Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 911: Hand, foot, and mouth disease is caused by which virus?

A. Enterovirus 70
B. Enterovirus 71 (Correct Answer)
C. Enterovirus 72
D. Enterovirus 68

Explanation: **Explanation:** **Hand, Foot, and Mouth Disease (HFMD)** is a common viral illness, primarily affecting children, characterized by fever and vesicular eruptions on the palms, soles, and oral mucosa. **1. Why Enterovirus 71 is correct:** HFMD is most commonly caused by viruses belonging to the *Picornaviridae* family, specifically the genus *Enterovirus*. The two most frequent causative agents are **Coxsackievirus A16** (the most common cause globally) and **Enterovirus 71 (EV-71)**. EV-71 is particularly significant in medical exams because it is associated with more severe clinical manifestations, including neurological complications like aseptic meningitis, encephalitis, and acute flaccid paralysis. **2. Why the other options are incorrect:** * **Enterovirus 70:** This virus is the primary cause of **Acute Hemorrhagic Conjunctivitis (AHC)**, often occurring in large epidemics. * **Enterovirus 72:** This was the former taxonomic designation for **Hepatitis A virus**. It causes acute infectious hepatitis, not vesicular skin rashes. * **Enterovirus 68:** This is primarily a **respiratory pathogen** associated with severe lower respiratory tract infections and, occasionally, acute flaccid myelitis (AFM) in children. **Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route and respiratory droplets. * **Clinical Triad:** Ulcers in the mouth (herpangina-like) + Maculopapular/vesicular rash on hands and feet. * **Complications:** While Coxsackie A16 is usually self-limiting, **EV-71** is the high-yield "danger" subtype linked to brainstem encephalitis and pulmonary edema. * **Differential Diagnosis:** Do not confuse HFMD with "Foot and Mouth Disease" (Aphthovirus), which affects cattle and rarely humans.

Question 912: Which of the following viruses, in addition to HSV-1 and HSV-2, produces the cytopathologic finding of multinucleated giant cells?

A. Adenovirus
B. Cytomegalovirus
C. Human papillomavirus
D. Varicella-zoster virus (Correct Answer)

Explanation: **Explanation:** The hallmark cytopathologic finding for certain herpesviruses is the formation of **multinucleated giant cells** with intranuclear inclusion bodies (Cowdry type A). This occurs due to the fusion of infected host cell membranes, a process mediated by viral glycoproteins. **Why Varicella-zoster virus (VZV) is correct:** VZV, like HSV-1 and HSV-2, belongs to the **Alphaherpesvirinae** subfamily. These viruses share the characteristic of inducing cell-to-cell fusion (syncytia). A **Tzanck smear** performed on scrapings from the base of a vesicle will show these characteristic multinucleated giant cells in infections caused by HSV-1, HSV-2, and VZV. **Why other options are incorrect:** * **Adenovirus:** Typically produces "smudge cells" (large, dark intranuclear inclusions) but does not form multinucleated giant cells. * **Cytomegalovirus (CMV):** While it causes cell enlargement (cytomegaly), its classic finding is a single, large "Owl’s eye" intranuclear inclusion. It does not typically present with multinucleation on a Tzanck smear. * **Human papillomavirus (HPV):** Characterized by **koilocytes** (squamous epithelial cells with perinuclear halos and wrinkled nuclei), not multinucleated giant cells. **High-Yield NEET-PG Pearls:** * **Tzanck Smear:** Used for rapid bedside diagnosis of HSV and VZV. It identifies multinucleated giant cells but *cannot* distinguish between HSV-1, HSV-2, and VZV. * **Cowdry Type A Inclusions:** Eosinophilic nuclear inclusions surrounded by a clear halo; seen in HSV and VZV. * **Syncytia Formation:** Also a key feature of Paramyxoviruses (like Measles and RSV) and HIV, but in the context of vesicular skin rashes, always think of the Alpha-herpes family.

Question 913: Which of the following is best used in the diagnosis of congenital syphilis?

A. FTA–ABS
B. TPHA
C. IgM–FTA ABS (Correct Answer)
D. TPI

Explanation: ### Explanation The diagnosis of congenital syphilis is challenging because maternal **IgG antibodies** (detected by standard tests like FTA-ABS or TPHA) cross the placenta and can persist in the neonate’s circulation for up to 15–18 months, leading to false-positive results. **Why IgM–FTA ABS is the Correct Answer:** Unlike IgG, **IgM antibodies do not cross the placenta.** Therefore, the detection of Treponema-specific IgM in the neonate’s serum indicates that the infant has produced these antibodies in response to an active infection. The **IgM–FTA ABS (19S-IgM FTA-ABS)** is the gold standard for confirming a diagnosis of congenital syphilis in a newborn. **Analysis of Incorrect Options:** * **A. FTA–ABS (Fluorescent Treponemal Antibody Absorption):** This measures total antibodies (primarily IgG). Since maternal IgG crosses the placenta, a positive result cannot distinguish between a truly infected infant and passive transfer of maternal antibodies. * **B. TPHA (Treponema pallidum Hemagglutination Assay):** Similar to FTA-ABS, this is a treponemal test that detects IgG. It remains positive for life and cannot differentiate between maternal transfer and neonatal infection. * **D. TPI (Treponema pallidum Immobilization Test):** Historically the "gold standard" for specificity, it is technically demanding and rarely used today. Like the others, it primarily detects IgG and is not useful for congenital diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Screening:** VDRL/RPR (Nontreponemal tests) are used for screening. A neonatal titer **fourfold higher** than the maternal titer suggests infection. * **Definitive Diagnosis:** Demonstration of *T. pallidum* by **Dark Ground Microscopy (DGM)** from skin lesions or umbilical cord is the most definitive method. * **Hutchinson’s Triad:** Late congenital syphilis features include Interstitial keratitis, Sensorineural deafness, and Hutchinson’s teeth.

Question 914: A child who has undergone a kidney transplant develops lymphoproliferative cancer. This is associated with which viral infection?

A. Cytomegalovirus (CMV)
B. Varicella-zoster virus (VZV)
C. Human papillomavirus (HPV)
D. Epstein-Barr virus (EBV) (Correct Answer)

Explanation: **Explanation:** The correct answer is **Epstein-Barr virus (EBV)**. This condition is known as **Post-Transplant Lymphoproliferative Disorder (PTLD)**. **Why EBV is correct:** In transplant recipients, the administration of potent immunosuppressive drugs (to prevent graft rejection) leads to a significant reduction in **T-cell mediated immunity**. EBV naturally infects B-lymphocytes and remains latent. Without T-cell surveillance (specifically Cytotoxic T-lymphocytes), EBV-infected B-cells undergo uncontrolled proliferation, driven by viral oncogenes like **LMP-1**. This can progress from benign polyclonal B-cell hyperplasia to malignant monoclonal B-cell lymphoma. **Why other options are incorrect:** * **Cytomegalovirus (CMV):** While CMV is the most common viral infection post-transplant, it typically causes fever, pneumonia, or retinitis, rather than lymphoproliferative cancer. * **Varicella-zoster virus (VZV):** Causes chickenpox or shingles. In transplant patients, it can lead to disseminated disease, but it is not oncogenic. * **Human papillomavirus (HPV):** Associated with cervical, anogenital, and oropharyngeal cancers, but not typically with systemic lymphoproliferative disorders in the context of acute post-transplant immunosuppression. **High-Yield NEET-PG Pearls:** * **EBV Association:** Also linked to Burkitt Lymphoma (t(8;14)), Nasopharyngeal Carcinoma, and Hodgkin Lymphoma. * **PTLD Management:** The first step in management is often the **reduction of immunosuppressive therapy** to allow the patient’s immune system to regain control over the B-cell proliferation. * **Diagnosis:** Elevated EBV viral load (via PCR) and biopsy showing B-cell expansion (CD20+).

Question 915: Which of the following viruses is known as the lymphoproliferative virus?

A. Adenovirus
B. Hepatitis A
C. Mumps
D. EB virus (Correct Answer)

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is termed a **lymphoproliferative virus** because of its unique ability to infect and transform **B-lymphocytes**. EBV binds to the **CD21 receptor** (CR2) on B-cells, leading to polyclonal B-cell activation and proliferation. While this usually results in Infectious Mononucleosis (self-limiting), it can lead to various lymphoid and epithelial malignancies, especially in immunocompromised states. **Analysis of Options:** * **Adenovirus (Option A):** Primarily causes respiratory infections, conjunctivitis (pink eye), and hemorrhagic cystitis. It is a DNA virus but does not possess lymphoproliferative properties. * **Hepatitis A (Option B):** A picornavirus that causes acute viral hepatitis. It is transmitted via the feco-oral route and does not involve lymphocyte proliferation or oncogenesis. * **Mumps (Option C):** A paramyxovirus characterized by parotitis and orchitis. It does not cause lymphoproliferation. * **EB Virus (Option D):** Correct. It is the prototype virus associated with lymphoproliferative disorders. **High-Yield NEET-PG Pearls:** * **Associated Malignancies:** Burkitt Lymphoma (starry-sky appearance), Nasopharyngeal Carcinoma, Hodgkin Lymphoma, and Post-transplant lymphoproliferative disorder (PTLD). * **Diagnosis:** Look for **Atypical Lymphocytes (Downey cells)** on peripheral smear—these are actually activated **CD8+ T-cells** reacting against the infected B-cells. * **Heterophile Antibody Test:** Positive (Monospot test) is a classic diagnostic marker for EBV-induced Infectious Mononucleosis.

Question 916: Which of the following statements regarding Hepatitis B virus (HBV) and Hepatitis D virus (HDV) is false?

A. Both can infect simultaneously
B. HDV causes more serious infection due to superinfection
C. HDV cannot infect in the absence of HBV
D. Both are DNA viruses (Correct Answer)

Explanation: **Explanation:** The correct answer is **D** because it is a factually incorrect statement. **Hepatitis B Virus (HBV)** is a partially double-stranded **DNA virus** (Hepadnaviridae), whereas **Hepatitis D Virus (HDV)** is a defective **RNA virus**. HDV requires the surface antigen (HBsAg) of HBV to provide its envelope for assembly and transmission. **Analysis of other options:** * **Option A (Both can infect simultaneously):** This is true and is termed **Co-infection**. It typically presents as acute hepatitis and often results in recovery, with a low risk of chronicity. * **Option B (HDV causes more serious infection due to superinfection):** This is true. **Superinfection** occurs when a chronic HBV carrier is later infected with HDV. This leads to a much higher risk of fulminant hepatitis, rapid progression to cirrhosis, and a high rate of chronic HDV infection. * **Option C (HDV cannot infect in the absence of HBV):** This is true. HDV is a "satellite" or defective virus; it lacks the genes to produce its own coat protein and must "borrow" HBsAg from HBV to infect other cells. **High-Yield Clinical Pearls for NEET-PG:** * **HBV Genome:** Circular, partially double-stranded DNA; replicates via **Reverse Transcriptase**. * **HDV Genome:** Single-stranded, circular, negative-sense RNA. It is the smallest known human virus. * **Serology:** In co-infection, both IgM anti-HBc and IgM anti-HDV are present. In superinfection, only IgM anti-HDV is present (IgG anti-HBc will be present as the patient is a chronic carrier). * **Prevention:** The HBV vaccine automatically protects against HDV because HDV cannot exist without HBV.

Question 917: A 35-year-old male patient presented with a history of jaundice for 15 days. The onset was preceded by a prodromal illness. His serum tested positive for HBsAg. A clinical diagnosis of acute Hepatitis B was made. What should be the next best confirmatory investigation?

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

Explanation: **Explanation** In the clinical scenario of acute Hepatitis B, the diagnosis is typically established by the presence of **HBsAg** and **IgM anti-HBc**. However, to confirm active viral replication and assess the patient's infectivity status, the detection of the **HBeAg (Hepatitis B e-antigen)** or its corresponding antibody is crucial. **Why Option A is Correct:** The question asks for the "next best confirmatory investigation" following an HBsAg positive result in an acute setting. **Anti-HBc IgM** (often referred to in shorthand or specific contexts as the core antibody) is the gold standard for confirming **acute** infection, especially during the "window period" when HBsAg may have disappeared but Anti-HBs has not yet appeared. In the context of the provided options, testing for the core antibody components is the standard protocol to differentiate acute from chronic infection. **Why Incorrect Options are Wrong:** * **B. HBeAg:** While it indicates high infectivity and active replication, it is not a "confirmatory" marker for the diagnosis of acute hepatitis itself; it is a marker of viral load. * **C. Anti-HBe IgM antibody:** This is a distractor. There is no specific "IgM" version of the anti-HBe antibody used in clinical practice; IgM is specific to the **Anti-HBc** (Core) antibody. * **D. HBV DNA by PCR:** While this is the most sensitive marker for viral quantification, it is generally reserved for monitoring treatment response in chronic cases or resolving diagnostic dilemmas, rather than the initial confirmation of acute Hepatitis B. **Clinical Pearls for NEET-PG:** * **Window Period:** The period where HBsAg is negative and Anti-HBs is not yet positive. The only marker present is **IgM Anti-HBc**. * **HBsAg:** First marker to appear in blood (even before symptoms). * **Anti-HBs:** Indicates immunity (via recovery or vaccination). * **HBeAg:** Indicates high transmissibility ("e" for envelope/infectivity).

Question 918: What is the incubation period of the Ebola virus?

A. 5-20 hours
B. 20-40 hours
C. 5-20 days (Correct Answer)
D. 20-40 days

Explanation: **Explanation:** The **Ebola Virus**, a member of the *Filoviridae* family, causes severe hemorrhagic fever. The incubation period—the interval from infection with the virus to the onset of symptoms—is typically **2 to 21 days**, with an average of 8 to 10 days. Therefore, **Option C (5-20 days)** is the most accurate range among the choices provided. **Why the other options are incorrect:** * **Options A and B (Hours):** Viral hemorrhagic fevers do not manifest within hours. Such rapid onset is characteristic of preformed bacterial toxins (e.g., *Staphylococcus aureus* food poisoning) or chemical poisoning. * **Option D (20-40 days):** This is too long. While rare cases may slightly exceed 21 days, the vast majority of patients present within the three-week window. This 21-day threshold is the gold standard for monitoring contacts and determining quarantine periods. **Clinical Pearls for NEET-PG:** * **Transmission:** Ebola is transmitted through direct contact with infected blood, secretions, or bodily fluids (including semen, where the virus can persist for months). It is **not** airborne. * **Reservoir:** The natural reservoir is believed to be **Fruit Bats** (*Pteropodidae* family). * **Pathogenesis:** The virus targets endothelial cells and mononuclear phagocytes, leading to a "cytokine storm," vascular leak, and disseminated intravascular coagulation (DIC). * **Diagnosis:** Gold standard is **RT-PCR** during the acute phase; ELISA is used for IgM/IgG detection later. * **Key Feature:** High case fatality rate (up to 90%). Management is primarily supportive, though the **Ervebo vaccine** (rVSV-ZEBOV) is now used for prevention.

Question 919: Which of the following is NOT true regarding Japanese encephalitis?

A. It is caused by a flavivirus.
B. Herons act as reservoir hosts.
C. It is transmitted by Culex mosquitoes.
D. Cattle serve as amplifier hosts. (Correct Answer)

Explanation: Japanese Encephalitis (JE) is a major cause of viral encephalitis in Asia. Understanding its transmission cycle is crucial for NEET-PG. ### **Explanation of the Correct Answer** **Option D is NOT true** because **Pigs**, not cattle, serve as the primary **amplifier hosts**. An amplifier host is one in which the virus multiplies to very high titers, sufficient to infect a biting mosquito. While cattle can be infected, they do not develop high enough viremia to pass the virus back to mosquitoes; they are considered "dead-end" hosts, similar to humans. ### **Analysis of Other Options** * **Option A:** JE is caused by the **Japanese Encephalitis Virus (JEV)**, which belongs to the family **Flaviviridae** (Genus: *Flavivirus*). It is a single-stranded RNA virus. * **Option B:** Ardeid birds, specifically **Herons and Egrets**, are the natural **reservoir hosts**. They maintain the virus in the environment (sylvatic cycle). * **Option C:** The primary vector is the **Culex mosquito**, specifically ***Culex tritaeniorhynchus***. These mosquitoes typically breed in stagnant water like rice fields. ### **High-Yield Clinical Pearls for NEET-PG** * **Transmission Cycle:** Pig-Mosquito-Bird cycle. Humans are **accidental, dead-end hosts**. * **Clinical Feature:** Characterized by "Mask-like facies" and extrapyramidal signs due to involvement of the **Thalamus and Basal Ganglia** (visible on MRI). * **Diagnosis:** **IgM Capture ELISA (MAC-ELISA)** of CSF or serum is the gold standard. * **Vaccination:** The **Jenvac** (indigenous inactivated) and **SA-14-14-2** (live attenuated) vaccines are used in India under the Universal Immunization Programme.

Question 920: What are the types of dengue serotypes?

A. 2
B. 4 (Correct Answer)
C. 5
D. 10

Explanation: **Explanation:** **1. Why Option B is Correct:** Dengue virus (DENV) is a single-stranded RNA virus belonging to the family **Flaviviridae**. There are **four distinct serotypes**: **DENV-1, DENV-2, DENV-3, and DENV-4**. While these serotypes share approximately 65% of their genomes, they are antigenically different. Infection with one serotype provides lifelong immunity to *that specific* serotype but only short-term cross-protection against others. **2. Why Other Options are Incorrect:** * **Option A (2):** This is incorrect. While some viruses have two main types (e.g., HSV-1 and HSV-2), Dengue has four. * **Option C (5):** This is a common distractor. In 2013, a "fifth" serotype (DENV-5) was reported in Malaysia following a sylvatic cycle; however, it remains confined to primates and is not considered part of the human epidemic cycle in clinical practice or standard textbooks. * **Option D (10):** This is incorrect and has no clinical relevance to Dengue classification. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Primarily *Aedes aegypti* (day-biter), followed by *Aedes albopictus*. * **Antibody-Dependent Enhancement (ADE):** Secondary infection with a *different* serotype is the major risk factor for **Dengue Hemorrhagic Fever (DHF)** and **Dengue Shock Syndrome (DSS)** due to the "Haldane effect" or immune enhancement. * **Diagnosis:** * **NS1 Antigen:** Best for early diagnosis (Day 1–5). * **IgM/IgG ELISA:** Positive after Day 5. * **Tourniquet Test:** A bedside clinical test used to assess capillary fragility in suspected DHF. * **Most Common Serotype in India:** Historically DENV-2 and DENV-1, though patterns shift periodically.

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