Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 801: Which of the following is an AIDS-defining opportunistic illness?

A. Oral candidiasis (thrush)
B. Invasive carcinoma of the cervix (Correct Answer)
C. Cyclosporiasis
D. Herpes zoster virus

Explanation: **Explanation:** The diagnosis of AIDS is made in an HIV-infected individual when the CD4+ T-cell count falls below 200 cells/mm³ or when they develop a specific **AIDS-defining illness** as categorized by the CDC. **1. Why Invasive Cervical Carcinoma is correct:** Invasive cervical carcinoma is one of the three malignancies classified as AIDS-defining (alongside Kaposi sarcoma and Non-Hodgkin lymphoma). It is caused by high-risk strains of **Human Papillomavirus (HPV)**. In HIV-positive patients, the lack of cell-mediated immunity allows HPV to persist and progress rapidly to malignancy, making it a hallmark of advanced immunosuppression. **2. Why other options are incorrect:** * **Oral Candidiasis (Thrush):** While very common in HIV patients, it is considered a "Category B" (Symptomatic, non-AIDS) condition. It usually occurs at CD4 counts between 200–500 cells/mm³. Only **Esophageal, Tracheal, or Bronchial Candidiasis** is AIDS-defining. * **Cyclosporiasis:** This causes diarrheal illness but is not on the official CDC AIDS-defining list. However, **Isosporiasis** (Cystoisospora) and **Cryptosporidiosis** (if lasting >1 month) are AIDS-defining. * **Herpes Zoster (Shingles):** This occurs frequently in HIV patients due to waning immunity but is not AIDS-defining. However, **chronic/disseminated Herpes Simplex (HSV)** ulcers (lasting >1 month) are AIDS-defining. **High-Yield NEET-PG Pearls:** * **Mnemonic for AIDS-defining Cancers:** "K-L-C" (Kaposi Sarcoma, Lymphoma [Burkitt’s/Immunoblastic/Primary CNS], and Cervical Carcinoma). * **CD4 Cut-offs:** * **<200:** Pneumocystis jirovecii pneumonia (PJP). * **<100:** Toxoplasmosis, Cryptococcosis. * **<50:** Mycobacterium avium complex (MAC), CMV Retinitis. * **Note:** Pulmonary Tuberculosis is AIDS-defining regardless of the CD4 count in an HIV-positive patient.

Question 802: All of the following are DNA oncogenic viruses except?

A. Epstein Barr virus
B. Hepatitis B virus
C. Adult T cell Leukemia/lymphoma virus (Correct Answer)
D. Kaposi sarcoma virus

Explanation: **Explanation:** The core concept tested here is the classification of oncogenic viruses based on their genetic material. **1. Why Option C is correct:** **Adult T-cell Leukemia/Lymphoma virus (HTLV-1)** is an **RNA virus**. It belongs to the Retroviridae family. Unlike DNA viruses that may integrate their DNA directly, HTLV-1 uses reverse transcriptase to convert its RNA genome into DNA, which then integrates into the host genome. It is the only RNA virus (other than HCV) strongly linked to human malignancy, specifically Adult T-cell Leukemia/Lymphoma (ATLL). **2. Why the other options are incorrect:** * **Epstein-Barr Virus (EBV):** A double-stranded DNA virus (Herpesviridae, HHV-4). It is associated with Burkitt lymphoma, Nasopharyngeal carcinoma, and Hodgkin lymphoma. * **Hepatitis B Virus (HBV):** A partially double-stranded DNA virus (Hepadnaviridae). It is a major cause of Hepatocellular Carcinoma (HCC) via chronic inflammation and integration of the HBx gene. * **Kaposi Sarcoma Virus (KSHV/HHV-8):** A double-stranded DNA virus (Herpesviridae). It causes Kaposi sarcoma, Primary effusion lymphoma, and Multicentric Castleman disease. **High-Yield Clinical Pearls for NEET-PG:** * **DNA Oncogenic Viruses:** Include HPV (16, 18), EBV, HBV, HHV-8, and Merkel Cell Polyomavirus. * **RNA Oncogenic Viruses:** HTLV-1 (Directly oncogenic) and Hepatitis C Virus (Indirectly oncogenic via chronic inflammation). * **HTLV-1 Mechanism:** It carries the **tax gene**, which activates host cell proliferation and inhibits tumor suppressor genes (p53). * **HBV vs. HCV:** Remember that HBV is a DNA virus, while HCV is an RNA virus. Both cause HCC.

Question 803: Which of the following diseases is transmitted by a virus?

A. Molluscum contagiosum (Correct Answer)
B. Taenia capitis
C. Rhinosporodiosis
D. Impetigo

Explanation: **Explanation:** **Correct Option: A. Molluscum contagiosum** Molluscum contagiosum is a common cutaneous infection caused by the **Molluscum Contagiosum Virus (MCV)**, which is a member of the **Poxviridae** family. It is a large, enveloped, double-stranded DNA virus. Clinically, it presents as firm, pearly, umbilicated papules. In children, it is spread via direct contact or fomites, while in adults, it is often considered a sexually transmitted infection (STI). **Why the other options are incorrect:** * **B. Tinea capitis:** This is a fungal infection of the scalp and hair shafts, most commonly caused by dermatophytes of the genera *Trichophyton* and *Microsporum*. * **C. Rhinosporidiosis:** This is a chronic granulomatous infection caused by ***Rhinosporidium seeberi***. While previously thought to be a fungus, it is now classified as a **Mesomycetozoean** (a group of aquatic protists). It typically presents as friable, leafy polyps in the nasal mucosa. * **D. Impetigo:** This is a highly contagious **bacterial** skin infection. It is primarily caused by *Staphylococcus aureus* or *Streptococcus pyogenes* (Group A Strep). It is characterized by "honey-colored crusts." **NEET-PG High-Yield Pearls:** * **Histology of Molluscum:** Look for **Henderson-Paterson bodies** (large, eosinophilic intracytoplasmic inclusion bodies) on biopsy. * **Poxvirus Fact:** Unlike most DNA viruses that replicate in the nucleus, Poxviruses replicate entirely in the **cytoplasm** because they carry their own DNA-dependent RNA polymerase. * **Immunocompromised patients:** Extensive or giant molluscum lesions are often an indicator of underlying HIV/AIDS.

Question 804: What is the highly specific confirmatory test for HIV antibodies?

A. ELISA
B. Southern blot
C. Northern blot
D. Western blot (Correct Answer)

Explanation: ### Explanation **1. Why Western Blot is Correct:** Western blot is considered the "gold standard" confirmatory test for HIV because it detects specific antibodies against individual HIV antigens (proteins). Unlike screening tests that detect total antibodies, Western blot separates viral proteins by molecular weight using electrophoresis. A positive result requires the presence of antibodies against specific gene products, typically **gp41, gp120/160, and p24**. Its high specificity (near 100%) ensures that false positives from screening tests are identified and excluded. **2. Why Other Options are Incorrect:** * **ELISA (Enzyme-Linked Immunosorbent Assay):** This is the standard **screening test**. While highly sensitive (to avoid missing cases), it has lower specificity than Western blot and can yield false positives in conditions like autoimmune diseases or recent vaccinations. * **Southern Blot:** This technique is used to detect specific **DNA** sequences. It is not used for routine HIV antibody testing. * **Northern Blot:** This technique is used to detect specific **RNA** sequences. While HIV is an RNA virus, Northern blot is a research tool and not a clinical diagnostic test for HIV antibodies. **3. Clinical Pearls for NEET-PG:** * **Current Protocol Change:** While Western blot is the traditional answer, the latest NACO/CDC guidelines often favor the **HIV-1/HIV-2 differentiation immunoassay** or **Nucleic Acid Testing (NAT)** for confirmation due to the long "indeterminate" window of Western blot. * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 3–12 weeks). * **Early Diagnosis:** To detect HIV during the window period, the **p24 antigen assay** or **RT-PCR (Viral Load)** are the investigations of choice. * **Screening in Neonates:** PCR is the gold standard for infants born to HIV-positive mothers, as maternal IgG antibodies can persist for up to 18 months, making ELISA/Western blot unreliable.

Question 805: Which of the following is NOT an oncogenic virus?

A. Epstein-Barr virus
B. Reovirus (Correct Answer)
C. Retrovirus
D. Human papillomavirus

Explanation: **Explanation:** The correct answer is **Reovirus**. Oncogenic viruses are those capable of inducing tumors by integrating their genetic material into the host genome or by expressing viral oncoproteins that interfere with cell cycle regulation (e.g., inhibiting p53 or Rb proteins). **Why Reovirus is the correct answer:** Reoviruses (Respiratory Enteric Orphan viruses) are double-stranded RNA viruses that are generally not associated with human malignancies. In fact, Reoviruses are currently being studied in **oncolytic virotherapy** because they specifically replicate in and kill cancer cells with activated Ras signaling pathways, while sparing normal cells. **Analysis of incorrect options:** * **Epstein-Barr Virus (EBV):** A potent oncogenic DNA virus (Herpesviridae) associated with Burkitt lymphoma, Nasopharyngeal carcinoma, and Hodgkin lymphoma. It transforms B-cells via the LMP-1 protein. * **Retrovirus:** This family includes **HTLV-1**, which causes Adult T-cell Leukemia/Lymphoma (ATL). They utilize reverse transcriptase to integrate into the host genome, potentially activating proto-oncogenes. * **Human Papillomavirus (HPV):** High-risk strains (16, 18) are the primary cause of cervical and oropharyngeal cancers. Their oncoproteins **E6 and E7** inhibit the tumor suppressors p53 and pRb, respectively. **High-Yield Clinical Pearls for NEET-PG:** * **DNA Oncogenic Viruses:** HPV, EBV, HBV, HHV-8 (Kaposi sarcoma), and Merkel cell polyomavirus. * **RNA Oncogenic Viruses:** HTLV-1 and Hepatitis C Virus (HCV). * **Mechanism:** Most DNA oncoviruses inhibit **p53** (guardian of the genome) and **pRb** (governor of the cell cycle) to promote uncontrolled proliferation.

Question 806: Which of the following is NOT a complication of chickenpox?

A. Meningitis
B. Pneumonia
C. Enteritis (Correct Answer)
D. Reye's Syndrome

Explanation: **Explanation:** Chickenpox, caused by the **Varicella-Zoster Virus (VZV)**, is primarily a respiratory-transmitted infection that manifests as a generalized pruritic vesicular rash. While the virus can affect multiple organ systems during its systemic phase, it does not typically involve the gastrointestinal tract. **1. Why Enteritis is the Correct Answer:** VZV does not cause inflammation of the intestinal lining (**Enteritis**). The virus has a predilection for the skin, lungs, and central nervous system. Gastrointestinal symptoms are not a recognized clinical feature or complication of primary varicella infection. **2. Analysis of Incorrect Options:** * **Pneumonia:** This is the **most serious complication in adults**. It typically occurs 3–5 days into the illness and can lead to severe respiratory distress. * **Meningitis/Encephalitis:** Neurological complications are well-documented. While **Cerebellar Ataxia** (presenting as unsteady gait) is the most common CNS complication in children, aseptic meningitis and encephalitis can also occur. * **Reye’s Syndrome:** This is a rare but fatal complication involving acute encephalopathy and fatty liver degeneration. It is strongly associated with the use of **Salicylates (Aspirin)** to treat fever during chickenpox or influenza in children. **Clinical Pearls for NEET-PG:** * **Secondary Bacterial Infection:** The *most common* complication of chickenpox in children is secondary skin infection (usually *Staph. aureus* or *Strep. pyogenes*). * **Congenital Varicella Syndrome:** Occurs if the mother is infected in the first 20 weeks of pregnancy; characterized by limb hypoplasia, scarring, and microcephaly. * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusion bodies. * **Treatment:** Acyclovir is the drug of choice, especially in adults and immunocompromised patients. Avoid Aspirin in children.

Question 807: All of the following are DNA viruses except?

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

Explanation: **Explanation:** The fundamental classification of viruses is based on their genetic material (DNA or RNA). To excel in NEET-PG, it is essential to memorize the DNA virus families, as they are fewer in number compared to RNA viruses. **Why Paramyxovirus is the correct answer:** Paramyxoviruses (e.g., Measles, Mumps, RSV) are **single-stranded, negative-sense RNA viruses**. They are enveloped and possess a helical capsid. Unlike DNA viruses, they replicate in the cytoplasm (except for some exceptions like Orthomyxoviruses). **Analysis of Incorrect Options (DNA Viruses):** * **Parvovirus:** This is a high-yield DNA virus because it is the **only** medically important virus that is **single-stranded DNA (ssDNA)**. All other DNA viruses are double-stranded. * **Herpesvirus:** A large family of **enveloped, double-stranded DNA (dsDNA)** viruses. This group includes HSV-1, HSV-2, VZV, EBV, and CMV. * **Poxvirus:** These are the largest and most complex **dsDNA** viruses. A key clinical pearl is that Poxviruses are the **only DNA viruses that replicate in the cytoplasm** (carrying their own DNA-dependent RNA polymerase). **High-Yield NEET-PG Pearls:** * **Mnemonic for DNA Viruses:** "**HHAPPPPy**" (Herpes, Hepadna, Adeno, Papova, Parvo, Pox). * **Symmetry:** All DNA viruses have icosahedral symmetry except Poxvirus (complex). * **Replication:** All DNA viruses replicate in the nucleus except Poxvirus. * **Shape:** Parvovirus is the smallest DNA virus; Poxvirus is the largest.

Question 808: Prion structure contains primarily?

A. Protein (Correct Answer)
B. DNA
C. RNA
D. Both DNA and RNA

Explanation: **Explanation:** **1. Why Protein is Correct:** Prions (Proteinaceous Infectious Particles) are unique pathogens because they are composed **entirely of protein** and lack any nucleic acid genome. The underlying medical concept involves the conformational change of a normal host cellular protein, **PrPc** (rich in alpha-helices), into a pathological, misfolded isoform called **PrPsc** (rich in beta-pleated sheets). This misfolded protein is resistant to protease enzymes, heat, and standard disinfection, allowing it to accumulate in the brain and cause neurodegeneration. **2. Why Other Options are Incorrect:** * **B, C, and D (DNA/RNA):** Unlike viruses, bacteria, or fungi, prions do not contain any genetic material. They violate the "Central Dogma" of biology because they replicate by inducing conformational changes in existing host proteins rather than through nucleic acid replication. Any agent containing DNA or RNA would be classified as a virus, viroid, or cellular organism. **3. High-Yield Clinical Pearls for NEET-PG:** * **Resistance:** Prions are notoriously resistant to conventional sterilization (autoclaving at 121°C). The recommended method is **autoclaving at 134°C for 1–1.5 hours** or using **1N NaOH** for 1 hour. * **Histopathology:** Characterized by **spongiform degeneration** (vacuolation of neurons), neuronal loss, and amyloid plaques without any inflammatory response. * **Key Diseases:** * **Humans:** Kuru (associated with cannibalism), Creutzfeldt-Jakob Disease (CJD), and Fatal Familial Insomnia. * **Animals:** Scrapie (sheep) and Bovine Spongiform Encephalopathy (Mad Cow Disease). * **Diagnosis:** Detection of **14-3-3 protein** in CSF is a significant diagnostic marker for CJD.

Question 809: Hepatitis C virus belongs to which family of viruses?

A. Togavirus
B. Flavivirus (Correct Answer)
C. Filovirus
D. Retrovirus

Explanation: **Explanation:** Hepatitis C Virus (HCV) is a small, enveloped, positive-sense single-stranded RNA virus. It is classified under the genus **Hepacivirus** within the **Flaviviridae** family. Unlike other members of the Flavivirus family (like Yellow Fever or Dengue), HCV is not an arbovirus; it is primarily transmitted parenterally. **Analysis of Options:** * **Flavivirus (Correct):** HCV shares the genomic structure and replication strategy characteristic of Flaviviridae. It encodes a single polyprotein that is cleaved into structural and non-structural proteins (NS3, NS5A, NS5B), which are targets for modern Direct-Acting Antivirals (DAAs). * **Togavirus:** This family includes Rubella and Alpha viruses (e.g., Chikungunya). While they are also (+)ssRNA viruses, their genomic organization differs from HCV. * **Filovirus:** These are negative-sense, filamentous RNA viruses, most notably causing Ebola and Marburg hemorrhagic fevers. * **Retrovirus:** This family (e.g., HIV) uses reverse transcriptase to integrate DNA into the host genome. HCV replicates entirely in the cytoplasm and does not have a DNA intermediate. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Most common cause of post-transfusion hepatitis (historically) and highly associated with IV drug use. * **Chronicity:** HCV has the highest rate of progression to chronic infection (~80%) among all hepatitis viruses. * **Genotypes:** Genotype 3 is the most common in India; Genotype 1 is the most common globally. * **Diagnosis:** Screening is done via Anti-HCV antibodies; confirmation requires HCV-RNA (PCR). * **Extra-hepatic Manifestation:** Strongly associated with **Mixed Cryoglobulinemia** and Membranoproliferative Glomerulonephritis (MPGN).

Question 810: Which form of hepatitis is considered non-parenteral?

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

Explanation: ### Explanation **Core Concept: Routes of Transmission** Hepatitis viruses are primarily categorized by their mode of transmission into two groups: **Enteric** (fecal-oral) and **Parenteral** (blood-borne/sexual). **Why Hepatitis E is Correct:** Hepatitis E (HEV) is a **non-enveloped RNA virus** transmitted via the **fecal-oral route**, primarily through contaminated water. Because it does not require blood-to-blood contact or mucosal exposure to infected body fluids for transmission, it is classified as **non-parenteral**. Hepatitis A is the only other major hepatitis virus that shares this non-parenteral, enteric transmission route. **Why the Other Options are Incorrect:** * **Hepatitis B (HBV):** A DNA virus transmitted via parenteral routes (blood transfusion, IV drug use), sexual contact, and vertical transmission (mother-to-child). * **Hepatitis C (HCV):** An RNA virus primarily transmitted through parenteral exposure, most commonly via infected blood (IV drug use or unscreened transfusions). * **Hepatitis D (HDV):** A defective RNA virus that requires the presence of HBV (HBsAg) to replicate; therefore, it follows the same parenteral transmission patterns as Hepatitis B. **NEET-PG High-Yield Pearls:** * **Vowels for the Bowels:** Remember that Hepatitis **A** and **E** are transmitted via the fecal-oral route (enteric). * **Pregnancy Risk:** HEV is notorious for causing high mortality (up to 20%) in **pregnant women**, often leading to Fulminant Hepatic Failure. * **Chronicity:** Unlike HBV, HCV, and HDV, Hepatitis E typically causes acute infection and does not lead to chronic hepatitis (except in severely immunocompromised patients/transplant recipients). * **Zoonosis:** HEV genotype 3 is associated with the consumption of undercooked pork or deer meat.

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Virus Structure and Classification

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Pathogenesis of Viral Infections

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DNA Viruses: Herpesviruses

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DNA Viruses: Poxviruses and Adenoviruses

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Hepatitis Viruses

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RNA Viruses: Orthomyxoviruses

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RNA Viruses: Paramyxoviruses

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Enteroviruses and Rhinoviruses

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Arboviruses

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HIV and Retroviruses

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Oncogenic Viruses

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Virology — MCQs

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