Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 851: Risk of damage to fetus by maternal rubella infection is maximum if the infection occurs during which period of pregnancy?

A. First trimester (0-12 weeks) (Correct Answer)
B. Second trimester (20-24 weeks)
C. Second trimester (24-28 weeks)
D. Third trimester (32-36 weeks)

Explanation: The risk of fetal damage following maternal rubella infection is inversely proportional to the gestational age at the time of infection. **Explanation of the Correct Answer:** The **first trimester (0–12 weeks)** is the period of organogenesis, during which the fetus is most vulnerable to the teratogenic effects of the Rubella virus. The virus crosses the placenta and causes chronic fetal infection, leading to cell death and inhibition of mitosis. If infection occurs within the first 8–12 weeks, the risk of **Congenital Rubella Syndrome (CRS)** or fetal death is as high as **80–90%**. **Explanation of Incorrect Options:** * **Options B & C (Second Trimester):** As the pregnancy progresses, the risk of major structural malformations decreases significantly. Between 13–16 weeks, the risk drops to about 15–20%, primarily manifesting as sensorineural hearing loss. After 20 weeks, the risk of defects is negligible. * **Option D (Third Trimester):** While the virus can still cross the placenta in the third trimester, it rarely causes structural defects because organogenesis is complete. The primary concern in late pregnancy is fetal growth restriction rather than the classic triad of CRS. **High-Yield Clinical Pearls for NEET-PG:** * **Gregg’s Triad (Classic CRS):** 1. Cataract (and Microphthalmia), 2. Sensorineural Deafness (most common), 3. Cardiac defects (Patent Ductus Arteriosus is most common). * **Other signs:** "Blueberry muffin" rash (extramedullary hematopoiesis) and radiolucent bone lesions ("celery stalking"). * **Diagnosis:** Detection of **Rubella-specific IgM** in cord blood or neonatal serum is diagnostic of congenital infection. * **Prevention:** Live attenuated **RA 27/3 vaccine**. It is contraindicated during pregnancy, and pregnancy should be avoided for 1 month after vaccination.

Question 852: Which of the following contains an RNA-dependent DNA polymerase as a structural component of the virion?

A. Adenoviruses
B. Orthomyxoviruses
C. Rhabdoviruses
D. RNA tumor viruses (Correct Answer)

Explanation: **Explanation:** The correct answer is **RNA tumor viruses** (Retroviruses). **1. Why RNA tumor viruses are correct:** RNA tumor viruses, such as Human T-cell Lymphotropic Virus (HTLV) and HIV, belong to the **Retroviridae** family. These viruses are unique because they possess the enzyme **Reverse Transcriptase (RNA-dependent DNA polymerase)** as an integral structural component within the viral capsid. This enzyme allows the virus to transcribe its single-stranded RNA genome into double-stranded DNA, which then integrates into the host cell's genome (provirus). This step is essential for replication and oncogenic transformation. **2. Why the other options are incorrect:** * **Adenoviruses (Option A):** These are non-enveloped **dsDNA** viruses. They use host cell DNA-dependent DNA polymerase for replication and do not require reverse transcriptase. * **Orthomyxoviruses (Option B):** (e.g., Influenza virus) These are negative-sense ssRNA viruses. They carry an **RNA-dependent RNA polymerase** (RdRp) to synthesize mRNA, but they do not produce DNA intermediates. * **Rhabdoviruses (Option C):** (e.g., Rabies virus) Like Orthomyxoviruses, these are negative-sense ssRNA viruses that carry their own **RNA-dependent RNA polymerase** (RdRp) within the virion, not a DNA polymerase. **High-Yield Clinical Pearls for NEET-PG:** * **Reverse Transcriptase** has three activities: RNA-dependent DNA polymerase, RNase H (degrades RNA from RNA-DNA hybrid), and DNA-dependent DNA polymerase. * **Hepatitis B Virus (Hepadnaviridae)** also uses reverse transcriptase during its replication cycle, but unlike Retroviruses, it is a **DNA virus** that packages the enzyme to convert an RNA intermediate back into DNA. * **RNA-dependent RNA polymerase** is a structural component of all **negative-sense RNA viruses** (e.g., Ortho-, Paramyxo-, Rhabdo-, Filo-, and Bunyaviruses).

Question 853: Which of the following is a marker of HIV infection in blood?

A. Reverse Transcriptase (Correct Answer)
B. DNA polymerase
C. RNA polymerase
D. None of the above

Explanation: ### Explanation **Correct Option: A. Reverse Transcriptase** **Why it is correct:** HIV is a retrovirus, meaning its genome consists of two identical strands of single-stranded positive-sense RNA. To replicate within a host cell, it must convert its RNA into DNA. This process is catalyzed by the enzyme **Reverse Transcriptase (RNA-dependent DNA polymerase)**, which is packaged within the viral core. The presence of this enzyme or its activity in the blood is a specific biochemical marker of HIV infection and viral replication. **Why the other options are incorrect:** * **B. DNA polymerase:** While HIV uses a form of DNA polymerase activity (inherent in the reverse transcriptase enzyme), "DNA polymerase" usually refers to host cell enzymes responsible for DNA replication. It is not a specific diagnostic marker for HIV. * **C. RNA polymerase:** This enzyme synthesizes RNA from a DNA template. In the HIV life cycle, the host cell's RNA polymerase II is hijacked to transcribe viral DNA into mRNA, but the enzyme itself is a host component and not a unique marker of the virus. **High-Yield Clinical Pearls for NEET-PG:** * **Structural Genes:** HIV has three major structural genes: *gag* (p24 antigen), *pol* (Reverse Transcriptase, Protease, Integrase), and *env* (gp120, gp41). * **Early Marker:** The **p24 antigen** is the earliest detectable protein marker in the blood (appearing before antibodies), making it crucial for diagnosing acute HIV infection (the "window period"). * **Screening vs. Confirmation:** ELISA is the standard screening test (high sensitivity), while Western Blot or Fourth-generation assays (p24 + Antibody) are used for confirmation. * **Viral Load:** RT-PCR (measuring viral RNA) is the gold standard for monitoring treatment efficacy and viral load.

Question 854: Which of the following does not indicate Hepatitis B replication?

A. HBcAg (Correct Answer)
B. HBeAg
C. HBV DNA
D. Viral copies

Explanation: **Explanation:** The correct answer is **HBcAg (Hepatitis B core Antigen)**. In clinical practice, **HBcAg is not detectable in the serum** because it is sequestered within the viral envelope (HBsAg). It remains localized within the hepatocyte nuclei. Therefore, its presence in a standard blood report cannot be used to monitor active viral replication. Instead, we measure **Anti-HBc antibodies** to determine exposure. **Why the other options are markers of replication:** * **HBeAg (Hepatitis B envelope Antigen):** This is a soluble protein secreted by the virus during active replication. Its presence in serum indicates high infectivity and active viral multiplication. * **HBV DNA:** This is the most sensitive and specific quantitative marker for viral load. It directly measures the genetic material of the virus in the blood. * **Viral copies:** This is simply the numerical quantification of HBV DNA. High copy numbers correlate directly with active replication and the risk of liver damage. **NEET-PG High-Yield Pearls:** 1. **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs. During this phase, **Anti-HBc IgM** is the only diagnostic marker present. 2. **Pre-core Mutant:** A condition where the patient is HBeAg negative but has high HBV DNA levels. This occurs due to a mutation in the pre-core region that prevents HBeAg secretion despite active replication. 3. **HBsAg:** The first marker to appear in blood after infection; its persistence beyond 6 months defines chronic hepatitis B. 4. **Anti-HBs:** Indicates immunity (either through recovery or vaccination).

Question 855: Which of the following is a Human RNA virus?

A. Poxvirus
B. Parvovirus
C. Adenovirus
D. Picornavirus (Correct Answer)

Explanation: **Explanation:** The classification of viruses into DNA or RNA types is a fundamental concept in medical microbiology and a frequent high-yield topic for NEET-PG. **Correct Answer: D. Picornavirus** Picornaviruses are a family of **single-stranded, positive-sense RNA viruses**. The name itself is a mnemonic: "Pico" (small) + "RNA." This family includes clinically significant viruses such as Poliovirus, Rhinovirus, Hepatitis A virus (HAV), and Coxsackievirus. They are non-enveloped and replicate in the cytoplasm. **Why the other options are incorrect:** * **A. Poxvirus:** These are the largest and most complex **DNA viruses**. Uniquely, unlike most DNA viruses that replicate in the nucleus, Poxviruses replicate in the cytoplasm because they carry their own DNA-dependent RNA polymerase. * **B. Parvovirus:** This is a **DNA virus**. It is particularly high-yield because it is the **only** medically important family of viruses that has a **single-stranded DNA (ssDNA)** genome (specifically B19 virus). * **C. Adenovirus:** These are non-enveloped, **double-stranded DNA (dsDNA)** viruses known for causing pharyngoconjunctival fever, hemorrhagic cystitis, and gastroenteritis. **High-Yield Clinical Pearls for NEET-PG:** * **DNA Virus Mnemonic:** "HHAPPPPy" – **H**erpes, **H**epadna, **A**deno, **P**apilloma, **P**olyoma, **P**ox, and **P**arvo. All are dsDNA except Parvo (ssDNA). * **Replication Site:** All DNA viruses replicate in the nucleus *except* Poxvirus. All RNA viruses replicate in the cytoplasm *except* Influenza (Orthomyxovirus) and Retroviruses. * **Picornavirus Members:** Remember **PERCH** – **P**olio, **E**cho, **R**hino, **C**oxsackie, and **H**epatitis A.

Question 856: When do antibodies to HSV begin to appear?

A. In a week and reach a peak in 3 weeks (Correct Answer)
B. Only after one year
C. No antibodies are present in primary HSV
D. Antibodies are present in recurrent and chronic apthous stomatitis

Explanation: ### Explanation **Correct Option: A (In a week and reach a peak in 3 weeks)** The immune response to a primary Herpes Simplex Virus (HSV) infection follows a predictable kinetic pattern. Following initial exposure and viral replication at the mucosal surface, the body initiates a humoral immune response. **IgM antibodies** typically appear within the first 7 days (one week) of infection, followed shortly by **IgG antibodies**. These antibody titers continue to rise as the B-cell response matures, reaching their maximum concentration (peak) approximately 3 to 4 weeks after the onset of the primary infection. **Analysis of Incorrect Options:** * **Option B:** Antibodies develop during the acute phase of the primary infection, not after a year. Waiting a year would imply a lack of immune recognition, which is incorrect for HSV. * **Option C:** Primary HSV infection *always* triggers an immune response. While the virus establishes latency in the sensory ganglia (evading total clearance), serum antibodies are detectable and used for seroconversion studies. * **Option D:** While antibodies are present in recurrent HSV, **Aphthous stomatitis** (canker sores) is a non-viral, inflammatory condition. It is a common distractor; unlike HSV, aphthous ulcers are not caused by a virus and do not involve HSV antibodies. **Clinical Pearls for NEET-PG:** * **Seroconversion:** A four-fold rise in IgG antibody titers between acute and convalescent sera is diagnostic of a primary infection. * **Latency:** HSV-1 and HSV-2 remain latent in the **Trigeminal** and **Sacral ganglia**, respectively. Antibodies do not prevent recurrence but may reduce the severity of subsequent outbreaks. * **Diagnosis:** While serology is useful for epidemiology, the **Tzanck Smear** (showing multinucleated giant cells with Cowdry Type A inclusions) and **PCR** (Gold Standard) are preferred for acute clinical diagnosis.

Question 857: Reactivation of Varicella-Zoster Virus (VZV) is known to occur in persons receiving immunosuppressive therapy. Which of the following is the best antiviral for treating this infection?

A. Amantadine
B. Boceprevir
C. Ribavirin
D. Valacyclovir (Correct Answer)

Explanation: **Explanation:** The question describes **Herpes Zoster (Shingles)**, which is the reactivation of the latent Varicella-Zoster Virus (VZV) within the sensory ganglia. In immunocompromised patients, prompt antiviral therapy is crucial to prevent cutaneous dissemination and visceral complications. **Why Valacyclovir is the Correct Choice:** Valacyclovir is the prodrug of Acyclovir. It is the preferred treatment for VZV reactivation because it has **superior oral bioavailability** compared to Acyclovir, leading to higher serum concentrations and less frequent dosing (TID vs. 5 times/day). It acts by inhibiting viral DNA polymerase after being phosphorylated by viral thymidine kinase. **Analysis of Incorrect Options:** * **Amantadine:** An M2 ion channel blocker formerly used for Influenza A. It has no activity against DNA viruses like VZV. * **Boceprevir:** A protease inhibitor used specifically in the treatment of Chronic Hepatitis C (HCV) genotype 1. * **Ribavirin:** A guanosine analogue used primarily for RSV (aerosolized) and Chronic Hepatitis C (in combination with interferon). It is not indicated for VZV. **High-Yield Clinical Pearls for NEET-PG:** * **Tzanck Smear:** A rapid bedside test showing **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions (seen in both HSV and VZV). * **Post-Herpetic Neuralgia (PHN):** The most common complication of Shingles; early treatment with Valacyclovir reduces its duration. * **Ramsay Hunt Syndrome:** Reactivation of VZV in the geniculate ganglion, presenting with facial palsy and vesicles in the external auditory canal. * **Drug of Choice for Disseminated VZV:** Intravenous (IV) Acyclovir is preferred over oral routes in severe or disseminated cases.

Question 858: Reverse transcriptase sequence in HIV is best described as:

A. RNA - DNA - RNA (Correct Answer)
B. DNA - RNA
C. DNA - RNA - DNA
D. RNA - DNA

Explanation: **Explanation:** The correct answer is **A. RNA - DNA - RNA**. This sequence describes the complete flow of genetic information during the HIV life cycle, from the entry of the viral genome to the production of new virions. 1. **Why Option A is Correct:** HIV is a retrovirus with a single-stranded positive-sense **RNA** genome. Upon entering the host cell, the enzyme **Reverse Transcriptase (RT)** performs two critical functions: * **RNA-dependent DNA polymerase activity:** It transcribes the viral **RNA** into a complementary **DNA** strand (forming an RNA-DNA hybrid, then double-stranded DNA). * This DNA integrates into the host genome (provirus). * The host’s cellular machinery then transcribes this integrated DNA back into messenger **RNA** and genomic RNA to assemble new viruses. Thus, the full cycle is **RNA (Genome) → DNA (Intermediate) → RNA (Progeny).** 2. **Why Other Options are Incorrect:** * **Option B & C:** These sequences start with DNA. HIV is an RNA virus; starting with DNA would describe a DNA virus (like HBV) that uses an RNA intermediate (pararetroviruses). * **Option D:** This is a common distractor. While "Reverse Transcription" specifically refers to the RNA to DNA step, the question asks for the *sequence in HIV*, implying the biological cycle. RNA to DNA alone is incomplete as it doesn't account for the production of new viral particles. **High-Yield Clinical Pearls for NEET-PG:** * **Reverse Transcriptase** has three activities: RNA-dependent DNA polymerase, RNase H (degrades the original RNA template), and DNA-dependent DNA polymerase. * **Lack of Proofreading:** RT lacks 3'–5' exonuclease activity, leading to high mutation rates and rapid development of drug resistance. * **Integration:** The enzyme **Integrase** is required to insert the viral DNA into the host chromosome. * **Drug Target:** Nucleoside Reverse Transcriptase Inhibitors (NRTIs like Zidovudine) and NNRTIs (like Efavirenz) specifically target this enzyme.

Question 859: Which of the following viral infections is transmitted by ticks?

A. Japanese encephalitis
B. Dengue fever
C. Kyasanur forest disease (KFD) (Correct Answer)
D. Yellow fever

Explanation: **Explanation:** The correct answer is **Kyasanur Forest Disease (KFD)**. This viral infection is caused by the KFD virus (Family: *Flaviviridae*) and is transmitted to humans through the bite of infected **hard ticks (*Haemaphysalis spinigera*)**. KFD is often referred to as "Monkey Fever" because it causes high mortality in monkeys (langurs and bonnet macaques), which serve as sentinels for human outbreaks. It is endemic to the Western Ghats of India (Karnataka). **Analysis of Incorrect Options:** * **Japanese Encephalitis (JE):** Transmitted by the bite of infected **_Culex_ mosquitoes** (primarily *Culex tritaeniorhynchus*). Pigs and water birds act as the natural reservoirs. * **Dengue Fever:** Transmitted by the **_Aedes aegypti_** (primary) and **_Aedes albopictus_** mosquitoes. * **Yellow Fever:** Also transmitted by **_Aedes aegypti_** (urban cycle) and *Haemagogus* mosquitoes (sylvatic cycle). **NEET-PG High-Yield Pearls:** 1. **Vector Differentiation:** Remember that most Flaviviruses (Dengue, Zika, West Nile, JE, Yellow Fever) are **Mosquito-borne**, but **KFD** and **Crimean-Congo Hemorrhagic Fever (CCHF)** are notable **Tick-borne** viral infections. 2. **KFD Diagnosis:** Diagnosed via PCR during the viremic phase or IgM ELISA later. 3. **Vaccination:** A formalin-inactivated KFD vaccine is used in endemic areas of India. 4. **CCHF Vector:** While KFD is transmitted by *Haemaphysalis*, CCHF is transmitted by **_Hyalomma_** ticks.

Question 860: Hep-2 cells are a type of:

A. Primary cell cultures
B. Diploid cell strain
C. Continuous cell lines (Correct Answer)
D. Explant culture

Explanation: **Explanation:** The correct answer is **C. Continuous cell lines.** **Understanding the Concept:** Cell cultures in virology are classified based on their origin and lifespan. **Continuous cell lines** (also known as permanent or immortalized cell lines) are derived from cancer cells or by transforming normal cells. They are capable of indefinite subculturing (infinite life span) and are haploid or aneuploid. **HEp-2 (Human Epithelioma type 2)** is a well-known continuous cell line originally derived from a human laryngeal carcinoma. **Analysis of Options:** * **A. Primary cell cultures:** These are normal cells taken directly from an animal or human organ (e.g., Monkey kidney, Human amnion). They can be subcultured only once or twice before dying. * **B. Diploid cell strain:** These are fibroblast cells that maintain a normal diploid chromosome number and can be subcultured up to 50 times before undergoing senescence (e.g., WI-38, MRC-5). * **D. Explant culture:** This involves placing small fragments of tissue directly into a growth medium, where cells migrate out from the tissue to form a monolayer. It is not a "type" of cell line like HEp-2. **High-Yield Clinical Pearls for NEET-PG:** * **HEp-2 Usage:** While originally used for virus isolation (e.g., Respiratory Syncytial Virus), its most common clinical use today is as a substrate for **Indirect Immunofluorescence (IIF)** to detect **Antinuclear Antibodies (ANA)** in systemic autoimmune rheumatic diseases. * **Other Continuous Cell Lines to Remember:** * **HeLa:** Derived from Cervical Cancer. * **Vero:** Derived from African Green Monkey Kidney. * **BHK-21:** Derived from Baby Hamster Kidney. * **Primary Cell Culture Example:** Rhesus monkey kidney cells (best for Myxoviruses).

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