Virology Practice Questions

Q: All of the following rabies vaccines are commercially available except?

Recombinant glycoprotein. The correct answer is **Recombinant glycoprotein** because, while it is a subject of ongoing research and clinical trials, it is not currently available as a commercially licensed vaccine for human use in the standard clinical setting. ### **Explanation of Options:** * **Killed sheep brain vaccine (Neural Tissue Vaccine/NTV):** This was the earliest type of rabies vaccine (e.g., Semple vaccine). Although largely phased out in many countries due to the risk of neuroparalytic complications (post-vaccinal encephalomyelitis), it remains historically "commercially available" in specific resource-limited regions. * **Human Diploid Cell Vaccine (HDCV):** Introduced in the 1960s, this is the "gold standard" of cell culture vaccines. It is highly immunogenic and safe but expensive to produce. * **Vero Continuous Cell Vaccine (PVRV):** This is a Purified Vero Cell Rabies Vaccine. It is widely used globally (including India) for both pre-exposure and post-exposure prophylaxis due to its high efficacy and lower cost compared to HDCV. ### **High-Yield Clinical Pearls for NEET-PG:** 1. **Classification:** Modern rabies vaccines are **Cell Culture Vaccines (CCVs)** or **Purified Duck Embryo Vaccines (PDEV)**. 2. **Neural Tissue Vaccines (NTV):** These are derived from the brain of sheep (Semple) or suckling mice (Fuenzalida-Palacios). They are discouraged by the WHO due to high reactogenicity. 3. **Current Regimen (WHO 2018):** The intradermal (ID) regimen is the preferred cost-effective method (e.g., **0.1 ml** at two sites on days **0, 3, and 7**). 4. **Recombinant Technology:** While a recombinant **rabies G protein** vaccine is not the standard, a **Recombinant Rabies G Protein Monoclonal Antibody** (e.g., Rabishield) is commercially available in India for passive immunization (replacing HRIG/ERIG). Do not confuse the vaccine with the monoclonal antibody.

Q: What is the typical cell found in the lymphoid tissue of a case of measles?

Warthin Finkeldey cells. ### Explanation **Correct Answer: C. Warthin-Finkeldey cells** **Warthin-Finkeldey cells** are the pathognomonic histological hallmark of **Measles (Rubeola)**. These are large, multinucleated giant cells formed by the fusion of infected lymphocytes and macrophages. They are typically found in lymphoid tissues such as the tonsils, lymph nodes, spleen, and appendix during the prodromal phase of the disease. These cells can contain up to 100 nuclei and may show both intracytoplasmic and intranuclear eosinophilic inclusion bodies. **Analysis of Incorrect Options:** * **A. Guarnieri bodies:** These are eosinophilic cytoplasmic inclusion bodies found in epithelial cells infected with **Variola (Smallpox)** or Vaccinia virus. They represent the site of viral replication in the cytoplasm. * **B. Cowdry bodies:** These are intranuclear eosinophilic inclusions. **Cowdry Type A** is associated with **Herpes Simplex Virus (HSV)** and Varicella-Zoster Virus (VZV), while **Cowdry Type B** is seen in Poliovirus and Adenovirus. * **D. Councilman bodies:** These are eosinophilic, apoptotic hepatocytes (acidophilic bodies) typically seen in the liver of patients with **Yellow Fever** or Viral Hepatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Measles Inclusions:** Unlike many viruses, Measles produces **both** intranuclear and intracytoplasmic inclusion bodies. * **Koplik’s spots:** Small white spots on an erythematous base (grains of salt on a red sea) found on the buccal mucosa opposite the lower 2nd molar; they are the clinical pathognomonic sign. * **Complications:** The most common complication is Otitis Media; the most common cause of death is Pneumonia (Hecht’s giant cell pneumonia). * **SSPE:** Subacute Sclerosing Panencephalitis is a late-onset, progressive neurological complication caused by a defective measles virus.

Q: A patient is diagnosed with Hepatitis B infection. Which of the following markers will always be present in his serum if he develops chronic hepatitis?

Anti HBc Ab. ### Explanation **Correct Answer: D. Anti HBc Ab** In Hepatitis B virus (HBV) infection, **Anti-HBc (Antibody to Hepatitis B core antigen)** is the most reliable marker of a past or current infection. Because the core antigen (HBcAg) is sequestered within the viral coat, it is not detectable in the serum. However, the body consistently produces antibodies against it. In chronic hepatitis, **Anti-HBc IgG** persists for life, regardless of whether the virus is replicating or if the patient has progressed to cirrhosis. It is the "constant" marker that signifies the patient has been infected at some point. **Why other options are incorrect:** * **A. HBc Ag:** This antigen is part of the internal core of the virion and is **never** found free in the serum; it is only detectable in liver biopsy samples. * **B. Anti HBs Ab:** This antibody indicates immunity (either via vaccination or recovery). In a patient with chronic hepatitis, the HBsAg remains positive, and Anti-HBs is typically **absent**, as the body has failed to clear the virus. * **C. HBe Ag:** This is a marker of active viral replication and high infectivity. While often present in early chronic phases, many chronic patients undergo "seroconversion" to Anti-HBe or have "Pre-core mutants" where HBeAg is **absent** despite chronic infection. **NEET-PG High-Yield Pearls:** * **Window Period:** The period where HBsAg disappears but Anti-HBs hasn't appeared yet. **Anti-HBc IgM** is the only diagnostic marker during this phase. * **Chronic Infection Definition:** Persistence of **HBsAg** for >6 months. * **Vaccination Marker:** A vaccinated individual will be **Anti-HBs positive** but **Anti-HBc negative** (since the vaccine only contains the surface antigen). * **Screening:** HBsAg is used for routine screening, but Anti-HBc is used in blood banks to rule out occult HBV.

Q: Plaque formation in virology is primarily used for which of the following purposes?

Determining the infectivity of a virus. ### Explanation **Plaque formation** is a gold-standard technique in virology used for the **quantification of infectious viral particles**. **Why Option C is Correct:** A "plaque" is a visible area of cell lysis or CPE (cytopathic effect) in a cell culture monolayer. Each plaque originates from a single **infectious** virus particle (virion). By counting these plaques, we calculate the **Plaque Forming Units (PFU)** per ml. This directly measures the **infectivity** (the ability of the virus to infect a host cell and replicate) rather than just the total number of physical particles (which may include dead or incomplete viruses). **Analysis of Incorrect Options:** * **Option A (Isolation and typing):** While viruses are isolated in cell cultures, "plaque formation" specifically refers to the quantification method. Typing is usually done via neutralization tests or molecular methods (PCR). * **Option B (Cloning and separation):** While a plaque can be used to "plaque-purify" a virus (cloning), this is a secondary application. Its primary diagnostic and research purpose is quantification. * **Option D (Multiplication rate):** Multiplication rates are determined by "one-step growth curves," which measure viral yield over time, not just the initial presence of infectious units. **High-Yield Clinical Pearls for NEET-PG:** * **Plaque Assay:** Measures **Infectivity**. * **Hemagglutination Assay:** Measures the **total number** of viral particles (both infectious and non-infectious). * **Plaque Reduction Neutralization Test (PRNT):** The gold standard for measuring the concentration of neutralizing antibodies against a virus. * **Pock Assay:** A variation of the plaque assay used for viruses (like Poxvirus) grown on the **Chorioallantoic Membrane (CAM)** of embryonated eggs.

Q: Kyasanur Forest Disease is caused by which type of virus?

Flavivirus. **Explanation:** **Kyasanur Forest Disease (KFD)**, also known as "Monkey Fever," is caused by the Kyasanur Forest Disease Virus (KFDV), which belongs to the family **Flaviviridae** and the genus *Flavivirus*. It is a tick-borne viral hemorrhagic fever endemic to the Western Ghats of India (specifically Karnataka). * **Why Option A is Correct:** KFDV is an enveloped, single-stranded, positive-sense RNA virus. It is classified as a Flavivirus, sharing structural and genetic similarities with other members like Yellow Fever, Dengue, and West Nile viruses. It is transmitted to humans via the bite of infected ticks (*Haemaphysalis spinigera*). * **Why Other Options are Incorrect:** * **Reovirus:** These are non-enveloped, double-stranded RNA viruses (e.g., Rotavirus). * **Calicivirus:** These are non-enveloped, positive-sense RNA viruses primarily causing gastroenteritis (e.g., Norovirus). * **Retrovirus:** These viruses use reverse transcriptase to integrate their genome into the host DNA (e.g., HIV). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** The hard tick, ***Haemaphysalis spinigera***, is the primary vector. * **Reservoir:** Rodents, shrews, and monkeys (monkeys act as "sentinel animals"—their sudden death often signals an outbreak). * **Clinical Presentation:** Characterized by sudden onset high fever, frontal headache, severe myalgia, and hemorrhagic manifestations. A "biphasic" illness pattern is often seen. * **Diagnosis:** PCR (early stage) or IgM ELISA (later stage). * **Prevention:** A **formalin-inactivated vaccine** is used in endemic areas of Karnataka.

Q: A patient develops clinical symptoms consistent with hepatitis. The patient recalls sticking themselves with a needle approximately 4 months prior after drawing blood from another patient. Serologic tests for HBsAg, antibodies to HBsAg, and hepatitis A virus (HAV) are all negative; however, the patient is positive for IgM core antibody. What is the most likely diagnosis?

Window period of hepatitis B infection. ### Explanation The correct answer is **D. Window period of hepatitis B infection.** **Understanding the Concept:** The "Window Period" is a specific phase in Hepatitis B virus (HBV) infection where **HBsAg** (the surface antigen) has disappeared because it is being cleared by the body, but **Anti-HBs** (the protective surface antibody) has not yet reached detectable levels. During this gap, both HBsAg and Anti-HBs are negative. The only reliable serologic marker of an acute infection during this phase is the **IgM anti-HBc (IgM core antibody)**. This patient’s profile (HBsAg negative, Anti-HBs negative, but IgM anti-HBc positive) is the classic definition of the window period. **Why other options are incorrect:** * **A. No hepatitis B infection:** The presence of IgM anti-HBc indicates a recent acute infection; it would be negative if the patient were never infected. * **B. Hepatitis A infection:** The patient tested negative for HAV serology, ruling this out. * **C. Late stage of hepatitis B infection:** In late/chronic stages or recovery, HBsAg would be negative but **IgG anti-HBc** would be present, and **Anti-HBs** would typically be positive (if recovered). IgM is specifically a marker of acute/recent infection. **NEET-PG High-Yield Pearls:** * **IgM anti-HBc:** The *only* marker positive during the window period. It is also the best marker for diagnosing **acute** HBV infection. * **HBsAg:** The first marker to appear (as early as 1–2 weeks post-exposure) and the first to disappear in recovery. * **Anti-HBs:** Indicates immunity (via recovery or vaccination). * **Anti-HBc:** Indicates a history of infection (never present in vaccinated individuals). * **HBeAg:** Indicates high viral replication and maximum infectivity.

Q: An emerging viral pathogen causing pyelonephritis in kidney allografts is:

Polyoma virus. **Explanation:** The correct answer is **Polyoma virus**, specifically the **BK virus (BKV)**. **1. Why Polyoma Virus is Correct:** Polyomaviruses (BK and JC viruses) are ubiquitous viruses that establish lifelong latent infections in the renal tubular epithelium and lymphocytes. In the context of profound immunosuppression, such as in **kidney allograft recipients**, the BK virus undergoes reactivation. This leads to **BK Virus-Associated Nephropathy (BKVAN)**, which clinically manifests as interstitial nephritis and pyelonephritis. It is a major cause of graft dysfunction and loss. Histologically, it is characterized by intranuclear "ground-glass" inclusion bodies (decoy cells) in urinary sediment. **2. Why Other Options are Incorrect:** * **Molluscum contagiosum:** A Poxvirus that causes benign, umbilicated skin papules. It does not affect the renal system or cause pyelonephritis. * **Herpes simplex virus (HSV):** While HSV can cause systemic infections in immunocompromised hosts, it typically presents as mucocutaneous lesions, esophagitis, or encephalitis, rather than primary graft pyelonephritis. * **Influenza virus:** An orthomyxovirus that primarily causes respiratory tract infections. It is not associated with renal allograft rejection or pyelonephritis. **3. High-Yield Clinical Pearls for NEET-PG:** * **BK Virus:** "B" stands for **B**ad **K**idney (Nephropathy/Ureteric stenosis). * **JC Virus:** "J" stands for **J**unk **C**erebrum (causes Progressive Multifocal Leukoencephalopathy - PML). * **Diagnosis:** Screening is done via **decoy cells** in urine cytology and confirmed by BK virus DNA PCR in plasma. * **Management:** The primary treatment strategy is the reduction of immunosuppressive therapy.

Q: An HIV patient complains of visual disturbances. Fundal examination shows bilateral retinal exudates and perivascular hemorrhages. Which of the following viruses is most likely responsible for this retinitis?

Cytomegalovirus. ### Explanation **Correct Option: C. Cytomegalovirus (CMV)** **Why it is correct:** Cytomegalovirus (CMV) retinitis is the most common opportunistic ocular infection in HIV/AIDS patients, typically occurring when the **CD4 count falls below 50 cells/mm³**. The classic fundoscopic description provided—**"bilateral retinal exudates and perivascular hemorrhages"**—is characteristic of CMV. This is often referred to as the **"Pizza-pie"** or **"Tomato-sauce and cheese"** appearance. The virus causes a full-thickness necrotizing retinitis that leads to visual field defects and, if untreated, total blindness. **Why other options are incorrect:** * **A & B (HSV and VZV):** While both can cause retinitis in HIV patients (e.g., Acute Retinal Necrosis), they typically present with rapid, painful vision loss and peripheral necrotizing lesions rather than the classic perivascular "pizza-pie" hemorrhage seen in CMV. * **D (Epstein-Barr Virus):** EBV is primarily associated with Oral Hairy Leukoplakia and Primary CNS Lymphoma in HIV patients; it is not a standard cause of retinitis. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** **Ganciclovir** (Intravenous or intravitreal) or Valganciclovir. Foscarnet/Cidofovir are second-line. * **CD4 Threshold:** Always suspect CMV when CD4 < 50 cells/mm³. * **Histology:** Look for **"Owl’s eye"** intranuclear inclusion bodies. * **Other CMV manifestations in AIDS:** Intractable diarrhea (CMV Colitis) and painful esophageal ulcers (CMV Esophagitis). * **Differential:** Unlike Toxoplasmosis (which shows "headlight in the fog" due to vitritis), CMV retinitis usually has minimal vitreous inflammation.

Q: The human immunodeficiency virus (HIV) has a particularly high affinity for which of the following cell types?

CD4 T Lymphocytes and monocytes. **Explanation:** The hallmark of HIV pathogenesis is its high affinity for cells expressing the **CD4 receptor** on their surface. The viral envelope glycoprotein **gp120** binds specifically to the CD4 molecule, which acts as the primary receptor for viral entry. 1. **Why Option B is Correct:** While **CD4+ T Lymphocytes** (Helper T cells) are the primary targets and their depletion leads to profound immunodeficiency, **Monocytes and Macrophages** also express CD4 receptors on their surface (albeit in lower densities). These cells, along with dendritic cells, serve as significant reservoirs for the virus, transporting it to various organs like the brain and lymphoid tissues. 2. **Why Other Options are Incorrect:** * **Options A & C (B cells):** B lymphocytes do not express the CD4 receptor; therefore, HIV cannot directly infect them via the gp120-CD4 interaction. * **Options C & D (CD8 T Lymphocytes):** CD8+ T cells (Cytotoxic T cells) lack the CD4 receptor. In fact, CD8+ T cell counts often initially rise as the body attempts to control the HIV infection. **High-Yield NEET-PG Pearls:** * **Co-receptors:** Binding to CD4 is not enough; HIV also requires co-receptors: **CCR5** (found on macrophages/monocytes; "M-tropic" strains) and **CXCR4** (found on T-helper cells; "T-mropic" strains). * **CCR5 Mutation:** Individuals with a homozygous **CCR5-Δ32 mutation** are resistant to infection by the most common strains of HIV-1. * **Trojan Horse:** Macrophages are often called the "Trojan Horse" of HIV because they are resistant to the cytopathic effects of the virus, allowing it to persist and spread throughout the body.

Question 1

All of the following rabies vaccines are commercially available except?

Accepted Answer

Recombinant glycoprotein

Answer

Killed sheep brain vaccine

Answer

Human diploid cell vaccine

Answer

Vero continuous cell vaccine

Question 2

What is the typical cell found in the lymphoid tissue of a case of measles?

Accepted Answer

Warthin Finkeldey cells

Answer

Guarnieri bodies

Answer

Cowdry bodies

Answer

Councilman bodies

Question 3

A patient is diagnosed with Hepatitis B infection. Which of the following markers will always be present in his serum if he develops chronic hepatitis?

Accepted Answer

Anti HBc Ab

Answer

HBc Ag

Answer

Anti HBs Ab

Answer

HBe Ag

Question 4

Plaque formation in virology is primarily used for which of the following purposes?

Accepted Answer

Determining the infectivity of a virus

Answer

Isolation and typing of viruses

Answer

Cloning and separation of specific viruses

Answer

Assessing the multiplication rate of a virus

Question 5

Kyasanur Forest Disease is caused by which type of virus?

Accepted Answer

Flavivirus

Answer

Reovirus

Answer

Calicivirus

Answer

Retrovirus

Question 6

A patient develops clinical symptoms consistent with hepatitis. The patient recalls sticking themselves with a needle approximately 4 months prior after drawing blood from another patient. Serologic tests for HBsAg, antibodies to HBsAg, and hepatitis A virus (HAV) are all negative; however, the patient is positive for IgM core antibody. What is the most likely diagnosis?

Accepted Answer

Window period of hepatitis B infection

Answer

No hepatitis B infection

Answer

Hepatitis A infection

Answer

Late stage of hepatitis B infection

Question 7

Atypical lymphocytosis is most likely to be found in which one of the following diseases?

Accepted Answer

Infectious mononucleosis induced by Epstein-Barr virus

Answer

Encephalitis caused by herpes simplex virus (HSV)

Answer

Parvovirus infection

Answer

Chronic hepatitis C

Question 8

An emerging viral pathogen causing pyelonephritis in kidney allografts is:

Accepted Answer

Polyoma virus

Answer

Molluscum contagiosum

Answer

Herpes simplex virus

Answer

Influenza virus

Question 9

An HIV patient complains of visual disturbances. Fundal examination shows bilateral retinal exudates and perivascular hemorrhages. Which of the following viruses is most likely responsible for this retinitis?

Accepted Answer

Cytomegalovirus

Answer

Herpes simplex virus

Answer

Varicella zoster virus

Answer

Epstein-Barr virus

Question 10

The human immunodeficiency virus (HIV) has a particularly high affinity for which of the following cell types?

Accepted Answer

CD4 T Lymphocytes and monocytes

Answer

CD4 T Lymphocytes and B cells

Answer

CD8 T Lymphocytes and B cells

Answer

CD8 T Lymphocytes and CD4 T Lymphocytes

Virology — MCQs

Virology — MCQs

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