Virology Practice Questions

Q: In HIV infection, gp120 envelope glycoproteins bind specifically to which cells?

CD4 T-cells. **Explanation:** The entry of HIV into host cells is a multi-step process initiated by the binding of the viral envelope glycoprotein **gp120** to specific receptors on the host cell surface. The primary receptor for HIV is the **CD4 molecule**. Therefore, HIV specifically targets cells expressing this marker, most notably **CD4+ T-helper cells**, but also macrophages and dendritic cells. * **Mechanism:** The gp120-CD4 interaction induces a conformational change in gp120, allowing it to bind to co-receptors (**CCR5** on macrophages/early infection or **CXCR4** on T-cells/late infection). This is followed by **gp41**-mediated fusion of the viral envelope with the host cell membrane. **Analysis of Incorrect Options:** * **A. CD8 T-cells:** These are cytotoxic T-cells that lack the CD4 receptor. While they are involved in the immune response *against* HIV, they are not the primary targets for viral entry. * **C. B-cells:** These cells are responsible for antibody production. While HIV causes B-cell dysregulation (hypergammaglobulinemia), they do not express CD4 and are not directly infected via gp120. * **D. NK cells:** Natural Killer cells are part of the innate immune system. They lack the CD4 receptor required for gp120 binding. **High-Yield NEET-PG Pearls:** 1. **gp120:** Responsible for **attachment** (docking) to the CD4 receptor. 2. **gp41:** Responsible for **fusion** and internalization (Targeted by the drug *Enfuvirtide*). 3. **CCR5 Mutation:** Individuals with a homozygous **CCR5-Δ32 mutation** are resistant to HIV infection. 4. **Maraviroc:** A CCR5 antagonist that prevents viral entry by blocking the co-receptor.

Q: Which of the following conditions is NOT associated with Human Herpesvirus 8 (HHV-8)?

Adult T cell lymphoma. **Explanation:** The correct answer is **Adult T-cell lymphoma (ATL)** because it is caused by **Human T-cell Lymphotropic Virus type 1 (HTLV-1)**, a retrovirus, rather than a herpesvirus. ATL is characterized by "flower cells" on peripheral smear and is endemic in regions like Japan and the Caribbean. **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi Sarcoma-associated Herpesvirus (KSHV), is an oncogenic virus that primarily infects B-cells and endothelial cells. It is associated with the following conditions: * **Kaposi Sarcoma (Option B):** A vascular tumor presenting as violaceous cutaneous nodules, commonly seen in AIDS patients. * **Primary Effusion Lymphoma (Option C):** Also known as **Body Cavity Lymphoma**, this is a rare B-cell lymphoma that presents as malignant effusions in the pleural, pericardial, or peritoneal spaces without a formal tumor mass. * **Multicentric Castleman’s Disease (Option D):** A lymphoproliferative disorder characterized by lymphadenopathy and systemic inflammation; the plasma cell variant is strongly linked to HHV-8. **High-Yield NEET-PG Pearls:** * **Transmission:** HHV-8 is primarily transmitted through saliva and sexual contact. * **Target Cells:** It encodes a viral homolog of **Cyclin D1**, which pushes the host cell into the S-phase, leading to uncontrolled proliferation. * **Association:** In Primary Effusion Lymphoma, co-infection with **EBV** (Epstein-Barr Virus) is frequently observed. * **Treatment:** Management of HHV-8 related diseases often involves Highly Active Antiretroviral Therapy (HAART) in HIV-positive patients.

Q: What is the most common cause of acute gastroenteritis?

Norovirus. **Explanation:** **Norovirus (Option A)** is currently the most common cause of acute gastroenteritis (AGE) worldwide across all age groups. While Rotavirus was historically the leading cause in children, the widespread implementation of the Rotavirus vaccine has shifted the epidemiology, making Norovirus the primary pathogen for both sporadic cases and large outbreaks (often associated with cruise ships, schools, and nursing homes). It is highly contagious due to its low infectious dose and resistance to common disinfectants like alcohol. **Why other options are incorrect:** * **Rotavirus (Option B):** Formerly the #1 cause in children under 5 years. It remains a significant cause in unvaccinated populations but has been surpassed by Norovirus in global prevalence. * **Salmonella (Option C):** A common cause of *bacterial* food poisoning (inflammatory diarrhea), but it is less frequent than viral etiologies in the general population. * **E. coli (Option D):** While Enterotoxigenic E. coli (ETEC) is the most common cause of *Traveler’s diarrhea*, it is not the most common cause of general acute gastroenteritis. **High-Yield Clinical Pearls for NEET-PG:** * **Family:** Norovirus belongs to the *Caliciviridae* family (ssRNA, non-enveloped). * **Transmission:** Fecal-oral route; characteristically causes "winter vomiting disease." * **Key Feature:** It is the most common cause of **outbreaks** in closed settings. * **Diagnosis:** RT-PCR is the gold standard for detection in stool samples. * **Resistance:** Norovirus is resistant to alcohol-based hand sanitizers; handwashing with soap and water is essential for prevention.

Q: Which of the following is the least common chronic complication of measles?

Subacute sclerosing panencephalitis. **Explanation:** The question asks for the **least common chronic complication** of measles. While measles is known for its acute symptoms, its complications are what lead to significant morbidity and mortality. **Why Subacute Sclerosing Panencephalitis (SSPE) is the correct answer:** SSPE is a progressive, fatal neurodegenerative disease caused by a persistent infection with a defective measles virus. While it is a severe **chronic** complication, it is extremely rare, occurring in approximately **1 in 10,000 to 1 in 100,000** cases of measles. It typically manifests 7–10 years after the initial infection. Because of its very low incidence compared to acute complications, it is the "least common" among the choices provided. **Analysis of Incorrect Options:** * **Diarrhoea:** This is the **most common** complication of measles overall (occurring in about 8% of cases), particularly in malnourished children. * **Pneumonia:** This is the **most common cause of death** associated with measles in children. It can be caused by the measles virus itself (Hecht’s giant cell pneumonia) or secondary bacterial infections. * **Otitis Media:** This is a very frequent bacterial complication, occurring in nearly 7–10% of cases, often leading to permanent hearing loss if untreated. **NEET-PG High-Yield Pearls:** * **Most common complication:** Diarrhoea. * **Most common cause of death:** Pneumonia. * **SSPE Diagnosis:** Look for high titers of anti-measles antibodies in the CSF and serum, and **periodic complexes** on EEG. * **Vitamin A:** Supplementation reduces the severity and mortality of measles complications. * **Koplik spots:** Pathognomonic sign found on the buccal mucosa opposite the lower second molars during the pre-eruptive stage.

Q: Which Human Papillomavirus (HPV) types are considered high-risk?

16 and 18. **Explanation:** Human Papillomavirus (HPV) is a double-stranded DNA virus with over 200 genotypes. These are clinically categorized based on their oncogenic potential into "High-risk" and "Low-risk" types. **1. Why Option A is Correct:** **HPV 16 and 18** are the most potent **high-risk (oncogenic)** types. They are responsible for approximately 70% of all cervical cancers worldwide. Their oncogenicity is primarily due to the overexpression of two early proteins: * **E6:** Binds to and degrades the **p53** tumor suppressor protein. * **E7:** Binds to and inactivates the **pRb** (Retinoblastoma) protein. This leads to uncontrolled cell cycle progression and genomic instability. **2. Why Other Options are Incorrect:** * **Option B (6 and 11):** These are **low-risk** types. They are the primary cause of **Condyloma acuminatum** (anogenital warts) and Recurrent Respiratory Papillomatosis (RRP). They rarely progress to malignancy. * **Options C & D:** Types 42, 44, 70, and 72 are generally considered low-risk or of undetermined significance and are not the primary drivers of cervical carcinogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Most common type in Cervical Cancer:** HPV 16 (followed by 18). * **Most common type in Oropharyngeal Cancer:** HPV 16. * **Screening:** The Papanicolaou (Pap) smear looks for **Koilocytes** (cells with perinuclear halo and wrinkled "raisinoid" nuclei). * **Vaccination:** The **9-valent vaccine (Gardasil 9)** covers types 6, 11, 16, 18, 31, 33, 45, 52, and 58. * **Schiller’s Test:** Used during colposcopy; cancerous areas are **Lugol’s iodine negative** (remain pale/yellow) due to lack of glycogen.

Q: A patient presents with acute symptoms of hepatitis and tests positive for HDV antigen. Given that HDV requires HBV for replication, which of the following sets of serological markers indicates chronic HBV infection with superinfection by HDV?

HBsAg+, HBeAg+, Anti-HBc IgM-, Anti-HBc IgG+, Anti-HBs-. ### Explanation The key to solving this question lies in distinguishing between **HBV/HDV Co-infection** and **HDV Superinfection**. Hepatitis D Virus (HDV) is a defective RNA virus that requires the Hepatitis B Surface Antigen (HBsAg) coat for its assembly and transmission. **1. Why Option B is Correct:** In **HDV Superinfection**, a patient who is already a chronic carrier of HBV (or has chronic hepatitis B) becomes infected with HDV. * **Chronic HBV status** is defined by the presence of **HBsAg** for >6 months and the presence of **Anti-HBc IgG**. * The absence of **Anti-HBc IgM** is crucial here, as IgM indicates an acute HBV infection. * Therefore, the profile **HBsAg+, Anti-HBc IgG+, and Anti-HBc IgM-** confirms a pre-existing chronic HBV state upon which the acute HDV infection has occurred. **2. Analysis of Incorrect Options:** * **Option A:** This profile (Anti-HBc IgM+) indicates an **acute HBV infection**. If HDV markers were also present, this would represent **Co-infection** (simultaneous infection with both viruses), not superinfection. * **Option C:** This indicates a **resolved HBV infection** (HBsAg negative, Anti-HBs positive, and Anti-HBc IgG positive). HDV cannot replicate without active HBsAg production. * **Option D:** This indicates **immunity via vaccination** (only Anti-HBs positive; Anti-HBc is negative as there was no exposure to the viral core). **3. High-Yield Clinical Pearls for NEET-PG:** * **Co-infection:** Usually results in acute hepatitis that resolves; low risk of chronicity. * **Superinfection:** Often leads to severe "flare-up" of hepatitis and carries a very high risk (up to 80%) of progressing to **chronic HDV**, cirrhosis, and liver failure. * **HDV Diagnosis:** Look for HDV-Ag or HDV-RNA in the blood. * **Prevention:** The HBV vaccine is the most effective way to prevent HDV infection in HBV-naive individuals.

Q: Subacute sclerosing panencephalitis (SSPE) is not diagnosed by which of the following?

Electroencephalogram (EEG). **Explanation:** Subacute Sclerosing Panencephalitis (SSPE) is a progressive, fatal neurodegenerative disease caused by a persistent infection with a mutant strain of the **Measles virus**. The diagnosis relies on demonstrating high titers of measles antibodies and viral presence in the CNS. **Why Option A is the Correct Answer:** While an **Electroencephalogram (EEG)** is a vital supportive tool in the clinical workup of SSPE—characteristically showing **periodic, high-voltage slow-wave complexes** (Radermecker complexes)—it is **not diagnostic** on its own. EEG findings are suggestive but non-specific, as similar patterns can occur in other encephalopathies. Definitive diagnosis requires microbiological or pathological evidence of the virus. **Analysis of Incorrect Options:** * **Option B & C:** A hallmark of SSPE is the presence of **intrathecal synthesis** of measles antibodies. Diagnosis requires demonstrating high titers of anti-measles IgG in both the **blood (serum)** and **CSF**. A CSF-to-serum antibody ratio is often used to confirm the diagnosis. * **Option D:** Demonstration of **Measles virus antigen** or viral RNA in brain tissue via biopsy (or autopsy) using immunohistochemistry or PCR is a definitive diagnostic method. Histology typically shows **Cowdry type A inclusion bodies**. **High-Yield Clinical Pearls for NEET-PG:** * **Latency:** SSPE typically occurs 5–10 years after an initial measles infection. * **Pathogenesis:** Caused by a "defective" measles virus (mutations in the **M (Matrix) protein** prevent normal viral budding). * **CSF Findings:** Raised gamma globulins (oligoclonal bands) but **normal** glucose and cell count. * **Clinical Stages:** Characterized by behavioral changes, followed by **myoclonic jerks**, and eventually dementia/coma.

Q: Which of the following is a true finding regarding Hepatitis C virus?

Antibody to HCV may not be detected in the acute stage. **Explanation:** **Hepatitis C Virus (HCV)**, a member of the *Flaviviridae* family, is characterized by a significant "window period." In the acute stage of infection, anti-HCV antibodies may take **6 to 12 weeks** (or longer) to develop. Therefore, a patient may be viremic and symptomatic while testing negative for antibodies. The definitive diagnosis during this early phase is made by detecting **HCV RNA** using PCR. **Analysis of Options:** * **Option A (Incorrect):** HCV is primarily transmitted via **parenteral routes** (blood transfusions, IV drug use). Hepatitis A and E are the primary viruses spread via the fecal-oral route. * **Option C (Incorrect):** HCV is notorious for its high chronicity rate. Approximately **75%–85%** of infected individuals develop chronic hepatitis, which can lead to cirrhosis and hepatocellular carcinoma (HCC). * **Option D (Incorrect):** While historically difficult to grow, HCV **can be cultured** in vitro using specific cell lines (e.g., Huh7 human hepatoma cells). This was a breakthrough that allowed for the development of Direct-Acting Antivirals (DAAs). **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause** of post-transfusion hepatitis (historically). * **HCV RNA** is the first marker to appear (as early as 1–2 weeks post-exposure). * **Genotype 3** is the most common genotype found in India. * Unlike Hepatitis B, there is **no vaccine** available for HCV due to the high antigenic variation in its E2 envelope glycoprotein (hypervariable regions).

Q: What is true about prions?

Associated with misfolding of protein. **Explanation:** Prions (Proteinaceous Infectious Particles) are unique pathogens that lack nucleic acids (DNA/RNA). The fundamental mechanism of prion disease involves the **misfolding of a normal host protein**, known as PrPc (cellular prion protein), into an abnormal, protease-resistant isoform called **PrPsc** (scrapie prion protein). This misfolded protein acts as a template, inducing other normal proteins to misfold, leading to neurodegeneration. **Analysis of Options:** * **A. Encoded by viral genome:** Incorrect. Prions are not viruses; they are encoded by the host's own **PRNP gene** located on chromosome 20. * **C. Non-infectious:** Incorrect. Prions are highly infectious and can be transmitted via contaminated neurosurgical instruments, corneal transplants, or ingestion of infected tissue (e.g., Kuru). * **D. Immunogenic:** Incorrect. Because prions are derived from host proteins, the immune system does not recognize them as foreign. Therefore, they **do not elicit an inflammatory or immune response** (no fever, no antibody production). **High-Yield Clinical Pearls for NEET-PG:** * **Resistance:** Prions are notoriously resistant to standard sterilization methods (autoclaving, UV light, and formalin). They require specific protocols like **1N NaOH for 1 hour** or gravity displacement autoclaving at **134°C**. * **Histopathology:** Characterized by **spongiform degeneration** (vacuolation of neurons), neuronal loss, and amyloid plaques without inflammation. * **Key Diseases:** Creutzfeldt-Jakob Disease (CJD), Kuru, Fatal Familial Insomnia (FFI) in humans; Bovine Spongiform Encephalopathy (Mad Cow Disease) in cattle. * **Diagnosis:** Detection of **14-3-3 protein** in CSF is a significant diagnostic marker.

Q: Which is the longest DNA segment of the hepatitis B virus genome?

P gene. **Explanation:** The Hepatitis B Virus (HBV) is a unique, partially double-stranded circular DNA virus (Hepadnaviridae). Its compact genome consists of approximately 3,200 nucleotides and contains four overlapping open reading frames (ORFs). **1. Why P gene is correct:** The **P gene** is the largest ORF, encompassing nearly **80% of the entire HBV genome**. It encodes the viral **DNA polymerase**, a multifunctional enzyme that possesses reverse transcriptase, DNA-dependent DNA polymerase, and RNase H activities. It is essential for viral replication and is the primary target for antiviral drugs like Tenofovir and Entecavir. **2. Why other options are incorrect:** * **S gene:** Encodes the surface proteins (HBsAg). While clinically significant for diagnosis, it is much shorter than the P gene. * **C gene:** Encodes the core protein (HBcAg) and the precore protein (HBeAg). It is significantly smaller than the P gene. * **X gene:** This is the **smallest ORF** in the HBV genome. It encodes the HBx protein, which acts as a transcriptional transactivator and is implicated in the development of hepatocellular carcinoma (HCC). **High-Yield Clinical Pearls for NEET-PG:** * **Genome Structure:** HBV has a "relaxed circular DNA" (rcDNA) which is converted into **cccDNA** (covalently closed circular DNA) in the host nucleus—the template for all viral transcripts. * **Replication:** HBV is the only DNA virus that replicates via an **RNA intermediate** using reverse transcriptase. * **Dane Particle:** The complete infectious virion is a 42 nm spherical particle. * **Smallest Gene:** X gene (associated with oncogenesis). * **Largest Gene:** P gene (encodes Polymerase).

Question 1

In HIV infection, gp120 envelope glycoproteins bind specifically to which cells?

Accepted Answer

CD4 T-cells

Answer

CD8 T-cells

Answer

B-cells

Answer

NK cells

Question 2

Which of the following conditions is NOT associated with Human Herpesvirus 8 (HHV-8)?

Accepted Answer

Adult T cell lymphoma

Answer

Castleman's disease

Answer

Kaposi sarcoma

Answer

Body cavity lymphoma

Question 3

What is the most common cause of acute gastroenteritis?

Accepted Answer

Norovirus

Answer

Rotavirus

Answer

Salmonella

Answer

E. coli

Question 4

Which of the following is the least common chronic complication of measles?

Accepted Answer

Subacute sclerosing panencephalitis

Answer

Diarrhoea

Answer

Pneumonia

Answer

Otitis media

Question 5

Which Human Papillomavirus (HPV) types are considered high-risk?

Accepted Answer

16 and 18

Answer

6 and 11

Answer

42 and 44

Answer

70 and 72

Question 6

A patient presents with acute symptoms of hepatitis and tests positive for HDV antigen. Given that HDV requires HBV for replication, which of the following sets of serological markers indicates chronic HBV infection with superinfection by HDV?

Accepted Answer

HBsAg+, HBeAg+, Anti-HBc IgM-, Anti-HBc IgG+, Anti-HBs-

Answer

HBsAg+, HBeAg+, Anti-HBc IgM+, Anti-HBc IgG-, Anti-HBs-

Answer

HBsAg-, HBeAg-, Anti-HBc IgM-, Anti-HBc IgG+, Anti-HBs+

Answer

HBsAg-, HBeAg-, Anti-HBc IgM-, Anti-HBc IgG-, Anti-HBs+

Question 7

Subacute sclerosing panencephalitis (SSPE) is not diagnosed by which of the following?

Accepted Answer

Electroencephalogram (EEG)

Answer

Antibodies to measles in cerebrospinal fluid (CSF)

Answer

Antibodies to measles in blood

Answer

Measles antigen in brain biopsy

Question 8

Which of the following is a true finding regarding Hepatitis C virus?

Accepted Answer

Antibody to HCV may not be detected in the acute stage

Answer

Spreads via the fecal-oral route

Answer

Does not cause chronic hepatitis

Answer

Cannot be cultured in vitro

Question 9

What is true about prions?

Accepted Answer

Associated with misfolding of protein

Answer

Encoded by viral genome

Answer

Non-infectious

Answer

Immunogenic

Question 10

Which is the longest DNA segment of the hepatitis B virus genome?

Accepted Answer

P gene

Answer

X gene

Answer

S gene

Answer

C gene

Virology — MCQs

Virology — MCQs

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