Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1111: What is the best specimen for rabies diagnosis in a living person?

A. Corneal smear
B. Cerebrospinal fluid (CSF)
C. Biopsy of hair follicle from the neck (Correct Answer)
D. Brain biopsy

Explanation: **Explanation:** The diagnosis of rabies in a living patient (antemortem) relies on detecting the virus in tissues with high nerve density or active viral shedding. **Why Option C is Correct:** The **full-thickness skin biopsy from the nape of the neck** is considered the gold standard for antemortem diagnosis. Rabies virus is highly neurotropic; it travels via cutaneous nerves to the base of hair follicles. Using **Direct Fluorescent Antibody (DFA)** testing or RT-PCR on this biopsy specimen offers high sensitivity and specificity. The nape of the neck is preferred because it has a high density of hair follicles and sensory nerves. **Analysis of Incorrect Options:** * **A. Corneal smear:** While historically used, it is no longer preferred due to low sensitivity and the risk of eye injury during collection. * **B. Cerebrospinal fluid (CSF):** Viral RNA or antibodies are rarely detected in CSF early in the disease. It is more useful for ruling out other types of encephalitis than confirming rabies. * **D. Brain biopsy:** While the brain is the definitive site for diagnosis (looking for **Negri bodies**), it is an invasive procedure and is generally reserved for post-mortem examination. **NEET-PG High-Yield Pearls:** * **Post-mortem Gold Standard:** DFA on brain tissue (specifically the Hippocampus/Ammon’s horn and Cerebellum). * **Negri Bodies:** Intracytoplasmic, eosinophilic inclusion bodies found in neurons (absent in 20-30% of cases). * **Other Antemortem Samples:** Saliva (for RT-PCR) and Serum (for antibodies in unvaccinated individuals). * **Rule of Thumb:** No single test is 100% sensitive; a combination of skin biopsy, saliva, and serum is often used clinically.

Question 1112: Which of the following is NOT true regarding Hantavirus?

A. It is a DNA virus (Correct Answer)
B. It is carried by rodents
C. It causes recurrent respiratory infections
D. Hemorrhagic manifestations may occur

Explanation: ### Explanation **1. Why Option A is the correct answer:** Hantaviruses belong to the family **Bunyaviridae**. A fundamental characteristic of this family is that they are **enveloped, single-stranded RNA viruses** (specifically negative-sense, segmented RNA). Therefore, the statement that it is a DNA virus is incorrect. In the NEET-PG context, remembering the "ROB" mnemonic (Reovirus, Orthomyxovirus, Bunyavirus) for segmented RNA viruses is crucial. **2. Analysis of other options:** * **Option B (Carried by rodents):** This is true. Hantaviruses are **zoonotic**. They are primarily transmitted to humans through contact with the urine, saliva, or feces of infected rodents (like the deer mouse or cotton rat). * **Option C (Respiratory infections):** This is true. Hantavirus is the causative agent of **Hantavirus Pulmonary Syndrome (HPS)**, characterized by sudden onset flu-like symptoms progressing to severe respiratory failure and non-cardiogenic pulmonary edema. * **Option D (Hemorrhagic manifestations):** This is true. In many parts of the world (especially Asia and Europe), Hantavirus causes **Hemorrhagic Fever with Renal Syndrome (HFRS)**, presenting with fever, hemorrhage, and acute kidney injury. **3. High-Yield Clinical Pearls for NEET-PG:** * **Genome:** Segmented RNA (3 segments: Large, Medium, Small). * **Transmission:** Inhalation of aerosolized rodent excreta (No human-to-human transmission, except for the Andes virus). * **Classic Triad (HFRS):** Fever, hemorrhage, and renal failure. * **Key Serotype:** *Sin Nombre virus* is the most common cause of Hantavirus Pulmonary Syndrome in North America. * **Diagnosis:** Primarily via Serology (ELISA for IgM) or RT-PCR.

Question 1113: What is lysogenic conversion?

A. New properties in a bacterium due to integration of phage genome (Correct Answer)
B. Transfer of DNA from one bacterium to another by a bacteriophage
C. Transfer of free DNA
D. Transfer of genome during physical contact

Explanation: **Explanation:** **Lysogenic conversion** (also known as phage conversion) occurs when a temperate bacteriophage infects a bacterium and integrates its genome (prophage) into the bacterial chromosome. This integration results in the bacterium acquiring **new phenotypic properties** or functions that it did not previously possess. 1. **Why Option A is Correct:** The prophage carries genes that are expressed by the host bacterium. In medical microbiology, this is most significant when the phage carries **virulence factors** or **toxin genes**. For example, a non-pathogenic strain of *Corynebacterium diphtheriae* becomes pathogenic only after being "converted" by the **Beta-phage**, which carries the gene for the diphtheria toxin. 2. **Why Other Options are Incorrect:** * **Option B (Transduction):** This is the process where a bacteriophage acts as a vector to transfer bacterial DNA from one cell to another. It is a mechanism of horizontal gene transfer, not the acquisition of properties from the phage genome itself. * **Option C (Transformation):** This refers to the uptake of "naked" or free DNA from the surrounding environment by a competent bacterium. * **Option D (Conjugation):** This involves the transfer of genetic material (usually plasmids) through direct physical contact via a sex pilus. **High-Yield Clinical Pearls for NEET-PG:** Remember the mnemonic **"COBEDS"** for toxins acquired via lysogenic conversion: * **C** – **C**holera toxin (*Vibrio cholerae*) * **O** – **O** antigen of *Salmonella* * **B** – **B**otulinum toxin (*Clostridium botulinum*) * **E** – **E**rythrogenic toxin (*Streptococcus pyogenes*) * **D** – **D**iphtheria toxin (*Corynebacterium diphtheriae*) * **S** – **S**higa toxin (*Shigella* and EHEC)

Question 1114: Australian antigen is:

A. HB Ag
B. HBs Ag (Correct Answer)
C. HBV
D. None of the above

Explanation: **Explanation:** The **Australian antigen** is the historical name for the **Hepatitis B surface antigen (HBsAg)**. It was discovered in 1965 by Nobel laureate Baruch Blumberg in the serum of an Australian Aboriginal person while studying genetic polymorphisms. This discovery was pivotal as it led to the identification of the Hepatitis B virus (HBV) and the subsequent development of diagnostic tests and vaccines. **Analysis of Options:** * **HBsAg (Option B):** This is the correct answer. HBsAg is the envelope protein of the Hepatitis B virus. It is the first serological marker to appear in the blood during an acute infection (even before symptoms) and its persistence beyond 6 months indicates chronic infection. * **HB Ag (Option A):** This is a vague term. Hepatitis B has several specific antigens: HBsAg (surface), HBcAg (core), and HBeAg (pre-core/envelope). "HB Ag" does not specify which component is being referred to. * **HBV (Option C):** This refers to the entire Hepatitis B Virus (the Dane particle), which consists of the DNA genome, the core, and the surface envelope. The Australian antigen refers specifically to the surface component, not the whole virion. **High-Yield Clinical Pearls for NEET-PG:** * **Dane Particle:** The complete infectious 42nm virion of HBV. * **HBsAg:** The earliest marker of infection; used for mass screening of blood donors. * **Anti-HBs:** Indicates immunity (either from past infection or vaccination). * **Window Period:** The interval where HBsAg disappears but Anti-HBs has not yet appeared. During this time, **Anti-HBc IgM** is the only reliable marker of acute infection. * **HBeAg:** A marker of high viral replication and high infectivity.

Question 1115: Which virus is responsible for infectious mononucleosis?

A. RNA paramyxo virus
B. Varicella zoster virus
C. Epstein Barr virus (Correct Answer)
D. Coxsackie virus A 16

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is the primary causative agent of **Infectious Mononucleosis (IM)**, often referred to as the "Kissing Disease." EBV specifically infects B-lymphocytes by binding to the **CD21 receptor** (CR2). The characteristic clinical triad includes fever, pharyngitis, and lymphadenopathy. A hallmark of this infection is the presence of **Downey cells** (atypical T-lymphocytes) in the peripheral blood smear. **Analysis of Incorrect Options:** * **RNA Paramyxovirus:** This family includes viruses like Mumps (parotitis), Measles (Rubeola), and RSV. They do not cause infectious mononucleosis. * **Varicella Zoster Virus (HHV-3):** Responsible for Chickenpox (primary infection) and Herpes Zoster/Shingles (reactivation). It presents with vesicular rashes, not the mononucleosis syndrome. * **Coxsackie Virus A16:** This is the most common cause of **Hand-Foot-and-Mouth Disease (HFMD)**, characterized by vesicular eruptions on the palms, soles, and oral mucosa. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The **Paul-Bunnell Test** (detecting heterophile antibodies) is the classic screening test. * **Complication:** Avoid prescribing Ampicillin or Amoxicillin in suspected IM cases, as it frequently induces a **maculopapular rash**. * **Malignancies:** EBV is strongly associated with Burkitt’s Lymphoma (t 8;14), Nasopharyngeal Carcinoma, and Hodgkin’s Lymphoma. * **Hematology:** Look for absolute lymphocytosis with >10% atypical lymphocytes on a peripheral smear.

Question 1116: Which type of Human Papillomavirus (HPV) is considered low risk?

A. Type-16
B. Type-6 (Correct Answer)
C. Type-18
D. Type-31

Explanation: ### Explanation Human Papillomavirus (HPV) is a double-stranded DNA virus that infects epithelial cells. It is categorized into **Low-risk** and **High-risk** types based on its association with malignancy. **Why Type-6 is Correct:** **HPV Type-6** (along with Type-11) is classified as **Low-risk**. These types primarily cause benign proliferative lesions such as **Condyloma acuminatum** (anogenital warts) and **Laryngeal papillomatosis**. They rarely integrate their DNA into the host genome, meaning they do not typically lead to squamous cell carcinoma. **Analysis of Incorrect Options:** * **Type-16 (Option A):** This is the most oncogenic high-risk type globally. It is responsible for approximately 50-60% of cervical cancers and is also strongly associated with oropharyngeal and anal cancers. * **Type-18 (Option C):** The second most common high-risk type, accounting for about 10-15% of cervical cancers. It is particularly associated with cervical **adenocarcinoma**. * **Type-31 (Option D):** A high-risk type that, along with types 33, 45, 52, and 58, is a significant contributor to cervical intraepithelial neoplasia (CIN) and invasive cancer. **High-Yield Clinical Pearls for NEET-PG:** * **Oncogenesis:** High-risk types (16, 18) produce oncoproteins **E6** (inhibits **p53**) and **E7** (inhibits **pRb**), leading to uncontrolled cell cycle progression. * **Cytopathology:** The hallmark of HPV infection on a Pap smear is the **Koilocyte** (a cell with a perinuclear halo and wrinkled "raisinoid" nucleus). * **Vaccination:** The **9-valent vaccine (Gardasil 9)** covers low-risk types 6, 11 and high-risk types 16, 18, 31, 33, 45, 52, and 58.

Question 1117: Which of the following methods can be used to inactivate the rabies virus?

A. Phenol
B. UV radiation
C. BPL (beta-propiolactone)
D. All of the above (Correct Answer)

Explanation: The rabies virus is an enveloped, negative-sense, single-stranded RNA virus belonging to the **Rhabdoviridae** family. Because it possesses a lipid envelope and a delicate RNA genome, it is highly susceptible to various physical and chemical agents. ### **Explanation of Options** * **Phenol (A):** Historically used in the preparation of the Semple vaccine, phenol is a chemical disinfectant that denatures proteins and disrupts the viral envelope, effectively inactivating the virus. * **UV Radiation (B):** Like most RNA viruses, rabies is sensitive to ultraviolet light. UV radiation causes cross-linking and damage to the viral nucleic acids, preventing replication. * **Beta-propiolactone (BPL) (C):** This is the **agent of choice** for modern inactivated rabies vaccines (like PCECV or HDCV). BPL is an alkylating agent that permanently alters the viral genome, ensuring the virus cannot replicate while maintaining the antigenicity of the surface G-proteins. Since all three methods—chemical denaturation (Phenol), physical irradiation (UV), and alkylation (BPL)—are effective, **Option D is correct.** ### **High-Yield Clinical Pearls for NEET-PG** * **Sensitivity:** Rabies virus is also inactivated by heat (56°C for 30 mins), lipid solvents (ether, chloroform), and detergents (soap and water—this is why immediate wound washing is the most critical first step). * **Vaccine Evolution:** * **Semple Vaccine:** Phenol-inactivated (Neural tissue vaccine; now obsolete due to risk of Encephalomyelitis). * **Modern Vaccines:** BPL-inactivated (Cell culture vaccines; safer and more immunogenic). * **Negri Bodies:** These are pathognomonic intracytoplasmic inclusion bodies found in the hippocampus (Ammon’s horn) and cerebellum (Purkinje cells) of infected brains.

Question 1118: Chikungunya virus belongs to which family?

A. Enterovirus
B. Herpes virus
C. Togavirus (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Chikungunya virus** is an enveloped, single-stranded, positive-sense RNA virus. It belongs to the genus **Alphavirus** within the **Togaviridae (Togavirus)** family. It is primarily transmitted to humans through the bite of infected *Aedes aegypti* and *Aedes albopictus* mosquitoes. **Analysis of Options:** * **Togavirus (Correct):** The Togaviridae family is divided into two main genera: *Alphavirus* (includes Chikungunya, Ross River, and Eastern Equine Encephalitis viruses) and *Rubivirus* (includes Rubella). * **Enterovirus (Incorrect):** These are members of the *Picornaviridae* family (e.g., Poliovirus, Coxsackievirus). They are non-enveloped RNA viruses typically transmitted via the fecal-oral route, not by arthropod vectors. * **Herpes virus (Incorrect):** These are large, enveloped, double-stranded DNA viruses (e.g., HSV, VZV, CMV). They are known for establishing latency and are not classified as arboviruses. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** High fever, rash, and **severe debilitating polyarthralgia** (joint pain). The name "Chikungunya" derives from a Kimakonde word meaning "to become contorted," referring to the stooped posture of patients due to joint pain. * **Vector:** *Aedes albopictus* is often associated with outbreaks in temperate regions due to a specific mutation (E1-A226V) in the virus. * **Diagnosis:** IgM ELISA is the standard for diagnosis (appears after 5 days); RT-PCR is used during the acute viremic phase (days 1–3). * **Distinction:** Unlike Dengue, Chikungunya rarely causes shock or severe hemorrhage, but the joint pain can persist for months (chronic stage).

Question 1119: Human immunodeficiency virus (HIV) has been isolated from many body fluids. Which of the following is a major source of transmission?

A. Tears
B. Sweat
C. Semen (Correct Answer)
D. Urine

Explanation: **Explanation:** The transmission of Human Immunodeficiency Virus (HIV) depends on the **viral load** (concentration of the virus) within a specific body fluid and the presence of infected CD4+ T-cells or macrophages. **Why Semen is Correct:** HIV is found in high concentrations in **semen** and **vaginal secretions**, both as free virus particles and within infected mononuclear cells. Sexual transmission (predominantly via semen) remains the most common mode of HIV spread globally. Other major high-risk fluids include blood, breast milk, and cerebrospinal fluid. **Why Other Options are Incorrect:** * **Tears, Sweat, and Urine:** While HIV has been isolated in trace amounts from these fluids in research settings, the viral concentration is **insignificantly low** to pose a risk of transmission. These are considered non-infectious fluids unless they are visibly contaminated with blood. **High-Yield Clinical Pearls for NEET-PG:** * **Risk of Transmission:** The highest risk of transmission per act is via **blood transfusion** (approx. 90%), followed by vertical transmission (mother-to-child) and receptive anal intercourse. * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). During this time, the person is highly infectious despite a negative ELISA. * **Target Cells:** HIV primarily infects cells expressing the **CD4 receptor** and co-receptors **CCR5** (macrophages/early infection) or **CXCR4** (T-cells/late infection). * **Screening vs. Confirmation:** ELISA is the standard screening test (high sensitivity), while **Western Blot** was traditionally the confirmatory test (high specificity). However, current NACO guidelines emphasize the use of three different rapid antibody tests for diagnosis.

Question 1120: Which of the following statements regarding viral replication and diseases is FALSE?

A. The general stages of viral replication include penetration, uncoating, macromolecular synthesis (transcription, protein synthesis, replication), assembly, and release by budding and lysis.
B. DNA viruses include Adenovirus, Human papilloma virus, Parvovirus B-19, BK and JC polyomavirus, and Poliovirus. (Correct Answer)
C. Ganciclovir is used for Cytomegalovirus (CMV) infections and acts on viral DNA.
D. Viruses that can cause congenital and neonatal disease include HSV-2, Echovirus, CMV, Parvovirus B19, VZV, HIV, and Hepatitis viruses.

Explanation: **Explanation:** The correct answer is **B** because it contains a factual error regarding viral classification. While Adenovirus, HPV, Parvovirus B19, and Polyomaviruses (BK/JC) are indeed DNA viruses, **Poliovirus** is a member of the *Picornaviridae* family, which consists of **single-stranded, positive-sense RNA viruses**. **Analysis of Options:** * **Option A (True):** This accurately describes the universal replication cycle. Viruses must attach, enter (penetration), release their genome (uncoating), hijack host machinery for synthesis, and finally exit via lysis (common in non-enveloped viruses) or budding (common in enveloped viruses). * **Option C (True):** Ganciclovir is the first-line treatment for CMV. It is a nucleoside analog that inhibits viral DNA polymerase, thereby terminating DNA chain elongation. * **Option D (True):** These viruses are well-known causes of vertical transmission. While the "TORCH" acronym is classic, the list of pathogens causing congenital/neonatal infections is broader, including HIV, Hepatitis B, and Enteroviruses (Echovirus). **High-Yield NEET-PG Pearls:** * **DNA Virus Mnemonic:** "HHAPPPPy" viruses (Herpes, Hepadna, Adeno, Papilloma, Polyoma, Parvo, Pox). * **The "Smallest" Rule:** **Parvovirus B19** is the smallest DNA virus and is the only one that is **single-stranded** (ssDNA). * **Poliovirus Key Facts:** It is a non-enveloped RNA virus, transmitted via the fecal-oral route, and specifically targets the **anterior horn cells** of the spinal cord, leading to lower motor neuron (LMN) paralysis.

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Virology — MCQs

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