Virology Practice Questions

Q: Which of the following influenza virus types is NOT currently circulating in the world?

H5N1. ### Explanation The correct answer is **C. H5N1**. **1. Why H5N1 is the correct answer:** In the context of human epidemiology, "circulating" refers to viruses that undergo regular, sustained human-to-human transmission (seasonal flu). **H5N1** is an **Avian Influenza (Bird Flu)** virus. While it causes sporadic, severe infections in humans through direct contact with infected poultry, it has **not** yet acquired the ability for sustained human-to-human transmission. Therefore, it is not considered a "circulating" human influenza subtype. **2. Analysis of Incorrect Options:** * **A. H1N1:** This is a subtype of Influenza A. The **A(H1N1)pdm09** strain has been circulating globally since the 2009 pandemic and is a standard component of the seasonal trivalent/quadrivalent vaccines. * **B. H3N2:** This is the other major subtype of Influenza A currently circulating in humans. It often causes more severe seasonal outbreaks in the elderly compared to H1N1. * **C. Influenza B:** Unlike Influenza A, Type B is almost exclusively a human pathogen and does not have subtypes (only lineages like Victoria and Yamagata). It circulates globally every year. **3. High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Major genetic changes (reassortment) leading to **Pandemics**. Only occurs in **Influenza A**. * **Antigenic Drift:** Minor point mutations leading to **Epidemics**. Occurs in both **Influenza A and B**. * **Nomenclature:** Hemagglutinin (H) is for attachment; Neuraminidase (N) is for viral release. * **Drug of Choice:** **Oseltamivir** (Neuraminidase inhibitor) is the preferred treatment for both circulating and avian strains. * **Current Human Circulation:** Currently, only **Influenza A (H1N1 and H3N2)** and **Influenza B** circulate regularly among humans.

Q: HPV types 6 and 11 are associated with genital warts. What is their oncogenic risk?

Low. **Explanation:** Human Papillomavirus (HPV) is a double-stranded DNA virus that exhibits tissue tropism for squamous epithelium. HPV types are classified into **Low-risk** and **High-risk** based on their potential to cause malignant transformation (oncogenicity). **Why Option B is Correct:** HPV types **6 and 11** are the most common causes of **Condyloma Acuminatum (Genital Warts)**. These types are classified as **Low-risk** because they primarily cause benign proliferative lesions. While they lead to significant morbidity due to their infectious nature and recurrence, they rarely integrate their DNA into the host genome, which is a prerequisite for malignant progression. **Analysis of Incorrect Options:** * **Option A (High):** High-risk HPV types include **16, 18, 31, 33, and 45**. These are strongly associated with Cervical Intraepithelial Neoplasia (CIN), cervical cancer, and oropharyngeal cancers due to the action of E6 and E7 oncoproteins which inhibit p53 and Rb tumor suppressor proteins, respectively. * **Option C (Nil):** While the risk is low, it is not "nil." In rare clinical scenarios, such as **Buschke-Löwenstein tumors** (giant condyloma acuminatum), these types can show locally aggressive behavior. * **Option D (Variable):** The oncogenic potential is not variable; it is a fixed characteristic of the specific viral genotype. **High-Yield Clinical Pearls for NEET-PG:** * **Most common HPV types in Genital Warts:** 6 and 11. * **Most common HPV types in Cervical Cancer:** 16 and 18. * **HPV 1 & 2:** Associated with Palmoplantar warts (Verruca vulgaris). * **HPV 5 & 8:** Associated with **Epidermodysplasia Verruciformis** and increased risk of Squamous Cell Carcinoma (SCC). * **Histopathology Hallmark:** **Koilocytes** (cells with perinuclear halo and wrinkled "raisinoid" nuclei).

Q: A patient has the following laboratory results for Hepatitis B virus infection: HBsAg Negative, AntiHBsAg Negative, IgM antiHBC Positive, IgG anti HBC Negative. What do these test results indicate?

Window period. ### Explanation The laboratory profile provided indicates the **Window Period** of a Hepatitis B virus (HBV) infection. **1. Why "Window Period" is correct:** The window period is the clinical interval during which **HBsAg** (the first marker to appear) has disappeared from the blood, but **Anti-HBs** (the neutralizing antibody) has not yet reached detectable levels. During this "gap," the only reliable marker of an acute infection is **IgM anti-HBc** (antibody against the core antigen). * **HBsAg (-):** Surface antigen is cleared. * **Anti-HBs (-):** Protective antibodies haven't appeared yet. * **IgM anti-HBc (+):** Confirms a recent/acute infection. **2. Why other options are incorrect:** * **Chronic Infection:** Would be characterized by the persistence of **HBsAg** for >6 months and the presence of **IgG anti-HBc**, not IgM. * **Immunization (Vaccination):** Only **Anti-HBs** would be positive. Since the vaccine contains only the surface protein, core antibodies (Anti-HBc) will always be negative. * **Previous Infection (Recovery):** Both **Anti-HBs** and **IgG anti-HBc** would be positive, indicating the patient has cleared the virus and developed immunity. **3. NEET-PG High-Yield Pearls:** * **IgM anti-HBc** is the **sole marker** of infection during the window period. * **HBsAg** is the first marker to appear (at 4–6 weeks) and indicates infectivity. * **Anti-HBs** signifies immunity (via recovery or vaccination). * **HBeAg** is a marker of active viral replication and high infectivity. * **Anti-HBc** (Total) is the best marker to screen for previous exposure, as it remains positive for life.

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.

Question 1

Which of the following influenza virus types is NOT currently circulating in the world?

Accepted Answer

H5N1

Answer

H1N1

Answer

H3N2

Answer

Influenza B virus

Question 2

HPV types 6 and 11 are associated with genital warts. What is their oncogenic risk?

Accepted Answer

Low

Answer

High

Answer

Nil

Answer

Variable

Question 3

A patient has the following laboratory results for Hepatitis B virus infection: HBsAg Negative, AntiHBsAg Negative, IgM antiHBC Positive, IgG anti HBC Negative. What do these test results indicate?

Accepted Answer

Window period

Answer

Chronic infection

Answer

Immunization

Answer

Previous infection

Question 4

Swine flu is due to which influenza virus subtype?

Accepted Answer

H1N1

Answer

H5N1

Answer

H2N2

Answer

H3N2

Question 5

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 6

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 7

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 8

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 9

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 10

Kyasanur Forest Disease is caused by which type of virus?

Accepted Answer

Flavivirus

Answer

Reovirus

Answer

Calicivirus

Answer

Retrovirus

Virology — MCQs

Virology — MCQs

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