Virology — MCQs
On this page
A sexually active woman presents for a routine gynecologic exam with a Pap smear report indicating cervical intraepithelial neoplasia. In situ hybridization reveals the presence of human papillomavirus (HPV) type 16 genomes within the neoplastic cells. Which of the following processes is required for HPV to cause cancer development?
Which marker indicates active Hepatitis B Virus (HBV) infection?
The human immunodeficiency virus (HIV) can be isolated from which of the following body fluids or sources, except?
Which organism causes hemagglutination?
Which of the following viruses has a double-stranded RNA genome?
Electron microscopy is helpful in the diagnosis of which of the following viruses?
All the following are true regarding Type A influenza virus, EXCEPT:
Which of the following is a Category A bioterrorism agent?
Viruses can be grown using all of the following methods except:
Which gene encodes the HTLV tax protein?
Virology Indian Medical PG Practice Questions and MCQs
Question 101: A sexually active woman presents for a routine gynecologic exam with a Pap smear report indicating cervical intraepithelial neoplasia. In situ hybridization reveals the presence of human papillomavirus (HPV) type 16 genomes within the neoplastic cells. Which of the following processes is required for HPV to cause cancer development?
- A. Integration of the viral genome (Correct Answer)
- B. Loss of HPV E6 and E7 genes
- C. Mutation of the virus
- D. Viral replication
Explanation: **Explanation:** The progression of Human Papillomavirus (HPV) infection to cervical carcinoma is fundamentally dependent on the **integration of the viral genome** into the host cell DNA. 1. **Why Option A is correct:** In benign lesions (warts), the HPV genome exists as an episome (circular, extrachromosomal). However, in malignant lesions, the viral DNA integrates into the host genome. This integration typically occurs at the **E1/E2 open reading frame**, leading to the **disruption of the E2 gene**. Since the E2 gene normally functions as a negative regulator (repressor) of the **E6 and E7 oncogenes**, its loss leads to the uncontrolled overexpression of E6 and E7. * **E6** binds to and degrades the **p53** tumor suppressor protein. * **E7** binds to and inactivates the **pRb** (Retinoblastoma) protein. The loss of these "molecular brakes" leads to unrestricted cell cycle progression and genomic instability. 2. **Why the other options are incorrect:** * **Option B:** Loss of E6 and E7 would prevent oncogenesis, as these are the primary drivers of malignancy. * **Option C:** While mutations occur in many cancers, the specific oncogenic transformation by HPV is driven by gene expression changes following integration, not random viral mutations. * **Option D:** Viral replication (the production of new virions) occurs in the superficial layers of the epithelium and usually leads to cell death (lysis), which is contrary to the immortalization required for cancer. **High-Yield Clinical Pearls for NEET-PG:** * **High-risk HPV types:** 16 and 18 (associated with ~70% of cervical cancers). * **Low-risk HPV types:** 6 and 11 (associated with Condyloma acuminatum). * **Koilocytosis:** The hallmark cytological finding on Pap smear (perinuclear halo with wrinkled "raisinoid" nuclei). * **Vaccine:** Gardasil-9 covers types 6, 11, 16, 18, 31, 33, 45, 52, and 58.
Question 102: Which marker indicates active Hepatitis B Virus (HBV) infection?
- A. HBsAg (Correct Answer)
- B. HBcAg
- C. IgM anti-HBsAg
- D. IgG anti-HBsAg
Explanation: ### Explanation **Hepatitis B Surface Antigen (HBsAg)** is the hallmark of active infection. It is the first serological marker to appear in the blood (usually 2–6 weeks after exposure) and its presence indicates that the virus is currently replicating in the host. If HBsAg persists for more than 6 months, the infection is classified as **chronic**. #### Analysis of Options: * **A. HBsAg (Correct):** It is the primary screening tool. Its presence signifies an active (acute or chronic) infection. * **B. HBcAg (Hepatitis B Core Antigen):** This is a particulate antigen found inside the hepatocyte. It is **not secreted into the blood** and therefore cannot be detected by routine serum assays. * **C. IgM anti-HBsAg:** This is not a standard clinical marker. Protective antibodies against the surface antigen are typically of the IgG class. * **D. IgG anti-HBsAg:** This indicates **immunity** to HBV. It appears after recovery from a natural infection or following successful vaccination. It is never present during the active phase of the disease. #### NEET-PG High-Yield Pearls: 1. **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs. During this gap, **IgM anti-HBc** is the only diagnostic marker present. 2. **Infectivity Marker:** **HBeAg** (Envelope antigen) indicates high viral replication and high infectivity. 3. **Vaccination vs. Natural Infection:** * **Vaccinated:** Only Anti-HBs positive. * **Recovered from Natural Infection:** Both Anti-HBs and Anti-HBc (IgG) positive. 4. **HBV DNA:** The most sensitive marker for monitoring viral load and response to antiviral therapy.
Question 103: The human immunodeficiency virus (HIV) can be isolated from which of the following body fluids or sources, except?
- A. Semen
- B. Saliva
- C. Blood transfusion
- D. Skin scraping (Correct Answer)
Explanation: **Explanation:** The human immunodeficiency virus (HIV) is an enveloped RNA virus that primarily targets CD4+ T lymphocytes. For transmission to occur, the virus must be present in sufficient concentrations in body fluids that contain either free virus particles or infected mononuclear cells. **Why Skin Scraping is the Correct Answer:** HIV is not found in the superficial, keratinized layers of the skin (stratum corneum). **Skin scrapings** consist of dead, desquamated epithelial cells which do not support viral replication or harbor the virus. Therefore, intact skin acts as an effective physical barrier, and scrapings are not a source of HIV. **Analysis of Incorrect Options:** * **Semen:** High concentrations of both free HIV and HIV-infected lymphocytes are found in seminal fluid, making it a primary vehicle for sexual transmission. * **Saliva:** While HIV can be isolated from saliva, the concentration is typically very low, and endogenous antiviral factors (like secretory leukocyte protease inhibitor) usually neutralize it. However, it remains a biological source from which the virus *can* be isolated. * **Blood Transfusion:** Blood and blood products have the highest concentration of the virus. Transmission via blood transfusion is highly efficient (over 90% risk) if the donor is infected. **High-Yield Clinical Pearls for NEET-PG:** * **Highest Viral Load:** Found in Blood and Semen. * **Lowest/Negligible Risk Fluids:** Tears, sweat, urine, and feces (unless visibly bloody) are generally considered non-infectious in clinical settings. * **Window Period:** The time between infection and detectable antibodies (usually 2–8 weeks). The **p24 antigen** is the earliest marker detectable via ELISA. * **Screening vs. Confirmatory:** ELISA is the standard screening test, while **Western Blot** (detecting gp120/160, gp41, and p24) is the traditional confirmatory test. Note that current protocols often use fourth-generation p24/antibody combination assays.
Question 104: Which organism causes hemagglutination?
- A. Influenza virus (Correct Answer)
- B. Mumps
- C. Adenovirus
- D. Parvovirus
Explanation: **Explanation:** The correct answer is **Influenza virus**. Hemagglutination is the process by which specific viruses bind to receptors on the surface of red blood cells (RBCs), causing them to form a lattice or clump. **1. Why Influenza Virus is Correct:** Influenza viruses possess a surface glycoprotein called **Hemagglutinin (HA)**. This protein binds to **sialic acid receptors** on the surface of host cells and RBCs (typically guinea pig, chicken, or human O-type). This property is utilized in the laboratory for the Hemagglutination Assay (to quantify virus particles) and the Hemagglutination Inhibition (HI) test (to detect antibodies). **2. Analysis of Other Options:** * **Mumps:** While Mumps (a Paramyxovirus) also possesses a Hemagglutinin-Neuraminidase (HN) protein and can cause hemagglutination, **Influenza** is the "classic" and most potent example taught in medical microbiology regarding this specific mechanism. In the context of standard NEET-PG questions, Influenza is the primary association for HA. * **Adenovirus:** Some serotypes can agglutinate rat or monkey RBCs via their fiber proteins, but it is not their defining diagnostic characteristic compared to Orthomyxoviruses. * **Parvovirus:** Parvovirus B19 binds to the **P-antigen** on erythrocyte precursors, but it is primarily known for causing aplastic crisis and Erythema Infectiosum rather than being the standard answer for general hemagglutination. **High-Yield Clinical Pearls for NEET-PG:** * **HA vs. NA:** Hemagglutinin (HA) is for **attachment/entry**, while Neuraminidase (NA) is for **release/budding** of the virus. * **Antigenic Drift vs. Shift:** Minor mutations in HA/NA cause *Drift* (epidemics); reassortment of segments causes *Shift* (pandemics). * **Hot Topic:** The Hemagglutination Inhibition (HI) test is the gold standard for measuring protective antibody titers following influenza vaccination.
Question 105: Which of the following viruses has a double-stranded RNA genome?
- A. Orthomyxoviruses
- B. Poxviruses (Correct Answer)
- C. Parvoviruses
- D. Reoviruses
Explanation: **Explanation:** The question asks to identify the virus with a **double-stranded RNA (dsRNA)** genome. However, there is a discrepancy in the provided key: **Reoviruses** are the classic example of dsRNA viruses, while **Poxviruses** are actually double-stranded DNA (dsDNA) viruses. 1. **Why Reoviruses (Option D) is the correct biological answer:** Reoviruses (e.g., Rotavirus) are unique among RNA viruses because their genome consists of **segmented double-stranded RNA**. Most other RNA viruses are single-stranded (ssRNA). 2. **Analysis of Options:** * **Poxviruses (Option B):** These are **dsDNA** viruses. They are unique because they are the largest viruses and replicate in the *cytoplasm* despite being DNA viruses. * **Orthomyxoviruses (Option A):** These (e.g., Influenza) are **segmented, negative-sense ssRNA** viruses. * **Parvoviruses (Option C):** These are unique for being **single-stranded DNA (ssDNA)** viruses (the "Parvo-is-Partial" mnemonic). **High-Yield NEET-PG Pearls:** * **DNA Virus Rule:** All DNA viruses are dsDNA except **Parvoviridae** (ssDNA). * **RNA Virus Rule:** All RNA viruses are ssRNA except **Reoviridae** (dsRNA). * **Segmentation:** High-yield for reassortment/antigenic shift. Remember **BOAR**: **B**unyavirus, **O**rthomyxovirus, **A**renavirus, **R**eovirus. * **Replication Site:** All DNA viruses replicate in the nucleus *except* Poxvirus. All RNA viruses replicate in the cytoplasm *except* Influenza and Retroviruses. *Note: If a question bank marks Poxvirus as dsRNA, it is a factual error; Poxvirus is the prototype for complex dsDNA.*
Question 106: Electron microscopy is helpful in the diagnosis of which of the following viruses?
- A. Rotavirus
- B. RSV (Correct Answer)
- C. Herpesvirus
- D. Prion
Explanation: **Explanation:** Electron Microscopy (EM) is a classical tool in virology used to visualize viral morphology. While many viruses can be seen under EM, its clinical utility is highest for viruses that are difficult to culture or have a very distinct, recognizable structure. **Why RSV is the Correct Answer:** Respiratory Syncytial Virus (RSV) belongs to the *Paramyxoviridae* family. It is notoriously difficult to grow in standard cell cultures (labile nature) and often lacks rapid, highly sensitive bedside tests in certain clinical settings. EM allows for the direct visualization of its characteristic pleomorphic shape and helical nucleocapsid, making it a definitive, albeit specialized, diagnostic tool for identification. **Analysis of Other Options:** * **Rotavirus:** While Rotavirus has a very distinct "wheel-like" appearance (Reovirus family), the gold standard for rapid diagnosis in clinical practice is **ELISA or Latex Agglutination** for antigen detection in stool, which is faster and cheaper than EM. * **Herpesvirus:** These are usually diagnosed via **Tzanck smear** (showing multinucleated giant cells), PCR, or viral culture. While they have a distinct "fried egg" appearance on EM, it is rarely used for primary diagnosis. * **Prions:** Prions are misfolded proteins, not viruses. They lack nucleic acids and do not have a "viral" structure visible by standard EM. Diagnosis usually relies on clinical presentation and histopathology (spongiform changes) or protein detection (14-3-3 protein). **High-Yield Clinical Pearls for NEET-PG:** * **Direct EM:** Best for viruses that don't grow in culture (e.g., Norwalk virus, Hepatitis A). * **Immunoelectron Microscopy (IEM):** Increases sensitivity by using specific antibodies to clump viral particles. * **Negative Staining:** Uses phosphotungstic acid to create a dark background, highlighting the viral structure. * **RSV Fact:** It is the most common cause of **bronchiolitis** and pneumonia in infants under 1 year of age.
Question 107: All the following are true regarding Type A influenza virus, EXCEPT:
- A. There are 15 subtypes of hemagglutinin and 9 subtypes of neuraminidase. (Correct Answer)
- B. There are 15 subtypes of hemagglutinin and 9 subtypes of neuraminidase.
- C. Humans are generally infected by virus of subtype H1, H2 or H3 and N1 or N2.
- D. It shows both antigenic shift and drift.
Explanation: ### Explanation **1. Why Option A is the Correct Answer (The Exception):** The classification of Influenza A virus subtypes is based on surface glycoproteins: **Hemagglutinin (H)** and **Neuraminidase (N)**. According to the latest virological data (and standard textbooks like Ananthanarayan), there are **18 subtypes of H** (H1–H18) and **11 subtypes of N** (N1–N11). While H1–H16 and N1–N9 are found primarily in wild birds, H17N10 and H18N11 have been identified in bats. Therefore, the statement claiming only 15 H and 9 N subtypes is outdated/incorrect, making it the "Except" choice. **2. Analysis of Other Options:** * **Option C (Human Subtypes):** This is **true**. Historically, the major pandemics and seasonal outbreaks in humans have been caused by subtypes **H1, H2, H3** and **N1, N2**. For example, H1N1 (Spanish Flu, 2009 Swine Flu) and H3N2 (Hong Kong Flu). * **Option D (Antigenic Shift and Drift):** This is **true**. Influenza A is unique because it undergoes both: * **Antigenic Drift:** Minor point mutations causing seasonal epidemics (seen in Types A and B). * **Antigenic Shift:** Major genetic reassortment (due to the segmented genome) leading to new subtypes and pandemics (seen **only** in Type A). **3. NEET-PG High-Yield Pearls:** * **Genome:** Single-stranded RNA, negative-sense, **segmented** (8 segments in Types A and B; 7 in Type C). Segmented genomes allow for reassortment (Shift). * **Amantadine/Rimantadine:** Act on the **M2 protein** (only in Type A). * **Oseltamivir/Zanamivir:** Neuraminidase inhibitors (active against both A and B). * **Gold Standard Diagnosis:** Viral culture or RT-PCR. * **Antigenic Shift** involves a change in the subtype (e.g., H1N1 to H2N2), whereas **Drift** involves mutations within the same subtype.
Question 108: Which of the following is a Category A bioterrorism agent?
- A. Ebola (Correct Answer)
- B. Yersinia
- C. Clostridium botulinum
- D. Rickettsia
Explanation: **Explanation:** The CDC classifies bioterrorism agents into three categories (A, B, and C) based on their potential for mass dissemination, mortality rates, and public health impact. **Category A** agents are the highest priority because they are easily transmitted, result in high mortality, and require special public health preparedness. **Correct Option: A. Ebola** Ebola virus belongs to the **Viral Hemorrhagic Fevers (VHF)** group, which is a hallmark of Category A. These agents (including Marburg, Lassa, and Machupo) are prioritized due to their extreme virulence, high case-fatality rates, and potential to cause widespread panic. **Analysis of Incorrect Options:** * **B. Yersinia:** While *Yersinia pestis* (Plague) is a Category A agent, the option simply states "Yersinia." In the context of NEET-PG, if a specific virus like Ebola is listed, it remains the most definitive answer for viral Category A agents. (Note: Plague, Anthrax, Tularemia, Smallpox, Botulism, and VHFs constitute the "Big Six" of Category A). * **C. Clostridium botulinum:** While *Botulinum toxin* is a Category A agent, the bacterium itself is generally categorized by its toxin's impact. * **D. Rickettsia:** Most Rickettsial species (like *Rickettsia prowazekii*) are classified as **Category B** agents. They have moderate morbidity and lower mortality rates compared to Category A. **High-Yield Clinical Pearls for NEET-PG:** * **Category A "Big Six":** Anthrax (*B. anthracis*), Botulism (*C. botulinum* toxin), Plague (*Y. pestis*), Smallpox (*Variola major*), Tularemia (*F. tularensis*), and Viral Hemorrhagic Fevers (Ebola, Marburg). * **Category B:** Includes food safety threats (*Salmonella*, *Shigella*), *Brucella*, *Glanders*, and *Q fever*. * **Category C:** Emerging pathogens with potential for future mass dissemination, such as **Nipah virus** and **Hantavirus**.
Question 109: Viruses can be grown using all of the following methods except:
- A. Tissue culture
- B. Embryonated eggs
- C. Animals
- D. Enriched media (Correct Answer)
Explanation: **Explanation:** The fundamental principle of virology is that **viruses are obligate intracellular parasites**. They lack the cellular machinery (ribosomes, enzymes) required for independent metabolism and protein synthesis. Therefore, they cannot grow on non-living, artificial culture media, regardless of how "enriched" the nutrients are. **Why "Enriched Media" is the correct answer:** Enriched media (like Blood Agar or Chocolate Agar) contain nutrients to support the growth of fastidious **bacteria**. Since viruses require a living host cell to replicate by hijacking its molecular machinery, they will never grow on inanimate agar or broth. **Analysis of other options:** * **Tissue Culture:** This is the most common modern method. It uses living cell lines (e.g., HeLa, Vero, WI-38) to provide the necessary intracellular environment for viral replication. * **Embryonated Eggs:** A classic method (typically using 10–12 day old chick embryos). Different viruses are inoculated into specific sites like the chorioallantoic membrane (Poxvirus), allantoic cavity (Influenza), or yolk sac (Chlamydia/Rickettsia). * **Animals:** The oldest method, still used for primary isolation of certain viruses (e.g., Coxsackie virus in suckling mice) and for studying pathogenesis or immune responses. **High-Yield Clinical Pearls for NEET-PG:** * **Detection of viral growth:** In tissue culture, growth is identified by the **Cytopathic Effect (CPE)**, such as cell swelling, fusion (syncytia), or inclusion bodies (e.g., Negri bodies in Rabies). * **Steinhardt’s Method:** The first use of tissue culture to grow Vaccinia virus. * **Influenza Vaccine:** Most commercial influenza vaccines are still produced using the **Embryonated Egg** method (allantoic cavity).
Question 110: Which gene encodes the HTLV tax protein?
- A. Gag
- B. Pol
- C. Env
- D. pX (Correct Answer)
Explanation: **Explanation:** Human T-cell Lymphotropic Virus (HTLV-1) is a complex retrovirus. Unlike simple retroviruses, it contains a unique **pX region** located at the 3' end of its genome, which is essential for its oncogenic potential. **1. Why pX is correct:** The **pX region** encodes several non-structural regulatory proteins, most notably **Tax** and **Rex**. * **Tax protein** is a potent transcriptional activator. It upregulates the expression of cellular genes involved in T-cell proliferation (like IL-2 and IL-2 receptors) and inactivates tumor suppressor genes (like p53). This leads to the immortalization of T-cells, eventually causing **Adult T-cell Leukemia/Lymphoma (ATL)**. **2. Why other options are incorrect:** * **Gag (Group-specific antigen):** Encodes the internal structural proteins of the virus, such as the capsid (p24), nucleocapsid, and matrix proteins. * **Pol (Polymerase):** Encodes essential viral enzymes, including Reverse Transcriptase, Integrase, and Protease. * **Env (Envelope):** Encodes the surface glycoproteins (gp46) and transmembrane proteins (gp21) responsible for viral attachment and entry. **Clinical Pearls for NEET-PG:** * **HTLV-1 Association:** Strongly linked to **Adult T-cell Leukemia/Lymphoma (ATL)** (characterized by "flower cells" on peripheral smear) and **Tropical Spastic Paraparesis (TSP)** (a demyelinating disease). * **Transmission:** Similar to HIV (Blood, Sexual contact, and Breastfeeding). * **Tax Protein:** It is the primary oncogenic driver; it induces genomic instability and inhibits DNA repair. * **Rex Protein:** Regulates viral mRNA splicing and export from the nucleus.
Practice by Chapter
Virus Structure and Classification
Practice Questions
Viral Replication
Practice Questions
Pathogenesis of Viral Infections
Practice Questions
DNA Viruses: Herpesviruses
Practice Questions
DNA Viruses: Poxviruses and Adenoviruses
Practice Questions
Hepatitis Viruses
Practice Questions
RNA Viruses: Orthomyxoviruses
Practice Questions
RNA Viruses: Paramyxoviruses
Practice Questions
Enteroviruses and Rhinoviruses
Practice Questions
Arboviruses
Practice Questions
HIV and Retroviruses
Practice Questions
Oncogenic Viruses
Practice Questions
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free