Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1171: Swine flu is caused by which influenza virus subtype?

A. H1N1 (Correct Answer)
B. H5N1
C. H3N1
D. H3N3

Explanation: **Explanation:** **Correct Answer: A. H1N1** Swine flu is caused by the **Influenza A virus subtype H1N1**. The 2009 pandemic was specifically caused by a triple-reassortant strain containing genetic material from human, avian, and swine influenza viruses. The nomenclature refers to the two primary surface glycoproteins: **Hemagglutinin (H)**, which facilitates viral entry into host cells, and **Neuraminidase (N)**, which assists in the release of new virions. **Analysis of Incorrect Options:** * **B. H5N1:** This is the primary subtype responsible for **Avian Influenza (Bird Flu)**. It is highly pathogenic in birds and can cause severe respiratory disease in humans with a high mortality rate, though human-to-human transmission is inefficient. * **C. H3N1:** While H3 subtypes exist (like H3N2, a common seasonal flu), H3N1 is not a major human pathogen and is typically associated with veterinary infections (e.g., in pigs) without widespread human outbreaks. * **D. H3N3:** This is a rare subtype primarily found in wild birds and does not cause significant human disease or the clinical syndrome known as Swine Flu. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Major genetic changes (reassortment) leading to new subtypes; responsible for **Pandemics**. * **Antigenic Drift:** Minor point mutations in H or N genes; responsible for **Epidemics** and the need for annual vaccine updates. * **Drug of Choice:** **Oseltamivir** (Tamiflu), a neuraminidase inhibitor, is the preferred treatment for H1N1. * **Diagnosis:** **Real-time RT-PCR** of nasopharyngeal swabs is the gold standard for confirmation.

Question 1172: Which is the confirmatory test for HIV infection?

A. ELISA
B. Immunodot
C. RIPA
D. Western Blot (Correct Answer)

Explanation: **Explanation:** The diagnosis of HIV infection follows a specific algorithm: a highly sensitive screening test followed by a highly specific confirmatory test. **1. Why Western Blot is Correct:** Western Blot is considered the gold standard **confirmatory test** for HIV. It detects specific antibodies against individual viral proteins (Antigens). For a result to be positive, antibodies must be present against at least two of the following three gene products: **p24** (gag), **gp41** (env), and **gp120/160** (env). Its high specificity ensures that false positives from screening tests are eliminated. **2. Why other options are incorrect:** * **ELISA (Enzyme-Linked Immunosorbent Assay):** This is the standard **screening test**. It is highly sensitive but can yield false positives due to cross-reactivity (e.g., in autoimmune diseases or recent vaccinations). * **Immunodot (Rapid Test):** These are simple, rapid screening tests used in bedside settings or peripheral centers. Like ELISA, they require confirmation. * **RIPA (Radioimmunoprecipitation Assay):** While highly specific and sensitive, it is technically demanding, expensive, and primarily used in research settings rather than routine clinical confirmation. **Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **Screening vs. Confirmation:** ELISA is for screening (high sensitivity); Western Blot is for confirmation (high specificity). * **Diagnosis in Infants:** In children <18 months, maternal antibodies persist; therefore, **PCR (DNA PCR for proviral DNA)** is the investigation of choice, not antibody tests. * **Recent Shift:** Current NACO guidelines and newer CDC algorithms often utilize a "Repeated ELISA" or "4th Generation p24 Antigen-Antibody Combo" approach, but for exam purposes, Western Blot remains the classic confirmatory answer.

Question 1173: Which of the following statements regarding Cytomegalovirus (CMV) is FALSE?

A. CMV is a double-stranded DNA virus.
B. CMV rarely causes significant problems in immunocompetent individuals.
C. Foscarnet can completely eliminate CMV infection. (Correct Answer)
D. CMV retinitis is rare when the CD4 count is greater than 200 cells/mm³.

Explanation: **Explanation:** The correct answer is **C**, as no current antiviral therapy, including Foscarnet, can completely eliminate Cytomegalovirus (CMV) from the body. **Why Option C is False:** CMV is a member of the *Herpesviridae* family. Like all herpesviruses, CMV establishes **lifelong latency** in the host (specifically in monocytes, macrophages, and CD34+ hematopoietic progenitor cells). Antiviral drugs like Ganciclovir, Foscarnet, and Cidofovir inhibit viral DNA polymerase and stop active replication, but they cannot eradicate the latent viral genome. Therefore, the infection is suppressed, not eliminated. **Analysis of Other Options:** * **Option A:** CMV is indeed a **double-stranded DNA (dsDNA)** virus, belonging to the Beta-herpesvirus subfamily. * **Option B:** In immunocompetent individuals, primary CMV infection is usually asymptomatic or presents as a self-limiting **mononucleosis-like syndrome** (Heterophile antibody negative). * **Option D:** CMV retinitis is an AIDS-defining illness. It typically occurs as an opportunistic infection when the **CD4 count falls below 50–100 cells/mm³**. It is extremely rare in patients with a CD4 count >200 cells/mm³. **High-Yield Clinical Pearls for NEET-PG:** * **Histology:** Look for **"Owl’s Eye" intranuclear inclusion bodies** (large cells with clear halos around the nucleus). * **Congenital CMV:** Most common viral cause of congenital defects; characterized by periventricular calcifications, microcephaly, and sensorineural hearing loss. * **Treatment of Choice:** **Ganciclovir** is the first-line agent. **Foscarnet** is used for ganciclovir-resistant strains but is limited by nephrotoxicity. * **Transplant Medicine:** CMV is the most common viral infection complicating solid organ transplants.

Question 1174: Heterophile antibody test is done for:

A. Rickettsial infections
B. Infectious mononucleosis (Correct Answer)
C. Smallpox
D. Japanese encephalitis

Explanation: **Explanation:** **Infectious Mononucleosis (IM)**, primarily caused by the **Epstein-Barr Virus (EBV)**, is characterized by the production of **heterophile antibodies**. These are IgM antibodies produced due to polyclonal B-cell activation that do not react with EBV antigens but instead agglutinate red blood cells from other species (sheep, horse, or ox). The **Paul-Bunnell test** and the rapid **Monospot test** detect these antibodies, making them the diagnostic gold standard for IM in adolescents and adults. **Analysis of Incorrect Options:** * **A. Rickettsial infections:** These are diagnosed using the **Weil-Felix test**. While this is also a heterophile antibody test, it specifically uses *Proteus* antigens ($OX19, OX2, OXK$) to detect cross-reacting antibodies against Rickettsia. * **C. Smallpox:** Diagnosis was historically made via clinical presentation, electron microscopy, or viral culture (Guarnieri bodies). Heterophile tests play no role here. * **D. Japanese encephalitis:** This is a Flavivirus infection diagnosed primarily through **IgM Capture ELISA** (MAC-ELISA) of the CSF or serum. **High-Yield Clinical Pearls for NEET-PG:** * **Paul-Bunnell Test:** Uses sheep RBCs. A titer of 1:56 or higher is considered significant. * **Differential Diagnosis:** If a patient has IM-like symptoms (fever, sore throat, lymphadenopathy) but is **Heterophile Negative**, consider **Cytomegalovirus (CMV)**, which is the most common cause of heterophile-negative mononucleosis. * **Peripheral Smear:** Look for **Downey cells** (atypical T-lymphocytes) which are characteristic of EBV infection. * **Ampicillin Rash:** Patients with EBV mononucleosis often develop a maculopapular rash if treated with Ampicillin or Amoxicillin.

Question 1175: Epstein-Barr virus (EBV) causes which of the following conditions?

A. Glandular fever
B. Burkitt's lymphoma
C. Pancreatic carcinoma (Correct Answer)
D. Nasopharyngeal carcinoma

Explanation: **Explanation:** The question asks to identify which condition is **NOT** typically associated with Epstein-Barr Virus (EBV), as Pancreatic carcinoma is the "odd one out" in this clinical context. **1. Why Pancreatic Carcinoma is the Correct Answer (The Exception):** Epstein-Barr Virus (EBV), a γ-herpesvirus (HHV-4), is known for its strong association with various B-cell and epithelial malignancies. However, **Pancreatic carcinoma** has no established causal link with EBV. Pancreatic cancer is primarily associated with smoking, chronic pancreatitis, and mutations in the KRAS, CDKN2A, TP53, and SMAD4 genes, rather than viral oncogenesis. **2. Analysis of Incorrect Options (Associations with EBV):** * **Glandular Fever (Infectious Mononucleosis):** This is the primary clinical manifestation of EBV infection, characterized by the triad of fever, pharyngitis, and lymphadenopathy. It is diagnosed via the Paul-Bunnell test (heterophile antibodies). * **Burkitt’s Lymphoma:** EBV is strongly linked to the African (endemic) variant of Burkitt’s lymphoma, characterized by the **t(8;14)** translocation involving the c-myc oncogene. * **Nasopharyngeal Carcinoma:** This is an epithelial tumor highly prevalent in Southern China, where EBV DNA is consistently found within the tumor cells. **3. High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** EBV binds to the **CD21** receptor (CR2) on B-cells and the MHC class II molecule. * **Hematology:** Peripheral smear shows **Atypical Lymphocytes (Downey cells)**, which are actually activated T-cells (CD8+) reacting against infected B-cells. * **Other Associations:** Oral Hairy Leukoplakia (in HIV patients), Hodgkin’s Lymphoma (Mixed cellularity subtype), and Gastric Carcinoma (approx. 10% of cases). * **Diagnosis:** Monospot test is the screening test of choice; VCA-IgM (Viral Capsid Antigen) indicates acute infection.

Question 1176: A mother presents to the neonatology OPD with her baby because of yellow extremities. On examination, there is a petechial rash over the body, hepatosplenomegaly, and microcephaly. What is the causative organism?

A. Cytomegalovirus (CMV) (Correct Answer)
B. Rubella virus
C. Herpes Simplex Virus (HSV)
D. Varicella-Zoster Virus (VZV)

Explanation: ### Explanation The clinical presentation described—**jaundice** (yellow extremities), **petechial rash** (often referred to as a "blueberry muffin" rash), **hepatosplenomegaly**, and **microcephaly**—is the classic tetrad of **Congenital Cytomegalovirus (CMV) infection**. CMV is the most common intrauterine infection worldwide. **Why Option A is Correct:** CMV is the leading cause of sensorineural hearing loss and mental retardation among the TORCH infections. The presence of **periventricular calcifications** (though not mentioned here) and microcephaly are hallmark neurological findings. The petechial rash occurs due to thrombocytopenia and extramedullary hematopoiesis. **Why Other Options are Incorrect:** * **B. Rubella virus:** While it also presents with a "blueberry muffin" rash and hepatosplenomegaly, the classic triad for Congenital Rubella Syndrome (Gregg’s Triad) includes **Cataracts, PDA (Cardiac defects), and Sensorineural deafness**. * **C. Herpes Simplex Virus (HSV):** Neonatal HSV typically presents in the first few weeks of life (not necessarily at birth) with **Skin-Eye-Mouth (SEM) vesicles**, encephalitis, or disseminated multi-organ failure. * **D. Varicella-Zoster Virus (VZV):** Congenital Varicella Syndrome is characterized by **cicatricial skin scarring** (zigzag patterns) and limb hypoplasia, rather than the generalized petechial rash seen here. **NEET-PG High-Yield Pearls:** * **Most common finding in CMV:** Most infants are asymptomatic at birth; however, **Sensorineural Hearing Loss (SNHL)** is the most common long-term sequela. * **Imaging:** CMV shows **periventricular** calcifications, whereas Toxoplasmosis shows **diffuse** intracerebral calcifications. * **Diagnosis:** Gold standard is **Viral culture or PCR of urine/saliva** within the first 3 weeks of life. * **Histology:** Look for "Owl’s eye" intranuclear inclusion bodies.

Question 1177: All of the following are caused by RNA viruses, EXCEPT:

A. HIV
B. Dengue
C. Herpangina
D. Fifth disease (Correct Answer)

Explanation: **Explanation:** The core concept tested here is the classification of viruses based on their genetic material. **Correct Answer: D. Fifth Disease** Fifth disease (also known as Erythema Infectiosum) is caused by **Parvovirus B19**. Parvovirus is a **DNA virus**. Specifically, it is unique for being a **non-enveloped, single-stranded DNA (ssDNA)** virus. In the NEET-PG context, remembering that "Parvo" is the only medically significant ssDNA virus is a high-yield fact. **Why the other options are incorrect:** * **A. HIV:** This is a Retrovirus. It contains two copies of single-stranded **RNA** (ssRNA) and uses reverse transcriptase to integrate into the host genome. * **B. Dengue:** Caused by the Dengue virus, which belongs to the *Flaviviridae* family. All Flaviviruses are enveloped, positive-sense **ssRNA** viruses. * **C. Herpangina:** Despite the name sounding like "Herpes" (which is DNA), Herpangina is caused by **Coxsackievirus A**, a member of the *Picornaviridae* family. All Picornaviruses are non-enveloped **ssRNA** viruses. **Clinical Pearls for NEET-PG:** 1. **Fifth Disease Presentation:** Characterized by the "slapped-cheek" rash and can cause aplastic crisis in patients with sickle cell anemia or hereditary spherocytosis. 2. **DNA Virus Mnemonic:** Remember **"HHAPPPPy"** viruses (Herpes, Hepadna, Adeno, Papilloma, Polyoma, Pox, Parvo). All are double-stranded except Parvo (ssDNA). 3. **Herpangina vs. Herpes:** Herpangina (Coxsackie) typically causes vesicles on the **posterior** pharynx/soft palate, whereas Herpetic Gingivostomatitis (HSV-1) involves the **anterior** mouth and gums.

Question 1178: The Paul-Bunnell test is positive in which of the following conditions?

A. Infectious mononucleosis (Correct Answer)
B. Multiple myeloma
C. Malignant neoplasms
D. Rubella

Explanation: **Explanation:** The **Paul-Bunnell test** is a classic diagnostic test used to detect **Infectious Mononucleosis (IM)**, caused by the **Epstein-Barr Virus (EBV)**. **1. Why Infectious Mononucleosis is correct:** In response to an EBV infection, the body produces **heterophile antibodies**. These are IgM antibodies that do not react with EBV antigens themselves but have the unique property of agglutinating red blood cells (RBCs) from other species, such as sheep, horse, or ox RBCs. The Paul-Bunnell test specifically uses **sheep RBCs**; a positive result (agglutination) confirms the presence of these heterophile antibodies, which are highly specific for IM in the clinical context of fever, pharyngitis, and lymphadenopathy. **2. Why other options are incorrect:** * **Multiple myeloma:** This is a plasma cell dyscrasia characterized by monoclonal (M) protein spikes, not heterophile antibodies. * **Malignant neoplasms:** While EBV is associated with malignancies like Burkitt lymphoma and Nasopharyngeal carcinoma, the Paul-Bunnell test is only positive during the acute phase of primary infection (IM), not the subsequent malignancies. * **Rubella:** This viral infection presents with a rash and lymphadenopathy but does not induce the production of heterophile antibodies. **High-Yield Clinical Pearls for NEET-PG:** * **Differential Diagnosis:** If a patient has IM-like symptoms but the Paul-Bunnell test is **negative**, consider **CMV infection** (the most common cause of heterophile-negative mononucleosis). * **Monospot Test:** A modern, rapid version of the Paul-Bunnell test using horse RBCs. * **Davidsohn Differential Test:** Used to distinguish IM antibodies from Forssman antibodies and serum sickness antibodies using guinea pig kidney extract and beef RBCs. * **Hematology:** Look for **atypical lymphocytes (Downey cells)** on a peripheral smear.

Question 1179: An elderly male presents with fever, cough, and shortness of breath for 2 weeks. He has a history of chronic bronchitis and diabetes, and recent travel to Wuhan City, China. What is the symmetry of the causative virus?

A. Naked helical symmetry
B. Complex symmetry
C. Enveloped helical symmetry (Correct Answer)
D. Icosahedral symmetry

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The clinical presentation (fever, cough, shortness of breath) combined with the travel history to **Wuhan, China**, identifies the causative agent as **SARS-CoV-2**, the virus responsible for COVID-19. SARS-CoV-2 belongs to the *Coronaviridae* family. Coronaviruses are characterized by a **positive-sense single-stranded RNA (+ssRNA)** genome. Structurally, they possess a **helical nucleocapsid** which is enclosed within a lipid **envelope** derived from the host cell membrane. This makes "Enveloped helical symmetry" the correct description. **2. Why the Incorrect Options are Wrong:** * **Option A (Naked helical symmetry):** In human virology, **all helical viruses are enveloped**. There are no known naked helical viruses that infect humans (naked helical viruses primarily infect plants, e.g., Tobacco Mosaic Virus). * **Option B (Complex symmetry):** This refers to viruses that do not fit into purely helical or icosahedral categories, most notably the **Poxviruses** (e.g., Smallpox, Molluscum contagiosum), which have a brick-shaped structure. * **Option D (Icosahedral symmetry):** This is the most common symmetry for many DNA and RNA viruses (e.g., Adenovirus, Herpesvirus, Poliovirus). While some enveloped viruses are icosahedral (e.g., Flaviviruses), Coronaviruses specifically utilize helical symmetry for their nucleocapsid. **3. Clinical Pearls for NEET-PG:** * **Largest RNA Virus:** Coronaviruses have the largest genome among RNA viruses (~30 kb). * **Receptor:** SARS-CoV-2 binds to the **ACE-2 receptor** (Angiotensin-Converting Enzyme 2) found in the lungs, heart, and kidneys. * **Club-shaped Spikes:** The "Corona" (crown-like) appearance under electron microscopy is due to the **S (Spike) protein** peplomers. * **Rule of Thumb:** Most negative-sense RNA viruses are helical and enveloped; Coronaviruses are a notable exception as they are **positive-sense** but still helical and enveloped.

Question 1180: Hep-2 cells are a type of:

A. Primary cell cultures
B. Diploid cell strain
C. Continuous cell lines (Correct Answer)
D. Explant culture

Explanation: **Explanation:** Cell cultures are classified into three types based on their origin, chromosomal characteristics, and number of divisions. **Hep-2 (Human Epithelioma type 2)** cells are derived from a human laryngeal carcinoma. Because they are derived from cancerous tissue, they are immortalized and can be subcultured indefinitely, making them a **Continuous Cell Line**. **Why the correct answer is right:** * **Continuous Cell Lines (Option C):** These are derived from cancer cells or by transforming normal cells. They are **heteroploid** (abnormal number of chromosomes), rapid-growing, and can be maintained through serial subculturing for an infinite number of generations. Hep-2 is a classic example used widely in virology and immunology. **Why the other options are wrong:** * **Primary Cell Cultures (Option A):** These are normal cells freshly taken from an organ (e.g., Monkey Kidney, Chick Embryo). They can only be subcultured once or twice before dying. * **Diploid Cell Strains (Option B):** These are fibroblast cells (e.g., WI-38, HL-8) that maintain a diploid chromosome number. They can be subcultured about 50 times before undergoing senescence. They are preferred for vaccine production. * **Explant Culture (Option D):** This involves growing small fragments of tissue (explants) directly on a surface, rather than dissociated cells. **High-Yield Facts for NEET-PG:** * **Hep-2 uses:** Traditionally used for isolating Respiratory Syncytial Virus (RSV), Adenovirus, and Enteroviruses. In immunology, it is the "gold standard" substrate for **ANA (Antinuclear Antibody)** testing via Indirect Immunofluorescence. * **Other Continuous Lines:** HeLa (Cervical cancer), Vero (Vervet monkey kidney), BHK-21 (Baby Hamster Kidney). * **Vaccine Production:** Human Diploid cells (WI-38, MRC-5) are used for producing vaccines like Rabies and Rubella because they are free from oncogenic potential.

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