Virology Practice Questions

Q: Bacteriophages are mostly used for what purpose?

Bacterial identification. **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.

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

Infectious mononucleosis.. **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**.

Q: All of the following are true about the Influenza virus EXCEPT:

The incubation period is typically 2-3 weeks.. **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).

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

Its RNA has a negative polarity.. **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).

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

IgG. **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.

Q: Painless diarrhea occurs with which of the following pathogens?

V. cholerae. **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 1

Bacteriophages are mostly used for what purpose?

Accepted Answer

Bacterial identification

Answer

Epidemiological tracing

Answer

As an antibacterial agent

Answer

Prophage conversion in bacteria

Question 2

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

Accepted Answer

Infectious mononucleosis.

Answer

Candidiasis.

Answer

Cytomegalovirus infection.

Answer

Histoplasmosis.

Question 3

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

Accepted Answer

The incubation period is typically 2-3 weeks.

Answer

Influenza A is the most common cause of outbreaks.

Answer

Type B influenza is associated with Reye's syndrome.

Answer

Influenza possesses two main glycoprotein antigens.

Question 4

Which of the following statements is true about the rabies virus?

Accepted Answer

Its RNA has a negative polarity.

Answer

It is a double-stranded RNA virus.

Answer

It contains a DNA-dependent RNA polymerase.

Answer

It affects motor neurons.

Question 5

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

Accepted Answer

IgG

Answer

IgM

Answer

IgA

Answer

IgE

Question 6

Painless diarrhea occurs with which of the following pathogens?

Accepted Answer

V. cholerae

Answer

Salmonella

Answer

Shigella

Answer

C. jejuni

Question 7

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

Accepted Answer

Both ELISA and Western Blot

Answer

ELISA

Answer

Western Blot

Answer

PCR

Question 8

Which is the most sensitive test for HW infection?

Accepted Answer

Western blot

Answer

ELISA

Answer

Agglutination test

Answer

CFT

Question 9

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

Accepted Answer

Coxsackie virus

Answer

Rubella

Answer

Mumps

Answer

AIDS

Question 10

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

Accepted Answer

Foreign service employees who are hospitalized in Zaire for bleeding ulcers

Answer

Members of a household in which there is a person who is HIV-positive

Answer

Receptionists at a hospital

Answer

Factory workers whose coworkers are HIV-positive

Virology — MCQs

Virology — MCQs

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