Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 321: Which of the following statements is true regarding chickenpox?

A. The virus is not found in the scabs. (Correct Answer)
B. The virus can be grown on chick embryo.
C. It is caused by an RNA virus.
D. It does not cross the placental barrier.

Explanation: **Explanation:** Chickenpox is caused by the **Varicella-Zoster Virus (VZV)**, a member of the *Herpesviridae* family. Understanding its transmission and virology is crucial for NEET-PG. **1. Why Option A is Correct:** The Varicella-Zoster virus is highly fragile and thermolabile. While the virus is present in high concentrations in the **vesicular fluid** and upper respiratory secretions, it is **not found in the scabs (crusts)**. The scabs consist of dried exudate and dead epithelial cells; by the time a lesion reaches the crusting stage, the virus has been inactivated. Therefore, a patient is no longer infectious once all lesions have crusted over. **2. Why the other options are Incorrect:** * **Option B:** Unlike many other viruses (like Influenza), VZV **cannot be grown on chick embryos**. It is highly host-specific and is typically cultured in human diploid cell lines (e.g., WI-38 or MRC-5). * **Option C:** VZV is a **DNA virus** (specifically, a double-stranded, enveloped DNA virus), not an RNA virus. * **Option D:** VZV **can cross the placental barrier**. Infection in the first 20 weeks of pregnancy can lead to **Congenital Varicella Syndrome** (characterized by cicatricial skin scarring, limb hypoplasia, and chorioretinitis). **Clinical Pearls for NEET-PG:** * **Secondary Attack Rate:** Very high (~90%) among susceptible household contacts. * **Incubation Period:** Usually 14–16 days (Range: 10–21 days). * **Period of Communicability:** 1–2 days before the appearance of the rash until all lesions have crusted (usually 4–5 days after rash onset). * **Rash Pattern:** Centripetal distribution (more on trunk) and "pleomorphic" (all stages of rash—papules, vesicles, and crusts—seen simultaneously). * **Dew-drop on a rose petal:** Classic description of the varicella vesicle.

Question 322: What is the most fatal complication of measles?

A. Pneumonia
B. Polyps
C. Subacute sclerosing panencephalitis (SSPE) (Correct Answer)
D. Otitis media

Explanation: **Explanation:** The correct answer is **Subacute sclerosing panencephalitis (SSPE)**. SSPE is a rare, progressive, and chronic inflammatory neurological disease caused by a persistent infection with a mutant strain of the measles virus. It typically manifests **7–10 years** after the initial measles infection. It is considered the **most fatal complication** because it is universally lethal; there is no known cure, and it leads to progressive cognitive decline, myoclonic jerks, and eventually death. **Analysis of Incorrect Options:** * **Pneumonia:** This is the **most common cause of death** from measles in children and the most common overall complication. However, while it causes more total deaths due to its frequency, it is not as "fatal" (in terms of case-fatality rate) as SSPE, which has a 100% mortality rate. * **Otitis Media:** This is the **most common complication** of measles overall, but it is rarely life-threatening. * **Polyps:** These are not a recognized complication of measles infection. **NEET-PG High-Yield Pearls:** * **Most common complication:** Otitis media. * **Most common cause of death:** Pneumonia (Hecht’s Giant Cell Pneumonia). * **SSPE Diagnosis:** Look for high titers of anti-measles antibodies in the CSF and serum (intrathecal synthesis) and **periodic complexes** on EEG. * **Vitamin A:** Supplementation reduces the severity and mortality of measles in children. * **Koplik spots:** Pathognomonic enanthem found on the buccal mucosa opposite the lower second molars during the pre-eruptive stage.

Question 323: The recent avian flu outbreak is caused by which of the following strains?

A. H1N1
B. H5N1 (Correct Answer)
C. H7N9
D. H7N7

Explanation: **Explanation:** **Correct Option: B (H5N1)** Influenza A viruses are classified based on two surface glycoproteins: **Hemagglutinin (H)** and **Neuraminidase (N)**. **H5N1** is a highly pathogenic avian influenza (HPAI) virus. While it primarily circulates among wild birds and poultry, recent global outbreaks have seen significant transmission to mammals and occasional "spillover" to humans. It is currently the predominant strain responsible for the ongoing global avian flu crisis. **Analysis of Incorrect Options:** * **A. H1N1:** This strain was responsible for the **1918 Spanish Flu** and the **2009 Swine Flu** pandemic. It is now considered a seasonal human influenza virus. * **C. H7N9:** This is another avian strain that caused a major outbreak in China in 2013. While it has high mortality in humans, it is not the strain driving the current global outbreak. * **D. H7N7:** This strain has caused sporadic outbreaks in poultry and rare, usually mild, infections in humans (conjunctivitis), but it is not the primary strain of current concern. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Major genetic changes (reassortment) leading to pandemics (e.g., H1N1 2009). * **Antigenic Drift:** Minor point mutations causing seasonal epidemics; this is why the flu vaccine is updated annually. * **Drug of Choice:** Neuraminidase inhibitors like **Oseltamivir** (Tamiflu) are used for both treatment and prophylaxis. * **Gold Standard Diagnosis:** Real-time RT-PCR is the preferred method for detecting avian influenza in clinical specimens.

Question 324: Which of the following organisms is known to cause severe encephalitis with direct transmission from pigs to humans?

A. Poliovirus
B. Measles virus
C. Nipah virus (Correct Answer)
D. West Nile virus

Explanation: **Explanation:** The correct answer is **Nipah virus (NiV)**, a highly pathogenic zoonotic paramyxovirus. In the initial 1998 outbreak in Malaysia, pigs acted as the **intermediate hosts**. The virus was transmitted to humans through direct contact with infected pigs or their contaminated tissues/fluids. Clinically, Nipah virus presents as severe, rapidly progressing encephalitis with a high fatality rate (40–75%). While the natural reservoir is the *Pteropus* fruit bat, the pig-to-human route is a classic epidemiological hallmark of this virus. **Analysis of Incorrect Options:** * **Poliovirus:** Transmitted via the fecal-oral route. It primarily affects the anterior horn cells of the spinal cord, leading to flaccid paralysis rather than primary encephalitis. * **Measles virus:** Transmitted via respiratory droplets. While it can cause Subacute Sclerosing Panencephalitis (SSPE) as a late complication, it does not involve pigs in its transmission cycle. * **West Nile virus:** An arbovirus transmitted to humans primarily through the bite of infected **Culex mosquitoes**. Birds are the natural reservoir; pigs are not the primary source of human infection. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** *Pteropus* species (Fruit bats). * **Transmission (India/Bangladesh):** Consumption of raw date palm sap contaminated with bat saliva/urine and human-to-human transmission are more common than the porcine route. * **Diagnosis:** RT-PCR or ELISA for IgM/IgG antibodies. * **Histopathology:** Characterized by systemic vasculitis and syncytia (multinucleated giant cells) formation in the brain and lungs.

Question 325: Which one of the following would be the treatment of choice for HSV infection?

A. Acyclovir (Correct Answer)
B. Killed virus vaccine
C. Herpes immune globulin
D. Azithromycin

Explanation: **Explanation:** **Acyclovir** is the gold standard treatment for Herpes Simplex Virus (HSV-1 and HSV-2) infections. It is a **guanosine analogue** that acts as a prodrug. Its mechanism of action is highly specific: it requires phosphorylation by the viral enzyme **thymidine kinase** to become active (acyclovir monophosphate). Host cell kinases then convert it to acyclovir triphosphate, which inhibits viral DNA polymerase and causes **DNA chain termination**. This selective toxicity makes it the drug of choice for HSV keratitis, encephalitis, and genital herpes. **Why other options are incorrect:** * **Killed virus vaccine:** There is currently no effective or commercially available vaccine (killed or live) for the prevention or treatment of HSV infections. * **Herpes immune globulin:** While passive immunization is used for some viruses (like VZIG for Varicella), it is not the standard of care for active HSV infections. It does not eliminate the virus or prevent latency. * **Azithromycin:** This is a macrolide antibiotic that inhibits the 50S bacterial ribosome. It is effective against bacteria (like *Chlamydia*) but has no activity against DNA viruses like HSV. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Acyclovir is the DOC for HSV encephalitis (IV administration) and neonatal herpes. * **Resistance:** Resistance to acyclovir usually occurs due to mutations in the viral **thymidine kinase** gene. In such cases, **Foscarnet** or **Cidofovir** (which do not require phosphorylation by viral enzymes) are used. * **Valacyclovir:** A prodrug of acyclovir with better oral bioavailability, often preferred for outpatient management of genital herpes. * **Tzanck Smear:** Look for **multinucleated giant cells** with Cowdry Type A intranuclear inclusion bodies in HSV lesions.

Question 326: Which of the following statements is true regarding human metapneumovirus?

A. It is a segmented negative-sense single-stranded RNA virus. (Correct Answer)
B. Its incidence accounts for 5% of all respiratory infections.
C. It spreads through sexual contact and blood transfusion.
D. It contains NS1 and NS2 antigens.

Explanation: ### Explanation **Human Metapneumovirus (hMPV)** is a significant respiratory pathogen belonging to the **Paramyxoviridae** family (subfamily Pneumovirinae). **1. Why Option A is Correct:** Human metapneumovirus is characterized by a **negative-sense, single-stranded RNA (ssRNA)** genome. While most Paramyxoviruses have non-segmented genomes, hMPV is classified within the same family as RSV. It utilizes an RNA-dependent RNA polymerase to replicate within the cytoplasm of host respiratory epithelial cells. **2. Why the Other Options are Incorrect:** * **Option B:** While hMPV is a common cause of upper and lower respiratory tract infections (LRTIs), its incidence is generally estimated to be between **7% and 15%** of all pediatric respiratory hospitalizations, often ranking second only to RSV. * **Option C:** hMPV is a respiratory virus. It spreads primarily through **respiratory droplets**, direct contact with contaminated secretions, or fomites. It is not a blood-borne or sexually transmitted infection. * **Option D:** **NS1 and NS2** (Non-Structural) proteins are characteristic features of **Respiratory Syncytial Virus (RSV)**. Human metapneumovirus is distinguished from RSV by the **absence** of these specific non-structural genes. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** It mimics RSV, causing bronchiolitis and pneumonia, especially in children, the elderly, and the immunocompromised. * **Seasonality:** Peak incidence typically occurs in **late winter and spring** (slightly later than the peak RSV season). * **Diagnosis:** **RT-PCR** is the gold standard for detection, as the virus is difficult to culture. * **Key Distinction:** Unlike RSV, hMPV lacks the NS1 and NS2 genes, which is a common molecular biology question in competitive exams.

Question 327: Which of the following statements about Hepatitis C Virus (HCV) is incorrect?

A. HCV has the highest rate of chronicity among all hepatitis viruses.
B. HCV can be routinely cultured in vitro. (Correct Answer)
C. HCV infection is diagnosed by detecting HCV RNA.
D. HCV is transmitted through the transfusion of infected blood or blood products.

Explanation: **Explanation:** **Hepatitis C Virus (HCV)**, a member of the *Flaviviridae* family, is known for its high genetic variability and difficulty in laboratory propagation. 1. **Why Option B is Incorrect (The Correct Answer):** Unlike many other viruses, **HCV cannot be routinely cultured in vitro** in standard diagnostic laboratories. While specialized research models (like the Huh7 cell line) exist, they are technically demanding and not used for clinical diagnosis. This lack of a robust culture system historically hindered vaccine development. 2. **Analysis of Other Options:** * **Option A:** HCV has the **highest rate of chronicity** (~75–85%) compared to HBV (~5–10% in adults). This is primarily due to its high mutation rate (quasispecies), which allows it to evade the host immune response. * **Option C:** Detection of **HCV RNA** via PCR is the gold standard for diagnosing active infection and monitoring treatment response (viral load). Anti-HCV antibodies only indicate exposure, not necessarily active disease. * **Option D:** HCV is primarily a **parenterally transmitted** virus. Before universal screening, blood transfusion was a major risk factor; currently, IV drug use is the most common route. **High-Yield NEET-PG Pearls:** * **Most common cause** of post-transfusion hepatitis (historically). * **Genotype 3** is the most prevalent genotype in India. * **Extrahepatic manifestations:** Essential mixed cryoglobulinemia, Porphyria cutanea tarda, and Lichen planus. * **Treatment:** Direct-acting antivirals (DAAs) like Sofosbuvir have revolutionized care, achieving cure rates >95%.

Question 328: Which of the following cell types are specific to a latent genital infection with HSV-2?

A. Trigeminal ganglia
B. Sacral ganglia (Correct Answer)
C. Vagal nerve ganglia
D. Neural sensory ganglia

Explanation: **Explanation:** **Herpes Simplex Virus (HSV)** is characterized by its ability to establish lifelong latency in the sensory nerve ganglia. The site of latency is determined by the primary site of infection and the specific nerve supplying that dermatome. 1. **Why Sacral Ganglia is Correct:** HSV-2 is the primary cause of **genital herpes**. Following the initial infection in the genital mucosa or skin, the virus undergoes retrograde axonal transport along the sensory neurons. It establishes latency in the **Sacral Ganglia (S2-S5)**. When the virus reactivates, it travels back down the same nerves to cause recurrent genital lesions. 2. **Analysis of Incorrect Options:** * **Trigeminal Ganglia:** This is the site of latency for **HSV-1**, which typically causes orofacial herpes (cold sores). The trigeminal nerve (CN V) provides sensory innervation to the face. * **Vagal Nerve Ganglia:** While some viruses can affect the vagus nerve, it is not a classic site for HSV latency. * **Neural Sensory Ganglia:** This is a general term. While technically true that HSV resides in sensory ganglia, the question asks for the *specific* site for a *genital* infection, making "Sacral Ganglia" the most precise answer. **High-Yield NEET-PG Pearls:** * **HSV-1:** Latency in Trigeminal Ganglia (Above the waist). * **HSV-2:** Latency in Sacral Ganglia (Below the waist). * **Varicella-Zoster Virus (VZV):** Latency in Dorsal Root Ganglia. * **Diagnosis:** Tzanck smear showing **Multinucleated Giant Cells** with Cowdry Type A inclusion bodies (intranuclear). * **Drug of Choice:** Acyclovir (inhibits viral DNA polymerase).

Question 329: What is the most common extracutaneous site of involvement in varicella infection?

A. Heart
B. Lungs
C. Liver
D. Central Nervous System (CNS) (Correct Answer)

Explanation: **Explanation:** Varicella-Zoster Virus (VZV) is a highly neurotropic alpha-herpesvirus. While primary varicella (chickenpox) is characterized by a generalized pruritic vesicular rash, the **Central Nervous System (CNS)** is the most frequent site of extracutaneous involvement. The most common CNS manifestation in children is **acute cerebellar ataxia** (presenting with nystagmus and unsteady gait), whereas **encephalitis** is a more severe but rarer complication seen more frequently in adults. **Analysis of Options:** * **Central Nervous System (CNS) (Correct):** Due to the virus's inherent neurotropism, neurological complications (ataxia, encephalitis, or aseptic meningitis) occur more frequently than involvement of other organ systems. * **Lungs:** Varicella pneumonia is the most serious complication in adults and pregnant women, but it is statistically less common than CNS involvement across the general population. * **Liver:** While subclinical elevation of liver enzymes is common, clinically significant hepatitis is rare except in immunocompromised individuals. * **Heart:** Myocarditis is an extremely rare complication of VZV infection. **NEET-PG High-Yield Pearls:** * **Most common complication in children:** Secondary bacterial infection of skin lesions (usually *S. pyogenes* or *S. aureus*). * **Most common CNS complication in children:** Acute Cerebellar Ataxia (good prognosis). * **Most serious complication in adults:** Varicella Pneumonia. * **Tzanck Smear:** Shows multinucleated giant cells with Cowdry type A intranuclear inclusion bodies (common to VZV and HSV). * **Congenital Varicella Syndrome:** Characterized by cicatricial skin scarring, limb hypoplasia, and chorioretinitis if infection occurs in the first 20 weeks of gestation.

Question 330: Fulminant hepatitis E is most commonly seen in which demographic group?

A. Pregnant women (Correct Answer)
B. Infants
C. Malnourished males
D. Adolescents

Explanation: **Explanation:** Hepatitis E Virus (HEV) is a non-enveloped RNA virus typically transmitted via the feco-oral route. While it usually causes a self-limiting acute viral hepatitis similar to Hepatitis A, it is notorious for causing **Fulminant Hepatic Failure (FHF)** in **pregnant women**, particularly during the second and third trimesters. **1. Why Pregnant Women?** The exact pathogenesis is multifactorial, involving a combination of altered host immune responses (shifted towards a Th2 profile), high levels of steroid hormones (progesterone and estrogen) which may enhance viral replication, and poor antioxidant defense. In this demographic, the case fatality rate can soar to **15–25%**, compared to <1% in the general population. **2. Analysis of Incorrect Options:** * **Infants:** While infants can contract HEV, the infection is usually mild or asymptomatic. Fulminant failure is not a characteristic feature in this age group. * **Malnourished males:** Though malnutrition can worsen the prognosis of any infection, there is no specific epidemiological link between malnutrition in males and fulminant HEV. * **Adolescents:** HEV most commonly affects young adults (15–40 years), but in non-pregnant individuals, it rarely progresses to fulminant failure. **High-Yield Clinical Pearls for NEET-PG:** * **Genotypes:** Genotypes 1 and 2 are associated with waterborne epidemics (common in India); Genotypes 3 and 4 are zoonotic (pork consumption). * **Chronic HEV:** Can occur in **immunocompromised** patients (e.g., organ transplant recipients), usually associated with Genotype 3. * **Diagnosis:** IgM anti-HEV is the gold standard for acute infection. * **Prognosis:** HEV has the highest mortality rate among all viral hepatitides when it occurs during pregnancy.

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