Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 261: Which viral disease is transmitted by the orofecal route?

A. Dengue
B. Poliovirus (Correct Answer)
C. Hepatitis B
D. Influenza virus

Explanation: **Explanation:** The **fecal-oral route** is a common mode of transmission for viruses that lack a lipid envelope (non-enveloped viruses), making them stable in the acidic environment of the stomach and bile. **Poliovirus (Option B)** is a member of the *Picornaviridae* family (genus *Enterovirus*). It is primarily transmitted through the ingestion of contaminated water or food. Once ingested, the virus replicates in the oropharynx and the Peyer’s patches of the intestine before entering the bloodstream (viremia) and potentially crossing the blood-brain barrier to cause paralytic poliomyelitis. **Why the other options are incorrect:** * **Dengue (Option A):** Transmitted via the bite of an infected **Aedes aegypti** mosquito (Vector-borne). * **Hepatitis B (Option C):** Transmitted through parenteral routes (blood transfusion, contaminated needles), sexual contact, or vertical transmission (mother to child). It is not transmitted via the fecal-oral route. * **Influenza virus (Option D):** Transmitted primarily through **respiratory droplets** and aerosols. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Fecal-Oral Viruses:** "Vowels (Hepatitis **A** and **E**) and **P**ol**i**o." * **Specimen of Choice:** For Polio diagnosis, **stool samples** are preferred over CSF, as the virus is shed in feces for several weeks but is rarely isolated from CSF. * **Vaccine Insight:** The Oral Polio Vaccine (Sabin) induces local **IgA immunity** in the gut, which is crucial for breaking the chain of fecal-oral transmission, unlike the Injectable Polio Vaccine (Salk).

Question 262: Viral enterotoxin is detected as a possible mechanism of pathogenesis in which of the following viruses?

A. Adenovirus
B. Rotavirus (Correct Answer)
C. Calicivirus
D. Astrovirus

Explanation: ### Explanation **Correct Answer: B. Rotavirus** The hallmark of Rotavirus pathogenesis is the production of the **NSP4 (Non-Structural Protein 4)**, which acts as the first identified **viral enterotoxin**. * **Mechanism:** NSP4 triggers a signal transduction pathway that increases intracellular calcium levels. This leads to the secretion of chloride and water from enterocytes into the intestinal lumen, resulting in secretory diarrhea. * **Dual Action:** Rotavirus causes diarrhea through two mechanisms: 1. **Malabsorptive:** Destruction of mature enterocytes at the villi tips. 2. **Secretory:** The enterotoxic effect of NSP4 and activation of the enteric nervous system. **Why other options are incorrect:** * **Adenovirus (Serotypes 40/41):** These cause gastroenteritis primarily through direct mucosal damage and atrophy of the villi, leading to malabsorption, rather than an enterotoxin. * **Calicivirus (e.g., Norovirus):** These are the most common cause of epidemic gastroenteritis. They cause blunting of villi and decreased brush border enzyme activity, but do not produce an enterotoxin. * **Astrovirus:** These cause mild diarrhea in children via epithelial cell lysis and inflammatory changes, lacking an enterotoxic component. **NEET-PG High-Yield Pearls:** * **Rotavirus** is the most common cause of severe dehydrating diarrhea in children worldwide. * **NSP4** is the key virulence factor; it is unique because enterotoxins are typically associated with bacteria (e.g., *Vibrio cholerae*). * **Diagnosis:** ELISA for VP6 antigen in stool is the standard (Latex agglutination is also used). * **Vaccines:** Rotavac (Indigenous Indian vaccine), Rotarix (Monovalent), and RotaTeq (Pentavalent) are live attenuated oral vaccines.

Question 263: Paul Bunnell antibodies are reactive in all except?

A. Ox (Correct Answer)
B. Sheep
C. Dog
D. Horse

Explanation: The **Paul-Bunnell Test** is a classic diagnostic tool for **Infectious Mononucleosis (IM)** caused by the Epstein-Barr Virus (EBV). It detects **heterophile antibodies**, which are IgM antibodies produced during EBV infection that have the unique property of agglutinating red blood cells (RBCs) from different animal species. ### Explanation of Options: * **Correct Answer (A) Ox:** Paul-Bunnell antibodies are **absorbed by Ox (Beef) RBCs**, meaning they react with and bind to them. However, in the context of the standard Paul-Bunnell agglutination test, the antibodies are typically **tested against sheep, horse, or dog RBCs** to observe agglutination. The specific "Paul-Bunnell antibodies" are defined by their ability to be absorbed by Ox RBCs but **not** by Guinea pig kidney cells (this is the basis of the Davidsohn Differential Test). Therefore, they are "reactive" in the sense of agglutinating Sheep/Horse/Dog cells, while Ox cells are used for absorption/removal of these antibodies. * **Incorrect Options (B, C, D):** Heterophile antibodies in IM characteristically agglutinate the RBCs of **Sheep, Horses, and Dogs**. These are the standard substrates used to visualize the positive agglutination reaction in a laboratory setting. ### High-Yield Clinical Pearls for NEET-PG: 1. **Davidsohn Differential Test:** This is used to distinguish IM heterophile antibodies from Forssman and Serum Sickness antibodies. * **IM Antibodies:** Absorbed by **Ox RBCs**; NOT absorbed by **Guinea pig kidney**. * **Forssman Antibodies:** Absorbed by **Guinea pig kidney**; NOT absorbed by **Ox RBCs**. 2. **Monospot Test:** A rapid latex agglutination test that uses **Horse RBCs** (more sensitive than sheep RBCs) to detect these antibodies. 3. **Age Factor:** Heterophile antibodies are often **absent in children** under 5 years old with EBV; in such cases, EBV-specific serology (Anti-VCA) is required.

Question 264: Infectious mononucleosis is primarily associated with which virus?

A. Human papillomavirus (HPV)
B. Epstein-Barr virus (Correct Answer)
C. Human Immunodeficiency Virus (HIV)
D. Varicella zoster virus

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is the primary causative agent of **Infectious Mononucleosis (IM)**, often referred to as the "kissing disease." The virus typically infects B-lymphocytes by binding to the **CD21 receptor** (CR2). The hallmark of the disease is the presence of **atypical lymphocytes** (Downey cells) in the peripheral blood smear, which are actually activated T-cells (CD8+) responding to the infected B-cells. **Why other options are incorrect:** * **Human papillomavirus (HPV):** Primarily associated with warts (verrucae) and mucosal lesions; high-risk types (16, 18) are strongly linked to cervical and oropharyngeal cancers. * **Human Immunodeficiency Virus (HIV):** Causes AIDS by depleting CD4+ T-cells. While acute HIV infection can present with a "mononucleosis-like" syndrome, it is not the primary cause of IM. * **Varicella zoster virus (VZV):** Causes chickenpox (primary infection) and herpes zoster/shingles (reactivation). **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Fever, pharyngitis (often with exudates), and lymphadenopathy (typically posterior cervical). * **Diagnosis:** **Paul-Bunnell Test** or Monospot test (detects heterophile antibodies). * **Complication:** Splenomegaly is common; patients must avoid contact sports to prevent **splenic rupture**. * **Drug Reaction:** Administration of **Ampicillin or Amoxicillin** in a patient with EBV often results in a characteristic maculopapular rash. * **Associated Malignancies:** Burkitt lymphoma, Nasopharyngeal carcinoma, and Hodgkin lymphoma.

Question 265: Viruses have various ways of entering the human body and producing disease. Which of the following descriptions accurately describes the route of transmission and target disease for the virus indicated?

A. Coronavirus: fecal-oral; peptic ulcers
B. Echovirus: fecal-oral; aseptic meningitis (Correct Answer)
C. HIV: respiratory droplet; anemia
D. Influenza virus: blood-borne; maculopapular rash

Explanation: **Explanation:** The correct answer is **B. Echovirus: fecal-oral; aseptic meningitis.** **1. Why the correct answer is right:** Echoviruses belong to the **Enterovirus** genus (family Picornaviridae). As the name suggests, Enteroviruses are primarily transmitted via the **fecal-oral route** because they are acid-stable and can survive the gastric environment. Once they replicate in the gastrointestinal tract, they can disseminate hematogenously to the central nervous system. Echoviruses are a leading cause of **aseptic (viral) meningitis**, characterized by fever, headache, and meningeal signs with clear CSF (lymphocytic pleocytosis and normal glucose). **2. Why the incorrect options are wrong:** * **A. Coronavirus:** Primarily transmitted via **respiratory droplets**. While some strains cause GI symptoms, they are classically associated with respiratory tract infections (Common cold, SARS, MERS, COVID-19), not peptic ulcers (which are primarily caused by *H. pylori* or NSAIDs). * **C. HIV:** Transmitted via **blood, sexual contact, or vertical transmission**. While HIV can cause various hematological abnormalities in advanced stages, its primary target is CD4+ T-lymphocytes, leading to immunodeficiency (AIDS). It is not spread by respiratory droplets. * **D. Influenza virus:** Transmitted via **respiratory droplets**. It causes respiratory illness (flu) characterized by fever, myalgia, and cough. It is not blood-borne and does not typically present with a maculopapular rash. **3. NEET-PG High-Yield Pearls:** * **Enteroviruses** (ECHO, Coxsackie, Polio) are the **most common cause of viral meningitis** overall. * **CSF Findings in Viral Meningitis:** Increased lymphocytes, normal glucose, and slightly elevated protein (distinguishes it from bacterial meningitis). * **Acid Stability:** Picornaviruses are acid-stable (except Rhinoviruses, which are acid-labile and thus restricted to the upper respiratory tract). * **Seasonality:** Enteroviral infections typically peak during summer and autumn months.

Question 266: How is rabies diagnosed?

A. Hair follicle smear
B. Corneal smear (Correct Answer)
C. Isolation from blood
D. Nerve biopsy

Explanation: **Explanation:** The diagnosis of Rabies in a living patient (antemortem) relies on detecting the virus or its components in tissues where the virus travels via centrifugal spread from the central nervous system. **1. Why Corneal Smear is Correct:** Rabies virus travels from the brain via sensory and autonomic nerves to highly innervated tissues. The cornea is one of the most densely innervated tissues in the body. A **Corneal Impression Smear** allows for the detection of Rabies virus antigens using **Direct Fluorescent Antibody (DFA)** testing. While its sensitivity is variable, it remains a classic, non-invasive diagnostic method described in standard textbooks for NEET-PG. **2. Why the other options are incorrect:** * **Hair follicle smear:** This is a distractor. The correct procedure is a **Full-thickness Skin Biopsy** (usually from the nape of the neck), where the virus is detected in the nerve plexuses surrounding the hair follicles, not a simple smear of the hair itself. * **Isolation from blood:** Rabies is a strictly neurotropic virus. It does not cause viremia; therefore, it cannot be isolated from blood. * **Nerve biopsy:** While nerves contain the virus, a formal nerve biopsy is unnecessarily invasive and not a standard diagnostic protocol when skin biopsies or corneal smears are available. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard (Post-mortem):** Detection of **Negri Bodies** (intracytoplasmic eosinophilic inclusions) in the hippocampus (Ammon’s horn) or cerebellum (Purkinje cells). * **Most Sensitive Antemortem Test:** RT-PCR of saliva or skin biopsy. * **DFA (Direct Fluorescent Antibody):** The most common method used to detect viral antigens in both animal brains and human skin/corneal samples. * **Fixed Virus:** Used for vaccine production (e.g., Pasteur’s virus); it has a short, fixed incubation period and does not produce Negri bodies.

Question 267: What is the most specific diagnostic test for AIDS?

A. Western blot (Correct Answer)
B. Southern blot
C. ELISA
D. None of the above

Explanation: **Explanation:** The diagnosis of HIV/AIDS follows a specific two-step algorithm: screening followed by confirmation. **Why Western Blot is the Correct Answer:** Western blot is considered the **gold standard confirmatory test** for HIV because of its high **specificity**. While screening tests look for general reactivity, the Western blot detects specific antibodies against individual HIV proteins (such as gp120, gp41, and p24). A positive result requires the presence of bands against multiple specific viral antigens, virtually eliminating false positives. **Analysis of Incorrect Options:** * **ELISA (Option C):** This is the **standard screening test**. It is highly sensitive (to ensure no cases are missed) but has lower specificity than Western blot, meaning it can occasionally yield false positives due to cross-reacting antibodies. * **Southern Blot (Option B):** This laboratory technique is used to detect specific **DNA** sequences. It is not used in the routine clinical diagnosis of HIV/AIDS. * **Note on Current Trends:** While Western blot remains the traditional "most specific" answer for exams, modern NAAT (Nucleic Acid Amplification Test) for HIV RNA is now frequently used for early diagnosis and confirmation in clinical practice. **NEET-PG High-Yield Pearls:** 1. **Screening Test of Choice:** ELISA (High sensitivity). 2. **Confirmatory Test of Choice:** Western blot (High specificity). 3. **Window Period Test:** p24 antigen assay or HIV RNA (PCR) are the earliest markers detectable. 4. **Diagnosis in Infants (<18 months):** PCR is the gold standard because maternal IgG antibodies can cause false positives on ELISA/Western blot. 5. **Monitoring Progression:** CD4+ T-cell count is the best predictor of clinical progression, while Viral Load (HIV RNA) is the best monitor of treatment (ART) efficacy.

Question 268: Human rotaviruses are characterized by which of the following statements?

A. They produce an infection that is primarily seen in adults
B. They produce cytopathic effects in many conventional tissue culture systems
C. They are lipid-containing RNA viruses possessing a double-shelled capsid
D. They can be sensitively and rapidly detected in stools by the enzyme-linked immunosorbent assay (ELISA) technique (Correct Answer)

Explanation: **Explanation:** **Rotavirus** is the most common cause of severe, dehydrating diarrhea in infants and young children worldwide. 1. **Why Option D is correct:** Rotaviruses are shed in very high concentrations in the feces (up to $10^{12}$ particles/gram). Because they are difficult to grow in standard cultures, diagnosis relies on the direct detection of viral antigens in stool samples. **ELISA** is the most widely used, rapid, and sensitive method for clinical diagnosis. Other methods include Latex Agglutination and Immunochromatography. 2. **Why other options are incorrect:** * **Option A:** Rotavirus primarily affects **infants and children (6 months to 2 years)**. Adults usually have immunity from prior exposure, leading to asymptomatic or mild infections. * **Option B:** Rotaviruses are notoriously **fastidious** and do not produce cytopathic effects (CPE) in conventional tissue cultures. They require specialized cell lines (e.g., MA104) and pretreatment with proteolytic enzymes like trypsin to enhance growth. * **Option C:** Rotaviruses are **non-enveloped** (naked) viruses. While they do possess a characteristic **double-shelled capsid** (giving them a wheel-like appearance, hence "Rota"), they do **not** contain lipids. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Reoviridae family; Double-stranded RNA (dsRNA) with **11 segments**. * **Appearance:** "Wheel-like" appearance on Electron Microscopy. * **Pathogenesis:** Produces a viral enterotoxin called **NSP4**, which induces secretory diarrhea by increasing intracellular calcium. * **Vaccines:** Live attenuated oral vaccines are available (Rotarix - monovalent; RotaTeq - pentavalent; Rotavac - indigenous Indian vaccine). * **Seasonality:** More common in winter months ("Winter diarrhea").

Question 269: Rubella virus infection is known to cause all of the following teratogenic effects except:

A. Microcephaly
B. Ventricular Septal Defect (VSD)
C. Conduction defects (e.g., heart block) (Correct Answer)
D. All of the above

Explanation: **Explanation:** Congenital Rubella Syndrome (CRS) is a classic TORCH infection characterized by a specific triad of defects: **Cataracts, Sensorineural deafness, and Cardiac malformations.** 1. **Why Option C is correct:** While Rubella is notorious for causing structural cardiac defects, it is **not** typically associated with **conduction defects** like congenital heart block. Congenital heart block is a high-yield association for **Neonatal Lupus Erythematosus**, caused by the transplacental passage of maternal anti-Ro (SSA) and anti-La (SSB) antibodies. 2. **Why Options A and B are incorrect:** * **Microcephaly (Option A):** This is a common feature of the "expanded" Congenital Rubella Syndrome. The virus inhibits cell division and causes angiopathy, leading to impaired brain growth and CNS involvement (including mental retardation and meningoencephalitis). * **Ventricular Septal Defect (Option B):** Rubella causes various structural heart defects. While **Patent Ductus Arteriosus (PDA)** and **Peripheral Pulmonary Artery Stenosis** are the most characteristic, VSD and ASD are also frequently documented in affected neonates. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad (Gregg’s Triad):** Cataracts, Deafness (most common), and Cardiac defects (PDA is the most specific). * **Dermatological Sign:** "Blueberry muffin" spots (due to extramedullary hematopoiesis). * **Radiology:** "Celery stalking" appearance of long bones (metaphyseal lucencies). * **Risk Timing:** The risk of malformation is highest (up to 80%) if the mother is infected during the **first trimester** (especially the first 8 weeks).

Question 270: All the following viruses are transmitted by arthropod vectors except:

A. Hantavirus (Correct Answer)
B. Dengue
C. Chikungunya
D. Japanese Encephalitis

Explanation: **Explanation:** The core concept tested here is the distinction between **Arboviruses** (Arthropod-borne) and **Roboviruses** (Rodent-borne). **1. Why Hantavirus is the Correct Answer:** Hantavirus belongs to the *Bunyaviridae* family but is a **Robovirus**. It is transmitted to humans via the inhalation of aerosolized excreta (urine, feces, or saliva) from infected **rodents** (e.g., deer mice). It does not require an arthropod vector for transmission. Clinically, it causes two major syndromes: Hantavirus Pulmonary Syndrome (HPS) and Hemorrhagic Fever with Renal Syndrome (HFRS). **2. Why the other options are incorrect:** * **Dengue:** A Flavivirus transmitted by the *Aedes aegypti* mosquito. * **Chikungunya:** A Togavirus (Alphavirus) also transmitted primarily by *Aedes aegypti* and *Aedes albopictus*. * **Japanese Encephalitis (JE):** A Flavivirus transmitted by the *Culex tritaeniorhynchus* mosquito, commonly associated with rice fields. **High-Yield Clinical Pearls for NEET-PG:** * **Arboviruses:** Include members of *Flaviviridae* (Dengue, JE, West Nile, Zika, Yellow Fever), *Togaviridae* (Chikungunya), and *Bunyaviridae* (Crimean-Congo Hemorrhagic Fever). * **Roboviruses:** Include Hantavirus and Arenaviruses (Lassa fever). * **Hantavirus Exception:** While most *Bunyaviridae* are arboviruses, Hantavirus is the notable exception. * **Diagnosis:** Hantavirus is typically diagnosed via IgM ELISA or RT-PCR; remember the "triad" of HFRS: fever, hemorrhage, and acute renal failure.

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