Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1021: Which of the following diseases is prevented by a live vaccine?

A. Measles (Correct Answer)
B. Cholera
C. Smallpox
D. Oral Polio

Explanation: **Explanation:** The correct answer is **Measles**. This question tests your knowledge of vaccine types, specifically distinguishing between live-attenuated and killed/inactivated vaccines. **1. Why Measles is Correct:** The Measles vaccine is a **live-attenuated viral vaccine**. It uses a weakened form of the virus (Edmonston-Zagreb strain is commonly used in India) to stimulate a robust immune response involving both humoral (B-cell) and cell-mediated (T-cell) immunity, mimicking a natural infection without causing the disease. **2. Analysis of Other Options:** * **Cholera:** The modern vaccines (e.g., Shanchol, Dukoral) are **killed/inactivated** whole-cell vaccines. While older parenteral vaccines existed, they are no longer recommended due to low efficacy. * **Smallpox:** While the Smallpox vaccine (Vaccinia virus) is a live vaccine, Smallpox has been **eradicated** globally (declared in 1980). In the context of current immunization schedules and standard medical exams, Measles is the primary answer for a disease currently "prevented" by routine live vaccination. * **Oral Polio (OPV):** OPV (Sabin) is indeed a live-attenuated vaccine. However, in many competitive exams, if multiple options are live vaccines, the question may be evaluating the most stable or primary component of the Universal Immunization Programme (UIP). *Note: If this were a "Multiple Correct" format, both A and D would be right; however, in single-best-answer formats, Measles is often the preferred classic example.* **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Live Vaccines:** "**BOY** **R**omes **O**n **M**y **C**hicken **I**tchy **T**yphoid" (**B**CG, **O**PV, **Y**ellow Fever, **R**otavirus, **M**easles/MMR, **C**hickenpox, **I**ntranasal Influenza, **T**yphoid oral). * **Contraindications:** Live vaccines are generally contraindicated in **pregnancy** and **immunocompromised** states (except HIV patients with CD4 >200 for certain vaccines). * **Measles Timing:** Administered at 9 completed months (with Vitamin A) and a second dose at 16–24 months.

Question 1022: Cell fusion of HIV with target cell is mediated by which component?

A. gp 120
B. gp41 (Correct Answer)
C. p24
D. p 18

Explanation: The entry of HIV into a host cell is a two-step process involving the envelope glycoprotein complex (**gp160**), which is cleaved into two subunits: **gp120** and **gp41**. ### **Why gp41 is the Correct Answer** **gp41** is the transmembrane subunit of the HIV envelope. Once gp120 binds to the CD4 receptor and a co-receptor (CCR5 or CXCR4), a conformational change occurs that exposes gp41. gp41 then acts as a "fusion peptide," inserting itself into the host cell membrane and pulling the viral and cellular membranes together. This **cell-to-cell fusion** allows the viral capsid to enter the cytoplasm. ### **Analysis of Incorrect Options** * **gp120 (Option A):** This is the surface subunit responsible for **attachment/docking**. It binds to the CD4 receptor. While essential for the process, it does not mediate the actual fusion of membranes. * **p24 (Option B):** This is the **capsid protein**. It forms the inner conical core of the virus. It is a major diagnostic marker (p24 antigenemia) but is not involved in membrane fusion. * **p18 (Option D):** This is the **matrix protein** (also known as p17) that lies just beneath the viral envelope, providing structural integrity. ### **High-Yield Clinical Pearls for NEET-PG** * **Enfuvirtide:** A fusion inhibitor drug that works by binding to gp41, preventing the conformational change required for viral entry. * **Maraviroc:** A drug that binds to the **CCR5 co-receptor** on the host cell, preventing gp120 binding. * **Mnemonic:** gp**120** is for **Attachment** (120 is "outside"), gp**41** is for **Fusion** (41 "penetrates" the membrane). * **Screening vs. Confirmatory:** p24 is the earliest marker detected in blood (Screening/Early diagnosis); Western Blot (detecting gp120, gp41, p24) was traditionally the confirmatory test.

Question 1023: Which of the following is NOT a characteristic feature of viruses?

A. They are filterable agents.
B. They are obligate intracellular parasites.
C. They contain either DNA or RNA, but never both.
D. They multiply by binary fission. (Correct Answer)

Explanation: ### Explanation **Why Option D is the correct answer:** Viruses do not multiply by **binary fission**, which is a characteristic method of asexual reproduction in bacteria. Instead, viruses replicate through a complex process of **disassembly and assembly**. Once inside a host cell, the viral genome directs the host’s metabolic machinery to synthesize individual viral components (nucleic acids and proteins), which are then assembled into new virions. This process includes a "latent period" where no infectious virus is detectable within the cell. **Why the other options are incorrect:** * **Option A (Filterable agents):** This is a classic characteristic. Viruses are significantly smaller than bacteria (ranging from 20–300 nm) and can pass through filters (like Chamberland filters) that retain bacteria. * **Option B (Obligate intracellular parasites):** Viruses lack their own metabolic machinery (ribosomes, ATP-generating systems). They are completely dependent on a living host cell for replication; they are inert outside the host. * **Option C (Either DNA or RNA):** A fundamental rule of virology is that a mature virus particle (virion) contains only one type of nucleic acid as its genetic material. While some large viruses (like Mimivirus) or certain stages of replication might show traces of both, for NEET-PG purposes, the "either/or" rule remains a defining feature. **High-Yield Clinical Pearls for NEET-PG:** * **Smallest Virus:** Parvovirus (DNA); Poliovirus/Picornavirus (RNA). * **Largest Virus:** Poxvirus (resembles a brick under electron microscopy). * **Exceptions to Symmetry:** Most viruses are either icosahedral or helical, but **Poxvirus** has a complex symmetry. * **DNA Viruses:** All are double-stranded except **Parvovirus** (single-stranded). * **RNA Viruses:** All are single-stranded except **Reovirus/Rotavirus** (double-stranded).

Question 1024: Which of the following is not typically associated with diarrhea?

A. Rotavirus
B. Calicivirus
C. Enterovirus
D. Rhabdovirus (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Rhabdovirus**. **1. Why Rhabdovirus is the correct answer:** Rhabdoviruses, most notably the **Rabies virus**, are neurotropic viruses. They do not infect the gastrointestinal tract; instead, they replicate in muscle tissue before migrating via retrograde axonal transport to the Central Nervous System (CNS). The clinical presentation involves encephalitis, hydrophobia, and autonomic dysfunction, but **not diarrhea**. **2. Why the other options are incorrect:** * **Rotavirus (Option A):** This is the **most common cause of severe diarrhea in infants and young children** worldwide. It belongs to the Reoviridae family and causes malabsorptive diarrhea by damaging enterocytes and producing the NSP4 enterotoxin. * **Calicivirus (Option B):** This family includes **Norovirus** (the leading cause of epidemic non-bacterial gastroenteritis in all ages) and Sapovirus. They are classic causes of "stomach flu" characterized by vomiting and watery diarrhea. * **Enterovirus (Option C):** While members of the Picornaviridae family (like Poliovirus, Coxsackievirus, and Echovirus) primarily replicate in the Peyer’s patches of the intestine, they are often asymptomatic in the gut or cause mild gastrointestinal upset/diarrhea before spreading systemically. **3. NEET-PG High-Yield Pearls:** * **Rotavirus:** Characterized by "Wheel-like" appearance on EM. The **NSP4 protein** acts as a viral enterotoxin. * **Norovirus:** Associated with outbreaks in closed settings like cruise ships, schools, and nursing homes. * **Adenovirus (Serotypes 40/41):** These are the "Enteric Adenoviruses," the second most common cause of viral diarrhea in children. * **Astrovirus:** Identified by a "Star-shaped" morphology; causes mild diarrhea.

Question 1025: Human papillomatosis is caused by?

A. Herpes Simplex Virus (HSV)
B. Human Papillomavirus (HPV) (Correct Answer)
C. Human Immunodeficiency Virus (HIV)
D. Hepatitis B Virus (HBV)

Explanation: ### Explanation **Correct Answer: B. Human Papillomavirus (HPV)** **Medical Concept:** Human papillomatosis (the formation of papillomas or warts) is caused by the **Human Papillomavirus (HPV)**, a small, non-enveloped, double-stranded DNA virus belonging to the *Papillomaviridae* family. HPV infects the basal keratinocytes of the epithelium. It induces cellular proliferation, leading to benign growths like common warts (*verruca vulgaris*), plantar warts, and genital warts (*condyloma acuminatum*). High-risk strains (HPV 16 and 18) are strongly associated with cervical and oropharyngeal malignancies due to the action of oncoproteins **E6** (inhibits p53) and **E7** (inhibits pRb). **Why Incorrect Options are Wrong:** * **A. Herpes Simplex Virus (HSV):** Causes vesicular and ulcerative lesions (e.g., cold sores or genital herpes), not papillomatous growths. It is characterized by latency in sensory ganglia. * **C. Human Immunodeficiency Virus (HIV):** A retrovirus that targets CD4+ T-cells, leading to immunosuppression. While HIV patients are at higher risk for HPV-related lesions, HIV itself does not cause papillomatosis. * **D. Hepatitis B Virus (HBV):** A hepadnavirus that primarily targets hepatocytes, leading to hepatitis, cirrhosis, and hepatocellular carcinoma. **High-Yield Clinical Pearls for NEET-PG:** * **Low-risk types:** HPV 6 and 11 (cause 90% of genital warts and Recurrent Respiratory Papillomatosis). * **High-risk types:** HPV 16 and 18 (most common causes of cervical cancer). * **Histopathology:** Look for **Koilocytes** (squamous epithelial cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Vaccination:** Gardasil-9 is a recombinant vaccine covering types 6, 11, 16, 18, 31, 33, 45, 52, and 58.

Question 1026: Which virus has more than one serotype?

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

Explanation: **Explanation:** The correct answer is **Influenza**. This is due to the unique genetic structure and high mutation rate of the Influenza virus, which belongs to the *Orthomyxoviridae* family. **Why Influenza is Correct:** Influenza viruses (Types A, B, and C) exhibit significant antigenic variation. **Influenza A**, in particular, has multiple serotypes based on two surface glycoproteins: **Hemagglutinin (H1–H18)** and **Neuraminidase (N1–N11)**. This diversity is driven by two mechanisms: 1. **Antigenic Drift:** Point mutations causing minor changes (responsible for seasonal epidemics). 2. **Antigenic Shift:** Genetic reassortment of segmented RNA leading to major changes and new serotypes (responsible for pandemics). **Why Other Options are Incorrect:** * **Measles (Rubeola):** Despite being highly infectious, the Measles virus is **antigenically stable**. There is only **one serotype**, which is why the live-attenuated vaccine (MMR) provides lifelong immunity. * **Mumps:** This virus also exists as a **single serotype**. Infection or vaccination confers long-lasting protection. * **Rubella (German Measles):** Similar to the above, Rubella has only **one serotype**. It is a Togavirus that does not undergo significant antigenic variation. **High-Yield NEET-PG Pearls:** * **Segmented Genomes:** Remember the mnemonic **"BOAR"** (Bunyavirus, Orthomyxovirus, Arenavirus, Reovirus). These viruses can undergo reassortment. * **Vaccine Strategy:** Because Measles, Mumps, and Rubella have single serotypes, the **MMR vaccine** is highly effective. In contrast, the Influenza vaccine must be reformulated annually to match circulating serotypes. * **Poliovirus:** Often compared in this context, Polio has **three serotypes** (1, 2, and 3).

Question 1027: Coxsackie A virus causes which of the following conditions?

A. Aseptic meningitis
B. Herpangina
C. Foot and mouth disease
D. Bornholm disease (Correct Answer)

Explanation: **Explanation:** **Coxsackie A and B** are subgroups of Enteroviruses within the Picornaviridae family. While there is clinical overlap, they characteristically involve different organ systems. **Why Option D is Correct:** **Bornholm disease** (also known as epidemic pleurodynia or "Devil’s Grip") is classically caused by **Coxsackie B virus**. It is characterized by the sudden onset of severe, paroxysmal chest and upper abdominal pain due to inflammation of the intercostal muscles (myositis). *Note: There appears to be a discrepancy in the provided key. In standard medical microbiology (e.g., Jawetz, Ananthanarayan), Bornholm disease and Myocarditis are the hallmark associations of **Coxsackie B**, while Herpangina and Hand-Foot-and-Mouth Disease are associated with **Coxsackie A**.* **Analysis of Other Options:** * **A. Aseptic meningitis:** Can be caused by both Coxsackie A and B (and Polioviruses), making it a less specific association for Coxsackie A alone. * **B. Herpangina:** This is the classic clinical manifestation of **Coxsackie A**. It presents with fever, sore throat, and vesiculopapular lesions on the posterior pharynx (soft palate/uvula). * **C. Foot and mouth disease:** This is a zoonotic disease of cattle caused by **Aphthovirus**. It should not be confused with "Hand-Foot-and-Mouth Disease" (HFMD), which is caused by Coxsackie A16. **High-Yield Clinical Pearls for NEET-PG:** * **Coxsackie A:** Associated with "Surface" infections—**Herpangina**, **Hand-Foot-and-Mouth Disease**, and Acute Hemorrhagic Conjunctivitis (A24). * **Coxsackie B:** Associated with "Body" (internal organ) infections—**B**ornholm disease, **B**eats (Myocarditis/Pericarditis), and **B**eta cells of the pancreas (linked to Type 1 Diabetes). * **Mnemonic:** **A** for **A**ngina (Herpangina); **B** for **B**ornholm and **B**eats (Heart).

Question 1028: What is true about HIV transmission?

A. HIV is not transmitted through semen.
B. There are more chances of HIV transmission during LSCS than during normal labour.
C. HIV is more infectious than hepatitis B.
D. HIV transmission is more common from male to female than from female to male. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**. Sexual transmission of HIV is biologically more efficient from **male to female** than from female to male. This is primarily due to two factors: 1. **Surface Area:** The vaginal and cervical mucosa provide a larger surface area for viral exposure compared to the male urethra. 2. **Viral Load:** Semen typically contains a higher concentration of HIV (both free virus and infected cells) than vaginal secretions, and it remains in contact with the female genital tract for a prolonged period post-intercourse. **Analysis of Incorrect Options:** * **Option A:** Semen is one of the primary vehicles for HIV transmission. The virus is found in both seminal fluid and mononuclear cells within the semen. * **Option B:** Normal vaginal delivery carries a **higher risk** of vertical transmission than a planned Lower Segment Cesarean Section (LSCS). LSCS (especially before the rupture of membranes) reduces the infant's exposure to infected maternal blood and vaginal secretions. * **Option C:** Hepatitis B Virus (HBV) is significantly **more infectious** than HIV. The risk of transmission after a needle-stick injury from an HBV-positive source is approximately 30%, compared to only 0.3% for HIV. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission Risk:** The highest risk of HIV transmission per act is via **blood transfusion** (approx. 90%), followed by receptive anal intercourse. * **Vertical Transmission:** Without intervention, the risk is 20–45%. With ART and elective LSCS, this can be reduced to <2%. * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). **p24 antigen** is the earliest marker detectable by ELISA. * **Rule of 3s (Needle-stick risk):** HBV (30%) > HCV (3%) > HIV (0.3%).

Question 1029: Which virus is responsible for causing cataracts, cardiac defects, and deafness when the fetus is exposed in utero?

A. Cytomegalovirus
B. Rubella (Correct Answer)
C. Varicella zoster
D. Rubeola

Explanation: **Explanation:** The correct answer is **Rubella**. This classic triad of clinical findings—**Cataracts, Cardiac defects (most commonly Patent Ductus Arteriosus), and Sensorineural Deafness**—is known as **Gregg’s Triad**, the hallmark of **Congenital Rubella Syndrome (CRS)**. The virus is most teratogenic when the mother is infected during the first trimester of pregnancy. **Why the other options are incorrect:** * **Cytomegalovirus (CMV):** While it is the most common congenital infection, its classic presentation includes periventricular calcifications, microcephaly, and chorioretinitis (rather than cataracts). * **Varicella Zoster Virus (VZV):** Congenital Varicella Syndrome is characterized by cicatricial skin scarring (zigzag patterns), limb hypoplasia, and rudimentary digits. * **Rubeola (Measles):** This virus is not typically considered a major teratogen. Maternal infection is associated with spontaneous abortion or preterm labor, but not a specific constellation of congenital malformations. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac defect:** Patent Ductus Arteriosus (PDA) is the most common, followed by peripheral pulmonary artery stenosis. * **Ocular findings:** "Salt and pepper" retinopathy is another high-yield finding in CRS. * **Dermatological finding:** "Blueberry muffin" spots (extramedullary hematopoiesis) can be seen in Rubella and CMV. * **Diagnosis:** Detection of Rubella-specific IgM in the neonate or persistence of IgG beyond 6 months. * **Prevention:** The MMR vaccine is a live-attenuated vaccine and is **contraindicated** during pregnancy. Women should avoid pregnancy for 1 month after vaccination.

Question 1030: Which positive test does not necessarily indicate HIV infection in a newborn?

A. ELISA for HIV IgG antibody (Correct Answer)
B. p24 antigen
C. Virus culture
D. ELISA for HIV IgA antibody

Explanation: **Explanation:** The diagnosis of HIV in newborns requires distinguishing between maternal antibodies and actual neonatal infection. **1. Why ELISA for HIV IgG is the correct answer:** IgG is the only immunoglobulin class that can cross the placenta from the mother to the fetus. If a mother is HIV-positive, her IgG antibodies will be present in the newborn’s blood regardless of whether the baby is infected. These maternal antibodies can persist for up to **18 months**. Therefore, a positive ELISA for HIV IgG in a newborn only confirms maternal exposure, not necessarily neonatal infection. **2. Why the other options are incorrect:** * **p24 antigen:** This is a viral structural protein. Its presence indicates active viral replication within the infant’s body. * **Virus culture:** This is a definitive (though slow) method to detect the live virus in the infant's blood, confirming infection. * **ELISA for HIV IgA antibody:** Unlike IgG, **IgA and IgM antibodies do not cross the placenta**. If these are detected in the newborn, it indicates that the infant’s own immune system has produced them in response to an active infection. **Clinical Pearls for NEET-PG:** * **Gold Standard for Diagnosis (<18 months):** DNA PCR (detecting proviral DNA) is the preferred test for early diagnosis in infants. * **Timing of PCR:** Usually performed at birth (within 48 hours), at 1–2 months, and at 4–6 months. * **Diagnosis (>18 months):** After 18 months, maternal antibodies have waned, so standard ELISA/Western Blot can be used for diagnosis just like in adults. * **Prophylaxis:** Nevirapine or Zidovudine is typically administered to the newborn to prevent vertical transmission.

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