Virology — MCQs

An 8-month-old girl presented with sudden onset of high fever (103 extdegree F). Despite the absence of signs of upper respiratory tract infection, meningitis, or encephalitis, her fever escalated to 105 extdegree F, leading to a febrile seizure. Upon examination by the pediatrician, the child's temperature had subsided, and a generalized papular rash was noted. What is the most likely diagnosis?

Virology Indian Medical PG Practice Questions and MCQs

Question 311: A patient's serum shows HbsAg and IgM to Hbc. What is the diagnosis?

A. Chronic hepatitis
B. Acute hepatitis (Correct Answer)
C. Acute infection of hepatitis C
D. Chronic infection of hepatitis B

Explanation: To understand the diagnosis of Hepatitis B, one must interpret the "Serological Window." **1. Why Option B is Correct:** The presence of **HBsAg** (Hepatitis B surface Antigen) indicates that the virus is currently present in the body. The presence of **IgM anti-HBc** (Immunoglobulin M antibody to Hepatitis B core antigen) is the hallmark of a **recent/acute infection** (typically within the last 6 months). When both are positive, it confirms a diagnosis of **Acute Hepatitis B**. **2. Why the other options are incorrect:** * **Options A & D (Chronic Hepatitis B):** In chronic infection, HBsAg persists for more than 6 months, but the body switches from producing IgM to **IgG anti-HBc**. Therefore, the presence of IgM specifically rules out chronicity. * **Option C (Acute Hepatitis C):** This is incorrect because HBsAg and anti-HBc are specific biomarkers for the Hepatitis B virus (HBV), not Hepatitis C (HCV). HCV diagnosis would require HCV RNA or Anti-HCV antibodies. **3. NEET-PG High-Yield Pearls:** * **Window Period:** This is the interval where HBsAg has disappeared but Anti-HBs has not yet appeared. During this time, **IgM anti-HBc** is the *only* positive marker (the "Window Marker"). * **HBeAg:** Indicates high viral replication and high infectivity. * **Anti-HBs:** Its presence indicates immunity (either via recovery or vaccination). * **Vaccination Profile:** A vaccinated individual will be positive for **Anti-HBs** only (negative for HBsAg and Anti-HBc).

Question 312: Lymphocytosis with atypical lymphocytes is seen in infection with which of the following viruses?

A. Herpes Simplex Virus (HSV)
B. Hepatitis B Virus (HBV)
C. Epstein-Barr Virus (EBV) (Correct Answer)
D. Respiratory Syncytial Virus (RSV)

Explanation: ### Explanation **Correct Answer: C. Epstein-Barr Virus (EBV)** **Why it is correct:** Epstein-Barr Virus (EBV) is the primary causative agent of **Infectious Mononucleosis (IM)**. The hallmark of this condition is absolute lymphocytosis where more than 10% of the lymphocytes are **atypical lymphocytes**, also known as **Downey cells**. The underlying medical concept is crucial: EBV infects B-cells via the **CD21 receptor**. However, the "atypical lymphocytes" seen on a peripheral blood smear are actually **activated CD8+ T-cells (Cytotoxic T-cells)** reacting against the EBV-infected B-cells. These cells are larger than normal lymphocytes, possess abundant cytoplasm, and have a "ballerina skirt" appearance as they indent around neighboring red blood cells. **Why the other options are incorrect:** * **A. HSV:** Typically causes localized vesicular lesions (cold sores or genital herpes). While it can cause systemic symptoms, it does not characteristically produce a peripheral smear dominated by atypical lymphocytosis. * **B. HBV:** Primarily targets hepatocytes. While it involves immune-mediated liver injury, the hematological profile does not typically feature Downey cells. * **D. RSV:** A major cause of bronchiolitis and pneumonia in infants. It is characterized by respiratory distress and syncytia formation in lung tissue, not systemic atypical lymphocytosis. **NEET-PG High-Yield Pearls:** * **Paul-Bunnell Test:** Detects heterophile antibodies; used for rapid diagnosis of EBV. * **Differential Diagnosis:** Cytomegalovirus (CMV) also causes a "mononucleosis-like syndrome" with atypical lymphocytes, but it is **Heterophile Antibody Negative**. * **Associated Malignancies:** EBV is linked to Burkitt Lymphoma (t 8;14), Nasopharyngeal Carcinoma, and Hodgkin Lymphoma. * **Clinical Triad of IM:** Fever, Pharyngitis, and Lymphadenopathy (posterior cervical). Splenomegaly is also a common finding.

Question 313: Which of the following diseases are transmitted by Aedes aegypti?

A. Yellow fever
B. Dengue
C. Chikungunya fever
D. All of the above (Correct Answer)

Explanation: The correct answer is **D. All of the above**. ### **Medical Concept** *Aedes aegypti*, commonly known as the "tiger mosquito" due to its white-striped markings, is a highly efficient vector for several medically significant arboviruses (arthropod-borne viruses). It is a day-biting mosquito that breeds in stagnant, clean water (e.g., flower pots, discarded tires). ### **Explanation of Options** * **Yellow Fever:** Caused by a Flavivirus. While primarily endemic in Africa and South America, *Aedes aegypti* is the principal urban vector. * **Dengue:** Caused by the Dengue virus (DENV 1-4, Flavivirus). *Aedes aegypti* is the primary vector, while *Aedes albopictus* serves as a secondary vector. * **Chikungunya:** Caused by an Alphavirus (Togaviridae). It is transmitted to humans through the bite of infected *Aedes aegypti* and *Aedes albopictus*. Since all three viral diseases utilize *Aedes aegypti* as their primary mode of transmission, "All of the above" is the correct choice. ### **High-Yield Clinical Pearls for NEET-PG** * **Zika Virus:** Also transmitted by *Aedes aegypti*. Remember the triad of Microcephaly, Guillain-Barré Syndrome, and conjunctivitis. * **Biting Habit:** *Aedes* is a **daytime biter** (peaks in early morning and late afternoon), unlike *Anopheles* or *Culex*, which are nocturnal. * **Nervous Biter:** It often bites multiple people to complete a single blood meal, leading to rapid outbreaks within households. * **Extrinsic Incubation Period:** The virus typically requires 8–12 days of incubation inside the mosquito before it can be transmitted to another human.

Question 314: A young male is admitted with a history of altered sensorium and hydrophobia. A clinical diagnosis of rabies was made, and corneal scrapings were taken. Which is the best test to confirm his diagnosis?

A. Seller's stain for Negri bodies
B. Indirect immunofluorescence
C. Real-time PCR
D. Viral culture (Correct Answer)

Explanation: **Explanation:** The clinical presentation of altered sensorium and hydrophobia is pathognomonic for **Rabies**. While various tests are available for diagnosis, the selection depends on whether the goal is rapid screening or definitive confirmation. **1. Why Viral Culture is the Correct Answer:** In the context of diagnostic microbiology, **Viral Culture** (using neuroblastoma cell lines or suckling mouse inoculation) remains the **"Gold Standard"** for confirmation. It provides definitive evidence of the presence of live, infectious virus. While it is time-consuming and rarely used for immediate clinical management, it is academically regarded as the most specific confirmatory test. **2. Analysis of Other Options:** * **Seller’s Stain (Negri Bodies):** This was historically used to identify intracytoplasmic inclusion bodies in neurons. However, it has low sensitivity (absent in ~20-30% of cases) and is now largely obsolete in modern diagnostics. * **Indirect Immunofluorescence (IFA):** While **Direct Fluorescent Antibody (DFA)** testing on skin biopsies (nuchal skin) or corneal scrapings is the "test of choice" for rapid antemortem diagnosis due to high sensitivity and speed, IFA is less commonly used as the primary confirmatory modality compared to culture or PCR. * **Real-time PCR:** This is highly sensitive and increasingly used for antemortem diagnosis (detecting viral RNA in saliva or CSF). However, in traditional medical examinations, culture maintains its status as the definitive confirmatory benchmark. **Clinical Pearls for NEET-PG:** * **Negri Bodies:** Most commonly found in the **Hippocampus (Ammon’s horn)** and **Cerebellum (Purkinje cells)**. * **Post-mortem Diagnosis:** DFA on brain tissue is the gold standard post-mortem. * **Antemortem Samples:** Saliva (PCR), Nuchal skin biopsy (DFA), and Serum/CSF (Antibody testing in unvaccinated individuals). * **Prophylaxis:** Once symptoms appear, rabies is virtually 100% fatal; hence, post-exposure prophylaxis (PEP) is the only life-saving intervention.

Question 315: Which virus is known to cause hepatocellular carcinoma?

A. Hepatitis B virus (Hepadnaviridae) (Correct Answer)
B. Enterovirus
C. Calicivirus
D. None of the above

Explanation: **Explanation:** Hepatocellular Carcinoma (HCC) is strongly associated with chronic viral hepatitis, primarily caused by **Hepatitis B Virus (HBV)** and Hepatitis C Virus (HCV). **Why Hepatitis B is correct:** HBV is a DNA virus belonging to the **Hepadnaviridae** family. It promotes oncogenesis through two main mechanisms: 1. **Insertional Mutagenesis:** The HBV DNA integrates into the host genome, causing genomic instability and activating proto-oncogenes. 2. **HBx Protein:** The virus produces the HBx protein, which acts as a transcriptional transactivator. It interferes with tumor suppressor genes (like p53) and disrupts cell cycle regulation, leading to malignant transformation even in the absence of cirrhosis. **Why the other options are incorrect:** * **Enterovirus (Picornaviridae):** This genus includes Poliovirus, Coxsackievirus, and Echovirus. They typically cause acute infections (meningitis, myocarditis, hand-foot-mouth disease) and are not associated with oncogenesis. * **Calicivirus:** This family includes Norovirus and Sapovirus, which are leading causes of acute viral gastroenteritis. They cause self-limiting infections and do not lead to chronic carriage or cancer. **High-Yield Clinical Pearls for NEET-PG:** * **HBV vs. HCV:** While both cause HCC, HBV is a DNA virus that can cause cancer *without* preceding cirrhosis. HCV (an RNA virus) almost always requires the development of cirrhosis before HCC occurs. * **Tumor Marker:** Alpha-fetoprotein (AFP) is the classic screening marker for HCC. * **Aflatoxin B1:** A potent co-carcinogen produced by *Aspergillus flavus* that works synergistically with HBV to increase HCC risk by causing mutations in the p53 gene. * **Vaccination:** The HBV vaccine is the first "anti-cancer" vaccine because it prevents HCC by preventing chronic HBV infection.

Question 316: Which of the following viral infections is characterized by the presence of inclusion bodies in neurons?

A. Rabies (Correct Answer)
B. Diphtheria
C. Yellow fever
D. Japanese encephalitis

Explanation: ### Explanation **Correct Answer: A. Rabies** Rabies is a neurotropic viral infection caused by the *Lyssavirus* (Rhabdoviridae family). The hallmark histopathological finding is the **Negri body**. These are pathognomonic, eosinophilic, intracytoplasmic inclusion bodies found within the cytoplasm of neurons, most commonly in the **Purkinje cells of the cerebellum** and the **pyramidal cells of the hippocampus (Ammon’s horn)**. They represent sites of viral replication (nucleocapsid accumulation). **Analysis of Incorrect Options:** * **B. Diphtheria:** This is a bacterial infection caused by *Corynebacterium diphtheriae*. It produces an exotoxin that inhibits protein synthesis. While it can cause neurological symptoms (polyneuropathy) due to demyelination, it does not produce viral inclusion bodies. * **C. Yellow Fever:** This is a flavivirus infection. Its characteristic inclusion bodies are **Councilman bodies**, which are eosinophilic globules found in the **hepatocytes** (liver), representing apoptotic hepatocytes, not neurons. * **D. Japanese Encephalitis (JE):** While JE is a neurotropic flavivirus that causes severe inflammation of the brain parenchyma, it does not typically present with well-defined, diagnostic inclusion bodies like Rabies. Diagnosis relies on IgM ELISA in CSF/Serum. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Intracytoplasmic, eosinophilic, found in neurons (Hippocampus/Cerebellum). * **Guarnieri Bodies:** Intracytoplasmic; seen in Variola (Smallpox) and Vaccinia. * **Cowdry Type A:** Intranuclear; seen in Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV). * **Cowdry Type B:** Intranuclear; seen in Poliovirus. * **Owl’s Eye Appearance:** Intranuclear inclusions seen in Cytomegalovirus (CMV). * **Henderson-Peterson Bodies:** Intracytoplasmic; seen in Molluscum contagiosum.

Question 317: Which of the following statements about perinatal transmission of HIV is incorrect?

A. It cannot be diagnosed by routine confirmatory tests.
B. Postnatal transmission is not possible. (Correct Answer)
C. The infant transmission rate is less than 50%.
D. The virus can be isolated from mother's milk.

Explanation: **Explanation:** **1. Why Option B is the Correct (Incorrect Statement):** Postnatal transmission of HIV is not only possible but is a significant route of infection. The virus is present in breast milk, and breastfeeding by an HIV-positive mother carries a substantial risk of transmission to the infant (estimated at 15–20% in the absence of interventions). Therefore, the statement "Postnatal transmission is not possible" is factually incorrect. **2. Analysis of Other Options:** * **Option A (Correct Statement):** Routine confirmatory tests like ELISA or Western Blot detect **maternal IgG antibodies**, which cross the placenta and can persist in the infant for up to 18 months. Thus, these tests cannot distinguish between maternal antibodies and true neonatal infection. Diagnosis requires **HIV DNA PCR** (Gold Standard). * **Option C (Correct Statement):** Without any medical intervention, the risk of mother-to-child transmission (MTCT) is approximately **25–40%** (i.e., less than 50%). With modern HAART and prophylaxis, this risk can be reduced to less than 1–2%. * **Option D (Correct Statement):** HIV is a cell-associated and free virus found in various body fluids, including breast milk. This is the biological basis for postnatal transmission. **3. Clinical Pearls for NEET-PG:** * **Timing of Transmission:** In utero (20%), Intrapartum/During delivery (50%), and Postpartum/Breastfeeding (30%). * **Diagnosis in Infants:** HIV DNA PCR is the investigation of choice for infants <18 months. The first test is usually done at 4–6 weeks of age. * **Prophylaxis:** In India (NACO guidelines), the mother receives lifelong ART, and the infant receives **Nevirapine syrup** for 6 weeks (extendable to 12 weeks if the mother is not on stable ART). * **Feeding:** Exclusive breastfeeding is recommended for the first 6 months if replacement feeding is not "Acceptable, Feasible, Affordable, Sustainable, and Safe" (AFASS). Mixed feeding should be strictly avoided.

Question 318: Which virus has a single-stranded RNA genome with segmented genes?

A. Influenza virus (Correct Answer)
B. Rotavirus
C. Reovirus
D. Measles virus

Explanation: **Explanation:** The correct answer is **Influenza virus**. The fundamental concept here is the classification of viral genomes based on their nucleic acid structure and segmentation. **1. Why Influenza Virus is Correct:** Influenza viruses (Orthomyxoviridae) possess a **single-stranded RNA (ssRNA)** genome that is **segmented**. Influenza A and B typically have 8 segments, while Influenza C has 7. This segmentation is clinically critical because it allows for **genetic reassortment** (Antigenic Shift) when two different strains infect the same cell, leading to pandemics. **2. Why the Other Options are Incorrect:** * **Rotavirus & Reovirus:** While these viruses have **segmented** genomes, they consist of **double-stranded RNA (dsRNA)**, not single-stranded. Rotavirus (a member of the Reoviridae family) typically has 11 segments. * **Measles Virus:** This is a member of the Paramyxoviridae family. It has a **single-stranded RNA** genome, but it is **non-segmented** (unipartite). **3. NEET-PG High-Yield Pearls:** * **Mnemonic for Segmented Viruses:** "**BOAR**" — **B**unyavirus, **O**rthomyxovirus (Influenza), **A**renavirus, and **R**eovirus. * **Antigenic Shift vs. Drift:** Segmentation allows for **Shift** (major changes/pandemics via reassortment). Point mutations cause **Drift** (minor changes/epidemics). * **Replication Exception:** Unlike most RNA viruses that replicate in the cytoplasm, **Influenza virus** replicates its genome in the **nucleus**. * **Amantadine/Rimantadine** target the M2 ion channel (only in Influenza A), while **Oseltamivir/Zanamivir** are Neuraminidase inhibitors effective against both A and B.

Question 319: SSPE is a rare complication of which viral infection?

A. Mumps
B. Measles (Correct Answer)
C. Rubella
D. Influenza

Explanation: **Explanation:** **Subacute Sclerosing Panencephalitis (SSPE)**, also known as Dawson disease, is a progressive, fatal neurodegenerative disease caused by a persistent infection with a **defective Measles virus**. **Why Measles is Correct:** SSPE occurs years (typically 5–10) after an initial measles infection, usually in children who contracted the virus before age two. The underlying mechanism involves a mutated measles virus that lacks the **M (Matrix) protein**, preventing the virus from budding. Instead, it spreads directly from cell to cell via syncytia formation, leading to widespread inflammation and demyelination in the CNS. **Analysis of Incorrect Options:** * **Mumps:** While mumps can cause acute viral meningitis or encephalitis, it does not lead to a chronic, progressive sclerosing panencephalitis like SSPE. * **Rubella:** Rubella is associated with **Progressive Rubella Panencephalitis (PRP)**, which is clinically similar to SSPE but much rarer and caused by the Rubella virus, not Measles. * **Influenza:** Influenza is associated with acute neurological complications like Reye Syndrome (if aspirin is used) or acute necrotizing encephalopathy, but not chronic persistent CNS infections. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Characterized by high titers of **anti-measles antibodies** in the CSF and serum (intrathecal synthesis). * **EEG Finding:** Pathognomonic **periodic, high-voltage slow-wave complexes** (Radermecker complexes). * **Histology:** Presence of **Cowdry Type A** intranuclear inclusion bodies in neurons and glial cells. * **Clinical Stages:** Progresses from behavioral changes to myoclonic jerks, followed by dementia and eventually a vegetative state.

Question 320: An 8-month-old girl presented with sudden onset of high fever (103 extdegree F). Despite the absence of signs of upper respiratory tract infection, meningitis, or encephalitis, her fever escalated to 105 extdegree F, leading to a febrile seizure. Upon examination by the pediatrician, the child's temperature had subsided, and a generalized papular rash was noted. What is the most likely diagnosis?

A. Erythema infectiosum caused by parvovirus B19
B. Hand-foot-and-mouth disease caused by Coxsackievirus A
C. Measles caused by Morbillivirus
D. Roseola infantum caused by human herpes virus 6 (Correct Answer)

Explanation: ### Explanation The clinical presentation described is classic for **Roseola Infantum** (also known as Exanthem Subitum or Sixth Disease). **1. Why the Correct Answer is Right:** Roseola infantum, caused primarily by **Human Herpesvirus 6 (HHV-6)**, typically affects infants aged 6–15 months. The hallmark of this condition is a **sudden high fever** (often >103°F) lasting 3–5 days in an otherwise well-appearing child. As the fever abruptly subsides (**defervescence**), a rose-pink, maculopapular rash appears, starting on the trunk and spreading to the face and extremities. The rapid rise in temperature makes Roseola the most common cause of **febrile seizures** in this age group. **2. Why Other Options are Incorrect:** * **Erythema Infectiosum (Parvovirus B19):** Characterized by a "slapped-cheek" appearance followed by a reticular (lace-like) rash on the body. It lacks the preceding high fever and sudden defervescence pattern. * **Hand-Foot-and-Mouth Disease (Coxsackievirus A16):** Presents with vesicular eruptions on the palms, soles, and oral mucosa (herpangina), rather than a generalized post-febrile papular rash. * **Measles (Morbillivirus):** Presents with the "3 Cs" (Cough, Coryza, Conjunctivitis) and Koplik spots. Crucially, in measles, the rash appears **while the fever is at its peak**, not after it disappears. **3. NEET-PG High-Yield Pearls:** * **Nagayama Spots:** Erythematous papules on the soft palate and uvula seen in some Roseola patients. * **HHV-6 Pathogenesis:** It infects T-lymphocytes (CD4+ cells). * **Sequence is Key:** Fever **THEN** Rash = Roseola. Fever **WITH** Rash = Measles/Rubella. * **Treatment:** Supportive; ganciclovir is reserved only for severe immunocompromised cases.

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