Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 211: Which of the following is an RNA virus?

A. Hepatitis B virus
B. Hepatitis C virus (Correct Answer)
C. Herpes virus
D. Adenovirus

Explanation: **Explanation:** The correct answer is **Hepatitis C virus (HCV)**. Viruses are classified based on their genetic material into either DNA or RNA viruses. HCV belongs to the **Flaviviridae** family and possesses a single-stranded, positive-sense RNA genome. **Why the other options are incorrect:** * **Hepatitis B virus (HBV):** It is a **DNA virus** (Hepadnaviridae). Notably, it is the only hepatitis virus that contains DNA; all others (A, C, D, E) are RNA viruses. * **Herpes virus:** This is a family of large, enveloped, **double-stranded DNA** viruses (e.g., HSV, CMV, EBV, VZV). * **Adenovirus:** This is a non-enveloped, **double-stranded DNA** virus, commonly associated with respiratory infections and conjunctivitis. **High-Yield NEET-PG Clinical Pearls:** 1. **HCV Characteristics:** It is the most common cause of post-transfusion hepatitis and has a high rate of progression to **chronic hepatitis** (approx. 80%) and cirrhosis. 2. **DNA Virus Mnemonic:** Remember "HHAPPPy" viruses: **H**erpes, **H**epadna (HBV), **A**deno, **P**apova, **P**arvo (the only ssDNA), and **P**ox (the only DNA virus replicating in the cytoplasm). 3. **The "Exception" Rule:** All Hepatitis viruses are RNA **except** Hepatitis B. 4. **HCV Screening:** The screening test of choice is Anti-HCV antibodies (ELISA), while the gold standard for confirming active infection and monitoring treatment is **HCV-RNA PCR**.

Question 212: A nurse has been found to be seropositive for both HbsAg and HbeAg. What is the likely diagnosis?

A. Acute hepatitis B infection (Correct Answer)
B. Concurrent hepatitis B and hepatitis E infection
C. Chronic hepatitis B infection
D. Past history of hepatitis B infection

Explanation: ### Explanation The presence of **HBsAg** (Hepatitis B surface Antigen) indicates that the individual is currently infected with the Hepatitis B virus (HBV). The presence of **HBeAg** (Hepatitis B envelope Antigen) is a marker of **active viral replication** and high infectivity. **1. Why Option A is correct:** In the early phase of an **Acute Hepatitis B infection**, HBsAg is the first marker to appear. Shortly after, HBeAg appears, signifying that the virus is actively multiplying. While HBsAg can also be present in chronic states, the combination of these markers in a clinical scenario (especially in a healthcare worker) most commonly points toward an acute infection or the highly replicative phase of the disease. **2. Why the other options are incorrect:** * **Option B:** Hepatitis E is a feco-oral virus. Seropositivity for HBsAg and HBeAg is specific to HBV replication and does not provide evidence for a co-infection with HEV. * **Option C:** Chronic Hepatitis B is defined by the persistence of HBsAg for **more than 6 months**. While a chronic carrier can be HBeAg positive (immunotolerant or reactive phase), "Acute Infection" is the primary diagnosis for a new seropositive finding unless chronicity is specified. * **Option D:** A past history of infection would show **Anti-HBs** (antibodies) and **Anti-HBc IgG**, while HBsAg and HBeAg would be negative. ### NEET-PG High-Yield Pearls: * **HBsAg:** First marker to appear; indicates current infection (Acute or Chronic). * **HBeAg:** Indicates active replication and **high infectivity**. * **Anti-HBc IgM:** The best marker for diagnosing **Acute HBV** (especially during the "Window Period"). * **Anti-HBs:** Indicates **immunity** (either from recovery or vaccination). * **Window Period:** The interval when HBsAg disappears but Anti-HBs hasn't appeared yet; only **Anti-HBc IgM** is detectable.

Question 213: What is the usual incubation period for the appearance of symptoms in a rabid animal?

A. 2 days
B. 7 days
C. 10 days (Correct Answer)
D. 1 month

Explanation: **Explanation:** The correct answer is **10 days**. This specific timeframe is critical in clinical practice and veterinary public health for the management of potential rabies exposure. **1. Why 10 days is correct:** In rabid animals (specifically dogs and cats), the rabies virus only appears in the saliva **3 to 5 days before** the onset of clinical symptoms. Once symptoms appear, the animal typically dies within 3 to 7 days. Therefore, if an animal remains healthy and alive for **10 days** after biting a human, it is medically certain that the saliva did not contain the virus at the time of the bite, and the victim does not require post-exposure prophylaxis (PEP). **2. Analysis of incorrect options:** * **A. 2 days:** This is too short. While the virus may be present in the saliva, the progression to death or observable symptoms usually takes longer. * **B. 7 days:** While many rabid animals die within a week of symptom onset, the 10-day observation period provides a necessary safety margin to account for the pre-symptomatic shedding period. * **D. 1 month:** While the *incubation period* (time from infection to illness) in humans can be months, the *observation period* for domestic animals is standardized at 10 days based on the viral shedding kinetics in their salivary glands. **High-Yield Clinical Pearls for NEET-PG:** * **Observation Rule:** Only applies to **dogs, cats, and ferrets**. It does not apply to wild animals (who should be euthanized and tested immediately). * **Site of Action:** Rabies virus binds to **Nicotinic Acetylcholine Receptors** at the neuromuscular junction. * **Diagnosis:** The gold standard for diagnosis in animals is the **Direct Fluorescent Antibody (DFA)** test on brain tissue (looking for Negri bodies in Hippocampus/Cerebellum). * **Management:** If the animal develops signs of rabies or dies within the 10-day period, the human must immediately start/complete the full PEP regimen.

Question 214: Which pathogens adhere to respiratory epithelium?

A. RSV
B. Influenza
C. Parainfluenza
D. All (Correct Answer)

Explanation: **Explanation:** The primary step in the pathogenesis of respiratory viral infections is the **adhesion** of the virus to specific receptors on the respiratory epithelial cells. This process is mediated by specialized surface glycoproteins (ligands) that recognize host cell receptors. * **Influenza Virus:** Utilizes the **Hemagglutinin (HA)** protein to bind to **sialic acid** receptors on the host respiratory epithelium. This is the critical first step for viral entry and membrane fusion. * **Parainfluenza Virus:** Belongs to the Paramyxoviridae family and uses its **Hemagglutinin-Neuraminidase (HN)** spikes to attach to sialic acid receptors on the ciliated epithelial cells of the upper and lower respiratory tract. * **Respiratory Syncytial Virus (RSV):** Unlike Influenza, RSV lacks Hemagglutinin. Instead, it uses its **G-protein (Attachment protein)** to adhere to the respiratory epithelium and its **F-protein (Fusion protein)** to enter cells and form characteristic syncytia (multinucleated giant cells). Since all three viruses rely on initial adhesion to the respiratory epithelium to establish infection, **Option D (All)** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **RSV:** The most common cause of **Bronchiolitis** and pneumonia in infants. Look for "narrowing of the airway" and "wheezing" in clinical stems. * **Parainfluenza:** The most common cause of **Croup (Laryngotracheobronchitis)**; characterized by a "barking cough" and the "Steeple sign" on X-ray. * **Influenza:** Known for **Antigenic Drift** (point mutations causing epidemics) and **Antigenic Shift** (genetic reassortment causing pandemics). * **Receptor Specificity:** Human influenza viruses prefer **α 2,6-linkage** sialic acid receptors (found in the upper respiratory tract), while avian strains prefer **α 2,3-linkage**.

Question 215: A vaccine is available for one of the most common causes of infantile gastroenteritis. This vaccine has recently been recalled. Which virus is this?

A. Cytomegalovirus
B. Rotavirus (Correct Answer)
C. Varicella-zoster virus
D. Adenovirus

Explanation: **Explanation:** **Rotavirus** is the most common cause of severe, dehydrating infantile gastroenteritis worldwide. The question refers to the historical and clinical context of the **Rotashield** vaccine (the first-generation live-attenuated rhesus-based vaccine), which was recalled in 1999 due to a statistically significant association with **intussusception**. While newer vaccines like Rotarix and RotaTeq are now part of the Universal Immunization Programme (UIP) and are safe, the "recall" association remains a classic high-yield fact in medical exams. **Analysis of Incorrect Options:** * **A. Cytomegalovirus (CMV):** While a major cause of congenital infections, there is currently no licensed vaccine available for CMV. * **C. Varicella-zoster virus:** The vaccine (live-attenuated Oka strain) is widely used to prevent chickenpox and shingles and has not been recalled for gastroenteritis-related issues. * **D. Adenovirus:** While Adenovirus types 40 and 41 cause gastroenteritis, the available vaccine (oral, live) is only used for military recruits to prevent respiratory outbreaks (types 4 and 7), not for infantile diarrhea. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Rotavirus belongs to the *Reoviridae* family; it is a dsRNA virus with a wheel-like appearance (*Rota* = wheel) under electron microscopy. * **Pathogenesis:** It produces an enterotoxin called **NSP4**, which induces secretory diarrhea by increasing intracellular calcium. * **Diagnosis:** The gold standard for rapid detection in stool is **ELISA** (detecting VP6 antigen) or Latex Agglutination. * **Current Vaccines:** Rotavac (India) and Rotasiil are current vaccines used in India's UIP, administered orally at 6, 10, and 14 weeks.

Question 216: A viral organism was isolated from a painful blister on the lip of a girl. The agent was found to have double-stranded, linear DNA and was enveloped. What is the most likely causative organism?

A. Epstein-Barr virus (EBV)
B. Herpes simplex virus (HSV) (Correct Answer)
C. Cytomegalovirus (CMV)
D. Poxvirus

Explanation: ### Explanation **Correct Option: B. Herpes simplex virus (HSV)** The clinical presentation of a **painful blister on the lip** is classic for **Herpes Labialis** (cold sores), most commonly caused by **HSV-1**. From a virological perspective, HSV belongs to the *Herpesviridae* family, which is characterized by a **double-stranded, linear DNA** genome, an icosahedral capsid, and a lipid **envelope** derived from the host nuclear membrane. **Analysis of Incorrect Options:** * **A. Epstein-Barr virus (EBV):** While EBV is a herpesvirus (DS DNA, enveloped), it typically causes Infectious Mononucleosis (fever, pharyngitis, lymphadenopathy) or Burkitt lymphoma, not localized painful vesicles on the lip. * **C. Cytomegalovirus (CMV):** Also a herpesvirus, but it usually presents as a mononucleosis-like syndrome or opportunistic infections in immunocompromised patients (e.g., retinitis). It does not cause labial blisters. * **D. Poxvirus:** Although Poxviruses (like Molluscum contagiosum or Variola) have DS DNA and an envelope, their DNA is **complex/brick-shaped** rather than simple icosahedral, and they replicate in the **cytoplasm** (unlike other DNA viruses). Clinically, they do not present as typical herpetic vesicles. **NEET-PG High-Yield Pearls:** * **Tzanck Smear:** Look for **Multinucleated Giant Cells** and **Cowdry Type A** intranuclear inclusion bodies in HSV lesions. * **Latency:** HSV-1 remains latent in the **Trigeminal ganglion**, while HSV-2 remains latent in the **Sacral ganglion**. * **Enveloping:** Herpesviruses are unique because they acquire their envelope by budding through the **inner nuclear membrane** of the host cell. * **Drug of Choice:** Acyclovir (inhibits viral DNA polymerase).

Question 217: Which of the following is NOT true about Human Papillomavirus (HPV)?

A. Human Herpesvirus (HHV) activates oncogenes. (Correct Answer)
B. HPV activates cyclins.
C. HPV suppresses tumor suppressor genes.
D. HIV infection accelerates HPV infection.

Explanation: ### Explanation The correct answer is **Option A: Human Herpesvirus (HHV) activates oncogenes.** This statement is incorrect because the question asks about the characteristics of **Human Papillomavirus (HPV)**, not HHV. While some Herpesviruses (like EBV or HHV-8) are oncogenic, they represent a different family of viruses with distinct mechanisms. HPV-induced oncogenesis specifically relies on the interaction of its viral proteins with host cell cycle regulators. **Analysis of other options:** * **Option B & C (HPV activates cyclins and suppresses tumor suppressor genes):** These are **true** statements regarding HPV pathogenesis. High-risk HPV types (16 and 18) produce two key oncoproteins: * **E6:** Binds to and degrades **p53** (the "guardian of the genome"), preventing apoptosis. * **E7:** Binds to and inactivates the **Retinoblastoma (pRb)** protein. This releases E2F transcription factors, which **activate cyclins** (specifically Cyclin E and A), pushing the cell into the S-phase of the cell cycle. * **Option D (HIV accelerates HPV):** This is **true**. Immunosuppression in HIV patients leads to higher persistence of HPV, increased viral load, and a significantly faster progression from cervical intraepithelial neoplasia (CIN) to invasive cervical cancer. ### High-Yield Clinical Pearls for NEET-PG: * **High-risk HPV types:** 16, 18 (most common for cancer), 31, and 33. * **Low-risk HPV types:** 6, 11 (cause Condyloma acuminata/genital warts). * **Koilocytes:** The pathognomonic finding on a Pap smear (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Vaccine:** Gardasil-9 is a recombinant vaccine targeting L1 capsid proteins. * **Mechanism Mnemonic:** **6**-p53 (E**6** affects p53); **7**-Rb (E**7** affects p**R**b).

Question 218: Hepatitis A virus (HAV) is not destroyed by:

A. 0.5 ppm chlorine (Correct Answer)
B. 1:4000 formalin
C. UV radiation
D. Boiling at 100°C for 5 minutes

Explanation: **Explanation:** Hepatitis A Virus (HAV) is a non-enveloped, single-stranded RNA virus belonging to the *Picornaviridae* family. Its lack of a lipid envelope makes it exceptionally hardy and resistant to many common environmental stressors and disinfectants. **1. Why 0.5 ppm Chlorine is the correct answer:** HAV is notably resistant to low concentrations of chlorine. While standard water chlorination is effective against many bacteria, HAV requires higher concentrations for complete inactivation. It is inactivated by **free residual chlorine at 1.0 to 1.5 ppm** (parts per million). Therefore, a concentration of 0.5 ppm is insufficient to destroy the virus. **2. Analysis of Incorrect Options:** * **1:4000 Formalin:** HAV is inactivated by treatment with formalin (1:4000) at 37°C for 72 hours. This method is historically significant in the production of inactivated HAV vaccines. * **UV Radiation:** Like most viruses, HAV is susceptible to ultraviolet radiation, which damages its RNA genome, rendering it non-infectious. * **Boiling at 100°C for 5 minutes:** HAV is relatively heat-stable (withstanding 60°C for an hour), but it is reliably inactivated by high heat. Boiling at 100°C for 5 minutes (or even 1 minute) is sufficient to destroy the virus. **Clinical Pearls for NEET-PG:** * **Transmission:** Primarily Feco-oral route. * **Stability:** HAV remains stable at low pH (pH 1), allowing it to survive the gastric acid barrier. * **Disinfection:** To effectively kill HAV on surfaces, a 1:100 dilution of sodium hypochlorite (household bleach) is typically recommended. * **Diagnosis:** The presence of **IgM anti-HAV** is the gold standard for diagnosing acute infection. * **Vaccination:** It is a killed vaccine, usually given in two doses (0 and 6–12 months).

Question 219: Negri bodies are characteristic inclusions seen in which of the following viral infections?

A. Rabies (Correct Answer)
B. Smallpox
C. Trachoma
D. Lymphogranuloma venereum

Explanation: **Explanation:** **Negri bodies** are the hallmark histopathological finding in **Rabies**, caused by the Lyssavirus. These are **intracytoplasmic, eosinophilic, round-to-oval inclusion bodies** found specifically in the cytoplasm of neurons. They represent sites of viral replication and are most commonly found in the **Purkinje cells of the cerebellum** and the **pyramidal cells of the hippocampus (Ammon’s horn)**. Their presence is pathognomonic for Rabies diagnosis in post-mortem brain tissue. **Analysis of Incorrect Options:** * **Smallpox (Variola virus):** Characterized by **Guarnieri bodies**, which are eosinophilic intracytoplasmic inclusions found in epithelial cells. * **Trachoma & Lymphogranuloma venereum (LGV):** Both are caused by *Chlamydia trachomatis* (a bacterium, not a virus). They exhibit **Halberstaedter-Prowazek (HP) bodies**, which are basophilic intracytoplasmic inclusion bodies containing glycogen. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** Negri bodies are best demonstrated using **Sellers’ stain** (basic fuchsin and methylene blue). * **Location:** While Negri bodies are diagnostic, they are absent in about 20-30% of confirmed rabies cases. * **Other Viral Inclusions (Quick Revision):** * **Cowdry Type A:** Herpes Simplex Virus (HSV), Varicella-Zoster Virus (VZV), Yellow Fever (Torres bodies). * **Cowdry Type B:** Poliovirus. * **Owl’s Eye appearance:** Cytomegalovirus (CMV) – Large intranuclear inclusions. * **Molluscum bodies (Henderson-Patterson bodies):** Molluscum contagiosum.

Question 220: Which of the following is a characteristic feature of congenital rubella syndrome?

A. Prevention through vaccination during early pregnancy.
B. Intrauterine growth restriction (IUGR). (Correct Answer)
C. Cataract formation.
D. Deafness occurring exclusively if acquired before 16 weeks of gestation.

Explanation: **Explanation:** Congenital Rubella Syndrome (CRS) occurs due to transplacental transmission of the Rubella virus, primarily when a non-immune mother is infected during the first trimester. **1. Why Option B is Correct:** **Intrauterine Growth Restriction (IUGR)** is a hallmark feature of CRS. The virus inhibits mitosis and causes chromosomal breakage in fetal cells, leading to a generalized decrease in the number of cells in developing organs. This results in multi-organ involvement and significant growth retardation. **2. Analysis of Incorrect Options:** * **Option A:** Vaccination with the **MMR (Live Attenuated)** vaccine is strictly **contraindicated** during pregnancy due to the theoretical risk of fetal infection. Women should be vaccinated at least 4 weeks *before* conception. * **Option C:** While **Cataract** is a classic feature of CRS (part of Gregg’s Triad), the question asks for a "characteristic feature" in a context where IUGR is the most systemic manifestation. However, in many clinical vignettes, cataracts are diagnostic. In this specific MCQ structure, IUGR represents the fundamental pathological impact on the fetus. * **Option D:** Sensorineural deafness is the **most common** finding in CRS. While the risk is highest before 16 weeks, it is not "exclusive" to that period; defects can occur up to 20 weeks, though the severity decreases as gestational age increases. **3. NEET-PG High-Yield Pearls:** * **Gregg’s Triad:** Cataracts, Sensorineural Deafness, and Cardiac defects (most commonly **Patent Ductus Arteriosus - PDA**). * **Classic Sign:** "Blueberry muffin" spots (extramedullary hematopoiesis). * **Diagnosis:** Detection of **Rubella-specific IgM** in the newborn or persistence of IgG beyond 6–12 months. * **Teratogenic Window:** The risk of fetal malformation is highest (up to 85%) if the mother is infected during the first 12 weeks of pregnancy.

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Virology — MCQs

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