Virology Practice Questions

Q: Which hepatitis virus is defective?

Hepatitis D virus (HDV). ### Explanation **Correct Answer: D. Hepatitis D virus (HDV)** **Why HDV is the correct answer:** Hepatitis D virus (HDV) is classified as a **defective virus** (specifically a sub-viral satellite) because it cannot complete its life cycle or cause infection on its own. It lacks the genetic information to synthesize its own outer envelope (surface proteins). To replicate and infect new cells, HDV must "borrow" the **Hepatitis B surface antigen (HBsAg)** from the Hepatitis B virus (HBV). Therefore, HDV infection can only occur in the presence of an active HBV infection. **Why the other options are incorrect:** * **A. HAV:** A Picornavirus (RNA) that is fully functional and transmitted via the fecal-oral route. It does not require a helper virus. * **B. HBV:** A Hepadnavirus (DNA) that is a complete, complex virus. It acts as the "helper virus" for HDV but is not defective itself. * **C. HCV:** A Flavivirus (RNA) that is fully capable of independent replication and is a leading cause of chronic liver disease. **High-Yield Clinical Pearls for NEET-PG:** * **Modes of Infection:** * **Co-infection:** Simultaneous infection with HBV and HDV (usually presents as acute hepatitis; low risk of chronicity). * **Super-infection:** HDV infection in a chronic HBV carrier (high risk of fulminant hepatitis and rapid progression to cirrhosis). * **Genome:** HDV has a circular, single-stranded negative-sense RNA genome. * **Antigen:** The only protein encoded by the HDV genome is the **Delta antigen (HDAg)**. * **Prevention:** The Hepatitis B vaccine is protective against HDV because HDV cannot infect without HBV.

Q: Which of the following statements is WRONG regarding a patient with polio?

Can transmit it by nasal discharge.. The correct answer is **A (Can transmit it by nasal discharge)**. ### **Explanation** Poliovirus is an **Enterovirus** primarily transmitted via the **fecal-oral route**. While the virus initially multiplies in the oropharynx and can be found in throat secretions for a short period (about 1 week), it is **not** transmitted through nasal discharge. The primary modes of transmission are contaminated water/food and direct contact with infected feces. ### **Analysis of Other Options** * **B. Subclinical infection is common:** This is correct. In over 90–95% of cases, polio infection is asymptomatic or subclinical. Only about 1% of infections result in paralytic polio. * **C. Type I is the most predominant during epidemics:** This is correct. Poliovirus has three serotypes (1, 2, and 3). Type 1 is the most common cause of epidemics and the most frequent cause of paralysis. (Note: Type 2 has been eradicated globally since 2015). * **D. The patient can be vaccinated:** This is correct. Infection with one serotype does not provide cross-immunity against the others. Therefore, a patient who has recovered from polio should still be vaccinated to ensure protection against the remaining serotypes. ### **High-Yield NEET-PG Pearls** * **Specimen of Choice:** For diagnosis, **stool** is the most reliable specimen as the virus is excreted in feces for 6–8 weeks. * **Pathogenesis:** The virus attaches to the **CD155 receptor** and specifically attacks the **anterior horn cells** of the spinal cord. * **Vaccine Difference:** * **Salk (IPV):** Killed vaccine, induces humoral immunity (IgG) only. * **Sabin (OPV):** Live attenuated, induces both humoral (IgG) and local mucosal immunity (IgA). It is responsible for "herd immunity" but carries a risk of VAPP (Vaccine-Associated Paralytic Polio).

Q: What is the marker test for vertical transmission of HIV?

p24 antigen. ### Explanation **Correct Option: A. p24 antigen** In the context of vertical transmission (mother-to-child), the gold standard for diagnosing HIV in infants under 18 months is **HIV DNA PCR** or **p24 antigen assay** [2]. The underlying medical concept is the **transplacental transfer of maternal IgG antibodies**. If a mother is HIV-positive, her antibodies will be present in the infant's blood for up to 18 months, regardless of whether the infant is actually infected. Therefore, tests that detect antibodies will yield a "false positive" result [1]. To confirm infection in a neonate, we must detect the virus itself (viral load/DNA) or its structural components, such as the **p24 capsid protein**, which appear before the host mounts an antibody response [2]. **Why other options are incorrect:** * **B. Serum ELISA:** This is a screening test that detects HIV antibodies [1]. In infants, it cannot differentiate between maternal antibodies and neonatal infection. * **C & D. Western Blot / Immunoblot:** These are confirmatory tests that detect specific antibodies against HIV proteins (like gp120, gp41). Like ELISA, they remain positive in infants due to maternal IgG, making them unreliable for diagnosing vertical transmission [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** p24 antigen is the first marker to appear after infection (usually within 1–3 weeks), making it useful for early diagnosis before seroconversion. * **Best Initial Test for Infants ( 18 months):** ELISA (4th generation tests now detect both p24 and antibodies). * **Confirmatory Test (Adults):** Western Blot (though newer algorithms favor Geenius™ HIV 1/2 supplemental assays) [1].

Q: Which of the following is a diploid cell strain?

Human embryonic lung cell strain. Cell cultures in virology are classified into three types based on their origin, chromosomal constitution, and lifespan. **Explanation of the Correct Answer:** **Option C (Human embryonic lung cell strain)** is the correct answer. **Diploid cell strains** are derived from primary cultures (usually fetal tissue) and consist of cells that maintain the normal diploid number of chromosomes. They can be subcultured for a limited number of generations (usually 50 passages) before undergoing senescence. Examples include **WI-38** and **MRC-5**, both derived from human embryonic lung tissue. They are highly significant in vaccine production (e.g., Rubella, Rabies, and Varicella vaccines). **Explanation of Incorrect Options:** * **A. Rhesus monkey kidney cell culture:** This is a **Primary cell culture**. These are derived directly from animal or human organs. They are the most sensitive for primary virus isolation but cannot be subcultured beyond 1–2 times. * **B. HeLa:** This is a **Continuous (Immortal) cell line**. Derived from a human cervical cancer, these cells have an aneuploid chromosome number and can be subcultured indefinitely. * **C. McCoy:** This is also a **Continuous cell line**. It is famously used for the cultivation of *Chlamydia trachomatis*. **High-Yield Facts for NEET-PG:** * **Primary Cultures:** Best for primary isolation (e.g., Monkey kidney for Myxoviruses). * **Diploid Strains:** Used for vaccine manufacture because they are non-oncogenic. * **Continuous Lines:** Derived from tumors or transformed cells (e.g., HeLa, HEp-2, Vero, BHK-21). * **Cytopathic Effect (CPE):** The structural changes in host cells caused by viral invasion, used for identification in these cultures.

Q: Which of the following serological markers is used for epidemiologic studies of Hepatitis B?

Anti HBc. **Explanation** The correct answer is **Anti-HBc (Antibody to Hepatitis B core antigen)**. **1. Why Anti-HBc is the correct answer:** In epidemiological studies, the goal is to determine the **total number of people who have ever been infected** with Hepatitis B (prevalence). Anti-HBc is the most reliable marker for this because it appears shortly after the onset of infection and **persists for life**, regardless of whether the patient recovers or becomes a chronic carrier. Unlike other markers, it does not appear after vaccination; therefore, its presence specifically indicates a natural infection (past or present). **2. Why the other options are incorrect:** * **HBeAg:** This is a marker of **active viral replication** and high infectivity. It is used to assess the degree of infectiousness, not for broad epidemiological prevalence. * **HBcAg:** This is a particulate antigen found inside the hepatocyte. It is **not detectable in the serum** under normal conditions and therefore cannot be used as a serological marker. * **HBsAg:** This is the first marker to appear and indicates **current infection** (acute or chronic). However, it disappears upon recovery. Using HBsAg alone would miss individuals who have cleared the virus, thus underestimating the total disease burden in a population. **3. NEET-PG High-Yield Pearls:** * **Window Period:** The period where HBsAg has disappeared but Anti-HBs has not yet appeared. During this time, **Anti-HBc IgM** is the only diagnostic marker. * **Vaccination vs. Natural Infection:** * **Vaccinated:** Only Anti-HBs is positive. * **Natural Infection (Recovered):** Both Anti-HBs and Anti-HBc (IgG) are positive. * **Anti-HBc IgM:** Indicates acute infection. * **Anti-HBc IgG:** Indicates past or chronic infection.

Q: Which of the following is the next most common cause of blood transfusion-related hepatitis after hepatitis B?

Hepatitis C. ### Explanation **Correct Option: C. Hepatitis C** The primary cause of post-transfusion hepatitis (PTH) globally is **Hepatitis B Virus (HBV)**, largely due to the "window period" where HBsAg is undetectable despite infectivity. **Hepatitis C Virus (HCV)** is the **second most common cause**. Before the introduction of mandatory blood screening for HCV in the 1990s, it was actually the leading cause of "Non-A, Non-B" post-transfusion hepatitis. While modern nucleic acid testing (NAT) has significantly reduced the risk, HCV remains a significant concern due to its high rate of chronicity (75–85%) following acute infection. **Analysis of Incorrect Options:** * **A. Hepatitis A:** This virus is transmitted via the **fecal-oral route**. It has a very brief viremic phase and does not lead to a chronic carrier state, making transfusion-related transmission extremely rare. * **B. Epstein-Barr Virus (EBV):** While EBV can cause hepatitis as part of infectious mononucleosis and can be transmitted via blood, it is a rare cause of clinically significant post-transfusion hepatitis compared to hepatotropic viruses. * **D. Hepatitis D:** HDV is a defective virus that requires the presence of **HBsAg** (HBV co-infection or superinfection) to replicate. While it is blood-borne, it is categorized as a complication of HBV rather than a standalone second-most common cause. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of PTH:** Hepatitis B (due to the window period). * **Most common cause of PTH in the 1980s:** Hepatitis C (formerly Non-A, Non-B). * **Screening:** Mandatory screening for blood donors in India includes HIV, HBV (HBsAg), HCV, Syphilis, and Malaria. * **Risk Reduction:** The use of **Nucleic Acid Testing (NAT)** has drastically reduced the "window period" for HCV from ~70 days to only 3–5 days.

Q: Which of the following viruses has NOT been associated with oncogenesis?

Varicella Zoster virus. **Explanation:** The association between viruses and cancer is termed **viral oncogenesis**. This occurs when a virus introduces oncogenes into a host cell or disrupts host tumor-suppressor genes (like p53 or Rb), leading to uncontrolled cell proliferation [2]. **Why Varicella Zoster Virus (VZV) is the correct answer:** VZV (Human Herpesvirus 3) is the causative agent of **Chickenpox** and **Herpes Zoster (Shingles)** [1]. Unlike other members of the Herpesviridae family (like EBV or HHV-8), VZV is not associated with malignancy [3]. It establishes latency in the dorsal root ganglia but does not possess the molecular machinery to transform host cells into a cancerous state [1]. **Analysis of Incorrect Options:** * **Human Papilloma Virus (HPV):** High-risk types (16, 18) produce E6 and E7 oncoproteins which inhibit p53 and Rb proteins, respectively, leading to **Cervical and Oropharyngeal carcinoma** [2], [4]. * **Epstein-Barr Virus (EBV):** Known as the first human virus associated with cancer. It is linked to **Burkitt lymphoma**, Nasopharyngeal carcinoma, and Hodgkin lymphoma. * **Human T-cell Leukemia Virus (HTLV-1):** A retrovirus that causes **Adult T-cell Leukemia/Lymphoma (ATLL)** by producing the *Tax* protein, which stimulates cell proliferation [4]. **High-Yield Clinical Pearls for NEET-PG:** * **DNA Oncogenic Viruses:** HPV, EBV, HBV, HHV-8 (Kaposi Sarcoma), and Merkel Cell Polyomavirus [3]. * **RNA Oncogenic Viruses:** HTLV-1 and Hepatitis C Virus (HCV) [4]. * **Key Mechanism:** Most DNA oncoviruses integrate into the host genome or exist as episomes [4], whereas HCV (an RNA virus) causes cancer primarily through chronic inflammation and hepatocyte regeneration.

Question 1

Which hepatitis virus is defective?

Accepted Answer

Hepatitis D virus (HDV)

Answer

Hepatitis A virus (HAV)

Answer

Hepatitis B virus (HBV)

Answer

Hepatitis C virus (HCV)

Question 2

Which of the following statements is WRONG regarding a patient with polio?

Accepted Answer

Can transmit it by nasal discharge.

Answer

Subclinical infection is common.

Answer

The most predominant poliovirus type during an epidemic is type I.

Answer

The patient can be vaccinated.

Question 3

An infant was brought to the casualty with complaints of watery diarrhoea and vomiting. He had mild fever. What is the MOST common cause of acute infantile gastroenteritis?

Accepted Answer

Rotavirus

Answer

Adenovirus

Answer

Norwalk virus

Answer

Influenza virus

Question 4

What is the marker test for vertical transmission of HIV?

Accepted Answer

p24 antigen

Answer

Serum ELISA

Answer

Western blot

Answer

Immunoblot

Question 5

Hepatitis B surface antigen (HBsAg) carrier state is not associated with which of the following conditions?

Accepted Answer

Infectious mononucleosis

Answer

Down's syndrome

Answer

Chronic renal failure

Answer

Polyarteritis nodosa (PAN)

Question 6

A nursing student has just completed her hepatitis B vaccine series. Assuming she has no prior exposure to hepatitis B, what laboratory finding would you expect?

Accepted Answer

Antibody against hepatitis B surface antigen (anti-HBs) alone

Answer

Positive test for hepatitis B surface antigen

Answer

Antibody against hepatitis B core antigen (anti-HBc)

Answer

Antibody against both hepatitis B surface and core antigen

Question 7

Which of the following is a diploid cell strain?

Accepted Answer

Human embryonic lung cell strain

Answer

Rhesus monkey kidney cell culture

Answer

HeLa

Answer

McCoy

Question 8

Which of the following serological markers is used for epidemiologic studies of Hepatitis B?

Accepted Answer

Anti HBc

Answer

HBe Ag

Answer

HBc Ag

Answer

HBs Ag

Question 9

Which of the following is the next most common cause of blood transfusion-related hepatitis after hepatitis B?

Accepted Answer

Hepatitis C

Answer

Hepatitis A

Answer

Epstein-Barr hepatitis

Answer

Hepatitis D

Question 10

Which of the following viruses has NOT been associated with oncogenesis?

Accepted Answer

Varicella Zoster virus

Answer

Human Papilloma Viruses

Answer

Epstein Barr virus

Answer

Human T cell leukemia virus

Virology — MCQs

Virology — MCQs

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