Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 771: Bacteriophages are mostly used for what purpose?

A. Bacterial identification (Correct Answer)
B. Epidemiological tracing
C. As an antibacterial agent
D. Prophage conversion in bacteria

Explanation: **Explanation:** **Bacteriophages** are viruses that infect bacteria. In medical microbiology, their primary and most common diagnostic use is **Bacterial Identification** through a process known as **Phage Typing**. 1. **Why Option A is Correct:** Phage typing relies on the high degree of **host specificity** exhibited by bacteriophages. A specific phage will only infect and lyse a particular strain of bacteria. By observing patterns of lysis (clearing zones) on a bacterial lawn, clinicians can identify specific species and strains (e.g., identifying *Staphylococcus aureus* or *Salmonella Typhi*). 2. **Why Other Options are Incorrect:** * **Option B:** While phage typing *contributes* to epidemiological tracing (tracking an outbreak source), its fundamental laboratory application is the identification of the organism itself. * **Option C:** Although "Phage Therapy" is an emerging field for treating multi-drug resistant infections, it is not yet the "most common" use in standard medical practice compared to diagnostic typing. * **Option D:** Prophage conversion (Lysogenic conversion) is a biological phenomenon where a phage integrates its DNA into a bacterium (e.g., giving *Corynebacterium diphtheriae* its toxigenicity), but this is a natural process rather than a primary intended "use" by scientists. **High-Yield Clinical Pearls for NEET-PG:** * **Lysogenic Conversion:** Important examples include **Diphtheria toxin**, **Cholera toxin**, and **Botulinum toxin**. The bacteria only become pathogenic when infected by a specific temperate phage. * **Transduction:** Bacteriophages are the vectors for horizontal gene transfer between bacteria via transduction (Generalized or Specialized). * **T-Even Phages:** The T4 phage is the classic model used to study the lytic cycle.

Question 772: The 'Kissing disease' is representative of which of the following infections?

A. Candidiasis.
B. Cytomegalovirus infection.
C. Histoplasmosis.
D. Infectious mononucleosis. (Correct Answer)

Explanation: **Explanation:** **Infectious Mononucleosis (IM)** is the correct answer because it is colloquially known as the **'Kissing disease.'** This name stems from its primary mode of transmission: the exchange of saliva containing the **Epstein-Barr Virus (EBV)**, a human herpesvirus (HHV-4). EBV infects the B-lymphocytes of the oropharynx, leading to a classic clinical triad of fever, pharyngitis, and lymphadenopathy. **Analysis of Options:** * **Candidiasis (A):** A fungal infection caused by *Candida albicans*. While oral thrush occurs in the mouth, it is opportunistic and not associated with the "kissing disease" moniker. * **Cytomegalovirus (B):** CMV can cause a mononucleosis-like syndrome (heterophile antibody negative), but the specific term "Kissing disease" is historically and classically reserved for EBV-induced IM. * **Histoplasmosis (C):** A systemic fungal infection caused by *Histoplasma capsulatum*, typically acquired via inhalation of bird or bat droppings, not through salivary contact. **High-Yield NEET-PG Pearls:** * **Diagnosis:** The **Paul-Bunnell Test** (detecting heterophile antibodies) is the gold standard for screening. * **Hematology:** Peripheral blood smears show characteristic **Atypical Lymphocytes (Downey cells)**, which are actually activated T-cells (CD8+) responding to infected B-cells. * **Clinical Sign:** Patients with IM who are mistakenly treated with **Ampicillin or Amoxicillin** often develop a characteristic maculopapular rash. * **Complication:** Splenic enlargement is common; patients are advised to avoid contact sports to prevent **splenic rupture**.

Question 773: All of the following are true about the Influenza virus EXCEPT:

A. Influenza A is the most common cause of outbreaks.
B. The incubation period is typically 2-3 weeks. (Correct Answer)
C. Type B influenza is associated with Reye's syndrome.
D. Influenza possesses two main glycoprotein antigens.

Explanation: **Explanation:** The correct answer is **B** because the incubation period of the Influenza virus is very short, typically ranging from **1 to 4 days** (average 2 days), not 2–3 weeks. Influenza is characterized by a rapid onset of symptoms following exposure, which is a key clinical feature distinguishing it from many other respiratory infections. **Analysis of Options:** * **Option A:** Influenza A is indeed the most common cause of seasonal outbreaks and is the only type capable of causing **pandemics** due to its ability to undergo both antigenic drift and shift. * **Option C:** Reye’s syndrome (acute encephalopathy and fatty liver) is a rare but serious complication associated with **Influenza B** and Varicella, especially in children who are given **Aspirin** (salicylates) during the viral prodrome. * **Option D:** The virus possesses two major surface glycoproteins: **Hemagglutinin (HA)**, which facilitates viral entry/attachment, and **Neuraminidase (NA)**, which aids in the release of new virions from host cells. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Drift:** Minor point mutations (causes seasonal epidemics; seen in Types A and B). * **Antigenic Shift:** Major genetic reassortment (causes pandemics; seen **only in Type A**). * **Diagnosis:** Reverse Transcription PCR (RT-PCR) is the gold standard. * **Treatment:** Oseltamivir (Neuraminidase inhibitor) is most effective when started within 48 hours of symptom onset. * **Vaccine:** Usually contains two strains of Influenza A and one or two of Influenza B (Trivalent/Quadrivalent).

Question 774: Which of the following statements is true about the rabies virus?

A. It is a double-stranded RNA virus.
B. It contains a DNA-dependent RNA polymerase.
C. Its RNA has a negative polarity. (Correct Answer)
D. It affects motor neurons.

Explanation: **Explanation:** The rabies virus belongs to the **Rhabdoviridae** family (genus *Lyssavirus*). Understanding its structure and pathogenesis is crucial for NEET-PG. **1. Why Option C is Correct:** The rabies virus is a **single-stranded, negative-sense RNA virus** (-ssRNA). Negative polarity means the viral RNA cannot be directly translated into proteins by host ribosomes. It must first be transcribed into a positive-sense mRNA template by the virus's own RNA-dependent RNA polymerase (RdRp). **2. Analysis of Incorrect Options:** * **Option A:** Rabies is a **single-stranded** RNA virus, not double-stranded. It is characterized by its unique **bullet-shaped** morphology. * **Option B:** Since it is an RNA virus that replicates in the cytoplasm, it carries an **RNA-dependent RNA polymerase**. DNA-dependent RNA polymerases are typically involved in human transcription (DNA to RNA). * **Option C:** While the virus travels via nerves, it primarily affects **sensory neurons** and moves via **retrograde axonal transport** to the CNS. It binds to **Nicotinic Acetylcholine Receptors (nAChR)** at the neuromuscular junction. **3. High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusion bodies found most commonly in **Purkinje cells of the cerebellum** and **pyramidal cells of the hippocampus**. * **Incubation Period:** Highly variable (1–3 months), depending on the distance of the bite site from the CNS. * **Prophylaxis:** Post-exposure prophylaxis (PEP) includes wound cleaning, Rabies Immunoglobulin (RIG), and the Modern Cell Culture Vaccine (days 0, 3, 7, 14, and 28). * **Street Virus vs. Fixed Virus:** "Street virus" is the fresh isolate from animals; "Fixed virus" is the attenuated strain used for vaccine production (Pasteur’s contribution).

Question 775: What type of rubella-specific antibodies are detected after vaccination or natural infection?

A. IgM
B. IgG (Correct Answer)
C. IgA
D. IgE

Explanation: **Explanation:** The detection of **IgG antibodies** is the hallmark of long-term immunity following either natural infection or vaccination with the Rubella (MMR) vaccine. **1. Why IgG is Correct:** In the primary immune response to Rubella, **IgG** appears shortly after IgM (usually within 1–2 weeks of the rash) and persists for life. Its presence indicates **past exposure or successful immunization**, providing protective immunity against reinfection. In the context of pregnancy screening, a positive IgG titer (without IgM) signifies that the mother is immune and the fetus is not at risk of Congenital Rubella Syndrome (CRS). **2. Why Other Options are Incorrect:** * **IgM:** These are the first antibodies to appear during an **acute/primary infection**. They disappear within 6 weeks to 3 months. While they are diagnostic of a current infection, they do not represent long-term post-vaccination status. * **IgA:** While secretory IgA may be found in the nasopharynx after natural infection (providing mucosal immunity), it is not the standard marker used to confirm systemic immunity or vaccination success in clinical practice. * **IgE:** These antibodies are involved in Type I hypersensitivity (allergic) reactions and parasitic infections; they play no role in Rubella immunity. **High-Yield Clinical Pearls for NEET-PG:** * **Vaccine Strain:** The Rubella vaccine uses the **RA 27/3** live attenuated strain (grown in human diploid cells). * **Congenital Rubella Syndrome (CRS):** The classic **Gregg’s Triad** includes Cataracts, Sensorineural deafness, and Cardiac defects (Patent Ductus Arteriosus). * **Diagnosis of CRS:** Detection of **IgM in the neonate** is diagnostic of CRS, as maternal IgM cannot cross the placenta (only IgG crosses). * **Vaccination Rule:** Live vaccines like MMR are **contraindicated in pregnancy**. Women should avoid pregnancy for at least 4 weeks (1 month) after receiving the Rubella vaccine.

Question 776: Painless diarrhea occurs with which of the following pathogens?

A. Salmonella
B. Shigella
C. C. jejuni
D. V. cholerae (Correct Answer)

Explanation: **Explanation:** The clinical presentation of diarrhea is primarily determined by whether the pathogen is **non-invasive (secretory)** or **invasive (inflammatory)**. **Why V. cholerae is correct:** *Vibrio cholerae* produces a potent enterotoxin (Cholera toxin) that activates adenylate cyclase, leading to increased cAMP levels in intestinal epithelial cells. This results in the massive secretion of isotonic fluid into the intestinal lumen without causing mucosal damage or inflammation. Because there is no invasion of the intestinal wall and no inflammatory response, the resulting "rice-water stools" are characteristically **painless**, voluminous, and devoid of blood or pus. **Why the other options are incorrect:** * **Shigella & C. jejuni:** These are classic **invasive** pathogens. They cause mucosal destruction and intense inflammation (colitis). This leads to **dysentery**, characterized by painful abdominal cramps (tenesmus) and small-volume stools containing blood and mucus. * **Salmonella:** Most *Salmonella* species (non-typhoidal) invade the intestinal mucosa and trigger an inflammatory response, typically presenting with fever and **crampy abdominal pain**. **NEET-PG High-Yield Pearls:** * **Mechanism of Cholera Toxin:** It causes ADP-ribosylation of the Gs protein, locking it in the "on" position. * **Stool Microscopy:** *V. cholerae* shows "darting motility" (inhibited by specific antisera in the Pfeiffer phenomenon). * **Culture Media:** TCBS (Thiosulfate-Citrate-Bile Salts-Sucrose) agar is the selective medium; *V. cholerae* produces large yellow colonies due to sucrose fermentation. * **Key Distinction:** Secretory diarrheas (Cholera, ETEC) are generally painless; Inflammatory diarrheas (Shigella, Campylobacter, EIEC) are generally painful/febrile.

Question 777: Which diagnostic tests are positive during the window period of an HIV-infected patient?

A. ELISA
B. Western Blot
C. Both ELISA and Western Blot (Correct Answer)
D. PCR

Explanation: ### Explanation The **window period** in HIV infection is the interval between the initial infection and the time when the body produces enough antibodies to be detected by standard screening tests. **Why the Correct Answer is Right:** In the context of traditional NEET-PG questions, the "window period" is defined as the time when **antibody-based tests** (like ELISA and Western Blot) are **negative**. However, the question asks which tests are positive. This is a common point of confusion in older question banks. Technically, **p24 antigen assays** and **Nucleic Acid Testing (PCR for HIV RNA)** are the first to become positive during this period. However, if we follow the logic of standard medical examinations where the "window period" ends once seroconversion occurs, the answer reflects the transition point. In modern 4th generation ELISA (which detects both p24 and antibodies), the window period is significantly shortened. **Analysis of Options:** * **A & B (ELISA & Western Blot):** These are antibody-dependent. They are typically **negative** during the early window period. If the question implies the *end* of the window period, both would turn positive nearly simultaneously (seroconversion). * **D (PCR):** This is the **earliest** test to become positive (as early as 10–12 days post-infection). It detects the viral genome itself, bypassing the need for an immune response. **Clinical Pearls for NEET-PG:** 1. **Order of Positivity:** HIV RNA (PCR) → p24 Antigen → ELISA (Antibody) → Western Blot. 2. **Best Screening Test:** 4th Gen ELISA (p24 Ag + Ab). 3. **Best Confirmatory Test:** Western Blot (though now being replaced by Geenius™ HIV-1/HIV-2 supplemental assay in newer protocols). 4. **Diagnosis in Infants:** PCR is the gold standard for babies born to HIV-positive mothers (due to persistence of maternal IgG antibodies for up to 18 months). 5. **Window Period Duration:** Usually 3–12 weeks for antibody tests.

Question 778: Reduced cerebrospinal fluid (CSF) sugar is a characteristic finding in which type of viral meningitis?

A. Rubella
B. Mumps
C. AIDS
D. Coxsackie virus (Correct Answer)

Explanation: **Explanation:** In typical viral meningitis (aseptic meningitis), CSF findings usually show normal glucose levels, lymphocytic pleocytosis, and mildly elevated protein. However, certain viruses are known exceptions that can cause **hypoglycorrhachia** (low CSF sugar), mimicking bacterial or tubercular meningitis. **1. Why Coxsackie virus is correct:** Enteroviruses, particularly **Coxsackie virus** and Echovirus, are the most common causes of viral meningitis. While most cases present with normal glucose, Coxsackie virus is a classic "exception" frequently cited in medical literature and exams where CSF glucose can be significantly reduced. This occurs due to alterations in glucose transport across the blood-brain barrier and increased glycolysis by inflammatory cells. **2. Analysis of Incorrect Options:** * **Mumps:** While Mumps is a well-known cause of low CSF sugar (occurring in up to 25% of mumps meningitis cases), in the context of standard NEET-PG patterns and specific question banks, **Coxsackie/Enteroviruses** are often prioritized as the primary answer when "viral meningitis" is discussed broadly. *Note: If both are present, Enteroviruses are statistically more common causes of the syndrome.* * **Rubella:** Rubella virus rarely causes meningitis; it is more associated with progressive rubella panencephalitis or congenital rubella syndrome. CSF glucose is typically normal. * **AIDS (HIV):** Acute HIV infection can cause aseptic meningitis during seroconversion, but the CSF glucose level remains characteristically normal. **High-Yield Clinical Pearls for NEET-PG:** * **The "Low CSF Sugar" Viral Trio:** Remember **Mumps, Herpes Simplex Virus (HSV), and Enteroviruses (Coxsackie/Echovirus)** as the three viral exceptions that can cause low CSF glucose. * **Normal CSF Glucose:** 40–70 mg/dL (or >60% of blood glucose). * **Differential Diagnosis:** If CSF sugar is low, always rule out Bacterial, Tubercular, Fungal (Cryptococcal), or Carcinomatous meningitis first. * **Mumps Meningitis:** Often associated with parotitis and a very high lymphocytic count (sometimes >1000 cells/mm³).

Question 779: Which is the most sensitive test for HW infection?

A. Western blot (Correct Answer)
B. ELISA
C. Agglutination test
D. CFT

Explanation: **Explanation:** The correct answer is **Western Blot**. In the context of HIV diagnostics, Western Blot is historically considered the most sensitive and specific confirmatory test because it detects antibodies against multiple specific viral proteins (such as gp120, gp41, and p24) rather than a total antibody pool. **Why Western Blot is correct:** While ELISA is the standard screening tool, Western Blot is used to confirm the diagnosis due to its high analytical sensitivity and specificity. It separates viral proteins by molecular weight via electrophoresis, allowing for the visualization of distinct bands. A positive result requires the presence of antibodies against at least two of the three major gene products (Env, Gag, and Pol). **Why other options are incorrect:** * **ELISA:** This is the most common **screening** test. While modern 4th generation ELISAs (which detect both p24 antigen and antibodies) are extremely sensitive, in the context of traditional board exams, Western Blot remains the definitive "gold standard" for sensitivity and confirmation. * **Agglutination test:** These are rapid tests (e.g., latex agglutination) used for quick screening. They have lower sensitivity and specificity compared to ELISA and Western Blot. * **CFT (Complement Fixation Test):** This is an older serological method rarely used for HIV diagnosis due to its complexity and lower sensitivity compared to modern enzyme-linked assays. **Clinical Pearls for NEET-PG:** * **Screening Test of Choice:** ELISA (High sensitivity, lower specificity). * **Confirmatory Test of Choice:** Western Blot (High specificity). * **Best test for Early Diagnosis (Window Period):** PCR for HIV-RNA (detectable within 10–12 days) or p24 antigen assay. * **Best test for Neonatal HIV:** DNA-PCR (Antibody tests are unreliable in infants due to persistence of maternal IgG). * **Monitoring Treatment:** Viral load (Quantitative RNA-PCR) is the best predictor of disease progression and treatment response.

Question 780: Which one of the following groups of people may be at increased risk for HIV infection?

A. Members of a household in which there is a person who is HIV-positive
B. Receptionists at a hospital
C. Factory workers whose coworkers are HIV-positive
D. Foreign service employees who are hospitalized in Zaire for bleeding ulcers (Correct Answer)

Explanation: **Explanation:** The transmission of HIV occurs primarily through blood-to-blood contact, sexual intercourse, and vertical transmission (mother-to-child). **Why Option D is Correct:** The correct answer relies on understanding the risk of **iatrogenic transmission** in regions with high HIV prevalence and limited medical resources. In the 1980s and 90s (the context of this classic epidemiological question), Zaire (now the Democratic Republic of the Congo) had high rates of HIV. A patient hospitalized for **bleeding ulcers** would likely require blood transfusions or invasive procedures. In such settings, the risk of infection is significantly elevated due to potentially unscreened blood products or the reuse of non-sterile medical equipment (needles/syringes). **Why Other Options are Incorrect:** * **Options A, B, and C:** These represent **casual, non-sexual, and non-parenteral contact**. HIV is not transmitted through respiratory droplets, sweat, saliva, or fomites. Living in the same household, working in the same factory, or interacting as a receptionist involves no exchange of infected body fluids. Extensive studies have confirmed that household members (who are not sexual partners) of HIV-positive individuals do not contract the virus through shared living spaces, utensils, or bathrooms. **High-Yield Clinical Pearls for NEET-PG:** * **Risk of Transmission:** The risk of HIV transmission via a single transfusion of screened blood is <1 in 1.5 million, but the risk from a single unit of **infected** blood is approximately **90-95%**. * **Needlestick Injury:** The average risk of HIV transmission after a percutaneous exposure to HIV-infected blood is **0.3%** (compared to 3% for HCV and 30% for HBV in non-immune individuals). * **Post-Exposure Prophylaxis (PEP):** Must be started within **72 hours** (ideally within 2 hours) and continued for 28 days. The current preferred regimen is TLD (Tenofovir + Lamivudine + Dolutegravir).

Practice by Chapter

Virus Structure and Classification

Practice Questions

Viral Replication

Practice Questions

Pathogenesis of Viral Infections

Practice Questions

DNA Viruses: Herpesviruses

Practice Questions

DNA Viruses: Poxviruses and Adenoviruses

Practice Questions

Hepatitis Viruses

Practice Questions

RNA Viruses: Orthomyxoviruses

Practice Questions

RNA Viruses: Paramyxoviruses

Practice Questions

Enteroviruses and Rhinoviruses

Practice Questions

Arboviruses

Practice Questions

HIV and Retroviruses

Practice Questions

Oncogenic Viruses

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free

Virology — MCQs

Virology — MCQs

On this page

Practice by Chapter

Want unlimited practice?