Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 391: Which of the following viruses does not produce viral esophagitis?

A. Herpes simplex
B. Adenovirus (Correct Answer)
C. Varicella
D. Cytomegalovirus

Explanation: **Explanation:** Viral esophagitis is a common opportunistic infection, primarily occurring in immunocompromised individuals (e.g., HIV/AIDS, transplant recipients, or those on chemotherapy). **Why Adenovirus is the correct answer:** While **Adenovirus** is a common cause of respiratory infections, conjunctivitis (pink eye), and hemorrhagic cystitis, it is **not** a recognized cause of viral esophagitis. It typically affects the respiratory and gastrointestinal tracts (causing diarrhea), but esophageal involvement is clinically negligible or non-existent. **Analysis of incorrect options:** * **Herpes Simplex Virus (HSV):** HSV-1 is the most common cause of viral esophagitis. It typically presents with "punched-out" ulcers and characteristic **Cowdry Type A** intranuclear inclusion bodies. * **Cytomegalovirus (CMV):** CMV is the second most common cause. Unlike HSV, it produces large, shallow, linear ulcerations. Histology shows "Owl’s eye" inclusion bodies (both intranuclear and intracytoplasmic). * **Varicella-Zoster Virus (VZV):** Though rarer than HSV or CMV, VZV can cause esophagitis, usually in children with chickenpox or immunocompromised adults with disseminated shingles. It presents with vesicular lesions similar to its cutaneous manifestation. **NEET-PG High-Yield Pearls:** 1. **HSV Esophagitis:** Multiple, small, deep ulcers. Biopsy shows multinucleated giant cells with Tzanck smear positivity. 2. **CMV Esophagitis:** Large, solitary, shallow/linear ulcers. It is a common AIDS-defining illness (CD4 < 50 cells/mm³). 3. **Treatment:** Acyclovir is the drug of choice for HSV/VZV; Ganciclovir is used for CMV. 4. **Candida albicans:** The most common overall cause of infectious esophagitis (presents with white plaques/pseudomembranes).

Question 392: Viruses can be cultured in all of the following except:

A. Chick embryo
B. Blood agar (Correct Answer)
C. Guinea pigs
D. Cell culture

Explanation: **Explanation:** The fundamental principle of virology is that **viruses are obligate intracellular parasites**. Unlike bacteria, they lack the metabolic machinery to replicate independently and require living host cells to synthesize their proteins and nucleic acids. **Why Blood Agar is the Correct Answer:** Blood agar is an **artificial (non-living) culture medium** used primarily for the growth of bacteria and fungi. Since it contains no living cells, it cannot support viral replication. Viruses will never grow on standard laboratory media like Nutrient agar, MacConkey agar, or Blood agar. **Analysis of Other Options:** * **Chick Embryo (Option A):** One of the oldest methods for viral cultivation. Different viruses are inoculated into specific sites such as the chorioallantoic membrane (e.g., Poxvirus), amniotic cavity (e.g., Influenza), or allantoic cavity. * **Guinea Pigs (Option B):** Animal inoculation (including mice, rabbits, and guinea pigs) provides a living system for viruses that do not grow well in vitro. It is also used to study pathogenesis and immune responses. * **Cell Culture (Option D):** The most common modern method. It involves growing mammalian cells in vitro (e.g., HeLa, Vero, or WI-38 lines) to provide the living substrate necessary for viral growth. **NEET-PG High-Yield Pearls:** * **Detection of Growth:** Viral growth in cell cultures is identified by the **Cytopathic Effect (CPE)**, such as cell rounding, lysis, or syncytia formation. * **Pock Formation:** On the chorioallantoic membrane (CAM) of a chick embryo, viruses like Variola and Vaccinia produce visible lesions called "pocks." * **Gold Standard:** While molecular methods (PCR) are faster, **Cell Culture** remains the "gold standard" for definitive viral identification.

Question 393: Which marker is positive in a patient who is a supercarrier of Hepatitis B?

A. HBeAg (Correct Answer)
B. HBsAg
C. Anti-HBc IgG
D. All of the above

Explanation: In Hepatitis B serology, the term **"Supercarrier"** refers to an individual who is not only chronically infected but also highly infectious to others. ### 1. Why HBeAg is the Correct Answer **HBeAg (Hepatitis B e-Antigen)** is the hallmark of **active viral replication**. When HBeAg is present in the blood, it indicates a high viral load and high infectivity. A "supercarrier" is defined by the presence of HBeAg, as these patients have a significantly higher risk of transmitting the virus via needle-stick injuries or vertical transmission (mother-to-child) compared to HBeAg-negative carriers. ### 2. Analysis of Incorrect Options * **HBsAg (Hepatitis B Surface Antigen):** While HBsAg is the first marker to appear and its persistence for >6 months defines a **chronic carrier**, it does not distinguish between low and high infectivity. All supercarriers are HBsAg positive, but not all HBsAg positive patients are supercarriers. * **Anti-HBc IgG:** This antibody indicates a past or chronic infection. It persists for life after exposure but does not correlate with the level of viral replication or infectivity. * **All of the above:** While a supercarrier will technically be positive for HBsAg and Anti-HBc IgG, **HBeAg** is the specific diagnostic marker that defines the "supercarrier" status (high infectivity state). ### 3. High-Yield Clinical Pearls for NEET-PG * **Best indicator of infectivity:** HBeAg (or HBV-DNA levels). * **First marker to appear:** HBsAg. * **Marker of "Window Period":** Anti-HBc IgM (HBsAg and Anti-HBs are both negative). * **Marker of Immunity:** Anti-HBs (indicates recovery or vaccination). * **Vertical Transmission:** If a mother is HBeAg positive, the risk of transmitting HBV to the newborn is ~90%.

Question 394: Maternal mortality is more in which type of Hepatitis virus infection?

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

Explanation: **Explanation:** **Hepatitis E Virus (HEV)** is the correct answer because it is uniquely associated with high maternal mortality, particularly during the **third trimester** of pregnancy. While HEV generally causes a self-limiting illness in the general population, pregnant women are at a significantly higher risk (up to **20-25% mortality rate**) of developing **Fulminant Hepatic Failure (FHF)**. The underlying pathophysiology is attributed to a combination of altered immune responses (Th2 shift), high viral loads, and hormonal changes (estrogen/progesterone) that exacerbate liver injury. **Analysis of Incorrect Options:** * **Hepatitis A (HAV):** Transmitted via the feco-oral route, it typically causes acute, self-limiting hepatitis and does not show increased severity or mortality specifically in pregnancy. * **Hepatitis B (HBV):** While it is a major cause of chronic liver disease and can be transmitted vertically (HBeAg positive mothers), it does not typically cause an acute increase in maternal mortality compared to non-pregnant individuals. * **Hepatitis C (HCV):** Primarily leads to chronic infection. While there is a risk of vertical transmission, it is not associated with acute fulminant hepatic failure or high mortality during pregnancy. **High-Yield Clinical Pearls for NEET-PG:** * **Virus Family:** HEV belongs to the *Hepeviridae* family (ssRNA, non-enveloped). * **Transmission:** Feco-oral route; most common cause of epidemic/water-borne hepatitis in India. * **Genotypes:** Genotypes 1 and 2 are associated with human epidemics and high maternal mortality. * **Complications:** Apart from FHF, HEV in pregnancy is linked to premature delivery and high fetal mortality. * **Diagnosis:** IgM anti-HEV is the gold standard for acute infection.

Question 395: Negri bodies are characteristic inclusions found in neurons infected with the rabies virus. In which part of the central nervous system are they most commonly found?

A. Brain stem
B. Cerebral cortex neurons
C. Hippocampus (Correct Answer)
D. Spinal cord

Explanation: **Explanation:** **Negri bodies** are pathognomonic intracytoplasmic, eosinophilic inclusion bodies found in neurons infected by the **Rabies virus** (a Lyssavirus of the Rhabdoviridae family). These bodies represent sites of viral replication and consist of viral nucleocapsid proteins. 1. **Why Hippocampus is correct:** While the rabies virus spreads throughout the entire central nervous system (CNS), Negri bodies have a predilection for specific areas. They are most consistently and abundantly found in the **Pyramidal cells of the Hippocampus (Ammon’s horn)** and the **Purkinje cells of the Cerebellum**. Identification of these inclusions in these specific sites remains the gold standard for post-mortem histological diagnosis. 2. **Analysis of Incorrect Options:** * **Brain stem & Spinal cord:** Although the virus travels through the spinal cord and involves the brain stem (leading to cranial nerve dysfunction), Negri bodies are less frequently visualized here compared to the hippocampus. * **Cerebral cortex:** While cortical neurons can contain inclusions, they are not the "most common" or characteristic site used for diagnostic identification. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Negri bodies are sharply outlined, round or oval, and typically measure 1–7 µm. They are **intracytoplasmic** (unlike Herpes, which is intranuclear). * **Staining:** Best visualized using **Sellers’ stain** (basic fuchsin and methylene blue). * **Diagnosis:** The most sensitive and preferred diagnostic test for rabies in animals/humans is the **Direct Fluorescent Antibody (DFA)** test on brain tissue or skin biopsy (from the nape of the neck). * **Clinical Course:** Rabies is characterized by a long incubation period (1–3 months) because of slow retrograde axonal transport (8–20 mm/day) to the CNS.

Question 396: An immunocompromised person with a history of seizures had an MRI that revealed a temporal lobe lesion. Brain biopsy results showed multinucleated giant cells with intranuclear inclusions. What is the most probable cause of the lesion?

A. Toxoplasmosis
B. Cytomegalovirus infection (Correct Answer)
C. Herpes simplex encephalitis
D. Progressive multifocal leukoencephalopathy

Explanation: **Explanation:** The correct answer is **Cytomegalovirus (CMV) infection**. In immunocompromised patients (such as those with HIV/AIDS), CMV can cause encephalitis characterized by subacute dementia or focal neurological deficits. The histopathological hallmark of CMV is the presence of **multinucleated giant cells** and large, eosinophilic **intranuclear inclusions** (classically described as "Owl’s eye" appearance). While CMV typically causes periventricular calcifications in neonates, in adults, it can present with focal lesions in various brain regions, including the temporal lobe. **Why other options are incorrect:** * **Toxoplasmosis:** While common in immunocompromised patients, it typically presents as multiple ring-enhancing lesions on MRI. Histology shows tachyzoites and bradyzoites, not intranuclear inclusions. * **Herpes Simplex Encephalitis (HSE):** HSE is the most common cause of sporadic fatal encephalitis and classically involves the temporal lobe. However, it typically affects immunocompetent individuals and is characterized by Cowdry Type A inclusions. The presence of multinucleated giant cells in an immunocompromised setting more strongly points toward CMV or HIV-related pathology. * **Progressive Multifocal Leukoencephalopathy (PML):** Caused by the JC virus, it affects the white matter (demyelination). Histology shows enlarged oligodendrocytes with "ground-glass" nuclei, but not multinucleated giant cells. **NEET-PG High-Yield Pearls:** * **CMV:** "Owl’s eye" inclusions (Intranuclear + Intracytoplasmic). * **HSV:** Cowdry Type A inclusions (Intranuclear only). * **Rabies:** Negri bodies (Intracytoplasmic only). * **PML:** JC Virus; affects subcortical white matter; non-enhancing lesions. * **Temporal Lobe Involvement:** Always consider HSV-1 first in immunocompetent patients, but look for specific histopathological clues for CMV in the immunocompromised.

Question 397: The common cold is caused primarily by:

A. Viruses (Correct Answer)
B. Bacteria
C. Fungi
D. Allergy

Explanation: **Explanation:** The common cold, or acute viral rhinosinusitis, is a self-limiting upper respiratory tract infection (URTI). **1. Why Viruses are Correct:** The vast majority (over 95%) of common colds are caused by viruses. The **Rhinovirus** (a Picornavirus) is the most frequent causative agent, accounting for 30–50% of cases. Other significant viral causes include Coronaviruses, Adenoviruses, Respiratory Syncytial Virus (RSV), and Parainfluenza viruses. These viruses infect the nasal epithelium, leading to inflammation, mucus hypersecretion, and the classic symptoms of rhinorrhea, sneezing, and sore throat. **2. Why Other Options are Incorrect:** * **Bacteria:** While bacteria like *Streptococcus pneumoniae* or *Haemophilus influenzae* can cause secondary infections (e.g., sinusitis or otitis media), they are not the primary cause of the common cold. Antibiotics are therefore ineffective for initial treatment. * **Fungi:** Fungal infections of the respiratory tract (like Aspergillosis or Mucormycosis) are rare and typically occur in immunocompromised individuals; they do not present as a standard "common cold." * **Allergy:** Allergic rhinitis can mimic cold symptoms (sneezing, watery eyes), but it is an IgE-mediated hypersensitivity reaction to environmental triggers (pollen, dust) rather than an infectious process. **NEET-PG High-Yield Pearls:** * **Most common cause:** Rhinovirus (binds to **ICAM-1** receptors). * **Seasonality:** Rhinoviruses peak in autumn/spring; Coronaviruses peak in winter. * **Adenovirus:** Often associated with "Pharyngoconjunctival fever" (sore throat + conjunctivitis). * **Treatment:** Purely symptomatic (decongestants, NSAIDs). Zinc gluconate may reduce duration if started within 24 hours.

Question 398: All are true about H1N1 influenza except?

A. Zanamivir is commonly given through the IV route. (Correct Answer)
B. Fatality is more common in some high-risk groups.
C. PCR is used for investigation.
D. The WHO latest trivalent influenza vaccine contains two influenza A subtypes (H3N2 and H1N1) and one influenza B component.

Explanation: ### Explanation **1. Why Option A is the correct answer (The Exception):** Zanamivir is a neuraminidase inhibitor primarily administered via **oral inhalation** (using a Diskhaler device). It is not commonly given through the IV route. While an IV formulation exists for emergency use in hospitalized patients with severe resistance, it is not the standard or "common" route. In contrast, Oseltamivir is given orally, and Peramivir is the neuraminidase inhibitor typically administered intravenously. **2. Analysis of Incorrect Options:** * **Option B:** Fatality in H1N1 is significantly higher in **high-risk groups**, including pregnant women (especially in the 2nd and 3rd trimesters), children under 5 years, the elderly, and individuals with comorbidities like chronic obstructive pulmonary disease (COPD), diabetes, or obesity. * **Option C:** **Real-time Reverse Transcriptase PCR (rRT-PCR)** is the gold standard and the most sensitive/specific investigation for diagnosing H1N1. It identifies the specific viral RNA from nasopharyngeal or throat swabs. * **Option D:** The standard **Trivalent Influenza Vaccine** recommended by the WHO traditionally includes two Influenza A strains (**H1N1 and H3N2**) and one Influenza B strain (from either the Victoria or Yamagata lineage). *Note: Quadrivalent vaccines, which include two B strains, are now becoming the preferred standard.* ### High-Yield Clinical Pearls for NEET-PG: * **Drug of Choice:** Oral **Oseltamivir** (75 mg BD for 5 days) is the treatment of choice for H1N1. * **Category Classification:** * **Category A:** Mild fever/cough; no Oseltamivir needed. * **Category B:** High fever or high-risk groups; Oseltamivir indicated. * **Category C:** Breathlessness, chest pain, cyanosis; requires hospitalization and Oseltamivir. * **Antigenic Shift vs. Drift:** H1N1 (2009 pandemic) was a result of **Antigenic Shift** (reassortment of human, avian, and swine genes).

Question 399: Serological tests for HIV typically become positive within how many weeks after infection?

A. 4 weeks
B. 8 weeks (Correct Answer)
C. 12 weeks
D. 36 weeks

Explanation: **Explanation:** The correct answer is **8 weeks**. This question refers to the **"Window Period"** in HIV infection—the interval between the initial infection and the point when antibodies become detectable by standard serological tests (seroconversion). 1. **Why 8 weeks is correct:** While modern 4th-generation assays (which detect both p24 antigen and antibodies) can detect infection earlier, the classic teaching for NEET-PG regarding standard antibody-based serological tests (like ELISA) is that most individuals develop a detectable antibody response within **6 to 8 weeks**. By 8 weeks, the majority of patients will have undergone seroconversion, making it the most reliable timeframe among the options provided for a positive serology. 2. **Why other options are incorrect:** * **4 weeks:** This is often too early for a definitive antibody response (ELISA). While the p24 antigen may be present, antibodies are usually still below the detection threshold. * **12 weeks:** Although 95-99% of people seroconvert by 12 weeks, the process typically begins and is detectable earlier (by 8 weeks). 12 weeks is generally considered the "cutoff" to rule out infection definitively. * **36 weeks:** This is far beyond the standard window period. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time when a person is infected and highly infectious, but the ELISA test is negative. * **First Marker to appear:** HIV-RNA (detected by PCR) followed by **p24 antigen**. * **Screening Test:** ELISA (High sensitivity). * **Confirmatory Test:** Western Blot (High specificity) — *Note: Current CDC guidelines favor the HIV-1/2 differentiation assay.* * **Best indicator of prognosis:** CD4+ T-cell count. * **Best indicator of treatment efficacy:** Viral load (HIV-RNA).

Question 400: Australia antigen is a marker for Hepatitis B infection. Which component of the Hepatitis B virus (HBV) does the Australia antigen represent?

A. Surface antigen (HBsAg) (Correct Answer)
B. E antigen (HBeAg)
C. Core antigen (HBcAg)
D. DNA polymerase

Explanation: **Explanation:** The **Australia antigen** is the historical name for the **Hepatitis B surface antigen (HBsAg)**. It was discovered in 1965 by Baruch Blumberg in the serum of an Australian Aboriginal person while studying protein polymorphisms. This discovery was pivotal as it led to the identification of the Hepatitis B virus (HBV). **Why Option A is correct:** HBsAg is the envelope protein of HBV. It is the first serological marker to appear in the blood after infection (usually 2–6 weeks before symptoms) and its persistence beyond 6 months indicates chronic infection. Because it was first identified in an Australian native, it was named the Australia antigen. **Why the other options are incorrect:** * **B. E antigen (HBeAg):** This is a soluble protein representing active viral replication and high infectivity. It is not the Australia antigen. * **C. Core antigen (HBcAg):** This is the nucleocapsid protein. Unlike HBsAg, it is not secreted into the blood and can only be demonstrated in hepatocytes via biopsy. * **D. DNA polymerase:** This is the enzyme responsible for viral replication (reverse transcriptase activity) located within the core, not the surface marker. **High-Yield Clinical Pearls for NEET-PG:** * **Screening Marker:** HBsAg is the primary marker used for screening blood donors and diagnosing acute/chronic HBV. * **Vaccine Component:** Recombinant HBsAg is the component used in the Hepatitis B vaccine. * **Window Period:** The time interval when HBsAg disappears but Anti-HBs has not yet appeared. During this phase, **Anti-HBc IgM** is the only diagnostic marker. * **Dane Particle:** The complete infectious virion (42 nm) consists of the HBsAg envelope surrounding the inner core.

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Virology — MCQs

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