Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 861: Which of the following viruses is brick-shaped?

A. Chicken pox
B. Small pox (Correct Answer)
C. CMV
D. EBV

Explanation: **Explanation:** The correct answer is **Smallpox (Variola virus)**. **1. Why Smallpox is correct:** Smallpox belongs to the **Poxviridae** family. Poxviruses are the largest and most complex of all animal viruses. Under electron microscopy, they exhibit a characteristic **brick-shaped** (rectangular) morphology with a complex internal structure consisting of a biconcave core and two lateral bodies. This is a classic high-yield morphological feature often tested in NEET-PG. **2. Why the other options are incorrect:** * **Chickenpox (Varicella-Zoster Virus), CMV (Cytomegalovirus), and EBV (Epstein-Barr Virus):** All three belong to the **Herpesviridae** family. Herpesviruses are characterized by an **icosahedral** capsid symmetry and are **spherical** in overall shape due to their lipid envelope. They are significantly smaller than poxviruses. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Size:** Poxviruses are the only viruses large enough to be seen under a light microscope (using special stains like Paschen’s stain). * **Replication:** Unlike most DNA viruses that replicate in the nucleus, Poxviruses replicate entirely in the **cytoplasm** because they carry their own DNA-dependent RNA polymerase. * **Inclusion Bodies:** Smallpox produces intracytoplasmic inclusion bodies known as **Guarnieri bodies**. * **Eradication:** Smallpox is the only human infectious disease to be globally eradicated (declared by the WHO in 1980). * **Molluscum Contagiosum:** Another member of the Poxviridae family, it also shares the brick-shaped morphology and produces Henderson-Patterson bodies.

Question 862: Which organism causes cervical carcinoma?

A. Human Papillomavirus (HPV) (Correct Answer)
B. Hepatitis A Virus (HAV)
C. Hepatitis B Virus (HBV)
D. Hepatitis C Virus (HCV)

Explanation: **Explanation:** **Human Papillomavirus (HPV)** is the primary etiological agent of cervical carcinoma. The oncogenic potential lies in high-risk strains (primarily **HPV 16 and 18**), which integrate their DNA into the host genome. This leads to the overexpression of two key oncoproteins: **E6**, which degrades the **p53** tumor suppressor protein, and **E7**, which inactivates the **Retinoblastoma (Rb)** protein. The loss of these cell cycle checkpoints results in unregulated cellular proliferation and malignant transformation. **Analysis of Incorrect Options:** * **Hepatitis A Virus (HAV):** An RNA virus transmitted via the fecal-oral route. It causes acute hepatitis but is never associated with chronic infection or oncogenesis. * **Hepatitis B Virus (HBV) & Hepatitis C Virus (HCV):** While both are strongly associated with carcinogenesis, they specifically cause **Hepatocellular Carcinoma (HCC)**, not cervical cancer. HBV is a DNA virus that integrates into the host genome, while HCV is an RNA virus that causes cancer primarily through chronic inflammation and cirrhosis. **High-Yield Clinical Pearls for NEET-PG:** * **High-risk HPV types:** 16, 18 (cause ~70% of cases), 31, and 33. * **Low-risk HPV types:** 6 and 11 (cause Genital Warts/Condyloma Acuminata). * **Screening:** Pap smear looks for **Koilocytes** (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Vaccination:** The Quadrivalent vaccine (Gardasil) targets types 6, 11, 16, and 18. The most effective time for administration is before the first sexual exposure (ages 9–14).

Question 863: One virus particle prevents the multiplication of a second virus. This phenomenon is known as:

A. Viral interference (Correct Answer)
B. Mutation
C. Superinfection
D. Permutation

Explanation: ### Explanation **Correct Answer: A. Viral Interference** **Viral interference** is a phenomenon where the infection of a host cell by one virus inhibits the multiplication of a second, subsequent virus. This can occur between similar or unrelated viruses. The underlying mechanisms include: * **Competition for receptors:** The first virus blocks or downregulates surface receptors needed by the second virus. * **Metabolic competition:** The first virus exhausts the host cell's cellular machinery (ribosomes, enzymes). * **Interferon (IFN) production:** The most common mechanism; the first virus induces the host cell to produce interferons, which establish an "antiviral state" in neighboring cells, preventing the replication of the second virus. **Why other options are incorrect:** * **B. Mutation:** Refers to a change in the nucleotide sequence of the viral genome. While mutations can lead to drug resistance or antigenic drift, they do not describe the interaction between two distinct viruses. * **C. Superinfection:** This occurs when a cell already infected with one virus is subsequently infected by a different strain or a different virus. Unlike interference, superinfection implies the successful co-existence or replacement, rather than the active prevention of the second virus's multiplication. * **D. Permutation:** This is a mathematical term referring to the arrangement of elements. It has no specific definition in viral replication or pathogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Defective Interfering (DI) Particles:** These are "incomplete" viruses that lack a functional genome but can still cause interference by outcompeting the wild-type virus for replication enzymes. * **Clinical Application:** Viral interference explains why the **Sabin (OPV) vaccine** is given in multiple doses; if a child has an existing enterovirus infection, it may "interfere" with the vaccine virus, leading to a failure of the immune response. * **Interferons (IFN-α, β):** These are the primary mediators of heterologous interference (interference between two different types of viruses).

Question 864: Which of the following statement is TRUE about polio?

A. Paralytic polio is most common
B. Spastic paralysis
C. Increased muscular activity leads to increased paralysis (Correct Answer)
D. Polio vaccine is given orally

Explanation: **Explanation:** The correct answer is **C: Increased muscular activity leads to increased paralysis.** This is a high-yield concept in Polio pathogenesis known as **"Provocation Polio."** During the pre-paralytic stage of the infection, excessive physical activity or muscular trauma (like IM injections) increases the risk and severity of paralysis in the specific muscle groups involved. This occurs because increased metabolic activity in the motor neurons facilitates the entry and replication of the poliovirus within the anterior horn cells of the spinal cord. **Analysis of Incorrect Options:** * **A. Paralytic polio is most common:** Incorrect. In reality, **Inapparent/Asymptomatic infection** is the most common outcome (>90-95%). Paralytic polio occurs in less than 1% of cases. * **B. Spastic paralysis:** Incorrect. Poliovirus specifically destroys the **Lower Motor Neurons (LMN)** in the anterior horn of the spinal cord. This results in **Asymmetrical Flaccid Paralysis** with loss of deep tendon reflexes, not spasticity. * **D. Polio vaccine is given orally:** While the Oral Polio Vaccine (OPV/Sabin) is given orally, this option is considered "less true" in a competitive context compared to the physiological fact in Option C. Furthermore, the global shift (including India’s Universal Immunization Programme) now emphasizes the **Inactivated Polio Vaccine (IPV)**, which is given via IM or intradermal routes. **High-Yield Clinical Pearls for NEET-PG:** * **Specimen of choice:** Stool (virus is excreted for weeks). * **Most common site of paralysis:** Spinal (legs > arms). * **Post-Polio Syndrome:** Occurs 30–40 years after recovery due to the gradual failure of over-extended motor neurons. * **Last case in India:** 13th January 2011 (Howrah, West Bengal). India was declared Polio-free in 2014.

Question 865: Which of the following viruses commonly cause gastroenteritis?

A. Rotavirus
B. Norwalk virus
C. Adenovirus
D. Enterovirus (Correct Answer)

Explanation: **Explanation:** The question asks which of the listed viruses **commonly** causes gastroenteritis. While the options provided include several gastrointestinal pathogens, the selection of **Enterovirus** as the "correct" answer in many traditional question banks (despite its name) is often a point of confusion that requires clarification of clinical definitions. **1. Why Enterovirus is the intended answer (The Concept):** The genus *Enterovirus* (including Poliovirus, Coxsackievirus, and Echovirus) belongs to the *Picornaviridae* family. These viruses are transmitted via the **fecal-oral route** and replicate primarily in the lymphoid tissues of the gastrointestinal tract (Peyer's patches). While they are famous for causing systemic diseases (meningitis, paralysis, myocarditis), their primary site of infection and shedding is the gut, making them a ubiquitous cause of viral shedding in stool, often associated with mild gastrointestinal upset in pediatric populations. **2. Analysis of Other Options:** * **Rotavirus:** The most common cause of severe, dehydrating diarrhea in infants and children worldwide (Reovirus family, wheel-shaped). * **Norwalk virus (Norovirus):** The leading cause of epidemic non-bacterial gastroenteritis outbreaks across all age groups (Calicivirus family). * **Adenovirus:** Specifically Serotypes 40 and 41 (Enteric Adenoviruses) are significant causes of childhood diarrhea. *Note: In modern clinical practice, Rotavirus and Norovirus are the most common causes of clinical gastroenteritis. However, if this question appears in a format where Enterovirus is marked correct, it refers to the "Enteric" nature of its primary replication cycle.* **3. High-Yield NEET-PG Pearls:** * **Rotavirus:** Double-stranded RNA, segmented (11 segments). Most common cause of infantile diarrhea. * **Norovirus:** Most common cause of cruise ship/institutional outbreaks. * **Enteroviruses:** Resistant to stomach acid (unlike Rhinoviruses). They do **not** typically cause "watery diarrhea" as their primary clinical presentation; they use the gut as a portal of entry for systemic spread. * **Hepatitis A and E:** Also transmitted via the fecal-oral route but target the liver.

Question 866: Which virus has a segmented genome?

A. Retrovirus
B. Rotavirus (Correct Answer)
C. Poliovirus
D. Rhabdovirus

Explanation: **Explanation:** The concept of a **segmented genome** is a high-yield topic in virology. Most viruses have a single continuous piece of nucleic acid, but some RNA viruses have genomes divided into separate pieces (segments). This allows for **genetic reassortment**, leading to significant antigenic shifts. **1. Why Rotavirus is Correct:** Rotavirus belongs to the **Reoviridae** family. It is characterized by a **double-stranded RNA (dsRNA)** genome consisting of **11 segments**. This segmentation is crucial for its genetic diversity. Clinically, Rotavirus is the most common cause of severe dehydrating diarrhea in infants and young children worldwide. **2. Analysis of Incorrect Options:** * **Retrovirus (e.g., HIV):** These possess a **diploid** genome (two identical copies of single-stranded RNA), but the genome itself is not segmented. * **Poliovirus:** A member of the **Picornaviridae** family, it has a single-stranded, positive-sense, **non-segmented** RNA genome. * **Rhabdovirus (e.g., Rabies):** This is a bullet-shaped virus with a single-stranded, negative-sense, **non-segmented** RNA genome. **3. NEET-PG High-Yield Clinical Pearls:** To remember the segmented RNA viruses, use the mnemonic **"BOAR"**: * **B**unyaviridae (3 segments) * **O**rthomyxoviridae (e.g., Influenza; 8 segments) * **A**renaviridae (2 segments) * **R**eoviridae (e.g., Rotavirus; 11 segments) **Key Fact:** Genetic reassortment in segmented viruses (especially Influenza) is the mechanism behind **Antigenic Shift**, which leads to pandemics. In contrast, **Antigenic Drift** (point mutations) occurs in both segmented and non-segmented viruses.

Question 867: Which of the following methods is adopted for screening HIV infection?

A. Virus isolation
B. Western blot followed by ELISA
C. ELISA followed by western blot technique (Correct Answer)
D. Polymerase chain reaction

Explanation: The standard diagnostic algorithm for HIV follows a two-step approach designed to maximize both sensitivity and specificity. **1. Why Option C is Correct:** * **ELISA (Screening):** The first step is an Enzyme-Linked Immunosorbent Assay (ELISA). It is highly **sensitive**, meaning it is excellent at detecting even minute amounts of antibodies/antigens to ensure no positive cases are missed. However, it can occasionally yield false positives. * **Western Blot (Confirmatory):** If the ELISA is reactive, a Western Blot is performed. This test is highly **specific** as it detects antibodies against specific viral proteins (like gp120, gp41, and p24). It confirms the diagnosis and eliminates false positives from the screening stage. **2. Why Other Options are Incorrect:** * **Option A (Virus Isolation):** Culturing HIV is technically demanding, expensive, and time-consuming. It is used in research settings, not for routine screening. * **Option B:** This reverses the logical order. We do not use a complex, expensive confirmatory test before a simple screening test. * **Option D (PCR):** While highly sensitive, PCR (DNA/RNA detection) is primarily used for diagnosing HIV in infants (where maternal antibodies interfere with ELISA), window period detection, or monitoring viral load. It is not the standard population screening tool. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **4th Generation ELISA:** Now the "Gold Standard" screening tool; it detects both **p24 antigen** and **HIV-1/2 antibodies**, significantly shortening the window period. * **Diagnosis in Infants:** PCR is the investigation of choice for babies born to HIV-positive mothers up to 18 months of age.

Question 868: Which of the following viruses is known to cause latency?

A. Herpes Simplex Virus Type II (HSV-II)
B. Cytomegalovirus (CMV)
C. Human Immunodeficiency Virus (HIV)
D. All of the above (Correct Answer)

Explanation: **Explanation:** Viral latency is a phase in certain viral life cycles where, after initial infection, the virus remains dormant within host cells without active replication. During this period, the viral genome is maintained (either as an episome or integrated into host DNA), allowing the virus to evade the immune system and reactivate later. * **Herpes Simplex Virus Type II (HSV-II):** As a member of the *Alphaherpesvirinae* subfamily, HSV-II establishes lifelong latency in the **sacral sensory nerve ganglia**. Reactivation typically results in recurrent genital herpes. * **Cytomegalovirus (CMV):** A member of the *Betaherpesvirinae* subfamily, CMV establishes latency in **mononuclear cells** (monocytes, lymphocytes) and myeloid progenitor cells in the bone marrow. * **Human Immunodeficiency Virus (HIV):** HIV is a retrovirus that integrates its DNA (provirus) into the host genome. It establishes a "latent reservoir" primarily in **resting CD4+ T cells**. This latency is the primary reason why current ART (Antiretroviral Therapy) cannot fully eradicate the virus. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Latency:** * **HSV-1:** Trigeminal ganglia. * **Varicella-Zoster Virus (VZV):** Dorsal root ganglia. * **Epstein-Barr Virus (EBV):** B-lymphocytes. * **Mechanism:** Herpesviruses maintain their genome as circular episomes, whereas HIV integrates into the host chromosome. * **Reactivation:** Often triggered by immunosuppression, stress, or fever. In HIV, "shock and kill" is a researched strategy to flush the virus out of its latent state.

Question 869: Owl's eye appearance inclusion bodies can be demonstrated in the diagnosis of which human herpesvirus (HHV) infection?

A. HHV-1
B. HHV-5 (Cytomegalovirus) (Correct Answer)
C. HHV-6
D. HHV-4 (Epstein-Barr virus)

Explanation: **Explanation:** The correct answer is **HHV-5 (Cytomegalovirus)**. **Why HHV-5 is correct:** Cytomegalovirus (CMV) infection is characterized by the formation of massive cellular enlargement (cytomegaly). The hallmark histopathological finding is the presence of large, **basophilic intranuclear inclusion bodies** surrounded by a clear halo, extending to the nuclear membrane. This specific morphology resembles an **"Owl’s eye."** These inclusions represent areas of active viral replication and are typically seen in epithelial cells of the renal tubules, bile ducts, or salivary glands. **Why other options are incorrect:** * **HHV-1 (Herpes Simplex Virus-1):** Characterized by **Cowdry Type A** inclusions (eosinophilic intranuclear inclusions) and multinucleated giant cells (Tzanck smear), but not the "Owl's eye" appearance. * **HHV-6 (Roseolovirus):** Primarily causes Roseola Infantum (Exanthem Subitum). While it infects T-cells, it does not produce the classic "Owl's eye" inclusions. * **HHV-4 (Epstein-Barr Virus):** Associated with infectious mononucleosis and various malignancies. The diagnostic hallmark is **atypical lymphocytes (Downey cells)** in the peripheral blood, not intranuclear inclusions. Note: "Owl's eye" nuclei are seen in Reed-Sternberg cells of Hodgkin Lymphoma (associated with EBV), but these are nucleoli, not viral inclusion bodies. **High-Yield Clinical Pearls for NEET-PG:** * **CMV** is the most common cause of congenital malformation (presents with periventricular calcifications and microcephaly). * In HIV patients, CMV is a major cause of **retinitis** ("pizza-pie" appearance) and **colitis**. * **Drug of choice:** Ganciclovir (Valganciclovir for prophylaxis). * **Culture:** CMV grows best in human fibroblast cell lines (demonstrating "shell vial" entry).

Question 870: Which virus families possess double-stranded DNA in four different isomers?

A. Poxviruses
B. Herpesviruses (Correct Answer)
C. Rabiesviruses
D. Orthomyxoviruses

Explanation: **Explanation:** The correct answer is **Herpesviruses**. This is a high-yield molecular biology concept frequently tested in NEET-PG. **Why Herpesviruses?** The genome of Herpesviruses (such as HSV and CMV) consists of a linear, double-stranded DNA molecule. This genome is organized into two components: **Unique Long (UL)** and **Unique Short (US)** regions. Each of these regions is flanked by inverted repeat sequences. Because these segments can invert their orientation independently of one another, the genome can exist in **four different structural isomers** (topoisomers). This genomic flexibility is a hallmark of the *Herpesviridae* family. **Analysis of Incorrect Options:** * **Poxviruses (Option A):** While they are dsDNA viruses, their genome is a single, continuous linear molecule with covalently closed ends (hairpin loops). They do not undergo the specific segmental inversion required to form four isomers. * **Rabiesviruses (Option B):** These belong to the *Rhabdoviridae* family and possess a **negative-sense, single-stranded RNA (-ssRNA)** genome, not DNA. * **Orthomyxoviruses (Option D):** These (e.g., Influenza) possess a **segmented, negative-sense, single-stranded RNA** genome. While they have segments, they do not have dsDNA isomers. **High-Yield Clinical Pearls for NEET-PG:** * **Herpesvirus Structure:** They are the only viruses that possess an **envelope**, a **tegument** (space between capsid and envelope), and a dsDNA genome. * **Replication:** Unlike most DNA viruses that replicate in the nucleus, **Poxviruses** are the exception—they replicate in the **cytoplasm** because they carry their own DNA-dependent RNA polymerase. * **Isomer Significance:** The four isomers of Herpesviruses are functionally equivalent; all four are infectious and capable of producing progeny.

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Virology — MCQs

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