Virology Practice Questions

Q: What is the primary vector responsible for Chikungunya fever transmission?

Aedes aegypti and Aedes albopictus. ***Aedes aegypti and Aedes albopictus*** - These mosquitoes are the primary vectors for **Chikungunya virus**, an **alphavirus** transmitted through the bite of infected females. - Both species are also well-known for transmitting other **arboviruses** such as **Dengue**, **Zika**, and **Yellow fever**. *Anopheles mosquito* - This vector is the primary transmission route for **Plasmodium** species, which cause **Malaria**. - Unlike Aedes, Anopheles species typically bite during the **night** or during **crepuscular** hours. *Culex mosquito* - This mosquito is most notably the vector for **Japanese Encephalitis** and **West Nile virus**. - It is also the primary vector for **lymphatic filariasis** caused by **Wuchereria bancrofti** in many regions. *Mansonia mosquito* - Mansonia species are primarily recognized as the vectors for **Brugian filariasis** (**Brugia malayi**). - They are characterized by their larvae's ability to attach to the roots of **aquatic plants** to obtain oxygen.

Q: Which virus is responsible for causing Nipah virus infection, an emerging zoonotic disease with high mortality rate?

Paramyxovirus. ***Paramyxovirus*** - **Nipah virus** belongs to the family **Paramyxoviridae** and the genus **Henipavirus**, characterized by a single-stranded RNA genome. - It is a **zoonotic pathogen** primarily transmitted by **Pteropus fruit bats**, causing severe respiratory illness and fatal encephalitis. *Bunyavirus* - This family includes pathogens like **Hantavirus** and **Crimean-Congo hemorrhagic fever virus**, which are typically vector-borne or rodent-borne. - Unlike Nipah, most Bunyaviruses possess a **segmented genome** comprising three circular RNA segments. *Filovirus* - This family consists of viruses like **Ebola** and **Marburg**, which primarily cause severe **viral hemorrhagic fever**. - While both are highly lethal, Filoviruses have a distinct **filamentous structure** and are not classified under the Henipavirus genus. *Arenavirus* - This family includes the **Lassa fever virus** and is generally associated with chronic infections in **rodents**. - Arenaviruses are characterized by a **ribosome-containing** virion appearance and are not taxonomically related to the Henipavirus responsible for Nipah.

Q: Which of the following statements regarding the Rabies virus is incorrect?

It has a space-vehicle-like shape.. **Explanation:** The Rabies virus belongs to the family **Rhabdoviridae** (genus *Lyssavirus*). The correct answer is **D** because the characteristic shape of the Rabies virus is **bullet-shaped**, not space-vehicle-like. The "space-vehicle" or "lunar lander" appearance is a classic description of **Bacteriophages**. **Analysis of Options:** * **A & C (Single-stranded, Negative-sense RNA):** These are correct structural features. The Rabies virus contains a single strand of RNA that must be converted into positive-sense mRNA by its own viral RNA polymerase before protein synthesis can occur. * **B (Linear genome):** The genetic material of the Rabies virus is a non-segmented, linear molecule of RNA. * **D (Incorrect Statement):** As mentioned, the virus is **bullet-shaped**, measuring approximately 75 nm x 180 nm. It is an enveloped virus covered with glycoprotein spikes (G proteins) which are essential for attachment to nicotinic acetylcholine receptors. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusions found most commonly in the **Purkinje cells of the cerebellum** and **Pyramidal cells of the hippocampus**. * **Receptor:** It binds to **Nicotinic Acetylcholine receptors (nAchR)** at the neuromuscular junction. * **Centripetal Spread:** The virus travels via retrograde axonal transport to the CNS. * **Prophylaxis:** The most common vaccine used in India is the **Purified Chick Embryo Cell Vaccine (PCECV)** or Human Diploid Cell Vaccine (HDCV), administered via the intramuscular (Essen) or intradermal (Thai Red Cross) regimen.

Q: What characterizes the latent phase of HIV infection?

All of the above. The **latent phase** (also known as the Clinical Latency or Asymptomatic stage) of HIV infection is often misunderstood as a period of viral inactivity. However, it is a state of **dynamic equilibrium** between the virus and the host immune system. ### **Explanation of Options:** * **Viral Replication (A):** Although the patient is asymptomatic, the virus is **not** dormant. Massive viral replication continues, primarily within the lymph nodes. Millions of CD4+ T cells are infected and destroyed daily, but the body compensates by producing new ones, keeping the CD4 count relatively stable for years. * **Sequestration in Lymphoid Tissue (B):** During this phase, the lymph nodes act as the primary reservoir. The virus is trapped within the follicular dendritic cell network of the lymphoid organs. This is why plasma viral loads may be low while the viral burden in the lymphoid tissue remains extremely high. * **Infectivity (C):** Even if the patient feels healthy and has a low viral load, they remain infectious. The virus can still be transmitted through blood, sexual contact, or from mother to child. Since all three processes occur simultaneously, **Option D (All of the above)** is correct. ### **High-Yield Clinical Pearls for NEET-PG:** * **The "Set Point":** The steady-state level of viremia achieved during the latent phase is called the "viral set point," which is a strong predictor of the rate of disease progression to AIDS. * **Duration:** Without ART, this phase typically lasts 8–10 years. * **PGL:** Persistent Generalized Lymphadenopathy (enlarged nodes in 2 or more extra-inguinal sites for >3 months) is a classic clinical finding during this stage. * **Virological Latency vs. Clinical Latency:** Clinical latency refers to the lack of symptoms; virological latency (true dormancy) only occurs in a small pool of "resting" memory CD4+ T cells.

Q: What is the nature of the DNA of the Hepatitis B virus (HBV)?

Partially double stranded. **Explanation:** The Hepatitis B Virus (HBV) belongs to the **Hepadnaviridae** family and possesses a unique genomic structure. Its genome is a **partially double-stranded circular DNA** (relaxed circular DNA or rcDNA). 1. **Why Option D is Correct:** The HBV genome consists of two strands of unequal length: * **L (-) Strand (Long strand):** A complete, full-length circular strand that is complementary to the viral mRNA. * **S (+) Strand (Short strand):** An incomplete strand that covers only about 50–80% of the genome length. Because one strand is shorter than the other, a portion of the genome remains single-stranded, making the overall molecule **partially double-stranded**. 2. **Why Other Options are Incorrect:** * **A & B:** While most DNA viruses are fully double-stranded (e.g., Herpes, Adenovirus) and some are single-stranded (e.g., Parvovirus B19), HBV is the unique exception that sits between these categories. * **C:** "Partially single-stranded" is technically descriptive of the gap, but the standard taxonomic and microbiological definition of the HBV genome is "partially double-stranded." **High-Yield Clinical Pearls for NEET-PG:** * **Replication:** HBV is the only DNA virus that utilizes **Reverse Transcriptase**. Inside the host nucleus, the partially double-stranded DNA is repaired by host enzymes to form **cccDNA** (covalently closed circular DNA), which serves as the template for transcription. * **Dane Particle:** The complete 42 nm infectious virion is known as the Dane particle. * **Surface Antigen:** HBsAg is produced in massive excess, appearing as spherical or tubular forms in the serum. * **DNA Polymerase:** The virus carries its own DNA polymerase which has both DNA-dependent DNA polymerase and RNA-dependent DNA polymerase (Reverse Transcriptase) activity.

Q: Which of the following Hepatitis viruses can be cultured in vitro?

Hepatitis A virus (HAV). ### Explanation The correct answer is **Hepatitis A virus (HAV)**. **Why HAV is the correct answer:** Hepatitis A virus (a Picornavirus) is unique among the primary hepatitis viruses because it can be successfully grown in **in vitro cell culture systems**. It was first isolated in 1979 using fetal rhesus monkey kidney cells (FRhK-4). While it grows slowly and is generally non-cytopathic (does not kill the host cells), its ability to be cultured has been instrumental in the development of the inactivated (killed) HAV vaccine. **Why the other options are incorrect:** * **Hepatitis B Virus (HBV):** HBV is highly fastidious and cannot be grown in standard cell cultures. Research relies on transfected cell lines or animal models (like the chimpanzee or woodchuck). * **Hepatitis D Virus (HDV):** As a defective virus, HDV requires the presence of HBV (specifically HBsAg) to replicate and assemble. It cannot be cultured independently in vitro. * **Hepatitis C Virus (HCV):** For decades, HCV was impossible to culture. While specialized "replicon" systems and specific strains (JFH-1) have been developed for research, it is not routinely culturable in the clinical or standard laboratory sense compared to HAV. **High-Yield Clinical Pearls for NEET-PG:** * **HAV:** Most common cause of acute viral hepatitis in children; transmitted via the **fecal-oral route**. * **HBV:** The only **DNA virus** among the hepatitis viruses (Hepatitis A, C, D, and E are all RNA). * **HCV:** Most common cause of **post-transfusion hepatitis** and chronic liver disease leading to cirrhosis. * **HEV:** Associated with high mortality (up to 20%) in **pregnant women** due to fulminant hepatic failure.

Q: High levels of Hepatitis B e-antigen (HBeAg) in serum indicate which of the following?

High infectivity of the virus. ### Explanation **Core Concept:** Hepatitis B e-antigen (HBeAg) is a soluble protein derived from the precore region of the HBV genome. It serves as a **surrogate marker for active viral replication**. When HBeAg is detectable in the serum, it signifies that the virus is actively multiplying, leading to a high viral load (HBV DNA) and, consequently, **high infectivity** of the patient’s blood and body fluids. **Analysis of Options:** * **Option B (Correct):** High HBeAg levels correlate directly with high titers of HBV DNA. This indicates the "replicative phase" of the infection, making the patient highly infectious to others (e.g., via needle-stick injuries or vertical transmission). * **Option A:** HBeAg is a secretory protein and is readily detectable in the serum during the early stages of acute infection and during chronic active hepatitis. * **Option C:** Low infectivity is associated with the appearance of **Anti-HBe antibodies** (seroconversion). When HBeAg disappears and Anti-HBe appears, it usually indicates a transition to a "non-replicative" or low-replicative state. * **Option D:** The recovering stage is characterized by the disappearance of HBsAg and the appearance of **Anti-HBs** (protective antibodies). While HBeAg disappears before HBsAg during recovery, its presence specifically marks active replication, not the resolution phase. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs. The only marker present is **Anti-HBc IgM**. * **Precore Mutants:** Some HBV strains have a mutation that prevents HBeAg production despite active replication. In these patients, HBeAg is negative, but HBV DNA remains high. * **Vertical Transmission:** If a mother is HBeAg positive, the risk of transmitting HBV to the newborn is **>90%**. If she is HBeAg negative (but HBsAg positive), the risk drops to about 10-20%.

Q: Which of the following is NOT associated with AIDS?

Hypogammaglobulinemia. **Explanation:** In AIDS, the hallmark of the disease is the progressive depletion of CD4+ T-helper cells [1], leading to profound immune dysregulation. **Why Hypogammaglobulinemia is the Correct Answer:** Patients with AIDS typically exhibit **Hypergammaglobulinemia** (specifically polyclonal gammaglobulinemia), not hypogammaglobulinemia. This occurs because of chronic, non-specific B-cell activation. Although the B-cells are increased in number and produce high levels of immunoglobulins (IgG and IgA), they are functionally defective and fail to mount an effective antibody response to new antigens or vaccines. **Analysis of Incorrect Options:** * **A. Increased p24 antibody:** In the early stages of HIV infection (seroconversion), the body produces antibodies against the p24 capsid antigen [2]. While p24 *antigen* levels rise during acute infection and late-stage AIDS, p24 *antibodies* are characteristic of the asymptomatic phase. * **C. Abnormal mitogen assay:** Since T-cell function is severely compromised, there is a decreased proliferative response to mitogens (like Phytohemagglutinin/PHA). This is a classic laboratory finding in cellular immunodeficiency. * **D. Anergy:** This refers to the lack of a delayed-type hypersensitivity (DTH) response to common recall antigens (e.g., Tuberculin/PPD). It occurs due to the profound loss of effector T-cells [1]. **High-Yield NEET-PG Pearls:** * **CD4:CD8 Ratio:** In healthy individuals, the ratio is ~2:1. In AIDS, this ratio **inverts** to <1:1 [1]. * **B-cell paradox:** AIDS is characterized by high quantitative globulins but poor qualitative function (increased risk of infections by encapsulated bacteria like *S. pneumoniae*). * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2-12 weeks). The p24 antigen is the earliest marker detectable during this phase [2].

Question 1

How does the Ebola virus cause severe hemorrhagic manifestations in infected patients?

Accepted Answer

Inhibition of interferon response and targeting of endothelial cells with coagulation dysfunction

Answer

Direct cytopathic effect on hepatocytes only

Answer

Selective destruction of bone marrow

Answer

Autoimmune destruction of platelets

Question 2

What is the primary vector responsible for Chikungunya fever transmission?

Accepted Answer

Aedes aegypti and Aedes albopictus

Answer

Anopheles mosquito

Answer

Culex mosquito

Answer

Mansonia mosquito

Question 3

Which virus is responsible for causing Nipah virus infection, an emerging zoonotic disease with high mortality rate?

Accepted Answer

Paramyxovirus

Answer

Bunyavirus

Answer

Filovirus

Answer

Arenavirus

Question 4

Which of the following statements regarding the Rabies virus is incorrect?

Accepted Answer

It has a space-vehicle-like shape.

Answer

It is a single-stranded RNA virus.

Answer

Its genetic material is linear.

Answer

It has a negative sense genome.

Question 5

What characterizes the latent phase of HIV infection?

Accepted Answer

All of the above

Answer

Viral replication

Answer

Sequestration in lymphoid tissue

Answer

Infectivity of the virus

Question 6

What is the nature of the DNA of the Hepatitis B virus (HBV)?

Accepted Answer

Partially double stranded

Answer

Single-stranded

Answer

Double-stranded

Answer

Partially single stranded

Question 7

Which of the following Hepatitis viruses can be cultured in vitro?

Accepted Answer

Hepatitis A virus (HAV)

Answer

Hepatitis B virus (HBV)

Answer

Hepatitis D virus (HDV)

Answer

Hepatitis C virus (HCV)

Question 8

High levels of Hepatitis B e-antigen (HBeAg) in serum indicate which of the following?

Accepted Answer

High infectivity of the virus

Answer

HBeAg is not seen in the serum

Answer

Low infectivity of the virus

Answer

Recovering stage

Question 9

Which of the following viruses produces disease or sequelae that are more severe if the infection occurs at a very young age?

Accepted Answer

Hepatitis B virus

Answer

Epstein-Barr virus

Answer

Measles virus

Answer

Poliovirus

Question 10

Which of the following is NOT associated with AIDS?

Accepted Answer

Hypogammaglobulinemia

Answer

Increased p 24 antibody

Answer

Abnormal mitogen assay

Answer

Anergy

Virology — MCQs

Virology — MCQs

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