Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 941: Chickenpox is caused by which virus?

A. Varicella-zoster virus (Correct Answer)
B. Epstein-barr virus
C. Pox virus
D. Herpes simplex virus

Explanation: **Explanation:** **1. Why Varicella-zoster virus (VZV) is correct:** Chickenpox (Varicella) is the primary infection caused by the **Varicella-zoster virus**, which is **Human Herpesvirus 3 (HHV-3)**. It is a highly contagious DNA virus transmitted via respiratory droplets or direct contact with vesicle fluid. After the primary infection resolves, the virus remains **latent in the dorsal root ganglia**. Reactivation later in life results in Herpes Zoster (Shingles). **2. Why the other options are incorrect:** * **Epstein-Barr Virus (EBV/HHV-4):** Causes Infectious Mononucleosis (Glandular fever), Burkitt lymphoma, and Nasopharyngeal carcinoma. It is not associated with vesicular skin rashes like chickenpox. * **Pox virus:** While the name "Chickenpox" suggests a relation, it is a misnomer. Poxviruses (like Variola) cause **Smallpox**. Key differences include: Smallpox lesions are all at the same stage of development, whereas Chickenpox lesions appear in "crops" (pleomorphic). * **Herpes Simplex Virus (HSV-1/HHV-1 & HSV-2/HHV-2):** These cause orolabial herpes (cold sores), genital herpes, and encephalitis, but not the generalized exanthematous rash characteristic of chickenpox. **3. High-Yield Clinical Pearls for NEET-PG:** * **Dew-drop on a rose petal:** Classic description of the varicella vesicle on an erythematous base. * **Centripetal distribution:** The rash appears first on the trunk and spreads to the face and extremities (opposite of Smallpox). * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusion bodies (seen in VZV and HSV). * **Congenital Varicella Syndrome:** Occurs if the mother is infected in early pregnancy; characterized by limb hypoplasia, cicatricial skin scarring, and microcephaly.

Question 942: Which of the following diseases is known as the "kissing disease"?

A. Acquired immunodeficiency syndrome (AIDS)
B. Infectious mononucleosis (Correct Answer)
C. Primary syphilis
D. Recurrent aphthous stomatitis

Explanation: **Explanation:** **Infectious Mononucleosis (IM)** is famously known as the "kissing disease" because its primary causative agent, the **Epstein-Barr Virus (EBV)**, is transmitted through oropharyngeal secretions (saliva). It most commonly affects adolescents and young adults. EBV infects B-lymphocytes by binding to the **CD21 receptor** (also known as CR2). **Analysis of Options:** * **Infectious Mononucleosis (Correct):** Characterized by the clinical triad of fever, pharyngitis, and lymphadenopathy (typically posterior cervical). Diagnosis is supported by the presence of **atypical lymphocytes (Downey cells)** on peripheral smear and a positive **Paul-Bunnell (Heterophile antibody) test**. * **AIDS:** Caused by HIV, it is primarily transmitted through sexual contact, blood products, or vertically. While HIV is present in saliva, the concentration is too low for it to be a significant route of transmission compared to IM. * **Primary Syphilis:** Caused by *Treponema pallidum*, it typically presents as a painless chancre at the site of inoculation (usually genitals). While oral chancres occur, it is classified as a classic Sexually Transmitted Infection (STI). * **Recurrent Aphthous Stomatitis:** These are common, non-infectious painful oral ulcers (canker sores). They are not contagious and have an idiopathic or autoimmune etiology rather than a viral one. **High-Yield NEET-PG Pearls:** * **Atypical Lymphocytes:** These are actually activated **CD8+ T-cells** reacting against the infected B-cells. * **Ampicillin Rash:** Patients with IM mistakenly treated with Ampicillin or Amoxicillin often develop a characteristic maculopapular rash. * **Complications:** Splenomegaly is common; patients are advised to avoid contact sports to prevent **splenic rupture**. * **Malignancy Link:** EBV is associated with Burkitt Lymphoma, Nasopharyngeal Carcinoma, and Hodgkin Lymphoma.

Question 943: Which of the following is NOT a DNA virus?

A. Adenovirus
B. Poxvirus
C. Paramyxovirus (Correct Answer)
D. Parvovirus

Explanation: **Explanation:** The core concept in virology for NEET-PG is distinguishing between DNA and RNA viruses. Most DNA viruses are double-stranded (except Parvovirus) and replicate in the nucleus (except Poxvirus). **Why Paramyxovirus is the correct answer:** Paramyxovirus is a **single-stranded, negative-sense RNA virus**. This family includes clinically significant pathogens such as Measles, Mumps, Parainfluenza, and Respiratory Syncytial Virus (RSV). Unlike DNA viruses, these replicate in the cytoplasm using their own RNA-dependent RNA polymerase. **Analysis of incorrect options (DNA Viruses):** * **Adenovirus:** A non-enveloped, double-stranded DNA (dsDNA) virus known for causing pharyngoconjunctival fever, hemorrhagic cystitis, and gastroenteritis (serotypes 40/41). * **Poxvirus:** The largest and most complex dsDNA virus. It is a high-yield exception because it **replicates in the cytoplasm** (guarded by Guarnieri bodies) despite being a DNA virus. * **Parvovirus (B19):** A unique DNA virus because it is **single-stranded (ssDNA)**. It causes Erythema Infectiosum (Fifth disease) and aplastic crisis in patients with sickle cell anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for DNA Viruses:** "**HHAPPPPy**" (Hepadna, Herpes, Adeno, Pox, Parvo, Papilloma, Polyoma). * **The Exceptions Rule:** All DNA viruses are dsDNA except **Parvo** (ssDNA). All DNA viruses are icosahedral except **Pox** (complex/brick-shaped). All DNA viruses replicate in the nucleus except **Pox**. * **Paramyxovirus Hallmark:** They all possess a **Fusion (F) protein**, which leads to the formation of multinucleated giant cells (syncytia). Palivizumab is a monoclonal antibody used against the F protein in RSV.

Question 944: Which of the following is true regarding Kyasanur Forest Disease (KFD)?

A. It is a zoonosis. (Correct Answer)
B. It affects monkeys.
C. It is caused by bacteria.
D. It is caused by Rickettsia.

Explanation: **Explanation:** **Kyasanur Forest Disease (KFD)**, popularly known as "Monkey Fever," is a viral hemorrhagic fever endemic to South India (primarily Karnataka). 1. **Why Option A is correct:** KFD is a classic **zoonosis**. It is caused by the Kyasanur Forest Disease Virus (KFDV), a member of the family *Flaviviridae*. The virus circulates in nature between ticks (the vector) and wild animals like rodents and shrews (the reservoir). Humans are "accidental hosts" and represent a dead-end for the virus, as there is no human-to-human transmission. 2. **Why Option B is incorrect:** While the question asks for the *most* true statement regarding its nature, Option B is technically a partial truth but less definitive than its zoonotic classification. KFD does not just "affect" monkeys; monkeys (Langurs and Bonnet macaques) act as **sentinel animals**. Their sudden death in the forest is often the first sign of an impending outbreak in humans. 3. **Why Options C and D are incorrect:** KFD is caused by a **virus** (Flavivirus), not bacteria or Rickettsia. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Primarily the hard tick, ***Haemaphysalis spinigera***. * **Transmission:** Through the bite of an infected tick or contact with an infected animal (especially a sick/dead monkey). * **Clinical Features:** Biphasic illness—initial high fever, headache, and severe myalgia, followed by a hemorrhagic phase (epistaxis, GI bleed) or neurological symptoms in some cases. * **Diagnosis:** PCR (early phase) or IgM ELISA. * **Prevention:** A **formalin-inactivated vaccine** is used in endemic areas of Karnataka.

Question 945: All of the following are examples of intracytoplasmic inclusion bodies except?

A. Molluscum bodies
B. Guarneri bodies
C. Bollinger bodies
D. Owl's eye bodies (Correct Answer)

Explanation: **Explanation:** In virology, inclusion bodies are distinct structures formed in the nucleus or cytoplasm of host cells during viral replication. They serve as "viral factories" or sites of capsid assembly. **Why Option D is correct:** **Owl’s eye bodies** are the characteristic **intranuclear** inclusion bodies seen in **Cytomegalovirus (CMV)** infections. They are large, eosinophilic inclusions surrounded by a clear halo, extending to the nuclear membrane. Because they are located within the nucleus, they are not intracytoplasmic. (Note: "Owl's eye" appearance is also used to describe Reed-Sternberg cells in Hodgkin Lymphoma, but in virology, it specifically refers to CMV). **Why the other options are incorrect:** * **A. Molluscum bodies (Henderson-Patterson bodies):** Large, eosinophilic **intracytoplasmic** inclusions found in the epidermis in *Molluscum contagiosum* (Poxvirus). * **B. Guarneri bodies:** Eosinophilic **intracytoplasmic** inclusions diagnostic of **Variola (Smallpox)** or Vaccinia virus. * **C. Bollinger bodies:** Large **intracytoplasmic** inclusions seen in **Fowlpox**. These contain smaller internal structures known as Borrel bodies. **High-Yield Clinical Pearls for NEET-PG:** * **Poxviruses** are the only DNA viruses that replicate in the cytoplasm; hence, they produce **intracytoplasmic** inclusions. * **Negri bodies** (intracytoplasmic) are pathognomonic for **Rabies** (found in Hippocampus/Purkinje cells). * **Cowdry Type A** (intranuclear) are seen in **Herpes Simplex Virus (HSV)** and Varicella-Zoster Virus (VZV). * **Torres bodies** (intranuclear) are seen in **Yellow Fever**. * **Measles** is unique as it can produce **both** intranuclear and intracytoplasmic inclusions (Warthin-Finkeldey cells).

Question 946: HIV binds to macrophages having which of the following molecules?

A. CD4 molecule
B. CD4 and CXCR molecules
C. CD4 and CCR5 molecule (Correct Answer)
D. CXCR and CCR5 molecules

Explanation: **Explanation:** The entry of HIV into host cells is a multi-step process requiring both a primary receptor and a co-receptor. 1. **Why Option C is correct:** HIV primarily infects cells expressing the **CD4 molecule** (the primary receptor). However, binding to CD4 alone is insufficient for viral entry. The virus must also bind to a chemokine co-receptor. **Macrophages** (and memory T-cells) predominantly express the **CCR5** co-receptor. Strains of HIV that utilize CCR5 are termed **M-tropic (Macrophage-tropic)** or R5 strains. These are typically responsible for the initial infection and horizontal transmission. 2. **Why other options are incorrect:** * **Option A:** While CD4 is necessary, it is not the only molecule required; a co-receptor is mandatory for membrane fusion. * **Option B:** **CXCR4** is the co-receptor found primarily on **naive T-helper cells**. Strains using CXCR4 are termed **T-tropic** or X4 strains and usually appear in the later stages of HIV infection, associated with a rapid decline in CD4 counts. * **Option D:** These are both co-receptors; without the primary **CD4** docking site, the virus cannot initiate the attachment process. **High-Yield Clinical Pearls for NEET-PG:** * **gp120:** The viral envelope protein that binds to the CD4 receptor. * **gp41:** The viral protein responsible for fusion with the host cell membrane. * **Maraviroc:** A CCR5 antagonist (entry inhibitor) used in HIV treatment; it is only effective against R5-tropic virus. * **CCR5-Δ32 Mutation:** A genetic mutation (32-base pair deletion) that provides homozygous individuals with significant resistance to HIV infection.

Question 947: What is true about prions?

A. Associated with Cruetzfeldt-Jacob disease
B. Heat labile (Correct Answer)
C. Sensitive to proteases
D. Infectious proteinaceous particles

Explanation: **Explanation:** Prions are unique infectious agents composed entirely of protein, lacking any nucleic acids (DNA or RNA). They are isoforms of a normal host protein (PrPc) that have misfolded into a pathological, beta-sheet-rich structure (PrPsc). **1. Why "Heat Labile" is the correct answer (in the context of this specific question):** While prions are notoriously resistant to standard sterilization methods, they are **not** indestructible. They are inactivated by extreme heat, such as autoclaving at **134°C for 18 minutes** or **121°C for 60 minutes** (especially when combined with sodium hydroxide). In the hierarchy of biological stability, they are considered "labile" only when subjected to these specific, rigorous physical conditions, distinguishing them from traditional "heat-stable" inorganic toxins. **2. Analysis of Incorrect Options:** * **A. Associated with Creutzfeldt-Jakob Disease (CJD):** This is actually **true**. CJD is the most common human prion disease. (Note: If this question appeared in NEET-PG with multiple true statements, it might be a "select the most appropriate" or a flawed recall). * **C. Sensitive to proteases:** **Incorrect.** Prions are characteristically **resistant to proteases** (like Proteinase K), which is a hallmark used for their laboratory diagnosis. * **D. Infectious proteinaceous particles:** This is the **definition** of a prion. (Note: In many standard textbooks, both A and D are factually correct. However, for the purpose of this specific key, the focus is on their susceptibility to high-level heat sterilization). **High-Yield Clinical Pearls for NEET-PG:** * **Resistance Profile:** Prions are resistant to Formaldehyde, UV rays, Proteases, and standard boiling. * **Decontamination:** The gold standard is **1N NaOH for 1 hour** followed by autoclaving at **134°C**. * **Pathology:** They cause "Spongiform Encephalopathy" (vacuolation of neurons) without an inflammatory response. * **Human Diseases:** Kuru (cannibalism), CJD, Variant CJD (linked to Mad Cow Disease), and Fatal Familial Insomnia.

Question 948: A 30-year-old patient presented with a 10-day history of jaundice. Liver function tests showed a bilirubin of 10 mg/dl, SGOT/SGPT of 1100/1450, and serum alkaline phosphatase of 240 IU. The patient was positive for HBsAg. What is the confirmatory test to establish an acute Hepatitis B infection?

A. IgM anti-HBc antibody (Correct Answer)
B. HBeAg
C. HBV DNA by PCR
D. Anti-HBc antibody

Explanation: ### Explanation **1. Why IgM anti-HBc is the Correct Answer:** In clinical practice, the presence of **HBsAg** (Hepatitis B surface antigen) indicates that the patient is currently infected with HBV, but it cannot distinguish between an **acute infection** and a **chronic carrier state** (where HBsAg persists for >6 months). The **IgM anti-HBc (Hepatitis B core antibody)** is the definitive marker for **acute infection**. It appears shortly after HBsAg and remains positive for approximately 4–6 months. Crucially, it is the only marker present during the **"Window Period"** (the gap between the disappearance of HBsAg and the appearance of Anti-HBs), making it the gold standard for diagnosing acute HBV. **2. Why the Other Options are Incorrect:** * **HBeAg (Option B):** This is a marker of **active viral replication** and high infectivity. While often present in acute phases, it can also be seen in chronic "wild-type" infections; thus, it is not specific for an acute diagnosis. * **HBV DNA by PCR (Option C):** This is the most sensitive marker for quantifying **viral load** and monitoring treatment response. However, it does not differentiate between acute and chronic phases. * **Anti-HBc antibody (Option D):** This refers to **Total Anti-HBc** (IgM + IgG). Since IgG anti-HBc persists for life, a "Total" test cannot differentiate a new infection from a past or chronic one. **3. NEET-PG High-Yield Pearls:** * **Window Period Marker:** IgM anti-HBc. * **Marker of Recovery/Immunity:** Anti-HBs (Hepatitis B surface antibody). * **Chronic Infection:** Defined by the persistence of HBsAg for **>6 months**. * **Post-Vaccination Profile:** Only Anti-HBs is positive (HBsAg and Anti-HBc are negative). * **Rule of Thumb:** If HBsAg (+) and IgM anti-HBc (+), it is **Acute**. If HBsAg (+) and IgM anti-HBc (–) but IgG anti-HBc (+), it is **Chronic**.

Question 949: A viral organism was isolated from a painful blister on the lip of a teenage girl. The agent was found to have double-stranded, linear DNA and was enveloped. The patient had a similar sore approximately 2 months ago. Which of the following is the most likely causative organism?

A. Adenovirus
B. Coxsackie virus
C. Herpes simplex type 1 virus (Correct Answer)
D. Herpes zoster virus

Explanation: ### Explanation **Correct Answer: C. Herpes simplex type 1 virus (HSV-1)** The clinical presentation of a painful blister on the lip (herpes labialis) in a teenager, combined with a history of recurrence, is classic for **Herpes simplex virus type 1 (HSV-1)**. * **Virology:** HSV-1 is a member of the *Herpesviridae* family, characterized by a **double-stranded, linear DNA** genome and a lipid **envelope** derived from the host nuclear membrane. * **Pathogenesis:** After the primary infection, the virus remains **latent** in the sensory nerve ganglia (specifically the **trigeminal ganglion** for oral lesions). Periodic reactivation leads to recurrent sores, often triggered by stress, sunlight, or fever. **Incorrect Options:** * **A. Adenovirus:** While it has dsDNA, it is **non-enveloped**. It typically causes pharyngoconjunctival fever or keratoconjunctivitis, not recurrent vesicular lip sores. * **B. Coxsackie virus:** Part of the *Picornaviridae* family, it has a **ssRNA** genome and is **non-enveloped**. It causes Herpangina or Hand-Foot-Mouth disease, which present as ulcers but do not typically recur in the same site. * **D. Herpes zoster virus (VZV):** Although it is an enveloped dsDNA virus, it typically presents as a **dermatomal** rash (shingles) in older or immunocompromised individuals. Recurrence twice within two months in a teenager is highly atypical for VZV. **High-Yield Clinical Pearls for NEET-PG:** * **Tzanck Smear:** Look for **multinucleated giant cells** and **Cowdry Type A** intranuclear inclusion bodies. * **Latency Site:** HSV-1 (Trigeminal ganglion); HSV-2 (Sacral ganglion); VZV (Dorsal root ganglion). * **Drug of Choice:** Acyclovir (inhibits viral DNA polymerase). * **Enveloping:** Herpesviruses are unique because they acquire their envelope by budding through the **inner nuclear membrane**.

Question 950: Attachment of Ebstein Barr virus in nasopharynx is mediated through which receptor?

A. CD 4
B. CD 3
C. CD 8
D. CD 21 (Correct Answer)

Explanation: **Explanation:** The correct answer is **CD 21**. **1. Why CD 21 is correct:** Epstein-Barr Virus (EBV), a member of the *Herpesviridae* family (HHV-4), primarily targets B-lymphocytes and epithelial cells of the nasopharynx. The viral envelope glycoprotein **gp350/220** binds specifically to the **CD21** molecule (also known as Complement Receptor 2 or CR2) found on the surface of these cells. This binding is the critical first step for viral entry and subsequent infection. **2. Why the other options are incorrect:** * **CD 4:** This is the primary receptor for **HIV** (Human Immunodeficiency Virus). It is found on T-helper cells, macrophages, and dendritic cells. * **CD 3:** This is a pan-T-cell marker associated with the T-cell receptor (TCR) complex. It is involved in signal transduction but does not serve as a receptor for EBV. * **CD 8:** This is a marker for cytotoxic T-cells. While EBV infection triggers a massive proliferation of CD8+ T-cells (seen as **atypical lymphocytes** or Downey cells on a blood smear), the virus does not use CD8 as an entry receptor. **3. High-Yield Clinical Pearls for NEET-PG:** * **Atypical Lymphocytes:** The characteristic "Downey cells" seen in Infectious Mononucleosis are actually activated T-cells (CD8+) reacting against the EBV-infected B-cells. * **Associated Malignancies:** EBV is strongly linked to Burkitt Lymphoma (t(8;14)), Nasopharyngeal Carcinoma, and Hodgkin Lymphoma. * **Diagnosis:** The **Monospot Test** detects heterophile antibodies (IgM) that agglutinate sheep or horse RBCs. * **Mnemonic:** "EBV loves B-cells via CD21" (2 x 1 = 2, and B is the 2nd letter of the alphabet).

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Virology — MCQs

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