Virology

Virology Indian Medical PG Question 1: Which of the following conditions is caused by EBV?

• A. Infectious mononucleosis
• B. Nasopharyngeal carcinoma
• C. Glandular fever
• D. All of the above (Correct Answer)

Virology Explanation: **Explanation:** The correct answer is **D. All of the above**. **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is a ubiquitous DNA virus with a strong tropism for B-lymphocytes and epithelial cells. It is associated with a wide spectrum of both benign and malignant conditions. 1. **Infectious Mononucleosis (IM) & Glandular Fever:** These terms are synonymous. IM is the acute clinical syndrome caused by primary EBV infection, typically in adolescents and young adults. It is characterized by the classic triad of **fever, pharyngitis, and lymphadenopathy**. Because it presents with prominent lymph node swelling and systemic symptoms, it is colloquially termed "Glandular Fever." 2. **Nasopharyngeal Carcinoma (NPC):** EBV is strongly oncogenic. It is etiologically linked to the undifferentiated type of NPC, particularly prevalent in Southern China and Southeast Asia. The virus establishes latency in epithelial cells, leading to malignant transformation. **Why other options are included:** Options A, B, and C are all correct manifestations of EBV; therefore, "All of the above" is the most comprehensive choice. **High-Yield Clinical Pearls for NEET-PG:** * **Atypical Lymphocytes:** On a peripheral smear, look for **Downey cells** (activated T-cells reacting against infected B-cells). * **Diagnosis:** The **Paul-Bunnell Test** (detecting heterophile antibodies) is the classic screening test. * **Other Malignancies:** EBV is also associated with **Burkitt Lymphoma** (starry-sky appearance, t(8;14)), Hodgkin Lymphoma (Mixed cellularity type), and Oral Hairy Leukoplakia in HIV patients. * **Receptor:** EBV binds to the **CD21** receptor (CR2) on B-cells.

Virology Indian Medical PG Question 2: Which of the following statements regarding the Rabies virus is incorrect?

• A. It is a single-stranded RNA virus.
• B. Its genetic material is linear.
• C. It has a negative sense genome.
• D. It has a space-vehicle-like shape. (Correct Answer)

Virology Explanation: **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.

Virology Indian Medical PG Question 3: What characterizes the latent phase of HIV infection?

• A. Viral replication
• B. Sequestration in lymphoid tissue
• C. Infectivity of the virus
• D. All of the above (Correct Answer)

Virology Explanation: 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.

Virology Indian Medical PG Question 4: What is the nature of the DNA of the Hepatitis B virus (HBV)?

• A. Single-stranded
• B. Double-stranded
• C. Partially single stranded
• D. Partially double stranded (Correct Answer)

Virology Explanation: **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.

Virology Indian Medical PG Question 5: Which of the following Hepatitis viruses can be cultured in vitro?

• A. Hepatitis A virus (HAV) (Correct Answer)
• B. Hepatitis B virus (HBV)
• C. Hepatitis D virus (HDV)
• D. Hepatitis C virus (HCV)

Virology Explanation: ### 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.

Virology Flashcard 1 of 5

Question: Which virus is displayed below? _____

Answer: Rhabdovirus (rabies) bullet-shaped

Virology Flashcard 2 of 5

Question: Which virus/viral family will have nuclear, eosinophilic inclusions within cells? _____

Answer: Herpesvirus family Cowdry bodies

Virology Flashcard 3 of 5

Question: kyanasur forest disease is caused by _____ virus

Answer: group b togavirus/flavivirus

Extra Information: 

Virology Flashcard 4 of 5

Question: rabies is caused by _____

Answer: lyssa virus-1

Extra Information: 

Virology Flashcard 5 of 5

Question: dengue is caused by _____virus

Answer: flavi

Extra Information: