Virology Practice Questions

Q: Which of the following flaviviruses is closely related to the Russian spring-summer encephalitis virus?

Kyasanur Forest Disease (KFD). **Explanation:** The **Russian spring-summer encephalitis (RSSE)** virus and **Kyasanur Forest Disease (KFD)** virus both belong to the **Tick-borne encephalitis (TBE) complex** within the *Flaviviridae* family. They share significant antigenic similarities and are both transmitted by the bite of infected ticks (specifically *Ixodes* for RSSE and *Haemaphysalis spinigera* for KFD). **Why Kyasanur Forest Disease (KFD) is correct:** KFD is often referred to as "Monkey Fever" and is endemic to the Western Ghats of India. It is antigenically closely related to RSSE. Both viruses cause a biphasic illness characterized by fever and hemorrhagic manifestations or neurological involvement. Because of this close relationship, the RSSE vaccine has historically been used to provide cross-protection against KFD. **Why other options are incorrect:** * **Dengue and Yellow Fever:** While these are also Flaviviruses, they belong to the **Mosquito-borne** group (transmitted by *Aedes aegypti*). They are antigenically distinct from the Tick-borne encephalitis complex. * **Chikungunya:** This is an **Alphavirus** (family *Togaviridae*), not a Flavivirus. It is transmitted by *Aedes* mosquitoes and primarily causes severe arthralgia. **High-Yield Clinical Pearls for NEET-PG:** * **Vector for KFD:** *Haemaphysalis spinigera* (Hard tick). * **Reservoirs for KFD:** Monkeys (Langurs and Bonnet macaques) are the common amplifiers; their death is often a sentinel event for an outbreak. * **TBE Complex Members:** Includes RSSE, KFD, Omsk Hemorrhagic Fever, and Powassan virus. * **Diagnosis:** PCR is the gold standard in the early phase; IgM ELISA is used later.

Q: A patient presented with features of acute hepatitis following a blood transfusion a few weeks ago. Which of the following serological markers indicates the acute phase of hepatitis B infection?

Anti HBc positive, HBsAg positive. ### Explanation **1. Why Option A is Correct:** In the acute phase of Hepatitis B Virus (HBV) infection, the first detectable serum marker is **HBsAg** (Hepatitis B surface Antigen). Shortly after, the body produces antibodies against the core antigen (**Anti-HBc**). Specifically, **IgM Anti-HBc** is the hallmark of acute infection. Since HBsAg indicates the presence of the virus and Anti-HBc (IgM) confirms a recent primary response, the combination of **HBsAg (+) and Anti-HBc (+)** is diagnostic of acute hepatitis B. **2. Analysis of Incorrect Options:** * **Option B (Anti-HBe +, HBsAg +):** This pattern typically indicates a later stage of infection or chronic hepatitis B with low viral replication (seroconversion from HBeAg to Anti-HBe). It does not define the acute phase. * **Option C (Anti-HBs +, HBsAg -):** This indicates **immunity**. If Anti-HBc is also present, it signifies recovery from a natural infection; if only Anti-HBs is present, it signifies successful vaccination. * **Option D (HBeAg -, HBsAg -):** This represents a state where the virus is not actively replicating or has been cleared. It is inconsistent with a patient currently presenting with acute hepatitis symptoms. **3. NEET-PG High-Yield Pearls:** * **Window Period:** The interval when HBsAg has disappeared but Anti-HBs has not yet appeared. During this time, **IgM Anti-HBc** is the *only* diagnostic marker present. * **Infectivity Marker:** **HBeAg** is the best indicator of high viral replication and high infectivity. * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months. * **Post-Transfusion Hepatitis:** While HBV can be transmitted via blood, **Hepatitis C (HCV)** was historically the most common cause of post-transfusion hepatitis before rigorous screening; however, HBV remains a high-yield topic for serological interpretation.

Q: All of the following viruses contain double-stranded DNA, except:

Parvovirus. **Explanation:** The fundamental rule of virology is that most DNA viruses are double-stranded (dsDNA) and most RNA viruses are single-stranded (ssRNA). However, there are two high-yield exceptions frequently tested in NEET-PG: **Parvoviridae** (the only medically important ssDNA virus) and **Reoviridae** (the only medically important dsRNA virus). 1. **Why Parvovirus is correct:** Parvovirus B19 belongs to the Parvoviridae family. It is a small, non-enveloped virus characterized by a **single-stranded DNA (ssDNA)** genome. This makes it the unique exception among the DNA viruses listed. 2. **Why the other options are incorrect:** * **Papilloma virus:** A member of the Papovaviridae family; it contains circular dsDNA. * **Herpes virus:** A large, enveloped virus containing linear dsDNA. * **Pox virus:** The largest and most complex virus; despite replicating in the cytoplasm (an exception for DNA viruses), it contains a linear dsDNA genome. **Clinical Pearls for NEET-PG:** * **Parvovirus B19:** Causes **Erythema Infectiosum** (Fifth disease), characterized by the "slapped-cheek" rash. It targets erythroid progenitor cells, leading to **Aplastic Crisis** in patients with chronic hemolytic anemias (e.g., Sickle Cell Disease) and **Hydrops Fetalis** if contracted during pregnancy. * **Mnemonic for DNA Viruses:** "**HHAPPPPy**" (Herpes, Hepadna, Adeno, Papilloma, Polyoma, Pox, Parvo). All are dsDNA except **Parvo** (ssDNA). All are icosahedral except **Pox** (complex). All replicate in the nucleus except **Pox** (cytoplasm).

Q: What characterizes the latent phase of HIV infection?

Viral replication. The concept of "latency" in HIV is often a point of confusion. In HIV infection, **Clinical Latency** does not equate to **Biological Latency**. ### **Explanation of the Correct Answer** **A. Viral Replication:** During the clinical latent phase (also known as the asymptomatic or chronic phase), the virus is **not** dormant. There is persistent, vigorous viral replication occurring primarily within the lymphoid organs. Billions of new virions are produced and destroyed daily. The "latency" refers only to the absence of outward clinical symptoms, while a dynamic equilibrium exists between viral load and the host's immune response (the viral set point). ### **Analysis of Incorrect Options** * **B. Sequestration in lymphoid tissue:** While the virus is highly concentrated in the lymph nodes during this phase, it is not "sequestered" in a static sense. It is actively replicating and circulating in the plasma, albeit at lower levels than during acute infection or AIDS. * **C & D. Infectivity vs. Non-infectivity:** HIV remains **highly infectious** during the latent phase. Even if the patient is asymptomatic, the virus is present in blood, semen, and vaginal secretions. Therefore, "Non-infectivity" is factually incorrect. ### **NEET-PG High-Yield Pearls** * **The Viral Set Point:** The steady-state level of viremia achieved during the latent phase is a strong predictor of the rate of disease progression to AIDS. * **Cellular Reservoir:** True biological latency (where the virus is integrated but not replicating) occurs in **Memory CD4+ T cells**. These reservoirs are the primary obstacle to a functional cure. * **Duration:** Without ART, the clinical latent phase typically lasts 8–10 years. * **Lymph Node Architecture:** During this phase, there is follicular hyperplasia in the lymph nodes; exhaustion of this architecture leads to the terminal stage (AIDS).

Q: What is the commonest hepatotropic virus that causes an increased chronic carrier state?

Hepatitis C Virus (HCV). **Explanation:** The correct answer is **Hepatitis C Virus (HCV)**. The question asks for the virus with the highest propensity to progress to a **chronic carrier state** once an individual is infected. 1. **Why HCV is correct:** While Hepatitis B is more common globally in terms of total numbers, HCV is notorious for its high rate of chronicity. Approximately **75%–85%** of patients infected with HCV fail to clear the virus and develop chronic infection. This is primarily due to the high mutation rate of the virus (lack of proofreading by RNA polymerase), which allows it to evade the host immune response. 2. **Why the other options are incorrect:** * **Hepatitis A (HAV) and Hepatitis E (HEV):** These are transmitted via the feco-oral route and cause **acute hepatitis only**. They do not lead to chronic carrier states or chronic liver disease (Exception: HEV can cause chronicity in severely immunocompromised individuals, but this is rare and not the "commonest"). * **Hepatitis B (HBV):** While HBV causes chronic infection, the rate depends on the age of acquisition. In adults, only about **5%–10%** become chronic carriers. Although the absolute number of HBV carriers is high, the *likelihood* of an individual infection becoming chronic is significantly lower than with HCV. **High-Yield NEET-PG Pearls:** * **Highest Chronicity Rate:** HCV (80%) > HBV (5% in adults, 90% in neonates). * **HCV Screening:** Anti-HCV antibodies (ELISA); **Confirmatory/Gold Standard:** HCV RNA (PCR). * **HCV Genotypes:** Genotype 3 is the most common in India. * **Fulminant Hepatitis in Pregnancy:** Classically associated with **HEV**. * **DNA Virus:** HBV is the only DNA hepatitis virus; all others (A, C, D, E) are RNA viruses.

Q: Which of the following is the pathogen responsible for blindness in advanced HIV infections?

Cytomegalovirus. **Explanation:** **Cytomegalovirus (CMV)** is the most common cause of blindness in patients with advanced HIV/AIDS, typically occurring when the **CD4+ T-cell count falls below 50 cells/mm³**. CMV retinitis is a late-stage opportunistic infection characterized by a full-thickness necrotizing retinitis. It presents classically as the **"Pizza-pie" or "Cheese and Ketchup" appearance** (confluent areas of white retinal necrosis with associated intraretinal hemorrhages). If left untreated, it leads to retinal detachment or optic nerve involvement, resulting in permanent blindness. **Analysis of Incorrect Options:** * **Epstein-Barr virus (EBV):** While EBV is associated with Ocular Adnexal Lymphoma and Burkitt’s lymphoma in HIV patients, it is not a primary cause of retinal blindness. * **Fungus:** Fungal infections like *Cryptococcus neoformans* can cause vision loss secondary to increased intracranial pressure (papilledema) or optic neuropathy, but they are less common causes of direct retinal blindness compared to CMV. *Candida* endophthalmitis usually occurs in IV drug users rather than as a primary manifestation of advanced HIV. * **Toxoplasma:** *Toxoplasma gondii* causes necrotizing retinochoroiditis in HIV patients. While serious, it is less prevalent than CMV and typically presents with more vitreous inflammation ("headlight in the fog" appearance), whereas CMV has minimal vitritis. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Intravenous **Ganciclovir** (or Valganciclovir). Foscarnet and Cidofovir are alternatives. * **Most common ocular finding in HIV:** HIV Microangiopathy (Cotton wool spots), which is benign and non-blinding. * **Immune Recovery Uveitis (IRU):** An inflammatory reaction in the eye that occurs when a patient with CMV retinitis starts HAART and their CD4 count rises.

Q: Which serological marker best diagnoses a recent Hepatitis B infection?

IgM anti-Hepatitis B core antibody. ### Explanation **Correct Option: D. IgM anti-Hepatitis B core antibody (IgM anti-HBc)** **Why it is correct:** IgM anti-HBc is the hallmark of **acute or recent** Hepatitis B infection (typically within the first 6 months). Its clinical significance is paramount during the **"Window Period"**—the interval where HBsAg has disappeared but Anti-HBs has not yet appeared. During this gap, IgM anti-HBc may be the **only** detectable serological marker of a recent infection. **Analysis of Incorrect Options:** * **A. HBsAg:** While it is the first marker to appear and indicates active infection, it does not distinguish between acute and chronic states. It can remain positive for decades in chronic carriers. * **B. IgG anti-HBe:** This antibody indicates reduced viral replication and low infectivity. It appears later in the course of infection and is not a primary tool for diagnosing a *recent* acute event. * **C. Anti-HBs:** This antibody signifies **immunity**, either through recovery from a natural infection or via vaccination. It appears only after the infection has resolved. **NEET-PG High-Yield Pearls:** 1. **Window Period Marker:** IgM anti-HBc is the diagnostic marker of choice when HBsAg and Anti-HBs are both negative. 2. **Vaccination vs. Natural Infection:** * **Vaccinated:** Only Anti-HBs is positive. * **Prior Natural Infection:** Both Anti-HBs and IgG anti-HBc are positive. 3. **Chronic Infection:** Defined by the persistence of HBsAg for >6 months. 4. **HBeAg:** Indicates high viral load and high infectivity ("e" for envelope/excess replication).

Q: The Dane particle is the?

HBV. **Explanation:** The **Dane particle** is the complete, infectious virion of the **Hepatitis B Virus (HBV)**. First identified by DS Dane in 1970 via electron microscopy, it is a spherical structure measuring approximately **42 nm** in diameter. It consists of an inner nucleocapsid core (containing HBcAg, the DNA genome, and DNA polymerase) surrounded by an outer lipoprotein envelope containing the surface antigen (HBsAg). **Analysis of Options:** * **Option A (HBV):** Correct. The 42 nm Dane particle represents the intact, double-shelled virus capable of replication. It is found in the serum along with smaller (22 nm) spherical and tubular forms, which are non-infectious surpluses of HBsAg. * **Option B (IgG anti-HAV):** Incorrect. This is a host antibody indicating past infection or immunity to Hepatitis A; it is not a viral particle. * **Option C (Delta Virus):** Incorrect. This refers to Hepatitis D (HDV), a defective RNA virus that requires the HBsAg coat from HBV to replicate but is not called the Dane particle. * **Option D (HBcAg):** Incorrect. This is the Hepatitis B core antigen, which is a component *inside* the Dane particle, not the particle itself. **High-Yield NEET-PG Pearls:** * **Genome:** HBV is the only DNA virus among the Hepatitis viruses (partially double-stranded circular DNA). * **Morphology:** Under EM, HBV shows three forms: Dane particles (infectious), spherical forms, and filamentous forms (both non-infectious HBsAg). * **Serology:** HBsAg is the first marker to appear in blood; Anti-HBs indicates immunity. * **DNA Polymerase:** HBV possesses reverse transcriptase activity during its replication cycle.

Q: Which staining method is useful for the antemortem diagnosis of rabies?

Direct fluorescent antibody stain. **Explanation:** The **Direct Fluorescent Antibody (DFA) test** is the gold standard for rabies diagnosis. It detects rabies virus antigens in clinical specimens. For **antemortem diagnosis**, the specimen of choice is a **full-thickness skin biopsy from the nape of the neck** (containing hair follicles and cutaneous nerves). DFA is preferred due to its high sensitivity and specificity, allowing for rapid detection before death. **Analysis of Options:** * **Sellers Stain (Option A):** This is used to visualize **Negri bodies** (intracytoplasmic inclusion bodies). While characteristic of rabies, Negri bodies are only present in about 70-80% of cases and are typically identified in **postmortem** brain tissue (Ammon’s horn). * **Macchiavello Stain (Option B):** This stain is historically used to identify **Rickettsiae** and **Chlamydia** (inclusion bodies), not the rabies virus. * **Giemsa Stain (Option C):** This is a versatile hematological stain used for malaria parasites, *Chlamydia*, and *Borrelia*, but it is not specific or diagnostic for rabies. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** DFA is the most reliable test for both antemortem (skin biopsy) and postmortem (brain tissue) diagnosis. * **Negri Bodies:** These are pathognomonic for rabies but their absence does *not* rule out the disease. * **Specimen for Antemortem Diagnosis:** Skin biopsy from the nape of the neck, saliva (for RT-PCR), and CSF. * **Prophylaxis:** Rabies is 100% fatal once symptoms appear, making post-exposure prophylaxis (PEP) with wound cleaning, vaccine, and RIG (if indicated) critical.

Question 1

Which of the following flaviviruses is closely related to the Russian spring-summer encephalitis virus?

Accepted Answer

Kyasanur Forest Disease (KFD)

Answer

Dengue

Answer

Chikungunya

Answer

Yellow fever

Question 2

A patient presented with features of acute hepatitis following a blood transfusion a few weeks ago. Which of the following serological markers indicates the acute phase of hepatitis B infection?

Accepted Answer

Anti HBc positive, HBsAg positive

Answer

Anti HBe positive, HBsAg positive

Answer

Anti HBs positive, HBsAg negative

Answer

HBeAg negative, HBsAg negative

Question 3

All of the following viruses contain double-stranded DNA, except:

Accepted Answer

Parvovirus

Answer

Papilloma virus

Answer

Herpes virus

Answer

Pox virus

Question 4

What characterizes the latent phase of HIV infection?

Accepted Answer

Viral replication

Answer

Sequestration in lymphoid tissue

Answer

Infectivity

Answer

Non-infectivity

Question 5

What is the commonest hepatotropic virus that causes an increased chronic carrier state?

Accepted Answer

Hepatitis C Virus (HCV)

Answer

Hepatitis E Virus (HEV)

Answer

Hepatitis A Virus (HAV)

Answer

Hepatitis B Virus (HBV)

Question 6

Which of the following is the pathogen responsible for blindness in advanced HIV infections?

Accepted Answer

Cytomegalovirus

Answer

Epstein-Barr virus

Answer

Fungus

Answer

Toxoplasma

Question 7

Which serological marker best diagnoses a recent Hepatitis B infection?

Accepted Answer

IgM anti-Hepatitis B core antibody

Answer

Hepatitis B surface antigen (HBsAg)

Answer

IgG anti-Hepatitis B e antibody

Answer

Anti-Hepatitis B surface antibody

Question 8

The Dane particle is the?

Accepted Answer

HBV

Answer

IgG anti HAV

Answer

Delta Virus

Answer

HBC Ag

Question 9

Which staining method is useful for the antemortem diagnosis of rabies?

Accepted Answer

Direct fluorescent antibody stain

Answer

Sellers stain

Answer

Macchiavello stain

Answer

Giemsa stain

Question 10

Infection with herpes simplex virus, a common human pathogen, is best described by which of the following statements?

Accepted Answer

It can be reactivated by emotional disturbances or prolonged exposure to sunlight.

Answer

The central nervous system and visceral organs are usually involved.

Answer

It rarely recurs in a host who has a high antibody titre.

Answer

Initial infection usually occurs by intestinal absorption of the virus.

Virology — MCQs

Virology — MCQs

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