Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 891: Which congenital infection has minimal teratogenic risk to the fetus?

A. HIV (Correct Answer)
B. Rubella
C. Varicella
D. CMV

Explanation: **Explanation:** The core concept in this question is the distinction between **teratogenicity** (structural malformations) and **vertical transmission** (infection of the fetus). **Correct Option: A. HIV** While HIV has a high rate of vertical transmission (if untreated), it is **not considered a teratogen**. HIV does not interfere with organogenesis; therefore, it does not cause structural birth defects or a specific "congenital syndrome." The primary risk to the infant is the development of pediatric AIDS later in life, rather than physical malformations at birth. **Incorrect Options:** * **B. Rubella:** A classic teratogen. Infection during the first trimester leads to **Congenital Rubella Syndrome (CRS)**, characterized by the triad of cataracts, sensorineural deafness, and cardiac defects (PDA). * **C. Varicella:** Maternal infection (especially between 8–20 weeks) can cause **Congenital Varicella Syndrome**, resulting in limb hypoplasia, cicatricial skin scarring, and microcephaly. * **D. CMV:** The most common intrauterine infection. It is a potent teratogen causing periventricular calcifications, microcephaly, and sensorineural hearing loss. **NEET-PG High-Yield Pearls:** * **Most common congenital infection:** CMV. * **Highest teratogenic risk period:** First trimester (organogenesis). * **HIV Management:** To minimize vertical transmission, HAART is given to the mother, and elective C-section is preferred if the viral load is >1000 copies/mL. Zidovudine is typically given to the neonate. * **Parvovirus B19:** Not typically structural but causes **Hydrops Fetalis** due to severe fetal anemia.

Question 892: Which of the following is true about Rabies virus?

A. Rabies is diagnosed by immunofluorescence. (Correct Answer)
B. Rabies causes lifelong immunity.
C. Rabies has various strains of viruses.
D. Rabies vaccine is always live attenuated.

Explanation: **Explanation:** **Correct Option (A):** Direct Fluorescent Antibody (DFA) test is the **gold standard** for diagnosing rabies. It involves detecting rabies virus antigens in brain tissue (post-mortem) or skin biopsies from the nape of the neck (ante-mortem). Immunofluorescence is highly sensitive and specific because it utilizes fluorescently labeled antibodies that bind specifically to the rabies nucleoprotein. **Incorrect Options:** * **B:** Rabies does not cause lifelong immunity because the disease is **100% fatal** once clinical symptoms appear. There are no "survivors" to develop natural immunity. * **C:** While there are different lineages, the Rabies virus (Lyssavirus genus) is **serologically monotypic**. This means there is only one major serotype, which is why a single vaccine provides protection against all strains globally. * **D:** Modern rabies vaccines (like PCEV or HDCV) are **inactivated (killed)** vaccines. Live attenuated vaccines are used for wildlife (oral baits) but are never used in humans due to safety concerns. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusions found in the hippocampus (Ammon’s horn) and cerebellum (Purkinje cells). * **Incubation Period:** Typically 1–3 months; it is shorter if the bite is closer to the CNS (e.g., face). * **Post-Exposure Prophylaxis (PEP):** Includes wound washing, Rabies Vaccine (Days 0, 3, 7, 14, 28), and Rabies Immunoglobulin (RIG) for Category III bites. * **Street Virus vs. Fixed Virus:** "Street virus" is the wild-type; "Fixed virus" is the laboratory strain used for vaccine production.

Question 893: Anti-HBc antibody indicates?

A. Resistance to Hepatitis B (Correct Answer)
B. Acute infection
C. Good prognosis
D. Hepatocellular Carcinoma

Explanation: **Explanation:** The presence of **Anti-HBc (Antibody to Hepatitis B core antigen)** is a critical marker in the serological diagnosis of Hepatitis B. 1. **Why Option A is Correct:** Anti-HBc indicates that an individual has been **infected** with the Hepatitis B virus (HBV) at some point in their life. Unlike Anti-HBs (which can result from vaccination), Anti-HBc only develops following a natural infection. Once a person recovers from a natural infection, they develop lifelong immunity (resistance) mediated by both Anti-HBc and Anti-HBs. In the context of this question, it serves as a marker of past exposure leading to immunity. 2. **Why Other Options are Incorrect:** * **B. Acute infection:** While IgM Anti-HBc is the first antibody to appear during acute infection, "Anti-HBc" (Total) persists for life. Therefore, it is not specific to the acute phase alone. * **C. Good prognosis:** Anti-HBc is a marker of exposure, not a prognostic indicator. Markers like the disappearance of HBeAg and the appearance of Anti-HBe are better indicators of a favorable prognosis (seroconversion). * **D. Hepatocellular Carcinoma (HCC):** HCC is associated with chronic HBV infection (persistent HBsAg), but Anti-HBc itself is not a diagnostic marker for malignancy. **High-Yield Clinical Pearls for NEET-PG:** * **The Window Period:** During the "serologic window" (when HBsAg has disappeared but Anti-HBs hasn't appeared yet), **IgM Anti-HBc** is the **only** detectable marker of acute infection. * **Vaccination vs. Natural Infection:** * Post-Vaccination: Only **Anti-HBs** positive. * Post-Natural Infection: Both **Anti-HBs** and **Anti-HBc** positive. * **IgM vs. IgG:** IgM Anti-HBc indicates acute/recent infection; IgG Anti-HBc indicates chronic or past infection.

Question 894: The Nef gene in HIV is primarily responsible for:

A. Enhancing the expression of viral genes
B. Enhancing viral replication
C. Decreasing viral replication (Correct Answer)
D. Viral maturation

Explanation: **Explanation:** The **Nef (Negative Factor)** gene is one of the regulatory/accessory genes of HIV. While its name suggests a purely inhibitory role, its function is complex and multifaceted. **Why the correct answer is C:** In the context of the NEET-PG curriculum and standard microbiological classification, **Nef** is traditionally described as a factor that **decreases viral replication** or acts as a "negative regulator." It achieves this by downregulating the expression of **CD4 receptors** and **MHC Class I molecules** on the surface of the host cell. By removing CD4 from the surface, it prevents superinfection and allows for the efficient release of new virions. By downregulating MHC-I, it helps the virus evade detection by Cytotoxic T-Lymphocytes (CTLs). Although it is essential for high viral loads *in vivo*, its classical designation in exams remains a negative regulator of replication. **Analysis of Incorrect Options:** * **A & B (Enhancing expression/replication):** These are primarily the functions of the **Tat** (Transactivator of transcription) and **Rev** (Regulator of expression of virion proteins) genes. Tat increases the transcription of viral genes, while Rev facilitates the export of unspliced viral RNA from the nucleus. * **D (Viral maturation):** This is the function of the **Pol** gene, specifically the **Protease** enzyme, which cleaves precursor polypeptides into functional proteins during or after budding. **High-Yield Clinical Pearls for NEET-PG:** * **Tat:** Potent transactivator; essential for viral "burst." * **Rev:** "Shuttle" protein; moves RNA from nucleus to cytoplasm. * **Vpu:** Specifically downregulates CD4 and enhances virion release (unique to HIV-1). * **Vif:** Overcomes the host cell's antiviral defense (APOBEC3G). * **Nef:** Essential for progression to AIDS; "Elite controllers" often have Nef-deficient strains.

Question 895: Which of the following bacteria grows better in alkaline pH?

A. Vibrio cholerae (Correct Answer)
B. Pseudomonas
C. Shigella
D. Salmonella

Explanation: **Explanation:** **Vibrio cholerae** is the correct answer because it is a classic example of an **alkaliphilic** bacterium. It thrives in environments with a high pH, typically ranging from **8.5 to 9.5**. This physiological characteristic is exploited in clinical microbiology to create selective culture media, such as **TCBS (Thiosulfate Citrate Bile salts Sucrose) agar** and enrichment broths like **Alkaline Peptone Water (APW)**, which inhibit the growth of most other intestinal commensals while allowing *Vibrio* to flourish. **Analysis of Incorrect Options:** * **Pseudomonas:** While *Pseudomonas aeruginosa* is highly adaptable and can tolerate a wide range of conditions, it is an obligate aerobe that prefers a neutral pH (around 7.0) for optimal growth. * **Shigella and Salmonella:** These are members of the *Enterobacteriaceae* family. They are generally **acid-tolerant** (especially *Shigella*, which has a very low infectious dose because it survives gastric acidity) and prefer a neutral to slightly acidic pH. They do not grow well in highly alkaline conditions. **High-Yield Clinical Pearls for NEET-PG:** * **Enrichment Media for V. cholerae:** Alkaline Peptone Water (pH 8.6) and Monsur’s Taurocholate Tellurite Peptone Water (pH 9.2). * **Selective Media:** TCBS agar is the gold standard; *V. cholerae* produces yellow colonies due to sucrose fermentation. * **Acid Sensitivity:** While *Vibrio* loves alkali, it is highly sensitive to stomach acid. Conditions that neutralize gastric acid (like achlorhydria or use of antacids) significantly reduce the infectious dose required for cholera. * **Halophilic Nature:** Most *Vibrio* species (except *V. cholerae* and *V. mimicus*) are halophilic (require NaCl for growth).

Question 896: Which hepatitis viruses are known to cause chronic hepatitis?

A. Hepatitis A
B. Hepatitis B
C. Hepatitis C (Correct Answer)
D. Hepatitis G

Explanation: **Explanation:** Chronic hepatitis is defined as inflammation of the liver lasting for more than six months. Among the options provided, **Hepatitis C Virus (HCV)** is the most notorious for its high rate of chronicity. Approximately 75–85% of individuals infected with HCV develop chronic infection, which can lead to cirrhosis and hepatocellular carcinoma (HCC). **Analysis of Options:** * **Hepatitis C (Correct):** It is the leading cause of chronic liver disease worldwide. Its high mutation rate (due to lack of proofreading in RNA polymerase) allows it to evade the immune system, leading to persistence. * **Hepatitis A:** This is an enterically transmitted virus (fecal-oral route) that causes only acute hepatitis. It **never** causes chronic infection or a carrier state. * **Hepatitis B:** While HBV *can* cause chronic hepatitis, the question asks which is "known" to do so in the context of the provided options. In adults, only about 5–10% of HBV cases become chronic (though this is much higher in neonates). However, in standard MCQ patterns, if both B and C are present, C is often the preferred answer for "highest risk of chronicity." * **Hepatitis G:** Now known as GB virus C, it is often a co-infection with HIV or HCV. While it can persist in the blood for years, it is generally considered non-pathogenic and does not cause significant chronic hepatitis. **High-Yield NEET-PG Pearls:** * **Vowels (A & E)** are transmitted by the fecal-oral route and **never** go chronic. * **Consonants (B, C, D)** are parenteral and **can** go chronic. * **Highest risk of chronicity:** HCV (80%) > HBV (5-10% in adults). * **Hepatitis E:** Usually acute, but can cause chronic hepatitis specifically in **immunocompromised/transplant patients**.

Question 897: Which of the following viruses is oncogenic?

A. Arenavirus
B. Retrovirus (Correct Answer)
C. Reovirus
D. Coronavirus

Explanation: **Explanation:** **Correct Answer: B. Retrovirus** Retroviruses are classic examples of oncogenic viruses. They induce malignancy through two primary mechanisms: 1. **Transducing Retroviruses:** These carry viral oncogenes (v-onc) directly into the host cell (e.g., Rous Sarcoma Virus). 2. **Cis-activating Retroviruses:** These integrate their genome near a host proto-oncogene, where the viral **Long Terminal Repeats (LTRs)** act as powerful promoters, leading to overexpression of host genes (Insertional Mutagenesis). *Clinical Example:* **HTLV-1** (Human T-cell Lymphotropic Virus) is the only retrovirus directly linked to human malignancy (Adult T-cell Leukemia/Lymphoma). **Why other options are incorrect:** * **A. Arenavirus:** These are typically zoonotic viruses (e.g., Lassa fever, LCMV) characterized by a "sandy" appearance on EM. They cause hemorrhagic fevers or meningitis, not cancer. * **C. Reovirus:** These are double-stranded RNA viruses (e.g., Rotavirus). Interestingly, some Reoviruses are being studied as *oncolytic* agents (killing cancer cells) rather than oncogenic ones. * **D. Coronavirus:** These cause respiratory and gastrointestinal infections (e.g., SARS-CoV-2, MERS). They do not integrate into the host genome and have no known oncogenic potential. **High-Yield Clinical Pearls for NEET-PG:** * **DNA Oncogenic Viruses:** HPV (16, 18), EBV, HHV-8 (Kaposi Sarcoma), and Hepatitis B (HBV). * **RNA Oncogenic Viruses:** HTLV-1 and Hepatitis C (HCV). Note that HCV is an RNA virus but does *not* integrate into the DNA; it causes cancer via chronic inflammation and hepatocyte regeneration. * **v-onc vs. c-onc:** Viral oncogenes lack introns, whereas cellular proto-oncogenes contain them.

Question 898: Prions are killed by:

A. Autoclave
B. Ethylene dioxide
C. Gamma radiation
D. Autoclave and NaOH (Correct Answer)

Explanation: **Explanation:** **Prions** are unique infectious agents composed entirely of protein (PrPSc), lacking any nucleic acids. Due to their highly stable, misfolded beta-sheet structure, they are notoriously resistant to standard sterilization methods that typically kill bacteria, viruses, and spores. **Why Option D is Correct:** Standard sterilization is insufficient for prions. The recommended protocol for complete inactivation involves a combination of **chemical and physical methods**. The most effective method is immersion in **1N Sodium Hydroxide (NaOH)** followed by gravity displacement **autoclaving at 121°C for 30–60 minutes**. The NaOH acts by denaturing the protein structure, making it more susceptible to heat-induced coagulation in the autoclave. **Why Other Options are Incorrect:** * **A. Autoclave:** Standard autoclaving (121°C for 15 mins) only reduces the titer of prions but does not ensure complete destruction. Prions can survive even higher temperatures if not combined with chemical treatment. * **B. Ethylene dioxide:** This is a gas used for heat-sensitive equipment. Prions are highly resistant to alkylating agents like ethylene dioxide and formaldehyde. * **C. Gamma radiation:** Prions are resistant to ionizing radiation because they lack a nucleic acid genome, which is the primary target of radiation. **High-Yield Clinical Pearls for NEET-PG:** * **Diseases:** Prions cause Transmissible Spongiform Encephalopathies (TSEs) like **Creutzfeldt-Jakob Disease (CJD)** in humans and Bovine Spongiform Encephalopathy (Mad Cow Disease). * **Disinfectants:** Prions are resistant to alcohol, formalin, and radiation. They are sensitive to **Sodium Hypochlorite (5%)** and **1N NaOH**. * **Diagnosis:** Characterized by "spongiform" changes in the brain (vacuolation) and the absence of an inflammatory response. * **Gold Standard Sterilization:** 134°C for 18 minutes in a pre-vacuum sterilizer is another accepted high-yield protocol.

Question 899: All of the following statements about the Ebola virus are true EXCEPT?

A. It is a member of the Filoviridae family.
B. The incubation period is 2 to 12 weeks. (Correct Answer)
C. It is transmitted by direct contact.
D. In severe cases, it can lead to renal and liver impairment.

Explanation: **Explanation:** The correct answer is **B** because the statement regarding the incubation period is incorrect. The incubation period for Ebola Virus Disease (EVD) is typically **2 to 21 days** (average 8–10 days), not 2 to 12 weeks. Patients are not infectious until they develop symptoms. **Analysis of Options:** * **Option A:** Ebola virus, along with Marburg virus, belongs to the **Filoviridae** family. These are enveloped, non-segmented, negative-sense RNA viruses characterized by their unique filamentous or "thread-like" appearance under electron microscopy. * **Option C:** Transmission occurs via **direct contact** with infected blood, secretions, organs, or other bodily fluids of infected people, or with surfaces contaminated with these fluids. It is not an airborne infection. * **Option D:** EVD is a systemic illness. In severe cases, multi-organ failure occurs, most notably **renal and liver impairment**, often accompanied by internal and external bleeding (hemorrhagic manifestations). **High-Yield Clinical Pearls for NEET-PG:** * **Natural Reservoir:** Fruit bats of the *Pteropodidae* family are considered the natural hosts. * **Diagnosis:** Real-time PCR (RT-PCR) is the preferred diagnostic test during the acute phase. * **Pathogenesis:** The virus targets endothelial cells, mononuclear phagocytes, and hepatocytes. * **Key Feature:** It causes a "cytokine storm," leading to increased vascular permeability and shock. * **Vaccine:** The **rVSV-ZEBOV** vaccine (Ervebo) is a live-attenuated recombinant vaccine used for prevention.

Question 900: Which of the following is true of Rotavirus?

A. Easily grown in cell culture
B. Double-stranded DNA virus
C. Most common cause of diarrheal disease in infants (Correct Answer)
D. Adults and old people account for 60% of infections

Explanation: **Explanation:** **Rotavirus** is a member of the *Reoviridae* family and is the leading cause of severe, dehydrating diarrhea in infants and young children (typically 6 months to 2 years of age) worldwide. 1. **Why Option C is Correct:** Rotavirus is the **most common cause of infantile gastroenteritis**. It infects the mature enterocytes of the small intestine, leading to malabsorption and osmotic diarrhea. The presence of the viral protein **NSP4**, which acts as an enterotoxin, further induces secretory diarrhea by increasing intracellular calcium. 2. **Why Other Options are Incorrect:** * **Option A:** Rotaviruses are notoriously **difficult to grow** in standard cell cultures. They require the addition of proteolytic enzymes like trypsin to the medium for successful replication. * **Option B:** Rotavirus is a **double-stranded RNA (dsRNA)** virus, not DNA. It is characterized by a unique **segmented genome (11 segments)** and a wheel-like appearance under electron microscopy (hence the name "Rota"). * **Option D:** Infections are most severe in children. Adults are rarely affected or have mild symptoms due to pre-existing immunity. The peak age of infection is **6–24 months**. **High-Yield NEET-PG Pearls:** * **Morphology:** Non-enveloped, icosahedral, triple-layered protein capsid (Wheel-like/Cartwheel appearance). * **Transmission:** Fecal-oral route. * **Diagnosis:** Antigen detection in stool via **ELISA** or Latex Agglutination is the gold standard. * **Vaccines:** Live attenuated oral vaccines are available (e.g., **Rotarix** - monovalent; **RotaTeq** - pentavalent; **Rotavac** - indigenous Indian vaccine). * **Seasonality:** More common in winter months ("Winter Diarrhea").

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Virology — MCQs

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