Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 651: What is the most common cause of viral meningoencephalitis?

A. Enterovirus
B. Arbovirus
C. Herpes simplex virus (Correct Answer)
D. Cytomegalovirus

Explanation: **Explanation:** The correct answer is **Herpes simplex virus (HSV)**. In the context of **meningoencephalitis** (inflammation involving both the meninges and the brain parenchyma), **HSV-1** is the most common cause of sporadic, non-epidemic cases worldwide. It typically affects the temporal lobes, leading to characteristic clinical features like personality changes, seizures, and focal neurological deficits. **Analysis of Options:** * **Herpes simplex virus (Correct):** HSV-1 is the leading cause of fatal sporadic viral encephalitis. It is crucial to distinguish this from HSV-2, which is a more common cause of viral *meningitis* (especially in neonates or as Mollaret’s meningitis). * **Enteroviruses:** These are the most common cause of **viral (aseptic) meningitis**, but they are less frequent causes of true encephalitis compared to HSV. * **Arboviruses:** These (e.g., Japanese Encephalitis, West Nile) are significant causes of **epidemic** encephalitis in specific geographic regions, but they are not the most common cause globally or sporadically. * **Cytomegalovirus (CMV):** CMV typically causes encephalitis only in **immunocompromised** individuals (e.g., advanced HIV/AIDS) and is not the leading cause in the general population. **High-Yield Clinical Pearls for NEET-PG:** * **Site Predilection:** HSV encephalitis has a high affinity for the **temporal lobes** (look for "hemorrhagic necrosis" on pathology). * **Diagnosis:** **CSF PCR** is the gold standard investigation. * **EEG Finding:** Periodic lateralized epileptiform discharges (**PLEDs**) are characteristic. * **Treatment:** Intravenous **Acyclovir** should be started empirically if HSV encephalitis is suspected, as it significantly reduces mortality.

Question 652: What is the extra gene of HTLV?

A. Gag
B. Pol
C. Env
D. Px (Correct Answer)

Explanation: **Explanation:** Human T-cell Lymphotropic Virus (HTLV-1) is a retrovirus belonging to the Deltaretrovirus genus. While all retroviruses share a basic genetic structure, HTLV is categorized as a **complex retrovirus** because it contains regulatory genes in addition to the standard structural genes. **Why Px is correct:** The **Px region** is the unique "extra" genetic component located at the 3' end of the HTLV genome. It encodes several non-structural regulatory proteins, most notably **Tax** and **Rex**. * **Tax protein:** Crucial for oncogenesis; it transactivates viral and cellular gene expression (like IL-2 and IL-2 receptor), leading to uncontrolled T-cell proliferation and eventually **Adult T-cell Leukemia/Lymphoma (ATLL)**. * **Rex protein:** Regulates viral mRNA splicing and transport. **Why other options are incorrect:** * **Gag (Group-specific Antigen):** A standard retroviral gene that encodes internal structural proteins (capsid p24, nucleocapsid, and matrix). * **Pol (Polymerase):** A standard gene encoding essential enzymes: Reverse Transcriptase, Integrase, and Protease. * **Env (Envelope):** A standard gene encoding surface glycoproteins (gp46) and transmembrane proteins (gp21) required for viral entry. **High-Yield Clinical Pearls for NEET-PG:** * **Disease Associations:** HTLV-1 is primarily associated with **ATLL** (flower cells on peripheral smear) and **HAM/TSP** (HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis). * **Transmission:** Similar to HIV (Blood, Sexual, Vertical), but **breastfeeding** is a major route for HTLV-1. * **Target Cells:** Unlike HIV which destroys CD4+ cells, HTLV-1 causes **malignant transformation** of CD4+ T-cells.

Question 653: Lassa fever virus belongs to which viral family?

A. Arenaviridae (Correct Answer)
B. Bunyaviridae
C. Flaviviridae
D. Reoviridae

Explanation: **Explanation:** **Lassa fever virus** is a member of the **Arenaviridae** family. The name "Arena" is derived from the Latin *arenosus* (sandy), referring to the grainy appearance of the virions under electron microscopy due to the presence of host ribosomes inside the viral envelope. **Why Arenaviridae is correct:** Arenaviruses are pleomorphic, enveloped viruses with a **bisegmented, ambisense RNA genome**. Lassa virus is the causative agent of Lassa fever, a viral hemorrhagic fever (VHF) endemic to West Africa. It is primarily transmitted to humans via contact with the excreta of the multimammate rat (*Mastomys natalensis*). **Why other options are incorrect:** * **Bunyaviridae:** While this family also causes VHFs (e.g., Crimean-Congo Hemorrhagic Fever, Hantavirus), they typically have a **trisegmented** RNA genome. * **Flaviviridae:** This family includes viruses like Dengue, Yellow Fever, and Zika. These are positive-sense, single-stranded RNA viruses, mostly transmitted by arthropod vectors (Arboviruses). * **Reoviridae:** These are non-enveloped viruses with a **segmented double-stranded RNA** genome (e.g., Rotavirus). **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** *Mastomys natalensis* (Multimammate rat). * **Clinical Feature:** The most common complication in survivors is **sensorineural deafness**. * **Treatment:** **Ribavirin** is the drug of choice if administered early. * **Other Arenaviruses:** Lymphocytic Choriomeningitis Virus (LCMV) and South American Hemorrhagic Fever viruses (Junin, Machupo).

Question 654: Hepatitis B virus E antigen (HBeAg) is a product of which gene?

A. S
B. C (Correct Answer)
C. P
D. X

Explanation: **Explanation:** The Hepatitis B Virus (HBV) genome is a circular, partially double-stranded DNA molecule containing four overlapping open reading frames (ORFs): **S, C, P, and X.** The **C (Core) gene** contains two initiation codons (the pre-core and core regions). 1. Translation from the **pre-core region** produces a precursor protein that is processed and secreted into the blood as **HBeAg** (Hepatitis B e antigen). 2. Translation from the **core region** produces the **HBcAg** (Hepatitis B core antigen), which forms the nucleocapsid and is not secreted into the serum. Therefore, HBeAg is a soluble protein derived from the C gene, serving as a marker of active viral replication and high infectivity. **Analysis of Incorrect Options:** * **Option A (S gene):** Codes for the surface glycoproteins, collectively known as **HBsAg** (Australia Antigen), which includes the Pre-S1, Pre-S2, and S domains. * **Option C (P gene):** The largest gene; it codes for the **DNA polymerase**, which possesses reverse transcriptase, DNA-dependent DNA polymerase, and RNase H activity. * **Option D (X gene):** Codes for the **HBx protein**, a transcriptional transactivator that plays a critical role in viral replication and the development of hepatocellular carcinoma (HCC). **High-Yield Clinical Pearls for NEET-PG:** * **HBeAg** is the best indicator of **high infectivity** and active viral replication. * The appearance of **Anti-HBe** (seroconversion) usually indicates a transition to a low-replicative state. * **Pre-core mutants:** Some HBV strains have a mutation in the pre-core region that prevents HBeAg production despite high viral loads (DNA levels). * **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs; **Anti-HBc IgM** is the only diagnostic marker during this phase.

Question 655: Which of the following viruses belongs to the Poxviridae family?

A. Variola virus (Correct Answer)
B. Coxsackie virus
C. ECHO virus
D. Herpes Simplex Virus (HSV)

Explanation: **Explanation:** The **Poxviridae** family consists of the largest and most complex viruses known to infect humans. **Variola virus**, the causative agent of Smallpox, is the prototypical member of this family. A key distinguishing feature of Poxviruses is that they are the only DNA viruses that **replicate entirely within the host cell cytoplasm**, as they carry their own DNA-dependent RNA polymerase. Morphologically, they are "brick-shaped" and possess a complex symmetry. **Analysis of Incorrect Options:** * **Coxsackie virus & ECHO virus:** Both belong to the **Picornaviridae** family (specifically the *Enterovirus* genus). These are small, non-enveloped, positive-sense single-stranded RNA viruses. They are common causes of aseptic meningitis, hand-foot-and-mouth disease (Coxsackie A), and myocarditis (Coxsackie B). * **Herpes Simplex Virus (HSV):** This belongs to the **Herpesviridae** family. Unlike Poxviruses, Herpesviruses are enveloped, icosahedral DNA viruses that replicate in the **nucleus** and are characterized by their ability to establish latent infections in sensory ganglia. **High-Yield Clinical Pearls for NEET-PG:** * **Guarnieri bodies:** These are eosinophilic intracytoplasmic inclusion bodies pathognomonic for Variola (Smallpox) and Vaccinia. * **Molluscum Contagiosum:** Another clinically significant Poxvirus characterized by umbilicated cutaneous papules containing "Henderson-Paterson bodies." * **Eradication:** Smallpox is the only human infectious disease to be globally eradicated (declared by the WHO in 1980). * **Vaccine:** The Smallpox vaccine uses the **Live Vaccinia virus**, not the Variola virus.

Question 656: Which age group is primarily affected by Hepatitis A virus?

A. Children (Correct Answer)
B. Adults
C. Elderly
D. Any age group

Explanation: **Explanation:** **Hepatitis A Virus (HAV)** is a small, non-enveloped RNA virus (Picornavirus) transmitted primarily via the **fecal-oral route**. In developing countries like India, where the virus is endemic, the majority of the population is exposed to HAV during early childhood due to suboptimal sanitation and contaminated water/food. 1. **Why Children are primarily affected:** In endemic regions, infection typically occurs in **children under the age of 5**. At this age, the infection is usually **asymptomatic or subclinical** (anicteric), leading to lifelong natural immunity. By the time individuals reach adulthood, most have already developed antibodies (Anti-HAV IgG), making clinical disease rare in older populations. 2. **Why other options are incorrect:** * **Adults:** While adults can be infected (often presenting with more severe, symptomatic jaundice), the *primary* epidemiological burden in endemic areas is among children. In developed nations, adults are more susceptible due to lack of childhood exposure. * **Elderly:** This group is rarely the primary target due to pre-existing immunity. However, if infected, they face the highest risk of complications like fulminant hepatic failure. * **Any age group:** While biologically possible, the epidemiological pattern specifically favors childhood acquisition in high-prevalence areas. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 2–6 weeks (Average 28 days). * **Diagnosis:** **IgM anti-HAV** is the gold standard for acute infection; **IgG anti-HAV** indicates past infection or vaccination. * **Key Feature:** HAV **never** causes chronic infection or a carrier state. * **Vaccine:** Live attenuated (H2 strain) or Inactivated (Formalin-killed) vaccines are available. * **Morphology:** Enterovirus 72, 27 nm, icosahedral symmetry.

Question 657: Which hepatitis virus is defective?

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

Explanation: ### Explanation **Correct Answer: D. Hepatitis D virus (HDV)** **Why HDV is the correct answer:** Hepatitis D virus (HDV) is classified as a **defective virus** (specifically a sub-viral satellite) because it cannot complete its life cycle or cause infection on its own. It lacks the genetic information to synthesize its own outer envelope (surface proteins). To replicate and infect new cells, HDV must "borrow" the **Hepatitis B surface antigen (HBsAg)** from the Hepatitis B virus (HBV). Therefore, HDV infection can only occur in the presence of an active HBV infection. **Why the other options are incorrect:** * **A. HAV:** A Picornavirus (RNA) that is fully functional and transmitted via the fecal-oral route. It does not require a helper virus. * **B. HBV:** A Hepadnavirus (DNA) that is a complete, complex virus. It acts as the "helper virus" for HDV but is not defective itself. * **C. HCV:** A Flavivirus (RNA) that is fully capable of independent replication and is a leading cause of chronic liver disease. **High-Yield Clinical Pearls for NEET-PG:** * **Modes of Infection:** * **Co-infection:** Simultaneous infection with HBV and HDV (usually presents as acute hepatitis; low risk of chronicity). * **Super-infection:** HDV infection in a chronic HBV carrier (high risk of fulminant hepatitis and rapid progression to cirrhosis). * **Genome:** HDV has a circular, single-stranded negative-sense RNA genome. * **Antigen:** The only protein encoded by the HDV genome is the **Delta antigen (HDAg)**. * **Prevention:** The Hepatitis B vaccine is protective against HDV because HDV cannot infect without HBV.

Question 658: Which of the following statements is WRONG regarding a patient with polio?

A. Can transmit it by nasal discharge. (Correct Answer)
B. Subclinical infection is common.
C. The most predominant poliovirus type during an epidemic is type I.
D. The patient can be vaccinated.

Explanation: The correct answer is **A (Can transmit it by nasal discharge)**. ### **Explanation** Poliovirus is an **Enterovirus** primarily transmitted via the **fecal-oral route**. While the virus initially multiplies in the oropharynx and can be found in throat secretions for a short period (about 1 week), it is **not** transmitted through nasal discharge. The primary modes of transmission are contaminated water/food and direct contact with infected feces. ### **Analysis of Other Options** * **B. Subclinical infection is common:** This is correct. In over 90–95% of cases, polio infection is asymptomatic or subclinical. Only about 1% of infections result in paralytic polio. * **C. Type I is the most predominant during epidemics:** This is correct. Poliovirus has three serotypes (1, 2, and 3). Type 1 is the most common cause of epidemics and the most frequent cause of paralysis. (Note: Type 2 has been eradicated globally since 2015). * **D. The patient can be vaccinated:** This is correct. Infection with one serotype does not provide cross-immunity against the others. Therefore, a patient who has recovered from polio should still be vaccinated to ensure protection against the remaining serotypes. ### **High-Yield NEET-PG Pearls** * **Specimen of Choice:** For diagnosis, **stool** is the most reliable specimen as the virus is excreted in feces for 6–8 weeks. * **Pathogenesis:** The virus attaches to the **CD155 receptor** and specifically attacks the **anterior horn cells** of the spinal cord. * **Vaccine Difference:** * **Salk (IPV):** Killed vaccine, induces humoral immunity (IgG) only. * **Sabin (OPV):** Live attenuated, induces both humoral (IgG) and local mucosal immunity (IgA). It is responsible for "herd immunity" but carries a risk of VAPP (Vaccine-Associated Paralytic Polio).

Question 659: Regarding Progressive multifocal leucoencephalopathy, all are true, except?

A. Caused by JC virus
B. Diffuse cortical matter involvement
C. Disease of white matter
D. Disease of grey matter (Correct Answer)

Explanation: **Explanation:** Progressive Multifocal Leukoencephalopathy (PML) is a severe demyelinating disease of the Central Nervous System. The core pathophysiology involves the **selective destruction of oligodendrocytes**, the cells responsible for producing and maintaining the myelin sheath in the brain. * **Why Option D is the correct answer:** PML is strictly a **white matter disease**. Since myelin is the primary component of white matter, the destruction of oligodendrocytes leads to extensive demyelination. It does **not** primarily involve the neuronal cell bodies found in the grey matter. Therefore, stating it is a "disease of grey matter" is factually incorrect. * **Why Option A is wrong:** PML is caused by the **JC virus** (John Cunningham virus), a human polyomavirus. It is a high-yield fact that this virus remains latent in the kidneys and lymphoid tissue of healthy individuals and reactivates during profound immunosuppression. * **Why Option B & C are wrong:** These options correctly describe the pathology. PML presents as **diffuse, asymmetric involvement of the subcortical white matter**. On MRI, these appear as multiple, non-enhancing T2/FLAIR hyperintense lesions without mass effect. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Most commonly seen in **AIDS patients** (CD4 count <200 cells/µL) and patients on monoclonal antibodies like **Natalizumab** (used in Multiple Sclerosis). * **Histopathology:** Look for the "Triad": 1. Demyelination, 2. **Bizarre giant astrocytes**, and 3. **Intranuclear inclusion bodies** in oligodendrocytes (ground-glass appearance). * **Diagnosis:** PCR for JC virus DNA in the Cerebrospinal Fluid (CSF) is the gold standard for non-invasive diagnosis.

Question 660: A potent vaccine is available for which type of Hepatitis?

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

Explanation: **Explanation:** The correct answer is **Hepatitis A**. A highly effective and potent vaccine has been available for Hepatitis A since the 1990s. It is an **inactivated (killed) vaccine** administered in two doses, providing long-term immunity (often lifelong) in over 95-99% of recipients. **Analysis of Options:** * **Hepatitis A (Correct):** The vaccine is recommended for travelers, MSM, and patients with chronic liver disease. In India, it is often given as a private market vaccine. * **Hepatitis C:** There is **no vaccine** available for HCV. This is primarily due to the high genetic variability of the virus and its ability to rapidly mutate (hypervariable regions in the E2 envelope glycoprotein), which allows it to evade the immune system. * **Hepatitis D:** There is no specific vaccine for HDV itself. However, because HDV is a "defective virus" that requires HBsAg for replication, it can be prevented by the **Hepatitis B vaccine**. * **Hepatitis E:** While a vaccine (Hecolin) has been developed and approved in **China**, it is not globally available or used in routine clinical practice in India or most other countries. **High-Yield Clinical Pearls for NEET-PG:** * **Hepatitis B Vaccine:** The first "anti-cancer" vaccine (prevents HCC). It is a **recombinant subunit vaccine** containing HBsAg. * **Route of Transmission:** Hepatitis A and E are transmitted via the **fecal-oral route** (Vowels go to the Bowels), while B, C, and D are parenteral. * **Pregnancy:** Hepatitis E has the highest mortality rate (up to 20%) in pregnant women due to fulminant hepatic failure. * **Post-Exposure Prophylaxis (PEP):** For Hep A, both the vaccine and Immunoglobulin (IG) can be used depending on the patient's age and health status.

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