Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 701: What is the most common CNS lesion caused by in HIV patients?

A. Cryptococcus (Correct Answer)
B. Herpes simplex
C. Neurocysticercosis
D. Mucormycosis

Explanation: **Explanation:** In the context of HIV/AIDS, **Cryptococcal meningitis** (caused by *Cryptococcus neoformans*) is the most common fungal infection and the overall most common cause of central nervous system (CNS) lesions/infections, particularly when the CD4 count falls below 100 cells/mm³. It typically presents as subacute meningitis rather than a focal mass lesion. **Analysis of Options:** * **A. Cryptococcus (Correct):** It is the leading cause of opportunistic CNS infection in HIV patients worldwide. Diagnosis is typically made via India Ink preparation of CSF (showing encapsulated yeast) or the highly sensitive Cryptococcal Antigen (CrAg) test. * **B. Herpes simplex:** While HSV can cause sporadic encephalitis in the general population, it is not the *most common* CNS complication in HIV. In HIV patients, CMV or JC virus (PML) are more frequently discussed viral CNS complications. * **C. Neurocysticercosis:** This is the most common cause of seizures and focal CNS lesions in the *general population* in developing countries (like India), but it is not specifically linked to the immunocompromised state of HIV. * **D. Mucormycosis:** This is an angioinvasive fungal infection primarily seen in patients with uncontrolled diabetes mellitus (ketoacidosis) or severe neutropenia, rather than being the most common lesion in HIV. **High-Yield Clinical Pearls for NEET-PG:** * **Most common CNS mass lesion in HIV:** Toxoplasmosis (shows ring-enhancing lesions on MRI). * **Most common CNS infection in HIV:** Cryptococcal meningitis. * **CSF Finding in Cryptococcus:** Low glucose, high protein, and positive **India Ink** (halos). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole maintenance. * **Latex Agglutination:** Detects the capsular polysaccharide antigen and is more sensitive than India Ink.

Question 702: Infectious mononucleosis is caused by EBV. Which of the following statements about infectious mononucleosis is FALSE?

A. Caused by Epstein-Barr virus
B. Also called the kissing disease
C. Diagnosed by the Paul-Bunnel test
D. Caused by an RNA virus (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**, as Epstein-Barr Virus (EBV) is a **DNA virus**, not an RNA virus. EBV belongs to the *Herpesviridae* family (specifically Gammaherpesvirinae, Human Herpesvirus 4). It possesses a linear, double-stranded DNA genome. **Analysis of Options:** * **Option A (True):** EBV is the primary etiological agent of Infectious Mononucleosis (IM). It specifically infects B-lymphocytes via the **CD21 receptor** (also known as CR2). * **Option B (True):** It is famously called "Kissing Disease" because the virus is shed in the oropharynx and primarily transmitted through **saliva**. * **Option C (True):** The **Paul-Bunnell test** is a classic diagnostic tool that detects **heterophile antibodies**. These are IgM antibodies produced during IM that agglutinate sheep or horse red blood cells. **NEET-PG High-Yield Pearls:** * **Atypical Lymphocytes:** The characteristic hematological finding in IM is the presence of **Downey cells** (activated T-cells/CD8+ cells reacting against infected B-cells). * **Triad of IM:** Fever, pharyngitis, and lymphadenopathy (typically posterior cervical). * **Ampicillin Rash:** Patients with IM who are mistakenly treated with Ampicillin or Amoxicillin often develop a characteristic maculopapular rash. * **Associated Malignancies:** EBV is strongly linked to Burkitt Lymphoma (starry-sky appearance), Nasopharyngeal Carcinoma, and Hodgkin Lymphoma. * **Diagnostic Alternative:** The **Monospot test** is the modern rapid screening equivalent of the Paul-Bunnell test.

Question 703: What is the most common mode of transmission of the poliovirus?

A. Droplet infection
B. Fecal-oral route (Correct Answer)
C. Blood transfusion
D. Venereal transmission

Explanation: **Explanation:** **Poliovirus** is an enterovirus belonging to the *Picornaviridae* family. The primary and most common mode of transmission is the **fecal-oral route**. The virus is ingested through contaminated water or food, multiplies in the oropharyngeal and intestinal mucosa (specifically in Peyer’s patches), and is subsequently excreted in high concentrations in the feces for several weeks. While the virus can be found in the throat shortly after infection, fecal shedding is the most significant driver of community transmission, especially in areas with poor sanitation. **Analysis of Incorrect Options:** * **A. Droplet infection:** While poliovirus can be detected in oropharyngeal secretions during the first week of illness, respiratory spread is rare and considered a minor route compared to the fecal-oral path. * **C. Blood transfusion:** Although a transient viremia occurs during the pathogenesis of polio (leading to CNS involvement), the virus is not typically transmitted via blood products. * **D. Venereal transmission:** Poliovirus is not a sexually transmitted infection (STI); it lacks the biological characteristics for venereal spread. **High-Yield Clinical Pearls for NEET-PG:** * **Specimen of choice:** For diagnosis, **stool** is the most reliable sample as the virus is excreted for 6–8 weeks. * **Pathogenesis:** The virus attaches to the **CD155 receptor** (PVR) on host cells. * **Target Cells:** It specifically destroys the **anterior horn cells** of the spinal cord, leading to asymmetrical flaccid paralysis. * **Vaccination:** India was declared Polio-free in 2014. Currently, the **bivalent Oral Polio Vaccine (bOPV)** and **Inactivated Polio Vaccine (IPV)** are used in the National Immunization Schedule.

Question 704: A patient is seen 1 month post-renal transplant with fever. Which of the following is the most likely organism responsible?

A. Polyoma virus/BK virus
B. Hepatitis C virus (Correct Answer)
C. Varicella virus
D. HHV-6

Explanation: In post-renal transplant patients, the timing of infection is the most critical diagnostic clue. Infections are generally categorized into three phases: **1. The Correct Answer: Hepatitis C Virus (HCV)** The first month post-transplant (Early Phase) is dominated by infections present in the recipient prior to transplant or those transmitted via the donor organ. **Hepatitis C** and Hepatitis B are frequently pre-existing or donor-derived. During this period, the high dose of induction immunosuppression can lead to the reactivation or exacerbation of these viral loads. **2. Analysis of Incorrect Options:** * **Polyoma virus (BK virus):** Typically causes BK virus-associated nephropathy (BKVAN) much later, usually **3 to 6 months** post-transplant, as it requires sustained immunosuppression to reactivate in the graft. * **HHV-6:** While it can occur early, it most commonly manifests between **2 to 6 weeks** (peaking at 1 month) but is statistically less common as a primary cause of fever compared to pre-existing viral states or surgical complications in the first month. * **Varicella Zoster Virus (VZV):** Reactivation (Shingles) or primary infection typically occurs in the late phase, usually **after 6 months**, when maintenance immunosuppression is ongoing. **Clinical Pearls for NEET-PG:** * **<1 Month:** Donor-derived infections (HCV, HBV, HIV) or surgical site infections (MRSA, Gram-negatives). * **1–6 Months:** Opportunistic infections due to peak immunosuppression (**CMV** is the most common, followed by EBV, HHV-6, and *Pneumocystis jirovecii*). * **>6 Months:** Community-acquired infections and late viral reactivations (VZV, BK virus). * **High-Yield:** CMV is the most common viral pathogen overall, but it rarely presents in the first 2 weeks; it typically peaks at 1–3 months.

Question 705: Hepatitis B virus in infected people can be detected in all of the following bodily fluids, EXCEPT:

A. Semen
B. Saliva
C. Stool (Correct Answer)
D. Blood

Explanation: **Explanation:** The Hepatitis B Virus (HBV) is a blood-borne pathogen primarily transmitted through parenteral, sexual, and perinatal routes. The presence of the virus in bodily fluids depends on the degree of viremia and the permeability of mucosal barriers. **Why Stool is the Correct Answer:** Unlike Hepatitis A and Hepatitis E, which are transmitted via the **fecal-oral route** and excreted in feces, Hepatitis B is **not found in stool**. The virus is highly sensitive to the bile salts and proteolytic enzymes present in the gastrointestinal tract, which degrade the viral envelope, rendering it non-infectious and undetectable in feces. **Analysis of Incorrect Options:** * **Blood:** This is the primary vehicle for HBV. It contains the highest concentration of infectious virions (Dane particles) and viral antigens (HBsAg). * **Semen & Vaginal Secretions:** HBV is present in significant concentrations in genital fluids, making sexual contact a major route of transmission. * **Saliva:** While the concentration is lower than in blood, HBV DNA and HBsAg are detectable in saliva. Although inefficient, transmission via human bites or shared items contaminated with saliva is biologically possible. **NEET-PG High-Yield Pearls:** * **Concentration Gradient:** HBV concentration is **High** in blood/serum; **Moderate** in semen, vaginal fluid, and saliva; and **Insignificant/Absent** in stool, urine, sweat, and tears. * **Infectivity:** HBV is 50–100 times more infectious than HIV and can survive on environmental surfaces for at least 7 days. * **Marker of Infectivity:** The presence of **HBeAg** in any of these fluids correlates with high viral replication and maximum infectivity.

Question 706: A 15-year-old girl presents with symptoms suggestive of rabies. What is the characteristic shape of the rabies virus?

A. Brick shape
B. Icosahedral shape
C. Bullet shape (Correct Answer)
D. Rod shape

Explanation: **Explanation:** The correct answer is **C. Bullet shape**. The Rabies virus belongs to the **Rhabdoviridae** family (genus *Lyssavirus*). Under electron microscopy, it exhibits a highly characteristic **bullet-shaped** morphology. This shape is formed by a cylindrical nucleocapsid surrounded by a lipid envelope containing glycoprotein spikes. One end of the virion is typically rounded (hemispherical), while the other is flat or concave. **Analysis of Incorrect Options:** * **A. Brick shape:** This is characteristic of the **Poxviridae** family (e.g., Variola and Molluscum contagiosum). These are the largest and most complex viruses. * **B. Icosahedral shape:** This is the most common viral symmetry, seen in many DNA viruses (like Herpesvirus and Adenovirus) and some RNA viruses (like Poliovirus). * **D. Rod shape:** This is typical of certain plant viruses (e.g., Tobacco Mosaic Virus) or filamentous viruses like **Ebola** (Filoviridae), which are long and thread-like rather than bullet-shaped. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** These are pathognomonic intracytoplasmic, eosinophilic inclusion bodies found most commonly in the **Purkinje cells of the cerebellum** and pyramidal cells of the **hippocampus**. * **Genome:** It is a negative-sense, single-stranded RNA virus. * **Pathogenesis:** The virus travels via **retrograde axonal transport** through peripheral nerves to the CNS. * **Prophylaxis:** Post-exposure prophylaxis (PEP) includes wound cleaning, Rabies Immunoglobulin (RIG), and the modern cell-culture vaccine (given on days 0, 3, 7, 14, and 28).

Question 707: Lymphoid tissue is the site of latent infection for which of the following herpes viruses?

A. Cytomegalovirus
B. Epstein barr virus (Correct Answer)
C. Herpes simplex virus type 1
D. Herpes simplex virus type 2

Explanation: **Explanation:** The hallmark of the **Herpesviridae** family is the ability to establish lifelong **latent infections**, where the virus remains dormant in specific host cells and can reactivate later. **Why Epstein-Barr Virus (EBV) is correct:** EBV (Human Herpesvirus 4) primarily infects **B-lymphocytes** and epithelial cells. After the initial infection (often presenting as Infectious Mononucleosis), the virus establishes latency in the **memory B-cells** located within **lymphoid tissues** (tonsils, spleen, and lymph nodes). It utilizes the host's B-cell proliferation machinery to maintain its genome without killing the cell. **Analysis of Incorrect Options:** * **Herpes Simplex Virus Type 1 (HSV-1):** Establishes latency in the **sensory nerve ganglia**, most commonly the **Trigeminal ganglion**. It typically causes orolabial lesions. * **Herpes Simplex Virus Type 2 (HSV-2):** Establishes latency in the **sacral ganglia**. It is primarily associated with genital herpes. * **Cytomegalovirus (CMV):** Establishes latency in **monocytes, macrophages, and CD34+ myeloid progenitor cells** (bone marrow), rather than lymphoid tissue specifically. **High-Yield NEET-PG Pearls:** * **Alpha-herpesvirinae (HSV-1, 2, VZV):** Latency in **Neurons**. * **Beta-herpesvirinae (CMV, HHV-6, 7):** Latency in **Mononuclear cells/Glands**. * **Gamma-herpesvirinae (EBV, KSHV/HHV-8):** Latency in **Lymphoid tissue (B-cells)**. * **EBV Association:** It is linked to several malignancies, including Burkitt Lymphoma, Nasopharyngeal Carcinoma, and Hodgkin Lymphoma. * **Diagnostic Test:** The **Paul-Bunnell Test** (Heterophile antibody test) is the classic screening tool for EBV-induced Infectious Mononucleosis.

Question 708: Which virus is the most common cause of acute hemorrhagic conjunctivitis?

A. Coxsackievirus A24 (Correct Answer)
B. Newcastle disease virus
C. Measles virus
D. Mumps virus

Explanation: **Explanation:** **Acute Hemorrhagic Conjunctivitis (AHC)** is a highly contagious ocular infection characterized by sudden onset of painful, red eyes, subconjunctival hemorrhage, and lid edema. **Why Coxsackievirus A24 is correct:** The two primary etiologic agents of AHC are **Enterovirus 70 (EV70)** and **Coxsackievirus A24 variant (CVA24v)**. Both belong to the *Picornaviridae* family. While EV70 was historically the first identified cause of pandemics, **Coxsackievirus A24** is currently recognized as the most frequent cause of large-scale outbreaks and sporadic cases worldwide. These viruses are transmitted via the feco-oral route or direct contact with eye secretions. **Analysis of Incorrect Options:** * **B. Newcastle disease virus:** This is primarily a pathogen of poultry. It can cause mild, self-limiting conjunctivitis in humans (usually laboratory workers or poultry handlers), but it is not a common cause of AHC. * **C. Measles virus:** Measles typically presents with a non-purulent catarrhal conjunctivitis as part of its prodromal phase (along with cough and coryza), but it does not cause the characteristic hemorrhagic presentation. * **D. Mumps virus:** Mumps is primarily associated with parotitis and orchitis; ocular involvement is rare and usually manifests as dacryoadenitis or episcleritis, not hemorrhagic conjunctivitis. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Very short (24–48 hours). * **Key Feature:** "Apollo Conjunctivitis" is a synonym for AHC (named after the 1969 Apollo 11 mission during which an outbreak occurred). * **Neurological Complication:** Enterovirus 70 is specifically associated with a rare, polio-like **radiculomyelitis** (cranial nerve palsies or paralysis). * **Adenovirus:** While Adenovirus (Serotypes 8, 19, 37) causes **Epidemic Keratoconjunctivitis (EKC)**, it is less commonly associated with the rapid, widespread subconjunctival hemorrhage seen in AHC.

Question 709: CD21 receptors bind to which virus?

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

Explanation: ### Explanation The correct answer is **Epstein-Barr virus (EBV)**. **1. Why EBV is correct:** The Epstein-Barr virus (Human Herpesvirus 4) specifically targets **B-lymphocytes**. The primary mechanism of entry involves the binding of the viral envelope glycoprotein **gp350/220** to the **CD21** molecule (also known as Complement Receptor 2 or CR2) on the surface of B-cells. This interaction is the hallmark of EBV pathogenesis, leading to the immortalization of B-cells and the clinical manifestation of Infectious Mononucleosis. **2. Why other options are incorrect:** * **Cytomegalovirus (CMV):** Uses **Integrins (heparan sulfate proteoglycans)** as its primary cellular receptor, not CD21. * **Rabies virus:** Primarily binds to the **Nicotinic Acetylcholine Receptor (nAChR)** at the neuromuscular junction, as well as NCAM (Neural Cell Adhesion Molecule). * **Herpes simplex virus (HSV):** Utilizes **Heparan sulfate** for initial attachment and **Nectin-1** (or HVEM - Herpesvirus Entry Mediator) for stable entry into host cells. **3. NEET-PG High-Yield Clinical Pearls:** * **Receptor Mnemonic:** Remember **"EBV = B-cells = CD21"**. * **Atypical Lymphocytes:** In EBV infection (Infectious Mononucleosis), the "atypical lymphocytes" seen on a peripheral smear are actually **CD8+ T-cells** reacting against the infected B-cells. * **Associated Malignancies:** EBV is linked to Burkitt Lymphoma (t(8;14)), Nasopharyngeal Carcinoma, and Hodgkin Lymphoma. * **Diagnosis:** The **Paul-Bunnell Test** (Heterophile antibody test) is the classic screening tool.

Question 710: Erythema infectiosum (fifth disease), a self-limited disease of children, is caused by which of the following?

A. Measles
B. Parvovirus (Correct Answer)
C. Rubella
D. Human herpesvirus type 6

Explanation: **Explanation:** **Erythema infectiosum**, also known as **Fifth Disease**, is caused by **Parvovirus B19**, a small, non-enveloped, single-stranded DNA virus. The disease typically presents in children with a characteristic "slapped-cheek" rash on the face, followed by a reticular (lace-like) erythematous rash on the trunk and extremities. The pathogenesis involves the virus targeting and replicating in **erythroid progenitor cells** (via the P antigen receptor), which can lead to a temporary cessation of erythropoiesis. **Analysis of Incorrect Options:** * **A. Measles:** Caused by the Rubeola virus (Paramyxovirus). It presents with the "3 Cs" (Cough, Coryza, Conjunctivitis), Koplik spots, and a maculopapular rash that spreads cephalocaudally. * **C. Rubella:** Also known as German Measles. It presents with a milder rash, post-auricular/suboccipital lymphadenopathy, and Forchheimer spots on the soft palate. * **D. Human Herpesvirus type 6 (HHV-6):** Causes **Roseola Infantum** (Sixth Disease). It is characterized by a high fever that resolves abruptly, followed by the appearance of a maculopapular rash. **High-Yield Clinical Pearls for NEET-PG:** * **Aplastic Crisis:** Parvovirus B19 can cause life-threatening acute aplastic crisis in patients with high red cell turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis). * **Hydrops Fetalis:** Infection during pregnancy can lead to severe fetal anemia, high-output cardiac failure, and fetal death. * **Arthropathy:** In adults, infection often presents as symmetrical polyarthritis resembling rheumatoid arthritis. * **Diagnosis:** Detection of IgM antibodies or PCR for viral DNA.

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