients, it usually presents as pulmonary disease or ileocecal tuberculosis (causing abdominal pain/obstruction). It is less commonly associated with isolated chronic diarrhea and AFB-positive stool compared to MAC in very low CD4 states. * **C. Mycobacterium leprae:** This organism causes Leprosy, affecting the skin and peripheral nerves. It is not a cause of diarrhea and cannot be cultured or found in stool. * **D. Mycoplasma:** These are the smallest free-living organisms and **lack a cell wall**. Therefore, they are not acid-fast and would not be seen on an AFB stain. ### High-Yield Clinical Pearls for NEET-PG: * **CD4 Thresholds:** MAC (<50 cells/mm³), CMV (<50 cells/mm³), Cryptococcosis (<100 cells/mm³), Toxoplasmosis (<100 cells/mm³). * **Prophylaxis:** Azithromycin or Clarithromycin is used for MAC prophylaxis when CD4 <50. * **Differential Diagnosis:** If stool shows **acid-fast oocysts** (rather than bacilli), consider *Cryptosporidium parvum*, *Isospora belli*, or *Cyclospora*. * **Culture:** MAC grows on LJ medium but much faster in liquid media (BACTEC). It produces smooth, non-pigmented colonies.

Question 169: Vaccination for which of the following hepatic diseases is with viral surface antigen and usually provides immunity?

A. Hepatitis A
B. Hepatitis B (Correct Answer)
C. Hepatitis C
D. Hepatitis D

Explanation: **Explanation:** The correct answer is **Hepatitis B**. The Hepatitis B vaccine is a **subunit recombinant vaccine** produced using recombinant DNA technology in yeast (*Saccharomyces cerevisiae*). It specifically utilizes the **Hepatitis B surface Antigen (HBsAg)**. When injected, the body produces **Anti-HBs antibodies**, which are neutralizing and provide long-term immunity. A titer of >10 mIU/mL is considered protective. **Analysis of Options:** * **Hepatitis A:** The vaccine is typically an **inactivated (killed) whole-virus vaccine** (e.g., Havrix). While it provides excellent immunity, it uses the entire virion rather than just a surface antigen. * **Hepatitis C:** There is currently **no vaccine** available for Hepatitis C due to the high antigenic variation and lack of a proofreading mechanism in its RNA polymerase. * **Hepatitis D:** There is no specific vaccine for HDV. However, because HDV is a defective virus that requires HBsAg for its coat, **vaccination against Hepatitis B** automatically protects an individual from HDV infection. **High-Yield Clinical Pearls for NEET-PG:** * **HBsAg** is the first serological marker to appear in acute infection and the key component of the vaccine. * **Anti-HBs** is the only marker present in a successfully vaccinated individual (Anti-HBc will be negative). * The HBV vaccine is given at **0, 1, and 6 months**. * **Non-responders:** Individuals who fail to develop a protective antibody titer after two complete series of vaccinations.

Question 170: Which is the usual marker for the detection of hepatitis B infection?

A. Hepatitis B surface antigen (HBsAg) (Correct Answer)
B. Hepatitis B surface antibody (HBsAb)
C. Hepatitis B core antigen (HBcAg)
D. Hepatitis B core antibody (HBcAb)

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, typically detectable 2 to 8 weeks before clinical symptoms or biochemical evidence (elevated ALT/AST) emerge. It indicates that the virus is present in the body (acute or chronic) and is the primary screening tool used to identify an active HBV infection. **Analysis of Incorrect Options:** * **Hepatitis B surface antibody (HBsAb/anti-HBs):** This marker indicates immunity. It appears after the disappearance of HBsAg or following successful vaccination. It is not used to detect an active infection but rather to confirm recovery or immune status. * **Hepatitis B core antigen (HBcAg):** This is an internal component of the virion. It is sequestered within the HBsAg coat and is **not** detectable in the serum; it can only be found in infected hepatocytes via biopsy. * **Hepatitis B core antibody (HBcAb/anti-HBc):** While IgM anti-HBc is a marker of acute infection (and the only marker positive during the "window period"), total anti-HBc indicates past or current infection but does not distinguish between the two as reliably as HBsAg for initial screening. **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. * **Chronic Infection:** Defined by the persistence of HBsAg in the blood for more than 6 months. * **Infectivity Marker:** **HBeAg** (Envelope antigen) indicates high viral replication and high infectivity. * **Vaccine Response:** A person vaccinated against HBV will be positive for **anti-HBs** only (negative for anti-HBc).

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