Virology Practice Questions

Q: Swine flu is due to which influenza virus subtype?

H1N1. **Explanation:** **Influenza A virus** is classified into subtypes based on two surface glycoproteins: **Hemagglutinin (H)** and **Neuraminidase (N)**. 1. **Why H1N1 is correct:** The **H1N1** subtype is the causative agent of **Swine Flu**. While H1N1 has circulated in humans for decades, a novel triple-reassortant strain emerged in 2009 (Pandemic 2009), originating from pigs, leading to a global pandemic. It is characterized by rapid person-to-person transmission via respiratory droplets. 2. **Analysis of Incorrect Options:** * **H5N1:** This is the highly pathogenic **Avian Influenza (Bird Flu)**. It primarily affects birds; human infection is rare but carries a high mortality rate (>50%). * **H2N2:** This subtype caused the **"Asian Flu" pandemic of 1957**. It is no longer in active circulation among humans. * **H3N2:** This is a subtype of seasonal influenza that caused the **"Hong Kong Flu" pandemic of 1968**. It remains a major cause of annual seasonal flu outbreaks alongside H1N1. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Major genetic changes (reassortment) leading to **Pandemics** (e.g., 2009 H1N1). * **Antigenic Drift:** Minor point mutations leading to **Epidemics** and the need for annual vaccine updates. * **Drug of Choice:** **Oseltamivir** (Neuraminidase inhibitor), effective against both Influenza A and B. * **Diagnosis:** **RT-PCR** of nasopharyngeal swabs is the gold standard. * **Spanish Flu (1918):** Also caused by an H1N1 subtype; it remains the deadliest pandemic in history.

Q: Which of the following inclusion bodies is seen in a patient with Rabies?

Negri bodies. **Explanation:** **Negri bodies** are the hallmark histopathological finding in **Rabies**, caused by the Lyssavirus. These are pathognomonic **intracytoplasmic, eosinophilic inclusion bodies** found most commonly in the **Purkinje cells of the cerebellum** and the **pyramidal cells of the hippocampus (Ammon’s horn)**. They represent sites of viral replication and consist of ribonucleoprotein aggregates. **Analysis of Incorrect Options:** * **Cowdry-B:** These are intranuclear inclusions seen in **Poliovirus** and Adenovirus infections. (Note: Cowdry-A inclusions are seen in Herpes Simplex Virus and Varicella-Zoster Virus). * **Guarneri bodies:** These are eosinophilic intracytoplasmic inclusions characteristic of **Variola (Smallpox)** and Vaccinia viruses. * **Bollinger bodies:** These are large, granular intracytoplasmic inclusions seen in **Fowlpox**. (Note: Borrel bodies are the smaller elementary bodies found within Bollinger bodies). **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Negri bodies are typically round or oval, 1–7 µm in size, and contain internal granules (inner bodies). * **Diagnosis:** While Negri bodies are specific, they are only present in about 70–80% of cases. The **Direct Fluorescent Antibody (DFA)** test on brain tissue or skin biopsy (from the nape of the neck) is the current "gold standard" for diagnosis. * **Transmission:** Rabies is most commonly transmitted via the bite of a rabid animal (dogs in India); the virus travels via **retrograde axonal transport** to the CNS.

Q: Tonsillar carcinoma is associated with infection of which virus?

Human Papillomavirus (HPV). **Explanation:** Tonsillar carcinoma is a subset of Oropharyngeal Squamous Cell Carcinoma (OPSCC). The correct answer is **Human Papillomavirus (HPV)**, specifically high-risk strains like **HPV-16** (found in over 90% of HPV-positive cases). **Why HPV is the correct answer:** HPV has a strong tropism for the reticulated epithelium of the palatine and lingual tonsils. The virus integrates into the host genome, leading to the overexpression of oncoproteins **E6 and E7**. E6 degrades the p53 tumor suppressor protein, while E7 inactivates the Retinoblastoma (Rb) protein, resulting in uncontrolled cell proliferation. **Why other options are incorrect:** * **HIV:** While HIV-infected individuals have a higher risk of various malignancies (like Kaposi sarcoma or Non-Hodgkin Lymphoma) due to immunosuppression, HIV is not the direct causative agent of tonsillar carcinoma. * **HSV:** Herpes Simplex Virus is primarily associated with mucocutaneous lesions (cold sores/genital herpes) and encephalitis, but it is not an oncogenic virus for oropharyngeal cancer. **High-Yield Clinical Pearls for NEET-PG:** 1. **Epidemiology:** HPV-positive tonsillar cancers typically occur in younger patients, often without the traditional risk factors of heavy smoking or alcohol use. 2. **Surrogate Marker:** **p16 immunohistochemistry** is used as a reliable surrogate marker for HPV infection in oropharyngeal biopsies. 3. **Prognosis:** HPV-positive oropharyngeal cancers generally have a **better prognosis** and higher sensitivity to radiotherapy/chemotherapy compared to HPV-negative (tobacco-related) cancers. 4. **Staging:** Due to the better prognosis, the AJCC 8th Edition has separate staging systems for HPV-mediated (p16+) oropharyngeal cancers.

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: A 1-year-old girl presents with a 3-day history of fever and diarrhea. Her temperature is 38°C (101°F), and her CBC shows a normal white blood cell count and increased hematocrit. Which of the following microorganisms is the most likely cause of diarrhea in this child?

Rotavirus. **Explanation:** The clinical presentation of a 1-year-old child with fever and watery diarrhea, accompanied by signs of dehydration (increased hematocrit), is classic for **Rotavirus** infection. **1. Why Rotavirus is correct:** Rotavirus is the most common cause of severe, dehydrating diarrhea in infants and young children worldwide (typically aged 6 months to 2 years). It primarily causes a **malabsorptive and osmotic diarrhea** by infecting the mature enterocytes of the villi in the small intestine, leading to villous atrophy. The presence of fever and a normal WBC count is consistent with a viral etiology rather than an invasive bacterial one. The increased hematocrit is a marker of hemoconcentration due to dehydration. **2. Why other options are incorrect:** * **Cytomegalovirus (CMV):** Usually causes diarrhea in immunocompromised individuals (e.g., HIV/AIDS) or as part of congenital infections. It is not a common cause of acute diarrhea in an otherwise healthy 1-year-old. * **Salmonella typhi:** Causes Enteric Fever. While it can cause diarrhea in children, it typically presents with high-grade prolonged fever, hepatosplenomegaly, and significant systemic toxicity. * **Shigella dysenteriae:** Causes **inflammatory/bloody diarrhea (dysentery)**. It is characterized by high fever, abdominal cramps, tenesmus, and a high WBC count (often with a left shift), which contradicts the normal WBC count in this case. **Clinical Pearls for NEET-PG:** * **Mechanism:** Rotavirus NSP4 enterotoxin induces secretory diarrhea (the first known viral enterotoxin). * **Seasonality:** Peak incidence occurs in winter months ("Winter diarrhea"). * **Diagnosis:** Enzyme Immunoassay (EIA) or Latex agglutination for Rotavirus antigen in stool. * **Prevention:** Live attenuated oral vaccines (Rotarix, RotaTeq, Rotavac) are part of the National Immunization Schedule in India.

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 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

Swine flu is due to which influenza virus subtype?

Accepted Answer

H1N1

Answer

H5N1

Answer

H2N2

Answer

H3N2

Question 2

Which of the following inclusion bodies is seen in a patient with Rabies?

Accepted Answer

Negri bodies

Answer

Cowdry-B

Answer

Guarneri bodies

Answer

Bollinger bodies

Question 3

Tonsillar carcinoma is associated with infection of which virus?

Accepted Answer

Human Papillomavirus (HPV)

Answer

Human Immunodeficiency Virus (HIV)

Answer

Herpes Simplex Virus (HSV)

Answer

None of the above

Question 4

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 5

A 1-year-old girl presents with a 3-day history of fever and diarrhea. Her temperature is 38°C (101°F), and her CBC shows a normal white blood cell count and increased hematocrit. Which of the following microorganisms is the most likely cause of diarrhea in this child?

Accepted Answer

Rotavirus

Answer

Cytomegalovirus

Answer

Salmonella typhi

Answer

Shigella dysenteriae

Question 6

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 7

Kyasanur Forest Disease is caused by which type of virus?

Accepted Answer

Flavivirus

Answer

Reovirus

Answer

Calicivirus

Answer

Retrovirus

Question 8

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 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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