Virology Practice Questions

Q: Lassa fever virus belongs to which viral family?

Arenaviridae. **Explanation:** **Lassa fever virus** is a member of the **Arenaviridae** family. The name "Arena" is derived from the Latin *arenosus* (sandy), referring to the grainy appearance of the virions under electron microscopy due to the presence of host ribosomes inside the viral envelope. **Why Arenaviridae is correct:** Arenaviruses are pleomorphic, enveloped viruses with a **bisegmented, ambisense RNA genome**. Lassa virus is the causative agent of Lassa fever, a viral hemorrhagic fever (VHF) endemic to West Africa. It is primarily transmitted to humans via contact with the excreta of the multimammate rat (*Mastomys natalensis*). **Why other options are incorrect:** * **Bunyaviridae:** While this family also causes VHFs (e.g., Crimean-Congo Hemorrhagic Fever, Hantavirus), they typically have a **trisegmented** RNA genome. * **Flaviviridae:** This family includes viruses like Dengue, Yellow Fever, and Zika. These are positive-sense, single-stranded RNA viruses, mostly transmitted by arthropod vectors (Arboviruses). * **Reoviridae:** These are non-enveloped viruses with a **segmented double-stranded RNA** genome (e.g., Rotavirus). **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** *Mastomys natalensis* (Multimammate rat). * **Clinical Feature:** The most common complication in survivors is **sensorineural deafness**. * **Treatment:** **Ribavirin** is the drug of choice if administered early. * **Other Arenaviruses:** Lymphocytic Choriomeningitis Virus (LCMV) and South American Hemorrhagic Fever viruses (Junin, Machupo).

Q: Hepatitis B virus E antigen (HBeAg) is a product of which gene?

C. **Explanation:** The Hepatitis B Virus (HBV) genome is a circular, partially double-stranded DNA molecule containing four overlapping open reading frames (ORFs): **S, C, P, and X.** The **C (Core) gene** contains two initiation codons (the pre-core and core regions). 1. Translation from the **pre-core region** produces a precursor protein that is processed and secreted into the blood as **HBeAg** (Hepatitis B e antigen). 2. Translation from the **core region** produces the **HBcAg** (Hepatitis B core antigen), which forms the nucleocapsid and is not secreted into the serum. Therefore, HBeAg is a soluble protein derived from the C gene, serving as a marker of active viral replication and high infectivity. **Analysis of Incorrect Options:** * **Option A (S gene):** Codes for the surface glycoproteins, collectively known as **HBsAg** (Australia Antigen), which includes the Pre-S1, Pre-S2, and S domains. * **Option C (P gene):** The largest gene; it codes for the **DNA polymerase**, which possesses reverse transcriptase, DNA-dependent DNA polymerase, and RNase H activity. * **Option D (X gene):** Codes for the **HBx protein**, a transcriptional transactivator that plays a critical role in viral replication and the development of hepatocellular carcinoma (HCC). **High-Yield Clinical Pearls for NEET-PG:** * **HBeAg** is the best indicator of **high infectivity** and active viral replication. * The appearance of **Anti-HBe** (seroconversion) usually indicates a transition to a low-replicative state. * **Pre-core mutants:** Some HBV strains have a mutation in the pre-core region that prevents HBeAg production despite high viral loads (DNA levels). * **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs; **Anti-HBc IgM** is the only diagnostic marker during this phase.

Q: Tropical spastic paraparesis is caused by which virus?

Human T cell lymphotropic virus. **Explanation:** **Tropical Spastic Paraparesis (TSP)**, also known as **HTLV-1 Associated Myelopathy (HAM)**, is a chronic progressive demyelinating disease of the spinal cord. 1. **Why Option A is correct:** The causative agent is the **Human T-cell Lymphotropic Virus Type 1 (HTLV-1)**. The virus triggers an immune-mediated inflammatory response, primarily affecting the **lateral corticospinal tracts** and posterior columns of the thoracic spinal cord. This leads to the classic clinical triad of progressive spastic leg weakness, bladder dysfunction, and sensory disturbances. It is most prevalent in tropical regions like the Caribbean, equatorial Africa, and parts of South America. 2. **Why other options are incorrect:** * **Hepatitis B Virus (HBV):** Primarily causes hepatitis, cirrhosis, and hepatocellular carcinoma; it does not have a primary neurotropic predilection for the spinal cord. * **Human Immunodeficiency Virus (HIV):** While HIV can cause "HIV-associated vacuolar myelopathy" (which mimics TSP), the specific clinical entity known as "Tropical Spastic Paraparesis" is etiologically linked to HTLV-1. * **Epstein-Barr Virus (EBV):** Associated with infectious mononucleosis, Burkitt lymphoma, and Nasopharyngeal carcinoma, but not chronic spastic paraparesis. **High-Yield Clinical Pearls for NEET-PG:** * **Target Site:** The **thoracic spinal cord** is the most common site of involvement. * **Histopathology:** Shows perivascular lymphocytic cuffing and leptomeningeal inflammation. * **Diagnosis:** Confirmed by detecting HTLV-1 antibodies in the serum and CSF (using ELISA or Western Blot). * **Transmission:** Similar to HIV (blood transfusion, sexual contact, and breast milk). * **Key Association:** HTLV-1 is also the primary cause of **Adult T-cell Leukemia/Lymphoma (ATL)**.

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.

Question 1

Lassa fever virus belongs to which viral family?

Accepted Answer

Arenaviridae

Answer

Bunyaviridae

Answer

Flaviviridae

Answer

Reoviridae

Question 2

Hepatitis B virus E antigen (HBeAg) is a product of which gene?

Accepted Answer

C

Answer

S

Answer

P

Answer

X

Question 3

Tropical spastic paraparesis is caused by which virus?

Accepted Answer

Human T cell lymphotropic virus

Answer

Hepatitis B virus

Answer

Human immunodeficiency virus

Answer

Epstein Barr virus

Question 4

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 5

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 6

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 7

What is the marker test for vertical transmission of HIV?

Accepted Answer

p24 antigen

Answer

Serum ELISA

Answer

Western blot

Answer

Immunoblot

Question 8

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 9

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 10

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

Virology — MCQs

Virology — MCQs

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