Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 111: Which of the following is NOT true about Parvovirus B-19?

A. Approximately 10% of infections spread by transplacental route. (Correct Answer)
B. Parvovirus B19 exclusively infects humans.
C. It is a DNA virus.
D. It affects erythroid progenitors, but individuals who totally lack Blood Group P antigen are resistant to infection.

Explanation: ### Explanation **1. Why Option A is the Correct Answer (The False Statement):** While Parvovirus B19 can indeed cross the placenta, the transmission rate is much higher than 10%. In a non-immune pregnant woman, the risk of transplacental transmission to the fetus is approximately **33% (one-third)**. While most fetal infections resolve spontaneously, about 5-10% may lead to complications like **Hydrops Fetalis** or fetal death, particularly if the infection occurs during the second trimester. **2. Analysis of Incorrect Options (True Statements):** * **Option B:** Parvovirus B19 is a strictly **human pathogen**. While other parvoviruses affect animals (e.g., canine parvovirus), B19 does not cross species. * **Option C:** It belongs to the family *Parvoviridae*. It is unique for being the only **Single-Stranded DNA (ssDNA)** virus of medical importance. * **Option D:** The virus utilizes the **P-antigen (Globoside)** on the surface of erythroid progenitor cells as its primary cellular receptor. Individuals with the rare "p phenotype" (who lack P-antigen) are naturally resistant to infection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Causes **Erythema Infectiosum (Fifth Disease)**, characterized by the classic "slapped-cheek" rash in children. * **Hematologic Impact:** It causes a temporary halt in erythropoiesis. In patients with high red cell turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis), it can trigger a life-threatening **Aplastic Crisis**. * **Diagnosis:** Detection of **IgM antibodies** (recent infection) or **PCR** for viral DNA (especially in immunocompromised patients or during aplastic crises). * **Morphology:** It is the **smallest** DNA virus and is **non-enveloped** (icosahedral symmetry).

Question 112: Which virus causes nephropathy in transplant recipients?

A. JC virus
B. BK virus (Correct Answer)
C. SV-40 virus
D. Merkel cell virus

Explanation: **Explanation:** The correct answer is **BK virus**. Both BK and JC viruses are members of the **Polyomaviridae** family. They typically cause primary infection in childhood and remain latent in the body. **1. Why BK Virus is correct:** In immunocompromised individuals, particularly **renal transplant recipients**, the BK virus reactivates in the kidney and urinary tract. This leads to **BK Virus-Associated Nephropathy (BKVAN)**, characterized by tubulointerstitial nephritis, which can lead to graft rejection. A key diagnostic feature in urine cytology is the presence of **"Decoy cells"** (cells with large intranuclear inclusion bodies). **2. Why other options are incorrect:** * **JC Virus:** While also a Polyomavirus, it primarily targets the CNS. Reactivation in AIDS or transplant patients causes **Progressive Multifocal Leukoencephalopathy (PML)**, a demyelinating disease of the white matter. * **SV-40 (Simian Virus 40):** This is a primate polyomavirus. While it was a famous contaminant of early polio vaccines and is used extensively in molecular biology research, it is not a recognized cause of human nephropathy. * **Merkel Cell Virus:** This polyomavirus is associated with **Merkel cell carcinoma**, a rare but aggressive form of skin cancer; it does not cause renal pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** **B**K virus affects the **B**ladder and **K**idney; **J**C virus affects the **J**unction (CNS white matter). * **Diagnosis:** Gold standard is a renal biopsy showing viral cytopathic effects; screening is done via PCR for viral load. * **Decoy Cells:** Must be distinguished from CMV inclusions or malignant cells in urine.

Question 113: Rotavirus infection is diagnosed by the presence of what?

A. Antigen in stool by ELISA (Correct Answer)
B. Virus in stool
C. Antigen in blood
D. Antibody in stool

Explanation: **Explanation:** Rotavirus is the most common cause of severe, dehydrating diarrhea in infants and young children worldwide. The diagnosis is primarily established by the detection of the **viral antigen (VP6 protein)** in the patient's stool. 1. **Why Option A is correct:** **ELISA (Enzyme-Linked Immunosorbent Assay)** is the gold standard and most widely used diagnostic method because it is highly sensitive, specific, and rapid. It detects the group-specific antigen (VP6) which is shed in high concentrations in the feces during the acute phase of the illness. 2. **Why Option B is incorrect:** While the virus is present in the stool, visualizing it requires **Immunoelectron Microscopy (IEM)**. This is technically demanding, expensive, and not used for routine clinical diagnosis. 3. **Why Option C is incorrect:** Rotavirus is a localized infection of the mature enterocytes of the small intestine. It does not typically cause significant viremia; therefore, blood antigen testing is not a standard diagnostic approach. 4. **Why Option D is incorrect:** While copro-antibodies (IgA) are produced, they are used more for research and epidemiological studies rather than acute clinical diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Rotavirus belongs to the *Reoviridae* family. It is a non-enveloped, **double-stranded RNA (dsRNA)** virus with a **segmented genome (11 segments)**. * **Appearance:** Under Electron Microscopy, it has a characteristic **"Wheel-like" appearance** (Latin *Rota* = wheel). * **Mechanism:** It produces a viral enterotoxin called **NSP4**, which induces calcium-dependent chloride secretion, leading to secretory diarrhea. * **Vaccines:** Two major live-attenuated oral vaccines are used: **Rotarix** (monovalent) and **RotaTeq** (pentavalent). In India, **Rotavac** is part of the National Immunization Schedule.

Question 114: The HIV virus binds directly to the surface receptors of CD4 lymphocytes with _____.

A. Reverse transcriptase
B. Integrase
C. Hemagglutinin
D. Glycoprotein 120 (Correct Answer)

Explanation: **Explanation:** The entry of HIV into a host cell is a multi-step process initiated by the binding of the virus to the **CD4 receptor** found on T-lymphocytes, macrophages, and dendritic cells. 1. **Why Glycoprotein 120 (gp120) is correct:** The HIV envelope contains spikes composed of two subunits: **gp120 (surface subunit)** and **gp41 (transmembrane subunit)**. Gp120 is specifically responsible for **attachment**. It binds directly to the CD4 molecule. This binding induces a conformational change in gp120, allowing it to interact with a co-receptor (CCR5 or CXCR4), which then triggers gp41 to mediate membrane fusion. 2. **Why other options are incorrect:** * **Reverse transcriptase (A):** An enzyme that converts viral RNA into DNA *after* the virus has entered the cell. * **Integrase (B):** An enzyme responsible for integrating the viral DNA into the host cell genome. * **Hemagglutinin (C):** A surface glycoprotein found on the **Influenza virus**, not HIV, used for binding to sialic acid receptors. **High-Yield Clinical Pearls for NEET-PG:** * **gp120:** Responsible for **attachment** (Target for attachment inhibitors). * **gp41:** Responsible for **fusion** (Target for the drug **Enfuvirtide**). * **p24:** The major capsid protein; it is the earliest serological marker to appear and is used for early diagnosis in the **p24 antigen assay**. * **Co-receptors:** **CCR5** is used by M-tropic strains (early infection), while **CXCR4** is used by T-mropic strains (late-stage/progression). **Maraviroc** is a drug that blocks the CCR5 receptor.

Question 115: Activation of the A1 subunit of cholera toxin causes increased activity of:

A. Adenylate cyclase (Correct Answer)
B. Guanylate cyclase
C. cGMP
D. Na K ATPase

Explanation: **Explanation:** Cholera toxin (produced by *Vibrio cholerae*) is a classic **A-B subunit toxin**. The mechanism of action involves the B-subunit binding to the **GM1 ganglioside** receptor on enterocytes, allowing the A-subunit to enter the cell. Once inside, the **A1 subunit** catalyzes the **ADP-ribosylation** of the **Gs (stimulatory) protein**. This modification locks the Gs protein in its "on" (active) state, preventing the hydrolysis of GTP to GDP. This leads to the constitutive activation of **Adenylate cyclase**, resulting in a massive increase in intracellular **cyclic AMP (cAMP)** levels. High cAMP levels activate Protein Kinase A, which phosphorylates the CFTR channel, leading to the hypersecretion of chloride, sodium, and water into the intestinal lumen, manifesting as "rice-water stools." **Analysis of Incorrect Options:** * **B & C (Guanylate cyclase/cGMP):** These are the targets of the **Heat-Stable (ST) toxin** of *Enterotoxigenic E. coli (ETEC)*. Cholera toxin specifically targets the cAMP pathway, not the cGMP pathway. * **D (Na K ATPase):** Cholera toxin does not directly activate this pump. In fact, the massive efflux of electrolytes and water overwhelms the resorptive capacity of the intestinal transporters. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** **C**holera toxin increases **c**AMP (both start with 'C'). * **ADP-ribosylation:** Other toxins using this mechanism include Diphtheria toxin, Pseudomonas Exotoxin A (both target EF-2), and Pertussis toxin (targets Gi protein). * **Treatment:** The mainstay is aggressive fluid resuscitation (ORS/IV fluids). ORS works because the **SGLT-1 (Sodium-Glucose cotransporter)** remains functional despite the toxin's action.

Question 116: Transplacental transmission occurs in all the following EXCEPT:

A. Cytomegalovirus
B. Herpes virus
C. Hepatitis E virus (Correct Answer)
D. Thalidomide

Explanation: **Explanation:** The question tests the knowledge of **vertical transmission** (specifically transplacental) versus other modes of perinatal infection. **1. Why Hepatitis E Virus (HEV) is the correct answer:** Hepatitis E is primarily transmitted via the **fecal-oral route**. While HEV is notorious for causing high mortality (up to 20%) in pregnant women due to fulminant hepatic failure, it is **not** typically characterized by transplacental transmission leading to congenital malformations. While rare cases of vertical transmission at the time of delivery have been reported, it is not a classic "TORCH" agent and does not cross the placenta to cause chronic intrauterine infection. **2. Analysis of other options:** * **Cytomegalovirus (CMV):** The most common cause of congenital viral infection. It readily crosses the placenta, leading to "Cytomegalic Inclusion Disease" (chorioretinitis, microcephaly, and periventricular calcifications). * **Herpes Simplex Virus (HSV):** While most neonatal HSV is acquired during delivery (birth canal), transplacental transmission can occur (Congenital HSV syndrome), leading to skin vesicles, scarring, and CNS abnormalities. * **Thalidomide:** Although a drug and not a virus, it is a classic **teratogen** that crosses the placental barrier, famously causing phocomelia (seal-like limbs). **NEET-PG High-Yield Pearls:** * **TORCH Complex:** Toxoplasmosis, Others (Syphilis, Varicella, Parvovirus B19), Rubella, CMV, and Herpes. All these cross the placenta. * **Hepatitis E & Pregnancy:** HEV genotype 1 and 2 are associated with high maternal mortality in the 3rd trimester. * **CMV:** Look for "Owl’s eye" intranuclear inclusions in histology. * **Rubella:** Classic triad includes Cataracts, Sensorineural deafness, and PDA (Patent Ductus Arteriosus).

Question 117: Which of the following viruses causes hemolysis of red blood cells?

A. Rubella
B. Human parvovirus B19 (Correct Answer)
C. Measles
D. Dengue virus

Explanation: **Explanation:** **Human Parvovirus B19** is the correct answer because of its unique tropism for erythroid progenitor cells. The virus binds to the **P-antigen** (globoside) on the surface of red blood cells and their precursors. Once inside, it replicates in the nucleus of rapidly dividing erythroblasts, leading to direct cytotoxicity and **lysis (hemolysis)** of the cells. In healthy individuals, this causes a transient drop in hemoglobin; however, in patients with high RBC turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis), it can trigger a life-threatening **Aplastic Crisis**. **Analysis of Incorrect Options:** * **Rubella:** A Togavirus that causes German Measles. While it can cause thrombocytopenia or vascular complications (congenital rubella syndrome), it does not directly infect or lyse RBCs. * **Measles:** A Paramyxovirus characterized by Koplik spots and a maculopapular rash. It primarily infects respiratory epithelium and immune cells (via CD150/SLAM), not erythroid cells. * **Dengue Virus:** A Flavivirus that causes "breakbone fever." Its primary hematological impact is **thrombocytopenia** (low platelets) and plasma leakage due to increased vascular permeability, rather than direct hemolysis of RBCs. **High-Yield Clinical Pearls for NEET-PG:** * **Erythema Infectiosum (Fifth Disease):** Characterized by the classic "slapped-cheek" rash in children. * **Hydrops Fetalis:** If a pregnant woman is infected, the virus crosses the placenta, lyses fetal RBCs, leading to severe anemia, high-output heart failure, and fetal edema. * **Receptor:** The P-antigen is the essential cellular receptor; individuals lacking this antigen are naturally resistant to B19 infection.

Question 118: Herpes Simplex Virus type 2 (HSV-2) predominantly affects which part of the body?

A. Face
B. Chest
C. Genital area (Correct Answer)
D. Back

Explanation: **Explanation:** The correct answer is **C. Genital area**. **Medical Concept:** Herpes Simplex Virus (HSV) belongs to the *Alphaherpesvirinae* subfamily. A classic clinical rule of thumb is that **HSV-1** typically affects sites **"above the waist"** (oral-facial), while **HSV-2** affects sites **"below the waist"** (genital). HSV-2 is the primary cause of genital herpes, characterized by painful vesicles and ulcers on the genitalia, perineum, or anal region. It is primarily transmitted through sexual contact and establishes latency in the **sacral ganglia**. **Analysis of Incorrect Options:** * **A. Face:** This is the characteristic site for **HSV-1**, which causes herpes labialis (cold sores) and gingivostomatitis. It establishes latency in the **trigeminal ganglion**. * **B & D. Chest and Back:** These dermatomal distributions are classic for **Varicella-Zoster Virus (VZV)** reactivation, known as Herpes Zoster (shingles). While HSV can occasionally cause cutaneous lesions elsewhere (e.g., Herpetic whitlow on fingers), it does not predominantly target the trunk. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The gold standard is PCR. However, the **Tzanck Smear** is a classic exam favorite; it shows **multinucleated giant cells** with **Cowdry Type A** intranuclear inclusion bodies. * **Neonatal Herpes:** Usually caused by HSV-2 during passage through the birth canal. * **Encephalitis:** HSV-1 is the most common cause of sporadic viral encephalitis, typically involving the **temporal lobes**. * **Treatment:** Acyclovir is the drug of choice, which acts by inhibiting viral DNA polymerase.

Question 119: Kaposi's sarcoma is caused by which of the following viruses?

A. Human Herpesvirus 5 (HHV-5)
B. Human Herpesvirus 5 (HHV-5)
C. Human Herpesvirus 7 (HHV-7)
D. Human Herpesvirus 8 (HHV-8) (Correct Answer)

Explanation: **Explanation:** **Kaposi’s Sarcoma (KS)** is a multicentric vascular neoplasm caused by **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi’s Sarcoma-associated Herpesvirus (KSHV). HHV-8 infects vascular endothelial cells, leading to the expression of viral oncogenes (like v-cyclin and v-FLIP) that promote angiogenesis and uncontrolled cell proliferation. It is classically associated with HIV/AIDS patients (AIDS-defining illness) but also occurs in endemic (African), classic (Mediterranean), and transplant-related forms. **Analysis of Options:** * **Option D (HHV-8):** Correct. It is the primary etiological agent for all forms of Kaposi’s Sarcoma. It is also linked to **Primary Effusion Lymphoma (PEL)** and **Multicentric Castleman Disease**. * **Option A & B (HHV-5):** Incorrect. HHV-5 is **Cytomegalovirus (CMV)**. It causes infectious mononucleosis-like syndrome, retinitis in AIDS patients, and is the most common viral cause of congenital malformations (e.g., periventricular calcifications). * **Option C (HHV-7):** Incorrect. HHV-7, along with HHV-6, is a causative agent of **Roseola Infantum (Exanthema Subitum)**, characterized by high fever followed by a maculopapular rash. **High-Yield Clinical Pearls for NEET-PG:** * **Histopathology:** Look for "slit-like vascular spaces" containing extravasated RBCs and spindle-shaped cells. * **Transmission:** Primarily through saliva (sexual and non-sexual routes). * **Associated Malignancies:** HHV-8 is unique among herpesviruses for its strong association with B-cell lymphomas (PEL). * **Treatment:** Highly Active Antiretroviral Therapy (HAART) often leads to regression of KS lesions in HIV patients.

Question 120: Which of the following viruses is not an enveloped virus but contains double-stranded RNA?

A. Adenovirus
B. Reovirus (Correct Answer)
C. Cytomegalovirus (CMV)
D. Hepatitis B virus

Explanation: ### Explanation The correct answer is **Reovirus**. This question tests your knowledge of viral structure, specifically the classification of genomes and envelopes. **1. Why Reovirus is correct:** The **Reoviridae** family (which includes Rotavirus and Coltivirus) is unique because it is one of the few virus families that possesses a **double-stranded RNA (dsRNA)** genome. Structurally, Reoviruses are **non-enveloped** (naked) and exhibit a characteristic double-layered icosahedral capsid. A high-yield mnemonic for dsRNA is: *"A **Double**-stranded **R**eovirus **R**aces"* (dsRNA = Reovirus). **2. Why the other options are incorrect:** * **Adenovirus (Option A):** While it is a non-enveloped (naked) virus, its genome consists of **double-stranded DNA (dsDNA)**, not RNA. It is a common cause of conjunctivitis and pharyngitis. * **Cytomegalovirus (Option C):** CMV belongs to the Herpesviridae family. These are **enveloped** viruses with a **dsDNA** genome. * **Hepatitis B Virus (Option D):** HBV is an **enveloped** virus. Its genome is unique—**partially double-stranded circular DNA**—and it uses reverse transcriptase during replication. **3. High-Yield Clinical Pearls for NEET-PG:** * **Rotavirus:** The most common cause of severe diarrhea in infants and children worldwide. It has a **segmented genome** (11 segments), allowing for genetic reassortment. * **Naked Viruses:** Remember the mnemonic **PAPP H**elp **C**alculate **R**eality (**P**apilloma, **A**deno, **P**arvo, **P**olyoma, **H**epna, **C**alici, **R**eo). These are generally more resistant to environmental heat and detergents. * **RNA Genomes:** Almost all RNA viruses are single-stranded (ssRNA) *except* for Reoviridae.

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Virology — MCQs

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