Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 421: A patient presents with genital discharge resembling "flow of seed" three days after sexual intercourse with a commercial sex worker. What culture medium should be used for the discharge material?

A. Thayer Martin medium (Correct Answer)
B. Mannitol salt agar
C. TCBS
D. Potassium tellurite agar

Explanation: ### Explanation **Clinical Correlation:** The patient presents with a classic case of **Gonorrhea**, caused by *Neisseria gonorrhoeae*. The term "flow of seed" (Greek: *gonos* = seed, *rhoia* = flow) refers to the thick, purulent urethral discharge characteristic of the infection. The short incubation period (2–5 days) and history of high-risk sexual exposure further support this diagnosis. **Why Thayer-Martin Medium is Correct:** *Neisseria gonorrhoeae* is a fastidious organism that requires enriched media for growth. **Thayer-Martin (TM) medium** is a selective medium based on Chocolate Agar. It contains specific antibiotics to inhibit commensal flora: * **Vancomycin:** Inhibits Gram-positive bacteria. * **Colistin:** Inhibits Gram-negative bacteria (except *Neisseria*). * **Nystatin:** Inhibits fungi. * **Trimethoprim:** Inhibits swarming of *Proteus*. **Analysis of Incorrect Options:** * **Mannitol Salt Agar (B):** A selective and differential medium used for *Staphylococcus aureus*. * **TCBS (Thiosulfate-Citrate-Bile Salts-Sucrose) (C):** The gold standard selective medium for *Vibrio cholerae*. * **Potassium Tellurite Agar (D):** Used for the isolation of *Corynebacterium diphtheriae* (produces black colonies). **High-Yield Clinical Pearls for NEET-PG:** * **Gram Stain:** Shows Gram-negative kidney-shaped diplococci within polymorphonuclear leukocytes (Intracellular). * **Biochemical Test:** *N. gonorrhoeae* is **Oxidase positive** and ferments only **Glucose** (not Maltose, unlike *N. meningitidis*). * **Transport Media:** If immediate culture is not possible, use **Stuart’s** or **Amies** medium. * **Gold Standard Diagnosis:** Nucleic Acid Amplification Test (NAAT).

Question 422: Herpes zoster multiplies in which of the following locations?

A. Peripheral nerve
B. Epithelium of skin
C. Dorsal root ganglion (Correct Answer)
D. Pharyngeal epithelial cells

Explanation: **Explanation:** The correct answer is **C. Dorsal root ganglion.** **Pathophysiology and Multiplication:** Herpes Zoster is caused by the reactivation of the **Varicella-Zoster Virus (VZV)**. During the primary infection (Chickenpox), the virus spreads from skin lesions via retrograde axonal transport to the sensory ganglia. Here, it remains in a state of **latency** within the neurons of the **Dorsal Root Ganglia** (or cranial nerve ganglia like the Trigeminal ganglion). Upon reactivation—often due to waning cell-mediated immunity—the virus begins active **multiplication** within these ganglionic neurons before traveling down the sensory nerve to the skin. **Analysis of Incorrect Options:** * **A. Peripheral nerve:** The peripheral nerve serves as the "conduit" or pathway for the virus to travel between the skin and the ganglion. While the virus is present here during transit, it does not primarily multiply within the nerve sheath or axons. * **B. Epithelium of skin:** While the virus causes characteristic vesicular rashes in the skin (dermatomal distribution), this is the site of the *end-organ manifestation* rather than the primary site of reactivation and multiplication in Zoster. * **D. Pharyngeal epithelial cells:** This is a common site for the initial entry and replication of many respiratory viruses (and primary Varicella), but it is not the site of latency or reactivation for Herpes Zoster. **NEET-PG High-Yield Pearls:** * **Latency Site:** VZV remains latent in the **Dorsal Root Ganglion**, whereas HSV-1 typically stays in the **Trigeminal Ganglion**. * **Clinical Presentation:** Characterized by a **unilateral, painful vesicular rash** that strictly follows a **dermatomal** distribution. * **Complication:** The most common complication is **Post-Herpetic Neuralgia (PHN)**. * **Diagnosis:** Tzanck smear showing **Multinucleated Giant Cells** (with Cowdry Type A inclusion bodies) is a classic exam finding.

Question 423: Which of the following is the characteristic site for the detection of Varicella-zoster virus (VZV) in active infection?

A. Cervical tissue
B. Synovial fluid
C. Blood
D. Skin (Correct Answer)

Explanation: Explanation: **Varicella-zoster virus (VZV)**, a member of the *Alphaherpesvirinae* subfamily, is the causative agent of chickenpox (primary infection) and herpes zoster (reactivation) [1], [3]. The virus is highly **epitheliotropic**, meaning it has a specific predilection for infecting and replicating within skin cells [1]. 1. **Why Skin is Correct:** During active infection, VZV travels from the dorsal root ganglia to the skin via sensory nerves. It replicates in the epidermis, leading to the characteristic "dewdrop on a rose petal" vesicular rash [1], [4]. The fluid within these vesicles contains a high viral load, making the **skin (vesicle fluid or scrapings)** the primary and most reliable site for detection via PCR, Tzanck smear, or viral culture [2]. 2. **Why Other Options are Incorrect:** * **Cervical tissue:** This is the characteristic site for Human Papillomavirus (HPV) or Herpes Simplex Virus-2 (HSV-2), not VZV. * **Synovial fluid:** While some viruses like Parvovirus B19 or Rubella can cause arthritis, VZV is rarely isolated from joint fluid. * **Blood:** Although a transient viremia occurs during the incubation period, the viral titer in the blood is low and fleeting compared to the high concentration found in skin lesions [1]. **NEET-PG High-Yield Pearls:** * **Tzanck Smear:** A classic bedside test showing **multinucleated giant cells** with **Cowdry Type A** intranuclear inclusion bodies (seen in VZV, HSV-1, and HSV-2) [2]. * **Latency:** VZV remains latent in the **dorsal root ganglia** or cranial nerve ganglia [1]. * **Dermatomal Distribution:** Reactivation (Shingles) typically follows a single unilateral dermatome [4]. * **Gold Standard:** While Tzanck is fast, **PCR** of skin lesion swabs is now the gold standard for definitive diagnosis [2].

Question 424: Which virus, besides Hepatitis B virus (HBV), is implicated in hepatocellular carcinoma?

A. Hepatitis C virus (HCV) (Correct Answer)
B. Herpes simplex virus
C. Hepatitis A virus (HAV)
D. Hepatitis E virus (HEV)

Explanation: **Explanation:** Hepatocellular Carcinoma (HCC) is strongly associated with chronic viral hepatitis that leads to cirrhosis. **Hepatitis C Virus (HCV)** is the correct answer because it is a major risk factor for HCC globally. Unlike HBV, which is a DNA virus that can integrate into the host genome (direct oncogenesis), HCV is an **RNA virus** that does not integrate into host DNA. Instead, HCV promotes carcinogenesis indirectly through **chronic inflammation, oxidative stress, and repeated cycles of hepatocyte necrosis and regeneration**, eventually leading to cirrhosis, which is the precursor to most HCV-related HCC cases. **Analysis of Incorrect Options:** * **Hepatitis A (HAV) and Hepatitis E (HEV):** These are transmitted via the fecal-oral route and cause **acute hepatitis** only. They do not cause chronic infection or cirrhosis, and therefore, they are not associated with HCC. (Note: HEV can be chronic in immunocompromised patients, but it is not a classic cause of HCC). * **Herpes Simplex Virus (HSV):** While HSV can cause fulminant hepatitis in rare cases (especially in pregnancy or immunocompromised states), it does not lead to chronic liver disease or malignancy. **NEET-PG High-Yield Pearls:** * **HBV vs. HCV:** HBV can cause HCC **without** cirrhosis (due to the X-protein and DNA integration). HCV almost always causes HCC **secondary** to cirrhosis. * **Most common cause:** Globally, HBV is the most common cause of HCC; however, in many Western nations, HCV is the leading cause. * **Tumor Marker:** Alpha-fetoprotein (AFP) is the classic screening marker for HCC. * **Aflatoxin B1:** A potent co-carcinogen for HCC, produced by *Aspergillus flavus*, which causes a specific mutation in the **p53 gene** (codon 249).

Question 425: Coxsackie B virus causes all except?

A. Aseptic meningitis
B. Herpangina (Correct Answer)
C. Myocarditis
D. Bornholm disease

Explanation: **Explanation:** The correct answer is **Herpangina** because it is primarily caused by **Coxsackie A virus**, not Coxsackie B. **1. Why Herpangina is the correct answer:** Herpangina is a febrile illness characterized by vesicular and ulcerative lesions on the posterior pharynx (soft palate, tonsils, and uvula). It is classically associated with **Coxsackie A viruses** (specifically types 1–10, 16, and 22). While both Group A and B are Enteroviruses, Group A typically targets the skin and mucous membranes, whereas Group B tends to target internal organs like the heart, pleura, and pancreas. **2. Analysis of Incorrect Options:** * **Aseptic Meningitis:** Both Coxsackie A and B are leading causes of viral (aseptic) meningitis. It is a common manifestation of Group B infections. * **Myocarditis:** Coxsackie B is the **most common viral cause** of acute myocarditis and pericarditis. It can lead to dilated cardiomyopathy. * **Bornholm Disease:** Also known as "Epidemic Pleurodynia" or the "Devil’s Grip," this condition is characterized by sudden, lancinating chest and abdominal pain due to inflammation of the intercostal muscles. It is almost exclusively caused by **Coxsackie B**. **High-Yield Clinical Pearls for NEET-PG:** * **Coxsackie A:** Think "Sores" (Herpangina, Hand-Foot-Mouth Disease). * **Coxsackie B:** Think "Body" (Myocarditis, Bornholm disease/Pleurodynia, Hepatitis, and even Type 1 Diabetes linkage via pancreatic damage). * **Hand-Foot-Mouth Disease (HFMD):** Most commonly caused by Coxsackie **A16** and Enterovirus 71. * **Rule of Thumb:** If the disease involves the heart or pleura, the answer is almost always Coxsackie B.

Question 426: The Paul Bunnell test is characteristic of which condition?

A. Infectious mononucleosis (Correct Answer)
B. Syphilis
C. Typhoid fever
D. Rheumatoid arthritis

Explanation: The **Paul-Bunnell test** is a classic diagnostic tool for **Infectious Mononucleosis (IM)**, caused by the **Epstein-Barr Virus (EBV)**. ### 1. Why Infectious Mononucleosis is Correct The underlying medical concept is the production of **Heterophile antibodies**. During an EBV infection, there is a polyclonal B-cell activation that leads to the production of IgM antibodies. These antibodies are not specific to EBV but have the unique property of agglutinating red blood cells (RBCs) from other species (sheep, horse, or ox). The Paul-Bunnell test specifically detects these antibodies by demonstrating the **agglutination of sheep RBCs**. ### 2. Why Other Options are Incorrect * **Syphilis:** Diagnosed via Treponemal (TPHA, FTA-ABS) and Non-treponemal tests (**VDRL, RPR**). VDRL uses cardiolipin antigen, not heterophile agglutination. * **Typhoid Fever:** Diagnosed via the **Widal test**, which detects antibodies against *Salmonella typhi* O and H antigens using bacterial agglutination. * **Rheumatoid Arthritis:** Diagnosed using the **Rheumatoid Factor (RF)** test (an IgM against the Fc portion of IgG) or the more specific Anti-CCP antibody test. ### 3. High-Yield Clinical Pearls for NEET-PG * **Monospot Test:** A modern, rapid latex agglutination version of the Paul-Bunnell test (uses horse RBCs). * **Differential Diagnosis:** If a patient has IM-like symptoms (fever, sore throat, lymphadenopathy) but the Paul-Bunnell test is **negative**, consider **Cytomegalovirus (CMV)**, which is the most common cause of heterophile-negative mononucleosis. * **Blood Film:** Look for **Downey cells** (atypical T-lymphocytes) which are characteristic of EBV infection. * **Specific EBV Serology:** Anti-VCA (Viral Capsid Antigen) IgM is the best marker for acute infection.

Question 427: Which type of poliovirus is responsible for most epidemics of poliomyelitis?

A. Type I virus (Correct Answer)
B. Type II virus
C. Type III virus
D. Combination of Type II and Type III viruses

Explanation: **Explanation:** Poliovirus is a member of the *Picornaviridae* family (genus *Enterovirus*) and exists in three distinct serotypes: Type 1 (Brunhilde), Type 2 (Lansing), and Type 3 (Leon). **Why Type I is Correct:** **Type I virus** is the most common cause of paralytic poliomyelitis and is responsible for the vast majority of epidemics. It is the most virulent and stable of the three types. Historically, Type I has been the hardest to eradicate from endemic regions due to its high transmissibility and propensity to cause large-scale outbreaks. **Analysis of Incorrect Options:** * **Type II virus:** This was the first serotype to be officially declared eradicated globally (in 2015). While it was highly immunogenic, it was less frequently associated with major epidemics compared to Type I. Most current Type 2 cases are "vaccine-derived" (cVDPV2) rather than wild-type. * **Type III virus:** This type is the least common cause of epidemics. It is, however, the most common cause of **Vaccine-Associated Paralytic Poliomyelitis (VAPP)** in some regions. Wild Poliovirus Type 3 was declared eradicated in 2019. * **Combination of Type II and III:** Epidemics are typically driven by a single dominant strain (historically Type I). A combination of II and III does not reflect the epidemiological reality of wild poliovirus transmission. **High-Yield NEET-PG Pearls:** * **Most common serotype in epidemics:** Type I. * **Most common cause of VAPP:** Type III (followed by Type II). * **Eradication Status:** Wild Poliovirus (WPV) Type 2 and Type 3 are eradicated; only WPV Type 1 remains endemic (primarily in Afghanistan and Pakistan). * **Specimen of choice:** Stool (highest viral shed). * **Culture:** Primary monkey kidney cell lines (shows characteristic "crenation" or rounding of cells).

Question 428: A patient with HIV has a viral load of 750,000 copies of HIV RNA/ml and a total CD4 count of 50 cells/mm³. This patient is at an increased risk for several infectious diseases. For which of the following diseases is the patient at no more added risk than an immunocompetent host?

A. Pneumocystis pneumonia
B. Mycobacterial disease
C. Kaposi's sarcoma
D. Pneumococcal pneumonia (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Pneumococcal pneumonia.** **1. Why Pneumococcal Pneumonia is the Correct Answer:** While HIV-infected patients have a higher *incidence* of invasive pneumococcal disease compared to the general population, the **pathogenesis** of *Streptococcus pneumoniae* infection is primarily dependent on humoral immunity (B-cells and opsonizing antibodies) rather than cell-mediated immunity (T-cells). Unlike the other options, the risk of developing pneumococcal pneumonia does not significantly correlate with a declining CD4 count. An immunocompetent host is just as susceptible to the primary infection if they lack specific antibodies, making it a "non-opportunistic" infection in the context of profound immunosuppression. **2. Analysis of Incorrect Options:** * **A. Pneumocystis pneumonia (PCP):** This is a classic opportunistic infection caused by *P. jirovecii*. The risk increases exponentially when the CD4 count falls below **200 cells/mm³**. * **B. Mycobacterial disease:** Both *M. tuberculosis* and *M. avium complex* (MAC) are highly dependent on T-cell-mediated macrophage activation. MAC, specifically, is a major risk when CD4 counts drop below **50 cells/mm³**. * **C. Kaposi's sarcoma:** Caused by HHV-8, this is an AIDS-defining illness. Its clinical progression and severity are directly linked to the degree of immunosuppression and high viral loads. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of community-acquired pneumonia (CAP) in HIV patients:** *Streptococcus pneumoniae*. * **Most common opportunistic infection in AIDS:** *Pneumocystis jirovecii*. * **CD4 < 200:** Prophylaxis for PCP (TMP-SMX). * **CD4 < 50:** High risk for MAC and CMV retinitis. * **Key Concept:** HIV patients are at risk for "normal" pathogens (like *S. pneumoniae*) early on, but "opportunistic" pathogens only emerge as the CD4 count declines.

Question 429: Which of the following is a primary cell culture?

A. Chick fibroblast (Correct Answer)
B. Hela
C. HEP-2
D. HL-8

Explanation: **Explanation:** Cell cultures are classified into three types based on their origin, chromosomal characteristics, and the number of times they can be subcultured. **1. Why Chick Fibroblast is Correct:** **Chick embryo fibroblast** is a **Primary Cell Culture**. These are derived directly from normal animal or human tissues (e.g., rhesus monkey kidney, human amnion, or chick embryo) by mechanical or enzymatic dissociation. * **Key Feature:** They consist of normal cells with a diploid number of chromosomes. * **Limitation:** They can be subcultured only once or twice before they die out. They are highly useful for the primary isolation of viruses and vaccine production. **2. Analysis of Incorrect Options:** * **B (HeLa) & C (HEp-2):** These are **Continuous Cell Lines** (also known as Immortal Cell Lines). They are derived from cancerous tissues and can be subcultured indefinitely. * **HeLa** is derived from a human cervical carcinoma. * **HEp-2** is derived from a human epithelioma of the larynx. * **D (HL-8):** This is a distractor; however, similar designations like **HL-60** refer to continuous leukemia cell lines. Continuous lines are heteroploid (abnormal chromosome number). **3. Clinical Pearls for NEET-PG:** * **Diplod Cell Strains:** (e.g., **WI-38, MRC-5**) are derived from human fetal lung tissues. They maintain a diploid karyotype and can be subcultured about 50 times. They are the preferred substrate for producing human viral vaccines (e.g., Rubella, Rabies). * **Vero cells:** Derived from African green monkey kidney; these are a common continuous cell line used in microbiology. * **Cytopathic Effect (CPE):** The structural changes in host cells caused by viral invasion, used to identify viruses in these cultures.

Question 430: What is the reason why most patients suffering from recurrent herpes labialis rarely give a history of having the acute form of herpetic gingivostomatitis?

A. Etiological agents differ
B. The acute form occurs only in severely immunocompromised individuals
C. The primary infection was subclinical (Correct Answer)
D. The patient has received antibodies during intrauterine life and the antibodies have persisted

Explanation: **Explanation:** The correct answer is **(C) The primary infection was subclinical.** **Concept:** Herpes Simplex Virus Type 1 (HSV-1) typically follows a pattern of primary infection, latency, and reactivation. While **Acute Herpetic Gingivostomatitis** is the classic clinical presentation of a primary HSV-1 infection (usually in children), it occurs in only about **10-15% of cases**. In the vast majority (85-90%), the primary infection is **subclinical or asymptomatic**. Despite the lack of symptoms, the virus still travels via retrograde axonal transport to settle in the **Trigeminal ganglion**, where it remains latent. Later in life, triggers like stress, fever, or UV light cause reactivation, leading to **Recurrent Herpes Labialis** (cold sores). Therefore, most patients do not recall an acute primary episode because they never clinically manifested one. **Analysis of Incorrect Options:** * **A. Etiological agents differ:** Incorrect. Both primary gingivostomatitis and recurrent herpes labialis are caused by the same agent, HSV-1. * **B. Occurs only in immunocompromised:** Incorrect. Primary gingivostomatitis occurs frequently in immunocompetent children; however, it is more severe or disseminated in the immunocompromised. * **C. Persistence of intrauterine antibodies:** Incorrect. Maternal IgG antibodies provide protection only for the first 6 months of life. They do not persist into the age when most primary infections occur, nor do they prevent the establishment of latency. **NEET-PG High-Yield Pearls:** * **Site of Latency:** HSV-1 resides in the **Trigeminal ganglion**; HSV-2 resides in the **Sacral ganglia**. * **Diagnosis:** The **Tzanck Smear** (showing multinucleated giant cells with Cowdry Type A inclusion bodies) is a classic bedside test, though PCR is now the gold standard. * **Recurrence:** Recurrent infections are generally less severe and more localized than primary infections due to existing partial immunity.

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Virology — MCQs

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