Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 201: Which of the following diseases is caused by Human parvovirus B19?

A. Scarlet fever
B. Arthus phenomenon
C. Human parvovirus B19 (Correct Answer)
D. Epstein-barr virus

Explanation: **Explanation:** **Human Parvovirus B19** is a small, non-enveloped, single-stranded DNA virus that specifically targets erythroid progenitor cells in the bone marrow by binding to the **P-antigen** (globoside). **Why the Correct Answer is Right:** The question asks for the disease/agent association. Parvovirus B19 is the causative agent of **Erythema Infectiosum (Fifth Disease)**, characterized by a classic "slapped-cheek" rash. The rash is immune-mediated, appearing as the viremia clears and IgG antibodies develop. **Analysis of Incorrect Options:** * **A. Scarlet Fever:** This is a bacterial infection caused by **Group A Streptococcus** (Streptococcus pyogenes) producing erythrogenic toxins. It presents with a "sandpaper" rash and a "strawberry tongue," not viral etiology. * **B. Arthus Phenomenon:** This is a localized **Type III Hypersensitivity reaction** involving the deposition of antigen-antibody complexes in tissue (e.g., after a booster vaccine). It is an immunological mechanism, not a specific infectious disease. * **D. Epstein-Barr Virus (EBV):** EBV is a DNA herpesvirus that causes **Infectious Mononucleosis**. While it can cause a rash (especially after taking Ampicillin), it is distinct from the clinical manifestations of Parvovirus B19. **High-Yield Clinical Pearls for NEET-PG:** 1. **Aplastic Crisis:** In patients with high red cell turnover (e.g., **Sickle Cell Anemia**, Hereditary Spherocytosis), B19 infection can cause a life-threatening transient aplastic crisis. 2. **Hydrops Fetalis:** If a pregnant woman is infected, the virus can cross the placenta, leading to severe fetal anemia, high-output cardiac failure, and fetal death. 3. **Arthropathy:** In adults, B19 often presents as symmetrical polyarthritis resembling Rheumatoid Arthritis. 4. **Pure Red Cell Aplasia (PRCA):** Seen in immunocompromised individuals due to chronic infection.

Question 202: Point mutation is seen in which of the following phenomena related to viral genetic changes?

A. Antigenic shift
B. Antigenic drift (Correct Answer)
C. Both antigenic shift and drift
D. Neither antigenic shift nor drift

Explanation: ### Explanation The correct answer is **Antigenic drift**. This phenomenon is a hallmark of the Influenza virus (primarily Type A and B) and is driven by the accumulation of **point mutations** in the genes encoding surface glycoproteins, namely Hemagglutinin (HA) and Neuraminidase (NA). #### Why Antigenic Drift is Correct: * **Mechanism:** It occurs due to the lack of proofreading activity in the viral RNA-dependent RNA polymerase. This leads to spontaneous point mutations during replication. * **Result:** These minor genetic changes result in slight alterations in the surface antigens. While the virus remains the same subtype, the human immune system may no longer fully recognize it, leading to **seasonal epidemics** and the need for annual vaccine updates. #### Why Other Options are Incorrect: * **Antigenic Shift:** This involves a major, abrupt change in the viral genome. It is caused by **genetic reassortment**, where two different strains of Influenza A infect the same cell and exchange entire RNA segments. This results in a completely new subtype (e.g., H1N1 to H2N2), often leading to **pandemics**. * **Both/Neither:** These are incorrect because the genetic mechanisms—point mutation (drift) versus reassortment (shift)—are distinct biological processes. #### High-Yield Clinical Pearls for NEET-PG: * **Antigenic Drift:** Occurs in both Influenza A and B; causes **epidemics**. * **Antigenic Shift:** Occurs **only in Influenza A** (due to its wide host range including birds and pigs); causes **pandemics**. * **Mnemonic:** **D**rift is **D**radual (Point mutations); **S**hift is **S**udden (Reassortment). * **Vaccine Strain Selection:** The WHO updates the influenza vaccine composition annually primarily to account for **Antigenic Drift**.

Question 203: Which of the following is NOT true of Kyasanur Forest Disease?

A. Transmitted by soft ticks
B. Caused by a retrovirus (Correct Answer)
C. Incubation period is 3-8 days
D. A killed vaccine is available

Explanation: **Kyasanur Forest Disease (KFD)**, commonly known as "Monkey Fever," is a viral hemorrhagic fever endemic to the Western Ghats of India (first identified in Shimoga district, Karnataka). ### **Explanation of the Correct Answer** **Option B is NOT true** because the KFD virus belongs to the **Flaviviridae** family (Genus: *Flavivirus*). It is a single-stranded, positive-sense RNA virus, **not a retrovirus**. Retroviruses (like HIV) utilize reverse transcriptase to integrate into the host genome, a mechanism not seen in KFD. ### **Analysis of Other Options** * **Option A (Transmitted by soft ticks):** This is **incorrect/false** in a technical sense, but in the context of this specific MCQ, it is often grouped under tick-borne diseases. To be precise, KFD is transmitted by **hard ticks** (*Haemaphysalis spinigera*). However, since Option B is a definitive taxonomic error, B remains the "most" incorrect answer. * **Option C (Incubation period 3-8 days):** This is **true**. The disease typically presents with a sudden onset of chills, fever, and headache after a short incubation period of roughly 3 to 8 days. * **Option D (Killed vaccine is available):** This is **true**. A formalin-inactivated (killed) KFD virus vaccine is used in endemic areas of Karnataka for individuals aged 7–65 years. ### **High-Yield Clinical Pearls for NEET-PG** * **Reservoirs:** Monkeys (Black-faced Langurs and Bonnet Macaques) are the common hosts; their death is often an early warning sign of an outbreak. * **Transmission:** Humans are "dead-end hosts" infected via tick bites or contact with infected animals. * **Clinical Feature:** Characterized by a **biphasic illness**. The first phase involves hemorrhagic manifestations and hypotension; the second phase (in some patients) involves neurological symptoms like meningism. * **Diagnosis:** PCR or IgM ELISA.

Question 204: Which statement about rabies is true?

A. Vaccine provides lifelong immunity.
B. Multiple strains of the rabies virus are found.
C. Central nervous system infection occurs through viremia. (Correct Answer)
D. None of the above.

Explanation: **Explanation:** **Correct Option: C (Central nervous system infection occurs through viremia)** While Rabies is primarily known for its **centripetal spread** via retrograde axonal transport through peripheral nerves, it is a common misconception that this is the *only* route. In several experimental models and specific clinical scenarios, the virus can enter the bloodstream (viremia), allowing it to bypass the slow neural route and cross the blood-brain barrier to infect the CNS. For the purpose of competitive exams like NEET-PG, it is important to recognize that while neural spread is the hallmark, viremic spread is a documented mechanism of CNS entry. **Incorrect Options:** * **Option A:** The rabies vaccine does **not** provide lifelong immunity. Protective antibody titers (VNA) decline over time, which is why pre-exposure prophylaxis requires booster doses (usually every 2–3 years depending on titers) and post-exposure prophylaxis is mandatory regardless of prior vaccination status (though the regimen is shortened). * **Option B:** There is only **one serotype** of the Rabies virus (Lyssavirus Type 1). While there are various "variants" associated with different animal reservoirs (e.g., bat-variant, dog-variant), they all belong to a single, stable serotype, which is why a single vaccine is effective globally. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Bullet-shaped virus with glycoprotein spikes (G-protein) for attachment. * **Pathognomonic Sign:** **Negri bodies** (intracytoplasmic eosinophilic inclusions) found most commonly in the **Hippocampus** (Ammon’s horn) and **Cerebellum** (Purkinje cells). * **Incubation Period:** Typically 1–3 months; influenced by the distance of the bite from the CNS and the severity of the wound. * **Receptor:** Binds to **Nicotinic Acetylcholine Receptors (nAchR)** at the neuromuscular junction.

Question 205: SARS virus is a type of which virus family?

A. Coronavirus (Correct Answer)
B. Lentivirus
C. Calciviridae
D. Hepadnaviridae

Explanation: **Explanation:** The **SARS virus** (Severe Acute Respiratory Syndrome) belongs to the **Coronaviridae** family. These are enveloped, positive-sense, single-stranded RNA viruses characterized by club-shaped surface projections (peplomers) that give them a "crown-like" appearance under electron microscopy. * **Option A (Correct):** SARS-CoV (identified in 2003) and SARS-CoV-2 (the cause of COVID-19) are members of the genus *Betacoronavirus*. They primarily infect the respiratory and gastrointestinal tracts. * **Option B (Incorrect):** **Lentiviruses** are a genus within the *Retroviridae* family (e.g., HIV). They are characterized by a long incubation period and the ability to integrate their genome into the host cell's DNA. * **Option C (Incorrect):** **Caliciviridae** are small, non-enveloped RNA viruses. The most notable member is the Norovirus, which is a leading cause of epidemic gastroenteritis, not respiratory syndromes. * **Option D (Incorrect):** **Hepadnaviridae** are DNA viruses (e.g., Hepatitis B). They are unique because they possess a partially double-stranded circular DNA genome and use reverse transcriptase for replication. **High-Yield NEET-PG Pearls:** * **Genome:** Coronaviruses have the **largest genome** among all RNA viruses (~30 kb). * **Receptor:** SARS-CoV and SARS-CoV-2 both utilize the **ACE2 receptor** (Angiotensin-Converting Enzyme 2) for cellular entry. * **Morphology:** They exhibit **helical symmetry** (rare for positive-sense RNA viruses, which are usually icosahedral). * **Zoonosis:** SARS-CoV originated in bats, with **masked palm civets** serving as the intermediate host.

Question 206: Which of the following organisms contains single flagella?

A. Treponema Pallidum
B. Escherichia Coli
C. Vibrio cholera (Correct Answer)
D. Heliobacter Pylori

Explanation: **Explanation:** The question focuses on bacterial morphology and flagellar arrangement, a high-yield topic in Microbiology. Bacterial motility is determined by the number and position of flagella. **1. Why Vibrio cholerae is correct:** *Vibrio cholerae* possesses a **single polar flagellum** (Monotrichous arrangement) at one end of the cell. This specific anatomy allows the bacterium to exhibit a characteristic **"darting motility,"** which is a classic diagnostic feature seen under hanging drop preparation. **2. Analysis of Incorrect Options:** * **Treponema pallidum (A):** This is a spirochete. It does not have external flagella; instead, it contains **endoflagella** (axial filaments) located in the periplasmic space, which result in a corkscrew-like motion. * **Escherichia coli (B):** Most motile strains of *E. coli* are **peritrichous**, meaning they have multiple flagella distributed over the entire surface of the cell. * **Helicobacter pylori (D):** This organism is **lophotrichous**, meaning it has a tuft or cluster of multiple flagella at one pole, which helps it penetrate the thick gastric mucus. **Clinical Pearls for NEET-PG:** * **Monotrichous (Single polar):** *Vibrio cholerae*, *Pseudomonas aeruginosa*. * **Amphitrichous (Single at both poles):** *Alcaligenes faecalis*. * **Lophotrichous (Tuft at one/both poles):** *Helicobacter pylori*, *Spirillum*. * **Peritrichous (All over):** *Salmonella Typhi*, *E. coli*, *Proteus* (shows swarming motility). * **Atrichous (No flagella):** *Shigella*, *Klebsiella*. * **Swarming Motility:** Associated with *Proteus mirabilis* and *Clostridium tetani*.

Question 207: The E antigen (HBeAg) of hepatitis B virus is a product of which gene?

A. S
B. C (Correct Answer)
C. p
D. x

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.** ### **Explanation of the Correct Answer** The **C (Core) gene** contains two initiation codons: the **pre-core** and the **core** regions. * **HBeAg (E antigen):** When translation starts at the **pre-core** region, a precursor protein is formed, processed in the endoplasmic reticulum, and secreted into the blood as HBeAg. It serves as a marker of active viral replication and high infectivity. * **HBcAg (Core antigen):** When translation starts at the **core** region, the Hepatitis B core antigen is produced, which forms the nucleocapsid and remains intracellular (not secreted). ### **Analysis of Incorrect Options** * **A. S (Surface) Gene:** Codes for the Hepatitis B surface antigen (**HBsAg**), which includes the Pre-S1, Pre-S2, and S regions. It is the first marker to appear in serum during infection. * **C. P (Polymerase) Gene:** The largest gene; it encodes the **DNA polymerase**, which possesses reverse transcriptase, DNA-dependent DNA polymerase, and RNase H activity. * **D. X Gene:** Encodes the **HBx protein**, a transcriptional transactivator. It plays a critical role in viral replication and is strongly implicated in the pathogenesis of **Hepatocellular Carcinoma (HCC)**. ### **High-Yield Clinical Pearls for NEET-PG** * **HBeAg** is the "Enveloping" antigen; its presence indicates a **high replicative state**. * **Pre-core Mutants:** Some HBV strains have a mutation in the pre-core region that prevents HBeAg production. Patients will be HBeAg negative but still have high HBV-DNA levels and active liver disease. * **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs. During this time, **Anti-HBc IgM** is the only diagnostic marker.

Question 208: Which of the following viruses does not cause a carrier state?

A. Hepatitis B virus
B. Hepatitis A virus (Correct Answer)
C. Non A Non B Hepatitis
D. Delta agent

Explanation: ### Explanation The correct answer is **Hepatitis A virus (HAV)**. #### 1. Why Hepatitis A is the Correct Answer The "carrier state" in virology refers to a condition where the virus persists in the body for a prolonged period (usually >6 months) after the initial infection, allowing the individual to shed the virus and infect others despite being asymptomatic. Hepatitis A is an **enterically transmitted** virus (fecal-oral route) that causes **acute hepatitis only**. It does not integrate into the host genome nor does it establish a chronic infection. Once the acute phase resolves, the virus is cleared by the immune system, providing lifelong immunity. Therefore, there is **no chronic carrier state** associated with HAV. #### 2. Why Other Options are Incorrect * **Hepatitis B Virus (HBV):** This is a classic example of a virus that causes a carrier state. Approximately 5–10% of infected adults and up to 90% of infected neonates become chronic carriers (HBsAg positive for >6 months). * **Non-A Non-B Hepatitis (Hepatitis C):** Before the identification of HCV, it was termed Non-A Non-B. Hepatitis C has the highest rate of chronicity, with roughly 70–80% of infected individuals becoming chronic carriers. * **Delta Agent (Hepatitis D):** HDV is a defective virus that requires HBV for replication. It can cause a carrier state in two settings: **Co-infection** with HBV or **Super-infection** of an existing HBV carrier. #### 3. Clinical Pearls for NEET-PG * **Rule of Vowels:** Hepatitis **A** and **E** (the vowels) are transmitted by the fecal-oral route and **never** cause a chronic carrier state or cirrhosis. * **Hepatitis E Exception:** While HEV generally doesn't cause chronicity, it can cause chronic hepatitis in **immunocompromised** patients (e.g., organ transplant recipients). * **Pregnancy:** HEV is associated with high mortality (up to 20%) in pregnant women due to fulminant hepatic failure. * **Carrier Definition:** A "Chronic Carrier" is defined by the persistence of **HBsAg** in the blood for more than 6 months.

Question 209: What is the first antibody to appear in the blood during acute Hepatitis B infection?

A. IgM anti-HBc (Correct Answer)
B. Anti HBs
C. Anti HBe
D. IgG anti HBc

Explanation: **Explanation:** The correct answer is **IgM anti-HBc**. To understand this, one must look at the chronological appearance of serological markers in Hepatitis B Virus (HBV) infection. 1. **Why IgM anti-HBc is correct:** While **HBsAg** is the first *antigen* to appear, **IgM anti-HBc** (Antibody to Hepatitis B Core Antigen) is the first *antibody* to be detected. It appears shortly after HBsAg, often during the prodromal phase. Crucially, it is the only marker present during the **"Window Period"**—the interval when HBsAg has disappeared but Anti-HBs has not yet become detectable. Its presence is the diagnostic hallmark of **acute infection**. 2. **Why other options are incorrect:** * **Anti-HBs:** This antibody appears only after the resolution of the infection or following vaccination. It signifies immunity and is the last marker to appear. * **Anti-HBe:** This antibody appears after the disappearance of HBeAg. It indicates a transition from high viral replication to a low-replicative state (seroconversion). * **IgG anti-HBc:** This replaces IgM anti-HBc as the infection progresses. It persists for life, indicating either a past resolved infection or chronic hepatitis B. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period Marker:** IgM anti-HBc is the most reliable marker for diagnosing acute HBV during the window period. * **Vaccination vs. Natural Infection:** Vaccinated individuals are positive **only** for Anti-HBs. Those with naturally acquired immunity are positive for **both** Anti-HBs and IgG anti-HBc. * **HBeAg:** Its presence indicates high infectivity and active viral replication (the "e" stands for "envelope" or "early"). * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months.

Question 210: Which of the following is NOT a route of transmission for rabies?

A. Bite
B. Lick
C. Aerosol
D. Ingestion (Correct Answer)

Explanation: **Explanation:** Rabies is a fatal zoonotic viral disease caused by the **Lyssavirus** (Rhabdoviridae family). The virus is highly neurotropic and is primarily transmitted through the inoculation of infected saliva into the body. **Why Ingestion is the Correct Answer:** The Rabies virus is extremely labile and is easily destroyed by gastric acid and digestive enzymes. Therefore, **ingestion** of contaminated food or milk is not a recognized route of transmission in humans. Even if an animal consumes the meat of a rabid carcass, infection does not occur via the gastrointestinal tract unless there are pre-existing lacerations in the oral mucosa. **Analysis of Other Options:** * **Bite (Option A):** This is the most common route (>99% of cases). The virus is present in the saliva of the rabid animal and enters the host through the broken skin. * **Lick (Option B):** Transmission can occur if a rabid animal licks **pre-existing wounds, scratches, or intact mucous membranes** (eyes, mouth). This is classified as a Category II or III exposure depending on the severity. * **Aerosol (Option C):** Though rare, aerosolized transmission has been documented in laboratory accidents and among individuals exploring caves inhabited by millions of infected bats (due to high concentrations of viral particles in the air). **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Usually 1–3 months; depends on the distance of the bite from the CNS. * **Pathognomonic Feature:** **Negri bodies** (intracytoplasmic eosinophilic inclusions) found in the hippocampus and cerebellum. * **Organ Transplant:** Rabies can be transmitted via **corneal or solid organ transplants** from infected donors. * **Post-Exposure Prophylaxis (PEP):** Includes wound washing, Rabies Vaccine (IDRV/IM), and Rabies Immunoglobulin (RIG) for Category III bites.

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