Virology Practice Questions

Q: Which of the following statements about rabies virus is incorrect?

It is a DNA virus.. **Explanation:** **1. Why Option A is the Correct Answer (The Incorrect Statement):** Rabies virus belongs to the family **Rhabdoviridae** and the genus *Lyssavirus*. It is a **single-stranded, negative-sense RNA virus**, not a DNA virus. It is characterized by its distinct bullet-shaped morphology and an envelope covered with glycoprotein spikes. **2. Analysis of Other Options:** * **Option B:** In rabies research, "Street virus" (found in nature) has a highly variable incubation period. However, the **"Fixed virus"** (used for vaccine production, derived by repeated serial passage in brains of rabbits) has a shortened and **fixed incubation period** (usually 4–6 days). * **Option C:** **Negri bodies** are pathognomonic intracytoplasmic eosinophilic inclusion bodies. They are most commonly and characteristically found in the **Pyramidal cells of the Hippocampus (Ammon’s horn)** and Purkinje cells of the cerebellum. * **Option D:** According to WHO and National guidelines, **Category III** (High risk) exposures include single or multiple transdermal bites or scratches, licks on broken skin, or contamination of mucous membranes with saliva. Any bite on the **fingers/hands** (highly innervated areas) or lacerated wounds are automatically classified as Class III, requiring both vaccine and Rabies Immunoglobulin (RIG). **Clinical Pearls for NEET-PG:** * **Shape:** Bullet-shaped virus. * **Genome:** ssRNA, linear, non-segmented, negative sense. * **Centripetal spread:** Moves via retrograde axonal transport to the CNS. * **Hydrophobia:** Occurs due to forceful spasms of the diaphragm and accessory respiratory muscles when attempting to swallow. * **Diagnosis:** Direct Fluorescent Antibody (DFA) test on skin biopsy (from the nape of the neck) or corneal impression is a gold standard intra-vitam test.

Q: Papillomavirus has been found in all of the following lesions except?

Condyloma latum. **Explanation:** The correct answer is **Condyloma latum** because it is a clinical manifestation of **Secondary Syphilis**, caused by the spirochete *Treponema pallidum*, not Human Papillomavirus (HPV). **1. Why Condyloma latum is the correct answer:** Condyloma lata are flat, moist, wart-like papules typically found in intertriginous areas (like the anogenital region) during the secondary stage of syphilis. They are highly infectious and contain a high load of spirochetes. In contrast, HPV-related lesions are usually more "verrucous" or cauliflower-like in appearance. **2. Why the other options are incorrect:** * **Oral papillomas:** These are benign epithelial tumors caused by HPV types 6 and 11. * **Verruca vulgaris:** Also known as common warts, these are caused by HPV (primarily types 2 and 4) and can occur on the oral mucosa. * **Condyloma acuminatum:** These are genital warts caused by low-risk HPV types 6 and 11. They are characterized by a "cauliflower-like" appearance and koilocytic changes on histology. **High-Yield Clinical Pearls for NEET-PG:** * **The "L" Rule:** Condyloma **L**atum = **L**ues (Syphilis); Condyloma **A**cuminatum = **A**PV (HPV). * **Koilocytes:** The hallmark histological finding for HPV infection (cells with perinuclear halos and wrinkled "raisinoid" nuclei). * **HPV Oncogenesis:** Types 16 and 18 are high-risk for cervical and oropharyngeal carcinoma due to E6 (inhibits p53) and E7 (inhibits Rb) proteins. * **Syphilis Diagnosis:** Condyloma latum is best diagnosed via Dark-field microscopy or serology (RPR/VDRL).

Q: Which of the following is NOT true of Kyasanur forest disease?

Caused by a retrovirus. ### Explanation **Kyasanur Forest Disease (KFD)**, also known as "Monkey Fever," is a viral hemorrhagic fever endemic to South India (primarily Karnataka). **Why Option B is the correct answer:** KFD is **not** caused by a retrovirus. It is caused by the **Kyasanur Forest Disease Virus (KFDV)**, which belongs to the family **Flaviviridae** (Genus: *Flavivirus*). It is a single-stranded RNA virus. Retroviruses (like HIV) use reverse transcriptase to integrate into the host genome, a mechanism not seen in KFDV. **Analysis of other options:** * **Option A (Transmitted by soft ticks):** This statement is **False**, making it a controversial option in some older texts. However, in the context of this specific question, the viral classification (Option B) is the more definitive "incorrect" statement. KFD is primarily transmitted by **Hard Ticks** (*Haemaphysalis spinigera*). * **Option C (Incubation period is 3-8 days):** This is **True**. The typical incubation period ranges from 3 to 8 days after a tick bite. * **Option D (A killed vaccine is available):** This is **True**. A formalin-inactivated (killed) KFDV vaccine is used in endemic areas for individuals aged 7–65 years. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoirs:** Rats, shrews, and monkeys (Langurs and Bonnet macaques). * **Amplifier Host:** Monkeys (Sudden death of monkeys in a forest is an early warning sign of an outbreak). * **Vector:** *Haemaphysalis spinigera* (Hard tick). * **Clinical Presentation:** Biphasic illness—initial febrile phase with severe headache and myalgia, followed by a second phase in some patients involving meningoencephalitis or hemorrhagic manifestations. * **Diagnosis:** PCR (early phase) or IgM ELISA.

Q: A 24-year-old male presented with a lesion on his genitalia after multiple sexual encounters. Which human papillomavirus type is the causative agent?

HPV 6, 11. **Explanation:** The clinical presentation of a genital lesion (typically **Condyloma acuminatum** or anogenital warts) following sexual contact is most commonly caused by **Human Papillomavirus (HPV) types 6 and 11**. These are classified as **"low-risk" HPV types** because they are associated with benign proliferative lesions rather than invasive squamous cell carcinoma. * **Option A (Correct):** HPV 6 and 11 are responsible for over 90% of cases of genital warts and are also the primary cause of recurrent respiratory papillomatosis. * **Option B (Incorrect):** HPV 16 and 18 are **"high-risk"** oncogenic types. They are the leading cause of cervical cancer, oropharyngeal cancer, and other anogenital malignancies (anal, penile, vulvar). They typically cause flat, subclinical lesions rather than overt warts. * **Options C & D (Incorrect):** HPV types 31, 33, 35, and 45 are also categorized as high-risk types. While they contribute to cervical dysplasia and neoplasia, they are less prevalent than types 16 and 18 and do not typically present as common genital warts. **NEET-PG High-Yield Pearls:** * **Koilocytes:** The hallmark histological finding of HPV infection (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Oncoproteins:** HPV E6 inhibits the **p53** tumor suppressor protein; HPV E7 inhibits the **pRb** (Retinoblastoma) protein. * **Vaccination:** The Quadrivalent vaccine (Gardasil) covers types 6, 11, 16, and 18, providing protection against both warts and cervical cancer. * **Diagnosis:** Usually clinical; confirmed by acetic acid test (acetowhitening) or biopsy if diagnosis is uncertain.

Q: A patient presented with acute onset of jaundice and raised aminotransferases. Preliminary serology showed HBsAg positivity. On further testing, which of the following is least likely to be found in this patient?

Anti-HBs antibodies. ### Explanation The patient presents with acute hepatitis and is **HBsAg positive**, indicating an active Hepatitis B virus (HBV) infection. **Why Anti-HBs is the correct answer:** Anti-HBs (Hepatitis B surface antibody) is a **neutralizing antibody** that appears only after HBsAg has been cleared from the blood. Its presence signifies either recovery from a natural infection or successful immunization. In an acute infection where HBsAg is still detectable, Anti-HBs will be absent. The period between the disappearance of HBsAg and the appearance of Anti-HBs is known as the **"Window Period,"** during which only Anti-HBc IgM is typically detectable. **Analysis of Incorrect Options:** * **HBeAg:** This is a marker of active viral replication and high infectivity. It is commonly found in the early stages of acute hepatitis B alongside HBsAg. * **HBV DNA:** This is the most sensitive marker of viral replication. It appears very early in the infection, often before HBsAg, and remains positive during the acute phase. * **HBV DNA Polymerase:** As an enzyme required for viral replication, its presence correlates with the presence of HBV DNA and HBeAg during active infection. **Clinical Pearls for NEET-PG:** * **First marker to appear:** HBsAg (even before symptoms or rise in ALT). * **Marker of infectivity:** HBeAg. * **Marker of "Window Period":** Anti-HBc IgM. * **Marker of immunity:** Anti-HBs. * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months.

Q: Which of the following is characteristic of Dengue hemorrhagic fever?

Most common in previously affected patients. ### Explanation The correct answer is **A: Most common in previously affected patients.** This phenomenon is explained by the **Immunological Theory of Halstead (Antibody-Dependent Enhancement - ADE)**. When a patient is infected with a different serotype of the Dengue virus (DENV 1-4) for the second time, the pre-existing non-neutralizing antibodies from the primary infection bind to the new virus. Instead of neutralizing it, these antibodies facilitate the entry of the virus into macrophages and monocytes via Fc receptors. This leads to an exaggerated immune response, a "cytokine storm," increased vascular permeability, and the clinical manifestations of Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). #### Analysis of Incorrect Options: * **B. DHF-2 is the most common cause:** This is factually incorrect. While DENV-2 is frequently associated with severe outbreaks and DHF, any of the four serotypes can cause DHF upon secondary infection. * **C. Associated with immunosuppression:** DHF is actually a result of an **overactive immune system** (hyper-immune response), not immunosuppression. The pathology is driven by excessive T-cell activation and cytokine release. * **D. Incubation period is 7-14 days:** The typical incubation period for Dengue is **3 to 14 days** (average 5–7 days). While 14 is the upper limit, it is not the standard characteristic range used to define the disease. #### NEET-PG High-Yield Pearls: * **Vector:** *Aedes aegypti* (Daytime biter, breeds in artificial collections of clean water). * **Hemorrhagic Marker:** Positive **Tourniquet test** (presence of >20 petechiae per square inch). * **Lab Diagnosis:** NS1 Antigen (Day 1-5), IgM/IgG ELISA (after Day 5). * **Critical Period:** Occurs during the **defervescence phase** (when fever subsides), usually between days 3–7 of illness. This is when plasma leakage and shock are most likely to occur.

Q: Full blown Immunodeficiency syndrome is characterized by which of the following?

High viral titres with low CD4 count. **Explanation:** The progression of HIV infection to **Full-blown AIDS (Stage 3)** is defined by the critical failure of the cell-mediated immune system. 1. **Why Option A is correct:** In the final stage of the disease, the virus has successfully exhausted the host's immune defenses. The **CD4+ T-lymphocyte count drops below 200 cells/mm³** (or <14%), which is the hallmark of immunodeficiency. Simultaneously, because the immune system can no longer suppress viral replication, the **viral load (HIV RNA titres) surges** significantly. This high viremia facilitates the development of life-threatening opportunistic infections and malignancies. 2. **Why other options are incorrect:** * **Option B & C:** Low viral titres are typically seen during the "Clinical Latency" phase or in "Elite Controllers," where the immune system or ART (Antiretroviral Therapy) keeps the virus in check. * **Option D:** High viral titres with high CD4 counts are characteristic of the **Acute HIV Syndrome** (initial infection), where the virus replicates rapidly before the immune system mounts a response, but the CD4 pool has not yet been depleted. **High-Yield Clinical Pearls for NEET-PG:** * **Normal CD4/CD8 Ratio:** 2:1. In AIDS, this ratio is **inverted** (<1:1). * **Indicator of Prognosis:** Viral load (HIV RNA) is the best predictor of disease progression. * **Indicator of Immune Status:** CD4+ T-cell count is the best indicator of current immune competence and risk for opportunistic infections. * **Pneumocystis jirovecii:** The most common opportunistic infection when CD4 falls below 200 cells/mm³.

Q: Which of the following microbes is the most common cause of gastroenteritis in children?

Rotaviruses. **Explanation:** **1. Why Rotavirus is Correct:** Rotavirus (a member of the *Reoviridae* family) is the **most common cause of severe dehydrating diarrhea** in infants and young children worldwide. It primarily affects the 6-month to 2-year age group. The virus infects the mature enterocytes of the villi in the small intestine, leading to malabsorption and osmotic diarrhea. Its characteristic "wheel-like" appearance under electron microscopy (Latin: *Rota* = wheel) is a classic diagnostic feature. **2. Analysis of Incorrect Options:** * **Picornaviruses:** This family includes Poliovirus, Rhinovirus, and Hepatitis A. While some (like Coxsackieviruses) can cause systemic illness, they are not the primary cause of pediatric gastroenteritis. * **Togaviruses:** This family includes Rubella and Alpha viruses (like Chikungunya). These typically present with rashes, fever, or arthralgia, not primary gastroenteritis. * **Paramyxoviruses:** This family includes Measles, Mumps, and RSV. These are primarily respiratory pathogens or cause systemic infections with parotitis; they do not cause diarrheal disease. **3. NEET-PG High-Yield Pearls:** * **Mechanism:** Rotavirus produces a viral enterotoxin called **NSP4**, which induces secretion by increasing intracellular calcium. * **Seasonality:** In temperate climates, it is more common in **winter** ("Winter diarrhea"). * **Vaccines:** Two major live-attenuated oral vaccines are used: **Rotarix** (monovalent) and **RotaTeq** (pentavalent). In India, **Rotavac** is part of the National Immunization Schedule. * **Diagnosis:** The gold standard for rapid diagnosis is **ELISA** for detecting VP6 antigen in stools. * **Note:** While Rotavirus is the most common in children, **Norovirus** is the most common cause of viral gastroenteritis outbreaks across all age groups (epidemic diarrhea).

Q: Coronaviruses are recognized by club-shaped surface projections that are 20 nm long and resemble solar coronas. These viruses are characterized by their ability to

cause severe respiratory illness. **Explanation:** Coronaviruses are large, enveloped, positive-sense single-stranded RNA (+ssRNA) viruses. Their name is derived from the characteristic **club-shaped surface projections** (S-proteins) that create a "halo" or solar corona appearance under electron microscopy. **Why Option B is Correct:** While coronaviruses have historically been associated with mild disease, they are clinically significant for their ability to cause **severe respiratory illness**. This was highlighted by the outbreaks of **SARS-CoV** (2003), **MERS-CoV** (2012), and the **SARS-CoV-2** (COVID-19) pandemic. These viruses infect the lower respiratory tract, leading to severe pneumonia, Acute Respiratory Distress Syndrome (ARDS), and multi-organ failure. **Analysis of Incorrect Options:** * **Option A:** While coronaviruses are the second most common cause of the **common cold** (after Rhinoviruses), the question asks for the defining clinical characteristic that distinguishes their medical importance in a postgraduate context. "Severe respiratory illness" is the more definitive clinical hallmark of the pathogenic strains. * **Option C:** Some coronaviruses (like certain animal strains) can infect intestinal cells causing diarrhea, but this is not the primary clinical manifestation in humans compared to respiratory distress. * **Option D:** Neurological symptoms (like anosmia or encephalopathy) can occur as complications, but they are secondary to the primary respiratory pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Genome:** Largest genome among RNA viruses (~30 kb). * **Receptor Binding:** SARS-CoV and SARS-CoV-2 bind to **ACE-2 receptors**, while MERS-CoV binds to **DPP-4 (CD26)**. * **Morphology:** Helical nucleocapsid (unique for a positive-sense RNA virus). * **Replication:** Occurs in the cytoplasm; they acquire their envelope by budding through the **ER-Golgi intermediate compartment (ERGIC)**.

Q: Which of the following is NOT a marker of the active replicative phase of chronic hepatitis B?

Anti-HBc. **Explanation:** To identify the replicative phase of Chronic Hepatitis B, we look for markers that signify active viral multiplication and the resulting liver injury. **Why Anti-HBc is the correct answer:** **Anti-HBc (Antibody to Hepatitis B core antigen)** is a marker of **exposure**, not replication. It appears shortly after the onset of infection and persists for life. In chronic infection, **Total Anti-HBc** (primarily IgG) remains positive regardless of whether the virus is actively replicating or in a latent/inactive state. Therefore, it cannot differentiate between the active replicative phase and the inactive carrier state. **Why the other options are markers of replication:** * **HBV DNA:** This is the most sensitive and quantitative marker of viral load. High levels directly indicate active viral replication. * **HBV DNA Polymerase:** This enzyme is required for the synthesis of viral DNA; its presence in the serum correlates directly with active viral multiplication. * **AST & ALT:** These liver transaminases are markers of hepatocellular injury. During the active replicative phase (specifically the "Immune Clearance" phase), the host’s immune system attacks infected hepatocytes, leading to elevated AST and ALT levels. **High-Yield Clinical Pearls for NEET-PG:** * **HBeAg:** The classic serological marker for high infectivity and active replication. Its disappearance and the appearance of **Anti-HBe** (seroconversion) usually signal a transition to the inactive state. * **Window Period:** The interval where HBsAg and Anti-HBs are both negative; **IgM Anti-HBc** is the sole diagnostic marker during this phase. * **HBsAg:** Persistence for **>6 months** defines chronic infection. * **Pre-core Mutants:** Patients may have high HBV DNA but be HBeAg negative; these cases still represent active replication.

Question 1

Which of the following statements about rabies virus is incorrect?

Accepted Answer

It is a DNA virus.

Answer

Vaccine virus has a fixed incubation period.

Answer

Negri bodies are found in the hippocampus.

Answer

All bites on fingers with laceration are class three injuries.

Question 2

Papillomavirus has been found in all of the following lesions except?

Accepted Answer

Condyloma latum

Answer

Oral papillomas

Answer

Verruca vulgaris of the oral mucosa

Answer

Condyloma acuminatum

Question 3

Which of the following is NOT true of Kyasanur forest disease?

Accepted Answer

Caused by a retrovirus

Answer

Transmitted by soft ticks

Answer

Incubation period is 3-8 days

Answer

A killed vaccine is available

Question 4

A 24-year-old male presented with a lesion on his genitalia after multiple sexual encounters. Which human papillomavirus type is the causative agent?

Accepted Answer

HPV 6, 11

Answer

HPV 16, 18

Answer

HPV 31, 33

Answer

HPV 35, 45

Question 5

A patient presented with acute onset of jaundice and raised aminotransferases. Preliminary serology showed HBsAg positivity. On further testing, which of the following is least likely to be found in this patient?

Accepted Answer

Anti-HBs antibodies

Answer

HBeAg

Answer

HBV DNA

Answer

HBV DNA polymerase

Question 6

Which of the following is characteristic of Dengue hemorrhagic fever?

Accepted Answer

Most common in previously affected patients

Answer

DHF-2 is the most common cause

Answer

Associated with immunosuppression

Answer

Incubation period is 7-14 days

Question 7

Full blown Immunodeficiency syndrome is characterized by which of the following?

Accepted Answer

High viral titres with low CD4 count

Answer

Low viral titres with low CD4 count

Answer

Low viral titres with high CD4 count

Answer

High viral titres with high CD4 count

Question 8

Which of the following microbes is the most common cause of gastroenteritis in children?

Accepted Answer

Rotaviruses

Answer

Picornaviruses

Answer

Togaviruses

Answer

Paramyxoviruses

Question 9

Coronaviruses are recognized by club-shaped surface projections that are 20 nm long and resemble solar coronas. These viruses are characterized by their ability to

Accepted Answer

cause severe respiratory illness

Answer

cause the common cold

Answer

infect intestinal cells

Answer

cause neurological disorders

Question 10

Which of the following is NOT a marker of the active replicative phase of chronic hepatitis B?

Accepted Answer

Anti-HBc

Answer

HBV DNA

Answer

HBV DNA polymerase

Answer

AST & ALT

Virology — MCQs

Virology — MCQs

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