Virology — MCQs

One day after a casual sexual encounter with a bisexual man recently diagnosed as antibody-positive for HIV, a patient is concerned about whether she may have become infected. A negative antibody titer is obtained. To test for seroconversion, when is the earliest you should reschedule repeat antibody testing after this sexual encounter?

Q60Easy

In HIV infection, which immune cells are primarily targeted?

Virology Indian Medical PG Practice Questions and MCQs

Question 51: What is the most sensitive test for the diagnosis of herpes simplex (HSV) meningitis in a newborn infant?

A. HSV IgG antibody
B. HSV polymerase chain reaction (PCR) (Correct Answer)
C. HSV culture
D. Tzanck smear

Explanation: **Explanation:** The diagnosis of Herpes Simplex Virus (HSV) infections of the Central Nervous System (CNS), including meningitis and encephalitis, has been revolutionized by molecular diagnostics. **Why PCR is the Correct Answer:** **HSV Polymerase Chain Reaction (PCR)** of the Cerebrospinal Fluid (CSF) is currently the **gold standard** and the most sensitive test for diagnosing HSV meningitis and encephalitis. It has a sensitivity and specificity exceeding 95%. In newborns, whose immune systems are immature and where viral loads in the CSF can be low, the ability of PCR to amplify minute amounts of viral DNA makes it far superior to traditional methods. **Analysis of Incorrect Options:** * **HSV IgG antibody:** Serology is unreliable in acute neonatal infections. IgG may represent transplacental transfer of maternal antibodies rather than active fetal infection. Furthermore, antibody production takes weeks to develop, making it useless for acute diagnosis. * **HSV culture:** While viral culture is specific, it has very **low sensitivity** for CSF samples. HSV is difficult to isolate from the fluid compared to skin vesicles, often leading to false negatives. * **Tzanck smear:** This is a rapid bedside test used for **mucocutaneous lesions** (looking for multinucleated giant cells). It cannot be used on CSF and does not differentiate between HSV-1, HSV-2, or VZV. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Intravenous **Acyclovir** is the mainstay of treatment for neonatal HSV. * **HSV-2 vs. HSV-1:** In newborns, HSV-2 is more common (acquired via the birth canal) and is more frequently associated with meningitis, whereas HSV-1 is the classic cause of sporadic encephalitis in older children and adults. * **Temporal Lobe:** In adults, HSV encephalitis characteristically involves the temporal lobes; however, in neonates, the involvement is often global/diffuse.

Question 52: Epstein-Barr virus belongs to which of the following viral groups?

A. Retrovirus
B. Herpesvirus (Correct Answer)
C. RNA virus
D. Poxvirus

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is a member of the **Herpesviridae** family. Specifically, it belongs to the **Gammaherpesvirinae** subfamily. Like all herpesviruses, EBV is a large, enveloped virus with a linear, double-stranded DNA (dsDNA) genome and an icosahedral capsid. A hallmark of this group is the ability to establish **latency** within the host; EBV specifically remains latent in B-lymphocytes. **Analysis of Incorrect Options:** * **A. Retrovirus:** These are RNA viruses (e.g., HIV) that use reverse transcriptase to convert their RNA genome into DNA. EBV is a DNA virus and does not utilize reverse transcription. * **C. RNA virus:** EBV is a DNA virus. Remembering the "HHAPPPPy" mnemonic (Herpes, Hepadna, Adeno, Papilloma, Polyoma, Pox, Parvo) helps identify the DNA virus families. * **D. Poxvirus:** While Poxviruses are also dsDNA viruses, they are much larger, replicate in the cytoplasm (unlike EBV which replicates in the nucleus), and include viruses like Variola and Molluscum contagiosum. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Features:** EBV is the primary causative agent of **Infectious Mononucleosis** (Glandular fever), characterized by the triad of fever, pharyngitis, and lymphadenopathy. * **Diagnosis:** Look for **Atypical lymphocytes (Downey cells)** on peripheral smear and a positive **Paul-Bunnell test** (Heterophile antibodies). * **Associated Malignancies:** EBV is strongly linked to **Burkitt lymphoma** (t(8;14) translocation), **Nasopharyngeal carcinoma**, and Hodgkin lymphoma. * **Receptor:** EBV enters B-cells by binding to the **CD21** receptor (also known as CR2).

Question 53: A 70-year-old nursing home patient refused the influenza vaccine and subsequently developed influenza. She died of acute pneumonia 1 week after contracting the "flu." What is the most common cause of acute post-influenzal pneumonia?

A. Legionella
B. Listeria
C. Staphylococcus aureus (Correct Answer)
D. Klebsiella

Explanation: ### Explanation **Correct Answer: C. Staphylococcus aureus** **Why it is correct:** Influenza virus infection damages the respiratory epithelium and impairs the mucociliary escalator, creating a fertile environment for secondary bacterial invasion. While *Streptococcus pneumoniae* is the most common cause of community-acquired pneumonia overall, **Staphylococcus aureus** is the classic and most feared cause of **post-influenzal pneumonia**. It typically presents as a "biphasic illness" where the patient initially improves from the flu but then develops a sudden, severe worsening of symptoms (high fever, productive cough, and respiratory distress). *S. aureus* pneumonia is often necrotizing and can lead to complications like lung abscesses or pneumatoceles. **Why the other options are incorrect:** * **A. Legionella:** This is associated with contaminated water sources (AC systems) and typically presents with GI symptoms (diarrhea) and hyponatremia. It is not specifically linked to post-viral secondary infections. * **B. Listeria:** This primarily causes meningitis or sepsis in neonates, the elderly, or immunocompromised individuals, usually via contaminated food. It is not a common cause of pneumonia. * **D. Klebsiella:** This is a common cause of pneumonia in chronic alcoholics or diabetics, characterized by "currant jelly sputum" and upper lobe involvement. It is not the primary pathogen associated with post-influenza sequelae. **High-Yield Clinical Pearls for NEET-PG:** * **Top 3 pathogens for post-viral pneumonia:** 1. *S. pneumoniae* (most frequent), 2. *S. aureus* (most characteristic/severe), 3. *H. influenzae*. * **Radiology:** *S. aureus* pneumonia often shows patchy infiltrates that can rapidly progress to cavitary lesions. * **MRSA:** In the modern clinical setting, community-acquired MRSA (CA-MRSA) is an increasing cause of fatal post-influenza pneumonia in previously healthy young adults.

Question 54: Which of the following is NOT an RNA virus?

A. Ebola virus
B. Vesicular stomatitis virus
C. Simian 40 (Correct Answer)
D. Rabies

Explanation: **Explanation:** The core concept tested here is the classification of viruses based on their genetic material. Most animal viruses are either DNA or RNA viruses. **Correct Answer: C. Simian 40 (SV40)** Simian virus 40 is a **DNA virus** belonging to the *Polyomaviridae* family. It is a small, non-enveloped virus with a circular, double-stranded DNA genome. It is historically significant in microbiology for its role in oncogenesis studies and its accidental presence in early polio vaccines. **Why the other options are incorrect:** * **A. Ebola virus:** This belongs to the *Filoviridae* family. It is an enveloped, non-segmented, negative-sense **RNA virus** known for causing severe hemorrhagic fever. * **B. Vesicular stomatitis virus (VSV):** This is a member of the *Rhabdoviridae* family. It is a bullet-shaped, enveloped, negative-sense **RNA virus**. It is often used in laboratory settings as a model for the study of the life cycle of RNA viruses. * **D. Rabies virus:** Also a member of the *Rhabdoviridae* family (Genus *Lyssavirus*), it is a classic example of a negative-sense, single-stranded **RNA virus**. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for DNA Viruses:** "**HHAPPPPy**" viruses — **H**erpes, **H**epadna (Hepatitis B), **A**deno, **P**apilloma, **P**olyoma (includes SV40 and JC/BK viruses), **P**arvo (the only ssDNA), and **P**ox (the only DNA virus that replicates in the cytoplasm). * **SV40 Fact:** It is a potent DNA tumor virus that induces tumors by inhibiting the tumor suppressor proteins **p53** and **pRb** via its Large T-antigen. * All RNA viruses replicate in the cytoplasm **except** Influenza and Retroviruses (which have nuclear phases).

Question 55: Post-exposure prophylaxis is indicated in all of the following conditions EXCEPT:

A. HIV
B. Japanese encephalitis (Correct Answer)
C. Varicella zoster
D. Swine influenza

Explanation: **Explanation:** Post-exposure prophylaxis (PEP) is the administration of drugs or vaccines after a potential exposure to a pathogen to prevent the development of disease. **Why Japanese Encephalitis (JE) is the correct answer:** JE is a vector-borne viral disease transmitted by the *Culex* mosquito. There is **no recommended PEP** for JE because there is no evidence that post-exposure vaccination or antiviral therapy prevents the onset of the disease once a person has been bitten by an infected mosquito. Prevention relies solely on pre-exposure vaccination and vector control. **Analysis of other options:** * **HIV:** PEP is a standard of care involving a 28-day course of Antiretroviral Therapy (ART), ideally started within 2 hours (and no later than 72 hours) after needle-stick injuries or sexual exposure. * **Varicella Zoster:** PEP is indicated for susceptible individuals (e.g., immunocompromised, pregnant women, or neonates) using **Varicella-Zoster Immunoglobulin (VZIG)** or the Varicella vaccine within 3–5 days of exposure. * **Swine Influenza (H1N1):** Oseltamivir (Tamiflu) is indicated as PEP for high-risk individuals (e.g., household contacts with comorbidities) who have been exposed to a confirmed case. **High-Yield Clinical Pearls for NEET-PG:** * **Rabies:** The most critical PEP in India; involves wound cleaning, RIG (Immunoglobulin), and modern cell culture vaccines (ARV). * **Hepatitis B:** PEP involves HBIG and the Hep B vaccine series for unvaccinated individuals after percutaneous exposure. * **Meningococcal Meningitis:** Chemoprophylaxis with **Rifampicin** (drug of choice), Ciprofloxacin, or Ceftriaxone is indicated for close contacts.

Question 56: Which virus commonly causes encephalitis?

A. Herpes Simplex Virus Type 1 (HSV-I) (Correct Answer)
B. Epstein-Barr Virus (EBV)
C. Infectious mononucleosis
D. Cytomegalovirus (CMV)

Explanation: **Explanation:** **Herpes Simplex Virus Type 1 (HSV-1)** is the most common cause of sporadic, non-epidemic fatal viral encephalitis worldwide. The underlying medical concept involves the virus’s neurotropic nature; after primary infection (usually oropharyngeal), the virus remains latent in the **trigeminal ganglion**. Reactivation leads to spread along the olfactory or trigeminal nerves, typically involving the **temporal lobes** and orbital-frontal cortex, causing hemorrhagic necrosis. **Analysis of Incorrect Options:** * **Epstein-Barr Virus (EBV):** While EBV can cause neurological complications like meningitis or Guillain-Barré syndrome, it is a rare cause of primary encephalitis. * **Infectious Mononucleosis:** This is a clinical syndrome (primarily caused by EBV) characterized by fever, pharyngitis, and lymphadenopathy, rather than a specific viral agent of encephalitis. * **Cytomegalovirus (CMV):** CMV typically causes encephalitis in **immunocompromised** patients (e.g., HIV/AIDS) rather than the general population. It more commonly presents as retinitis or ventriculitis in these settings. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** PCR of Cerebrospinal Fluid (CSF) for HSV DNA. * **Imaging:** MRI is the modality of choice, showing characteristic hyperintensity in the **temporal lobes**. * **EEG Finding:** Periodic lateralizing epileptiform discharges (PLEDs). * **Treatment:** Immediate intravenous **Acyclovir** is the drug of choice; do not wait for viral culture results. * **Note:** While HSV-1 causes encephalitis in adults, **HSV-2** is a more common cause of meningitis in adults and encephalitis in neonates (acquired during birth).

Question 57: Maternal viremia most commonly spreads to the fetus in utero via which virus?

A. Cytomegalovirus (CMV) (Correct Answer)
B. Rubella virus
C. Human Immunodeficiency Virus (HIV)
D. Herpes Simplex Virus (HSV)

Explanation: **Explanation:** **Cytomegalovirus (CMV)** is the most common cause of congenital (in utero) infection worldwide. It spreads to the fetus primarily via **transplacental transmission** following maternal viremia. While many viruses can cross the placenta, CMV has the highest incidence, affecting approximately 0.2% to 2% of all live births. It is the leading non-genetic cause of sensorineural hearing loss and neurodevelopmental delay in children. **Analysis of Incorrect Options:** * **Rubella Virus:** While a classic cause of congenital rubella syndrome (CRS), its incidence has drastically declined due to widespread MMR vaccination. It is now much less common than CMV. * **HIV:** Transmission can occur in utero, but without intervention, the majority of mother-to-child transmission (MTCT) occurs **intrapartum** (during labor and delivery) or via breastfeeding, rather than purely through transplacental viremia. * **Herpes Simplex Virus (HSV):** Congenital (in utero) HSV is rare (only ~5%). The vast majority of neonatal HSV infections (85-90%) are acquired **perinatally** through direct contact with infected maternal genital secretions during birth. **High-Yield NEET-PG Pearls:** * **Most common intrauterine infection:** CMV. * **Most common clinical finding in CMV:** Most neonates are asymptomatic at birth (90%). * **Classic Triad of Congenital CMV:** Periventricular calcifications, microcephaly, and sensorineural hearing loss. * **Diagnosis:** Detection of CMV DNA in urine or saliva via PCR within the first 3 weeks of life is the gold standard. * **Key Distinction:** CMV = Periventricular calcifications; Toxoplasmosis = Diffuse intracerebral calcifications.

Question 58: What is the primary oncogene expression of HPV?

A. E1E2
B. E1E3
C. E3E5
D. E6E7 (Correct Answer)

Explanation: **Explanation:** Human Papillomavirus (HPV), particularly high-risk types 16 and 18, causes malignant transformation primarily through the expression of two early genes: **E6 and E7**. These are considered the primary oncogenes because they neutralize host tumor suppressor proteins. * **E6 Protein:** Binds to the **p53** tumor suppressor protein, leading to its ubiquitination and subsequent degradation via the proteasome. This prevents p53-mediated apoptosis and cell cycle arrest. * **E7 Protein:** Binds to the hypophosphorylated (active) form of the **Retinoblastoma (Rb)** protein. This releases the **E2F transcription factor**, which promotes the transition of the cell from the G1 to the S phase, leading to uncontrolled proliferation. **Analysis of Incorrect Options:** * **E1 & E2:** These are involved in viral DNA replication and transcriptional regulation. Loss of E2 (due to viral integration into the host genome) actually leads to the *overexpression* of E6 and E7. * **E3 & E5:** E3 is not a major functional gene in HPV. E5 has some oncogenic potential (interacting with growth factor receptors), but it is not the "primary" driver compared to E6/E7. **High-Yield Clinical Pearls for NEET-PG:** * **HPV 16 & 18:** Responsible for ~70% of Cervical Cancer cases. * **HPV 6 & 11:** Low-risk types causing Genital Warts (Condyloma acuminatum). * **Integration:** Malignancy occurs when the circular HPV genome breaks at the **E2 ORF** and integrates into the host DNA, removing the "brake" on E6/E7 expression. * **Screening:** Koilocytes (cells with perinuclear halo and wrinkled nuclei) on a Pap smear are pathognomonic for HPV infection.

Question 59: One day after a casual sexual encounter with a bisexual man recently diagnosed as antibody-positive for HIV, a patient is concerned about whether she may have become infected. A negative antibody titer is obtained. To test for seroconversion, when is the earliest you should reschedule repeat antibody testing after this sexual encounter?

A. 1 to 2 weeks
B. 16 to 20 weeks
C. 6 to 12 weeks (Correct Answer)
D. 12 to 15 weeks

Explanation: ### Explanation The core concept in this question is the **"Window Period"** of HIV infection. This is the interval between the initial infection and the point when the body produces enough antibodies to be detected by standard screening tests (ELISA). **1. Why 6 to 12 weeks is correct:** Following exposure, the immune system typically takes time to mount a detectable humoral response. While modern 4th-generation assays (which detect both p24 antigen and antibodies) can shorten this period, the traditional "window period" for reliable antibody seroconversion is **6 to 12 weeks**. By 3 months (12 weeks), more than 95% of infected individuals will test positive for antibodies. **2. Why the other options are incorrect:** * **A (1 to 2 weeks):** This is too early for an antibody response. During this phase (Eclipse phase), only viral RNA or p24 antigen might be detectable, but antibodies are absent. * **B & D (12 to 20 weeks):** While testing at these intervals would be accurate, they do not represent the *earliest* recommended time to detect seroconversion. Most patients seroconvert well before the 16-20 week mark. **3. Clinical Pearls for NEET-PG:** * **Order of Detection:** Viral RNA (7-10 days) → p24 Antigen (14-20 days) → HIV Antibodies (3-12 weeks). * **Screening Test:** ELISA is the standard screening tool (High sensitivity). * **Confirmatory Test:** Western Blot (detects antibodies to specific proteins like gp120, gp41, and p24) is the traditional confirmatory test, though modern algorithms often use HIV-1/HIV-2 differentiation assays. * **Post-Exposure Prophylaxis (PEP):** Should be started as soon as possible, ideally within **2 hours** and no later than **72 hours** after exposure, continuing for 28 days.

Question 60: In HIV infection, which immune cells are primarily targeted?

A. CD4+ T-lymphocytes (Correct Answer)
B. CD8+ T-lymphocytes
C. Monocytes
D. B-lymphocytes

Explanation: **Explanation:** The Human Immunodeficiency Virus (HIV) primarily targets cells expressing the **CD4 receptor** on their surface. The viral envelope glycoprotein **gp120** binds with high affinity to the CD4 molecule, which acts as the primary receptor. This binding, along with co-receptors (CCR5 or CXCR4), allows the virus to enter the cell. **CD4+ T-lymphocytes (Helper T-cells)** are the most abundant cells expressing this receptor and serve as the primary reservoir for viral replication, leading to their progressive depletion and the eventual development of AIDS. **Analysis of Options:** * **CD8+ T-lymphocytes:** These are cytotoxic T-cells that lack the CD4 receptor. While they play a role in the immune response *against* HIV, they are not the primary targets for infection. * **Monocytes:** While monocytes and macrophages do express low levels of CD4 and can be infected (acting as viral reservoirs), they are not the *primary* target compared to the massive depletion seen in CD4+ T-cells. * **B-lymphocytes:** These cells lack CD4 receptors and are not directly infected by HIV. However, they become dysfunctional due to the lack of "help" from depleted CD4+ T-cells. **High-Yield Clinical Pearls for NEET-PG:** * **Co-receptors:** **CCR5** is used by M-tropic strains (early infection), while **CXCR4** is used by T-tropic strains (late infection). * **Indicator of Progression:** The **CD4 count** is the best indicator of immune status, while **Viral Load (HIV RNA)** is the best predictor of disease progression. * **Critical Threshold:** A CD4 count **<200 cells/mm³** defines the transition to AIDS and necessitates prophylaxis for *Pneumocystis jirovecii*.

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

Virology — MCQs

Virology — MCQs

On this page

Practice by Chapter

Want unlimited practice?