Virology Practice Questions

Q: What culture media is used for the cultivation of HSV?

Chorioallantoic membrane. **Explanation:** **1. Why Chorioallantoic Membrane (CAM) is correct:** Herpes Simplex Virus (HSV) is an obligate intracellular parasite, meaning it cannot grow on artificial, non-living media. It requires living cells for replication. The **Chorioallantoic Membrane (CAM)** of an embryonated chicken egg is a classic method for cultivating several DNA viruses. When HSV is inoculated onto the CAM, it produces characteristic macroscopic lesions called **pocks**. The morphology of these pocks can help differentiate between HSV-1 (small pocks) and HSV-2 (large pocks). **2. Why the other options are incorrect:** * **A. Chocolate agar:** This is an enriched non-selective medium used for fastidious bacteria like *Neisseria* and *Haemophilus influenzae*. It contains lysed red blood cells but no living cells. * **B. Robertson's cooked-meat (RCM) broth:** This is an anaerobic culture medium used primarily for the cultivation of *Clostridium* species. * **C. Sabouraud's agar (SDA):** This is a selective medium used for the cultivation of fungi (yeasts and molds). **3. High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for HSV:** While CAM is used historically, **Cell Culture** (e.g., Human embryonic lung fibroblasts or Vero cells) is the modern gold standard. HSV produces a characteristic "ballooning" cytopathic effect (CPE). * **Tzanck Smear:** A rapid bedside test showing **multinucleated giant cells** with Cowdry Type A intranuclear inclusion bodies (Lipschutz bodies). * **Drug of Choice:** Acyclovir is the mainstay of treatment for HSV infections. * **Pock-forming viruses:** Besides HSV, Poxviruses (like Variola and Vaccinia) also produce pocks on CAM.

Q: Herpangina is caused by which virus?

Enterovirus. **Explanation:** **Herpangina** is a common febrile illness characterized by small, painful vesicular or ulcerative lesions on the posterior oropharynx (soft palate, tonsils, and uvula). **1. Why Enterovirus is correct:** Herpangina is primarily caused by **Coxsackievirus Group A** (specifically types A1–A10, A12, and A22), which belongs to the **Enterovirus** genus within the *Picornaviridae* family. These viruses are transmitted via the fecal-oral route or respiratory droplets. While Coxsackie A is the most common cause, other enteroviruses like Coxsackie B and Enterovirus 71 can also be implicated. **2. Why the other options are incorrect:** * **Rhinoviruses:** These are the most common cause of the "common cold" (upper respiratory tract infections). They typically cause rhinorrhea and nasal congestion rather than vesicular oropharyngeal lesions. * **Myxovirus:** This group includes Orthomyxoviruses (Influenza) and Paramyxoviruses (Measles, Mumps). These present with systemic respiratory symptoms or specific glandular swelling, not the localized posterior pharyngeal ulcers seen in Herpangina. * **Rabies virus:** A rhabdovirus that causes fatal encephalitis. Clinical features include hydrophobia, aerophobia, and spasms, but not vesicular pharyngitis. **Clinical Pearls for NEET-PG:** * **Herpangina vs. Hand-Foot-Mouth Disease (HFMD):** Both are caused by Coxsackie A (usually A16 for HFMD). The key difference is the distribution: Herpangina is limited to the **posterior** pharynx, while HFMD involves the anterior mouth, palms, and soles. * **Herpetic Gingivostomatitis:** Caused by HSV-1; unlike Herpangina, it typically involves the **anterior** mouth (gingiva and buccal mucosa) and presents with high fever and lymphadenopathy. * **Seasonality:** Enteroviral infections typically peak during summer and autumn months.

Q: Rapid progression of disease with full-blown manifestation in AIDS occurs when the T4 cell count falls below which value?

200/microliter. ### Explanation The progression of HIV infection to **AIDS (Acquired Immunodeficiency Syndrome)** is clinically and immunologically defined by the depletion of CD4+ T-lymphocytes (T4 cells). **1. Why Option C is Correct:** According to the CDC classification, a diagnosis of AIDS is made when the **CD4+ T-cell count falls below 200 cells/μL** (or a CD4 percentage of total lymphocytes <14%). At this critical threshold, the immune system is severely compromised, leading to the "full-blown" manifestation of the disease characterized by life-threatening **opportunistic infections** (e.g., *Pneumocystis jirovecii* pneumonia) and AIDS-defining malignancies (e.g., Kaposi sarcoma). **2. Analysis of Incorrect Options:** * **Option A (1000/μL):** This is within the normal range for a healthy adult (500–1500 cells/μL). * **Option B (500/μL):** Between 200–500 cells/μL, patients are in the "Intermediate Stage." While they may show symptoms like lymphadenopathy or oral thrush, they do not yet meet the criteria for AIDS. * **Option D (50/μL):** This represents **Advanced HIV infection**. At this level, patients are at risk for specific "late-stage" infections such as *Mycobacterium avium complex* (MAC) and Cytomegalovirus (CMV) retinitis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **Best Predictor of Progression:** CD4+ T-cell count. * **Best Predictor of Treatment Response:** Viral load (HIV RNA levels). * **Prophylaxis Thresholds:** * Start prophylaxis for *Pneumocystis jirovecii* when CD4 < 200. * Start prophylaxis for *Toxoplasma gondii* when CD4 < 100. * Start prophylaxis for *MAC* when CD4 < 50.

Q: Which of the following viral infections is NOT typically transmitted from human to human?

Japanese B encephalitis. ### Explanation The correct answer is **Japanese B encephalitis (JEV)**. **1. Why Japanese B Encephalitis is the correct answer:** Japanese Encephalitis is a **zoonotic viral infection** caused by a Flavivirus. It follows a complex transmission cycle involving **Culex mosquitoes** (primarily *Culex tritaeniorhynchus*) as the vector, and **pigs or water birds** as the natural reservoirs/amplifying hosts. Humans are considered **"dead-end hosts"** because the level of viremia in human blood is typically insufficient to infect a biting mosquito. Therefore, direct human-to-human transmission does not occur. **2. Why the other options are incorrect:** * **SARS (Severe Acute Respiratory Syndrome):** Caused by a coronavirus, it is highly contagious and spreads primarily through respiratory droplets and direct contact between humans. * **Bird’s Flu (Avian Influenza, e.g., H5N1):** While primarily a disease of birds, limited and non-sustained human-to-human transmission has been documented, especially among close family contacts. * **Poliomyelitis:** This is an exclusively human pathogen. It is transmitted via the **fecal-oral route** (and occasionally respiratory droplets) from one person to another. **3. NEET-PG High-Yield Pearls:** * **Vector for JEV:** *Culex tritaeniorhynchus* (breeds in stagnant water/rice fields). * **Amplifying Host:** Pigs (they develop high-level viremia without getting sick). * **Dead-end Hosts:** Humans and Horses. * **Vaccine:** Live attenuated (SA-14-14-2) and Inactivated (Jenvac) vaccines are available. * **Other "Dead-end" infections:** Rabies, West Nile Virus, and Hydatid disease (Echinococcosis).

Q: Infection with which of the following agents is particularly dangerous for anemic patients?

Parvovirus. **Explanation:** **1. Why Parvovirus B19 is the Correct Answer:** Parvovirus B19 is uniquely dangerous for anemic patients because it has a specific tropism for **erythroid progenitor cells**. The virus enters these cells via the **P-antigen** (globoside) receptor and replicates within them, leading to direct cytotoxicity and the temporary cessation of erythropoiesis. In healthy individuals, this brief pause in red blood cell (RBC) production is clinically silent. However, in patients with high RBC turnover (e.g., **Sickle Cell Anemia, Hereditary Spherocytosis, Thalassemia**), the bone marrow cannot compensate for the loss. This results in a life-threatening **Aplastic Crisis**, characterized by a sudden drop in hemoglobin and a dangerously low reticulocyte count. **2. Why Other Options are Incorrect:** * **Adenovirus:** Primarily causes respiratory infections, conjunctivitis (pink eye), and hemorrhagic cystitis. It does not target erythroid precursors. * **Cytomegalovirus (CMV):** A member of the Herpesviridae family, it typically causes infectious mononucleosis-like symptoms or severe systemic disease in immunocompromised hosts (retinitis, colitis), but not selective bone marrow suppression of RBCs. * **Herpes Simplex Virus (HSV):** Primarily associated with mucocutaneous lesions (cold sores, genital herpes) and encephalitis; it does not impact erythropoiesis. **3. NEET-PG High-Yield Clinical Pearls:** * **Erythema Infectiosum (Fifth Disease):** Classic presentation in children featuring a "slapped-cheek" rash. * **Hydrops Fetalis:** If a pregnant woman is infected, the virus can cross the placenta, causing severe fetal anemia, high-output cardiac failure, and fetal death. * **Diagnosis:** Look for **"Giant Pronormoblasts"** in the bone marrow and a **low reticulocyte count** (distinguishes aplastic crisis from hemolytic crisis). * **Receptor:** P-antigen (individuals lacking P-antigen are resistant to Parvovirus B19).

Q: What is the most common cause of sporadic encephalitis?

HSV. **Explanation:** **Herpes Simplex Virus (HSV)**, specifically **HSV-1**, is the most common cause of sporadic (non-epidemic) fatal encephalitis worldwide. The underlying medical concept involves the virus's neurotropic nature; it typically reaches the brain via retrograde axonal transport along the trigeminal nerve or olfactory bulb. A hallmark of HSV encephalitis is its predilection for the **temporal lobes**, leading to hemorrhagic necrosis. **Analysis of Options:** * **HSV (Correct):** Responsible for nearly 90% of adult cases of sporadic viral encephalitis. It presents with acute onset fever, headache, seizures, and focal neurological deficits (aphasia or behavioral changes due to temporal lobe involvement). * **EBV (Incorrect):** While EBV can cause neurological complications like meningitis or Guillain-Barré syndrome, it is a rare cause of isolated encephalitis. * **Poliovirus (Incorrect):** This is an enterovirus that primarily targets the anterior horn cells of the spinal cord, leading to asymmetric flaccid paralysis (Poliomyelitis) rather than encephalitis. * **CMV (Incorrect):** CMV encephalitis is typically seen in immunocompromised individuals (e.g., AIDS patients) and neonates (congenital CMV), rather than as a cause of sporadic encephalitis in the general population. **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 hyperintensity in the **temporal lobes** and orbital-frontal regions. * **EEG Finding:** Periodic Lateralized Epileptiform Discharges (PLEDs). * **Treatment:** Immediate IV **Acyclovir** (do not wait for PCR results if clinical suspicion is high).

Q: Influenza is caused by which type of virus?

Type A. **Explanation:** Influenza viruses belong to the family **Orthomyxoviridae** and are classified into types A, B, C, and D based on their core proteins (nucleoprotein and matrix protein). **Why Type A is the correct answer:** While Types A, B, and C all cause human disease, **Influenza Type A** is the most significant pathogen. It is the only type capable of causing **pandemics** because it undergoes both **antigenic drift** (minor mutations) and **antigenic shift** (major genetic reassortment). It has a wide host range, infecting humans, birds, and pigs, which facilitates the emergence of novel strains. **Analysis of Incorrect Options:** * **Type B:** This type primarily infects humans and is a common cause of seasonal epidemics. However, it does not cause pandemics because it does not undergo antigenic shift (it lacks an animal reservoir). * **Type C:** This type causes only mild respiratory illness or sporadic cases and does not cause epidemics or pandemics. * **Type D:** This type primarily affects cattle and is not known to cause illness in humans. **High-Yield NEET-PG Clinical Pearls:** * **Genome:** Segmented, single-stranded, negative-sense RNA. Type A and B have **8 segments**, while Type C has **7 segments**. * **Antigenic Shift:** Reassortment of segments between different strains (e.g., human and avian) in a single host (e.g., a pig). This leads to pandemics. * **Antigenic Drift:** Point mutations in Hemagglutinin (HA) and Neuraminidase (NA) leading to seasonal epidemics. * **Drug of Choice:** Oseltamivir (Neuraminidase inhibitor) is effective against both Type A and B. * **Gold Standard Diagnosis:** Viral culture or RT-PCR.

Question 1

What culture media is used for the cultivation of HSV?

Accepted Answer

Chorioallantoic membrane

Answer

Chocolate agar

Answer

Robertson's cooked-meat broth

Answer

Sabouraud's agar

Question 2

Herpangina is caused by which virus?

Accepted Answer

Enterovirus

Answer

Rhinoviruses

Answer

Myxovirus

Answer

Rabies virus

Question 3

Rapid progression of disease with full-blown manifestation in AIDS occurs when the T4 cell count falls below which value?

Accepted Answer

200/microliter

Answer

1000/microliter

Answer

500/microliter

Answer

50/microliter

Question 4

Which of the following viral infections is NOT typically transmitted from human to human?

Accepted Answer

Japanese B encephalitis

Answer

SARS

Answer

Bird's flu

Answer

Poliomyelitis

Question 5

Infection with which of the following agents is particularly dangerous for anemic patients?

Accepted Answer

Parvovirus

Answer

Adenovirus

Answer

Cytomegalovirus

Answer

Herpes simplex virus

Question 6

Infection with hepatitis D virus (HDV) can occur simultaneously with infection with hepatitis B virus (HBV) or in a carrier of hepatitis B virus because HDV is a defective virus that requires HBV for its replicative function. What serologic test can be used to determine whether a patient with HDV is an HBV carrier?

Accepted Answer

Anti-HDV IgM

Answer

Anti-HBe

Answer

Anti-HBc IgM

Answer

HBsAg quantification

Question 7

What is the most common cause of sporadic encephalitis?

Accepted Answer

HSV

Answer

EBV

Answer

Poliovirus

Answer

CMV

Question 8

Hantavirus is an emerging pathogen that is best described by which of the following statements?

Accepted Answer

Influenza-like symptoms are followed rapidly by acute respiratory failure

Answer

Hemolysis is common in infected patients

Answer

It is acquired by inhalation of aerosols of the urine and feces of infected rodents

Answer

Transmission from human to human is common

Question 9

Influenza is caused by which type of virus?

Accepted Answer

Type A

Answer

Type B

Answer

Type C

Answer

Type D

Question 10

What is true about a bacteriophage?

Accepted Answer

All of the above.

Answer

It is a virus.

Answer

It causes transduction.

Answer

It causes lysis of bacteria.

Virology — MCQs

Virology — MCQs

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