Virology Practice Questions

Q: Which test is used for the diagnosis of HIV infection during the window period?

p24 antigen. **Explanation:** The **window period** in HIV infection is the interval between the initial infection and the production of detectable antibodies (usually 3–4 weeks). During this phase, standard antibody tests (ELISA) will yield a false negative result. **Why p24 antigen is the correct answer:** The **p24 antigen** is a structural protein of the HIV capsid. It is the first marker to appear in the blood, becoming detectable as early as **10–14 days** after infection, well before seroconversion (antibody production). Modern 4th-generation ELISA tests combine p24 antigen detection with antibody testing to significantly shorten the window period. **Analysis of Incorrect Options:** * **p18 antigen:** This is a matrix protein of HIV-1. While it is a structural component, it is not used as a primary diagnostic marker for early infection because it does not reach detectable levels as reliably or as early as p24. * **gp120 and gp41:** These are envelope glycoproteins. While they are highly immunogenic and used in **Western Blot** to confirm HIV infection by detecting the *antibodies* formed against them, the antigens themselves are not typically measured for early diagnosis during the window period. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest Marker:** HIV-RNA (detected by NAT/PCR) is the very first marker (detectable at ~10 days), followed by p24 antigen. * **Best Screening Test:** 4th Generation ELISA (p24 Ag + Ab combo). * **Confirmatory Test:** Western Blot (detects antibodies to gp41, gp120, and p24). * **Monitoring Progress:** CD4+ T-cell count is used to monitor immune status. * **Monitoring Treatment:** Viral load (HIV-RNA) is the best predictor of treatment efficacy and disease progression.

Q: Which virus reactivation is known to involve the eye?

Herpes zoster. **Explanation:** The correct answer is **Herpes zoster (Option A)**. **1. Why Herpes Zoster is Correct:** Herpes zoster is caused by the reactivation of the **Varicella-Zoster Virus (VZV)**, which remains latent in the sensory ganglia (like the trigeminal ganglion) after a primary chickenpox infection. When it reactivates along the **Ophthalmic division (V1) of the Trigeminal nerve**, it causes **Herpes Zoster Ophthalmicus (HZO)**. This typically presents with a painful vesicular rash in a dermatomal distribution and can lead to keratitis, uveitis, and secondary glaucoma. **2. Why other options are incorrect:** * **Cytomegalovirus (CMV):** While CMV causes retinitis (especially in HIV/AIDS patients with CD4 <50), it is generally considered an **opportunistic infection** or a manifestation of primary/persistent infection in the immunocompromised, rather than a classic "reactivation" syndrome defined by dermatomal or neural involvement like VZV. * **Epstein-Barr Virus (EBV):** EBV is primarily associated with infectious mononucleosis, Burkitt lymphoma, and nasopharyngeal carcinoma. It rarely involves the eye. * **Enterovirus 70:** This virus is a major cause of **Acute Hemorrhagic Conjunctivitis (AHC)**. However, this is an **acute primary infection** (often occurring in epidemics), not a reactivation of a latent virus. **3. NEET-PG High-Yield Pearls:** * **Hutchinson’s Sign:** Vesicles on the tip or side of the nose indicate involvement of the nasociliary branch of the trigeminal nerve and are highly predictive of ocular involvement in Herpes Zoster. * **Dendritic Ulcers:** While both HSV and VZV cause them, VZV ulcers are "pseudodendrites" (smaller, lack terminal bulbs, and are poorly stained with fluorescein) compared to the true dendrites of HSV. * **Treatment:** Oral Acyclovir, Valacyclovir, or Famciclovir started within 72 hours of rash onset.

Q: A microbiologist working on influenza virus in a lab observes reversal of hemagglutination. What is this phenomenon called?

Elution. ### Explanation **1. Why Elution is the Correct Answer:** The influenza virus possesses two major surface glycoproteins: **Hemagglutinin (HA)** and **Neuraminidase (NA)**. * **Hemagglutination:** Initially, the HA spikes bind to sialic acid receptors on Red Blood Cells (RBCs), forming a lattice (clumping). * **Elution:** Upon incubation at 37°C, the **Neuraminidase (NA)** enzyme acts as a "receptor-destroying enzyme." It cleaves the sialic acid bonds, releasing the virus from the RBC surface. This reversal of clumping, where the virus detaches and the RBCs settle to the bottom of the tube, is known as **Elution**. **2. Why Other Options are Incorrect:** * **A. Hemolysis:** This refers to the rupture of RBCs with the release of hemoglobin. While some viruses (like Mumps) can cause hemolysis, the reversal of clumping specifically describes elution. * **C. Complement Fixation:** This is an immunological test used to detect specific antibodies or antigens using the complement system. It is not a property of viral surface enzymes. * **D. Precipitation:** This occurs when a soluble antigen reacts with a soluble antibody to form an insoluble complex. Hemagglutination involves particulate antigens (cells), not soluble ones. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Neuraminidase Inhibitors:** Drugs like **Oseltamivir** and **Zanamivir** work by inhibiting the NA enzyme, thereby preventing the elution/release of new virions from host cells. * **Antigenic Drift vs. Shift:** Drift involves point mutations in HA/NA (epidemics); Shift involves genetic reassortment (pandemics). * **H1N1:** The "swine flu" strain is a classic example of antigenic shift. * **Diagnosis:** The Hemagglutination Inhibition (HI) test is the gold standard for detecting antibodies against influenza.

Q: HTLV-II has been implicated in the etiology of which condition?

Hairy cell leukemia. **Explanation:** **Human T-cell Lymphotropic Virus type II (HTLV-II)** is a retrovirus closely related to HTLV-I. While HTLV-I is the definitive causative agent of Adult T-cell Leukemia/Lymphoma (ATLL), **HTLV-II** has been specifically isolated from and implicated in the etiology of **Hairy Cell Leukemia (HCL)**, particularly certain atypical variants. Although the primary driver of HCL is the **BRAF V600E mutation**, the association with HTLV-II remains a classic high-yield association in viral oncogenesis. **Analysis of Incorrect Options:** * **B. AIDS:** This is caused by the Human Immunodeficiency Virus (HIV-1 and HIV-2), which targets CD4+ T-cells, leading to profound immunosuppression. * **C. Adult T-cell Lymphoma (ATLL):** This is caused by **HTLV-I**, not HTLV-II. HTLV-I is also associated with Tropical Spastic Paraparesis (TSP). * **D. Zinc deficiency:** This is a nutritional disorder leading to acrodermatitis enteropathica, impaired wound healing, and immune dysfunction; it has no viral etiology. **High-Yield Clinical Pearls for NEET-PG:** * **Hairy Cell Leukemia (HCL):** A B-cell neoplasm characterized by "hairy" cytoplasmic projections [1]. * **Key Marker:** **TRAP positive** (Tartrate-Resistant Acid Phosphatase). * **Immunophenotype:** CD11c, CD25, CD103, and Annexin A1 (most specific). * **Clinical Feature:** Massive splenomegaly and **"Dry tap"** on bone marrow aspiration due to increased reticulin fibrosis [1]. * **Genetic Hallmark:** **BRAF V600E** mutation is present in nearly 100% of classic HCL cases. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 612.

Q: A 32-year-old unvaccinated woman presented with fever, headache, malaise, and ear pain along with parotid gland swelling. A week later, her fever resolved, but she developed pelvic pain and tenderness. Which virus is the likely causative agent?

Mumps virus. ### Explanation **Correct Option: B. Mumps virus** The clinical presentation of fever, malaise, and **parotid gland swelling** (parotitis) is a classic manifestation of the Mumps virus. The subsequent development of pelvic pain and tenderness in a female patient indicates **oophoritis** (inflammation of the ovaries), which is a known complication of Mumps in post-pubertal females. In males, the equivalent complication is epididymo-orchitis. **Analysis of Incorrect Options:** * **A. Cytomegalovirus (CMV):** While CMV can cause sialadenitis (salivary gland inflammation) in immunocompromised patients, it typically presents as mononucleosis-like syndrome or congenital infections. It does not characteristically cause oophoritis. * **C. Rabies virus:** This neurotropic virus presents with hydrophobia, aerophobia, and encephalopathy following an animal bite. It does not involve the parotid glands or ovaries. * **D. Respiratory syncytial virus (RSV):** RSV is a leading cause of bronchiolitis and pneumonia in infants. It does not cause systemic involvement of the salivary glands or reproductive organs. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** Paramyxoviridae; **Genus:** Rubulavirus. * **Transmission:** Respiratory droplets. * **Most Common Complication:** Aseptic meningitis (often asymptomatic). * **Most Common Extra-salivary Site:** Orchitis (usually unilateral; rarely leads to sterility). * **Other Complications:** Pancreatitis (look for elevated serum amylase), sensorineural hearing loss (usually permanent), and myocarditis. * **Prevention:** Live attenuated vaccine (Jeryl Lynn strain) administered as part of the MMR vaccine.

Q: RSV causes all EXCEPT:

ARDS. Respiratory Syncytial Virus (RSV) is the most common cause of lower respiratory tract infections (LRTI) in infants and young children worldwide. **Explanation of the Correct Answer:** **Option B (ARDS)** is the correct answer because RSV typically causes localized respiratory disease rather than Acute Respiratory Distress Syndrome (ARDS). While severe RSV can lead to respiratory failure requiring mechanical ventilation, ARDS is a specific clinical syndrome characterized by diffuse alveolar damage and non-cardiogenic pulmonary edema, usually triggered by sepsis, trauma, or severe pneumonia (like COVID-19 or Influenza). RSV's primary pathology is focused on the bronchioles (bronchiolitis). **Explanation of Incorrect Options:** * **Option A & D (Coryza/Common Cold):** In older children and healthy adults, RSV most commonly presents as a mild upper respiratory tract infection (URTI) manifesting as coryza (nasal congestion, sneezing, sore throat) and the common cold. * **Option C (Bronchitis/Bronchiolitis):** RSV is the leading cause of **bronchiolitis** and can also cause bronchitis and pneumonia in infants. It leads to inflammation, mucus plugging, and narrowing of the small airways. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Cause:** RSV is the #1 cause of **Bronchiolitis** and **Pneumonia** in children under 1 year of age. * **Surface Proteins:** It possesses **G-protein** (for attachment) and **F-protein** (for fusion and entry). It lacks Hemagglutinin (H) and Neuraminidase (N), unlike other Paramyxoviruses. * **Cytopathology:** It induces the formation of **multinucleated giant cells (Syncytia)** via the F-protein. * **Prophylaxis:** **Palivizumab** (a monoclonal antibody against the F-protein) is used for high-risk preterm infants. * **Treatment:** **Ribavirin** (aerosolized) may be used in severe, hospitalized cases.

Q: Conjunctivitis is caused by all EXCEPT:

CMV. **Explanation:** The correct answer is **CMV (Cytomegalovirus)**. While CMV is a significant ocular pathogen, it primarily affects the **posterior segment** of the eye, causing **retinitis** (especially in immunocompromised patients like those with HIV/AIDS). It does not typically cause conjunctivitis. **Analysis of Options:** * **Adenovirus:** This is the **most common cause** of viral conjunctivitis. It presents as Pharyngoconjunctival Fever (Serotypes 3, 7) or Epidemic Keratoconjunctivitis (Serotypes 8, 19, 37), the latter being highly contagious and associated with subepithelial corneal infiltrates. * **Enterovirus 70 & Coxsackievirus A24:** These are the classic causative agents of **Acute Hemorrhagic Conjunctivitis (AHC)**. AHC is characterized by rapid onset, eyelid swelling, and prominent subconjunctival hemorrhages. These viruses belong to the Picornaviridae family and are known for causing large-scale outbreaks. **High-Yield Clinical Pearls for NEET-PG:** 1. **Adenovirus:** Look for "follicular conjunctivitis" and preauricular lymphadenopathy in clinical vignettes. 2. **CMV Retinitis:** Classically described as a **"Pizza-pie appearance"** or "Cottage cheese and ketchup" fundus due to retinal necrosis and hemorrhage. 3. **Herpes Simplex Virus (HSV):** A common cause of dendritic keratitis (corneal involvement), but can also cause follicular conjunctivitis. 4. **Chlamydia trachomatis:** Serotypes A, B, Ba, and C cause Trachoma (leading cause of infectious blindness), while D-K cause inclusion conjunctivitis.

Q: In HIV infection, gp120 envelope glycoproteins bind specifically to which cells?

CD4 T-cells. **Explanation:** The entry of HIV into host cells is a multi-step process initiated by the binding of the viral envelope glycoprotein **gp120** to specific receptors on the host cell surface. The primary receptor for HIV is the **CD4 molecule**. Therefore, HIV specifically targets cells expressing this marker, most notably **CD4+ T-helper cells**, but also macrophages and dendritic cells. * **Mechanism:** The gp120-CD4 interaction induces a conformational change in gp120, allowing it to bind to co-receptors (**CCR5** on macrophages/early infection or **CXCR4** on T-cells/late infection). This is followed by **gp41**-mediated fusion of the viral envelope with the host cell membrane. **Analysis of Incorrect Options:** * **A. CD8 T-cells:** These are cytotoxic T-cells that lack the CD4 receptor. While they are involved in the immune response *against* HIV, they are not the primary targets for viral entry. * **C. B-cells:** These cells are responsible for antibody production. While HIV causes B-cell dysregulation (hypergammaglobulinemia), they do not express CD4 and are not directly infected via gp120. * **D. NK cells:** Natural Killer cells are part of the innate immune system. They lack the CD4 receptor required for gp120 binding. **High-Yield NEET-PG Pearls:** 1. **gp120:** Responsible for **attachment** (docking) to the CD4 receptor. 2. **gp41:** Responsible for **fusion** and internalization (Targeted by the drug *Enfuvirtide*). 3. **CCR5 Mutation:** Individuals with a homozygous **CCR5-Δ32 mutation** are resistant to HIV infection. 4. **Maraviroc:** A CCR5 antagonist that prevents viral entry by blocking the co-receptor.

Q: Which of the following conditions is NOT associated with Human Herpesvirus 8 (HHV-8)?

Adult T cell lymphoma. **Explanation:** The correct answer is **Adult T-cell lymphoma (ATL)** because it is caused by **Human T-cell Lymphotropic Virus type 1 (HTLV-1)**, a retrovirus, rather than a herpesvirus. ATL is characterized by "flower cells" on peripheral smear and is endemic in regions like Japan and the Caribbean. **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi Sarcoma-associated Herpesvirus (KSHV), is an oncogenic virus that primarily infects B-cells and endothelial cells. It is associated with the following conditions: * **Kaposi Sarcoma (Option B):** A vascular tumor presenting as violaceous cutaneous nodules, commonly seen in AIDS patients. * **Primary Effusion Lymphoma (Option C):** Also known as **Body Cavity Lymphoma**, this is a rare B-cell lymphoma that presents as malignant effusions in the pleural, pericardial, or peritoneal spaces without a formal tumor mass. * **Multicentric Castleman’s Disease (Option D):** A lymphoproliferative disorder characterized by lymphadenopathy and systemic inflammation; the plasma cell variant is strongly linked to HHV-8. **High-Yield NEET-PG Pearls:** * **Transmission:** HHV-8 is primarily transmitted through saliva and sexual contact. * **Target Cells:** It encodes a viral homolog of **Cyclin D1**, which pushes the host cell into the S-phase, leading to uncontrolled proliferation. * **Association:** In Primary Effusion Lymphoma, co-infection with **EBV** (Epstein-Barr Virus) is frequently observed. * **Treatment:** Management of HHV-8 related diseases often involves Highly Active Antiretroviral Therapy (HAART) in HIV-positive patients.

Q: What is the most common cause of acute gastroenteritis?

Norovirus. **Explanation:** **Norovirus (Option A)** is currently the most common cause of acute gastroenteritis (AGE) worldwide across all age groups. While Rotavirus was historically the leading cause in children, the widespread implementation of the Rotavirus vaccine has shifted the epidemiology, making Norovirus the primary pathogen for both sporadic cases and large outbreaks (often associated with cruise ships, schools, and nursing homes). It is highly contagious due to its low infectious dose and resistance to common disinfectants like alcohol. **Why other options are incorrect:** * **Rotavirus (Option B):** Formerly the #1 cause in children under 5 years. It remains a significant cause in unvaccinated populations but has been surpassed by Norovirus in global prevalence. * **Salmonella (Option C):** A common cause of *bacterial* food poisoning (inflammatory diarrhea), but it is less frequent than viral etiologies in the general population. * **E. coli (Option D):** While Enterotoxigenic E. coli (ETEC) is the most common cause of *Traveler’s diarrhea*, it is not the most common cause of general acute gastroenteritis. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** Norovirus belongs to the *Caliciviridae* family (ssRNA, non-enveloped). * **Transmission:** Fecal-oral route; characteristically causes "winter vomiting disease." * **Key Feature:** It is the most common cause of **outbreaks** in closed settings. * **Diagnosis:** RT-PCR is the gold standard for detection in stool samples. * **Resistance:** Norovirus is resistant to alcohol-based hand sanitizers; handwashing with soap and water is essential for prevention.

Question 1

Which test is used for the diagnosis of HIV infection during the window period?

Accepted Answer

p24 antigen

Answer

p18 antigen

Answer

gp120 antigen

Answer

gp41 antigen

Question 2

Which virus reactivation is known to involve the eye?

Accepted Answer

Herpes zoster

Answer

Cytomegalovirus (CMV)

Answer

Epstein-Barr Virus (EBV)

Answer

Enterovirus 70

Question 3

A microbiologist working on influenza virus in a lab observes reversal of hemagglutination. What is this phenomenon called?

Accepted Answer

Elution

Answer

Hemolysis

Answer

Complement fixation

Answer

Precipitation

Question 4

HTLV-II has been implicated in the etiology of which condition?

Accepted Answer

Hairy cell leukemia

Answer

AIDS

Answer

Adult T-cell lymphoma

Answer

Zinc deficiency

Question 5

A 32-year-old unvaccinated woman presented with fever, headache, malaise, and ear pain along with parotid gland swelling. A week later, her fever resolved, but she developed pelvic pain and tenderness. Which virus is the likely causative agent?

Accepted Answer

Mumps virus

Answer

Cytomegalovirus

Answer

Rabies virus

Answer

Respiratory syncytial virus

Question 6

RSV causes all EXCEPT:

Accepted Answer

ARDS

Answer

Coryza in kids

Answer

Bronchitis

Answer

Common cold

Question 7

Conjunctivitis is caused by all EXCEPT:

Accepted Answer

CMV

Answer

Enterovirus 70

Answer

Coxsackievirus A 24

Answer

Adenovirus

Question 8

In HIV infection, gp120 envelope glycoproteins bind specifically to which cells?

Accepted Answer

CD4 T-cells

Answer

CD8 T-cells

Answer

B-cells

Answer

NK cells

Question 9

Which of the following conditions is NOT associated with Human Herpesvirus 8 (HHV-8)?

Accepted Answer

Adult T cell lymphoma

Answer

Castleman's disease

Answer

Kaposi sarcoma

Answer

Body cavity lymphoma

Question 10

What is the most common cause of acute gastroenteritis?

Accepted Answer

Norovirus

Answer

Rotavirus

Answer

Salmonella

Answer

E. coli

Virology — MCQs

Virology — MCQs

On this page

Practice by Chapter

Want unlimited practice?