Virology Practice Questions

Q: Which of the following is NOT a prion disease?

Progressive multifocal leucoencephalopathy. **Explanation:** The correct answer is **D. Progressive multifocal leucoencephalopathy (PML)**. The fundamental distinction lies in the causative agent. **Prion diseases** (Transmissible Spongiform Encephalopathies) are caused by **prions**, which are misfolded, infectious proteins (PrPSc) that lack nucleic acids. In contrast, **PML** is a viral disease caused by the **JC virus** (a double-stranded DNA Polyomavirus). PML occurs due to the reactivation of the JC virus in immunocompromised individuals (e.g., AIDS patients), leading to the destruction of oligodendrocytes and subsequent CNS demyelination. **Analysis of Incorrect Options:** * **Bovine Spongiform Encephalopathy (BSE):** Also known as "Mad Cow Disease," this is a classic prion disease in cattle that can be transmitted to humans as variant Creutzfeldt-Jakob Disease (vCJD). * **Transmissible Mink Encephalopathy (TME):** A rare, fatal neurodegenerative prion disease affecting farmed mink. * **Scrapie:** The prototypical prion disease found in sheep and goats, characterized by intense pruritus (leading animals to "scrape" against fences) and ataxia. **High-Yield Clinical Pearls for NEET-PG:** * **Prion Characteristics:** Resistant to standard sterilization (autoclaving at 121°C). They require **134°C for 1 hour** or immersion in **1N NaOH** for disinfection. * **Histopathology:** Prion diseases show "spongiform change" (vacuolation of neurons/gray matter) without any inflammatory response. * **Human Prion Diseases:** Include Kuru (associated with cannibalism), Creutzfeldt-Jakob Disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), and Fatal Familial Insomnia (FFI). * **PML Hallmark:** On MRI, it presents as multifocal, non-enhancing white matter lesions without mass effect.

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

Human parvovirus B19. **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.

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

Antigenic drift. ### 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**.

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

Caused by a retrovirus. **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.

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

C. 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.

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

IgM anti-HBc. **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.

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

Ingestion. **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.

Q: Which of the following infections has the highest chance of transmission by blood transfusion?

HBV. **Explanation:** The risk of transfusion-transmitted infections (TTI) is determined by the prevalence of the virus in the donor population, the duration of the "window period," and the sensitivity of screening methods. **Why HBV is the Correct Answer:** Hepatitis B Virus (HBV) remains the most common transfusion-transmitted viral infection worldwide. The primary reason is the **long window period** (averaging 30–60 days) and the presence of **Occult HBV Infection (OBI)**. In OBI, individuals are HBsAg negative but possess HBV DNA in their blood. Even with Nucleic Acid Testing (NAT), the low viral load in occult cases can sometimes escape detection, leading to a higher transmission rate compared to other viruses. **Analysis of Incorrect Options:** * **HIV (Option A):** While highly feared, the transmission risk is significantly lower than HBV due to a shorter window period (especially with NAT) and lower prevalence among voluntary donors. * **HTLV-1 (Option C):** Human T-cell Lymphotropic Virus has a very low prevalence in the general population compared to Hepatitis viruses, making it a rare cause of TTI. * **HCV (Option D):** Hepatitis C previously had a high transmission rate, but the introduction of highly sensitive NAT has reduced the window period to approximately 3–5 days, making its transmission risk lower than HBV. **NEET-PG High-Yield Pearls:** * **Order of Transmission Risk:** HBV > HCV > HIV. * **Most common infection transmitted by blood transfusion:** HBV. * **Most common cause of Post-Transfusion Hepatitis (PTH):** Historically HCV, but currently, HBV is more frequent in many developing regions due to OBI. * **Window Period:** The time between infection and the point when a laboratory test can detect the antigen/antibody. * **Screening:** Mandatory screening in India includes HIV 1&2, HBV (HBsAg), HCV, Syphilis, and Malaria.

Q: A viral organism was isolated from a painful blister on the lip of a girl. The agent was found to have double-stranded, linear DNA and was enveloped. What is the most likely causative organism?

Herpes simplex virus (HSV). ### Explanation **Correct Option: B. Herpes simplex virus (HSV)** The clinical presentation of a **painful blister on the lip** is classic for **Herpes Labialis** (cold sores), most commonly caused by **HSV-1**. From a virological perspective, HSV belongs to the *Herpesviridae* family, which is characterized by a **double-stranded, linear DNA** genome, an icosahedral capsid, and a lipid **envelope** derived from the host nuclear membrane. **Analysis of Incorrect Options:** * **A. Epstein-Barr virus (EBV):** While EBV is a herpesvirus (DS DNA, enveloped), it typically causes Infectious Mononucleosis (fever, pharyngitis, lymphadenopathy) or Burkitt lymphoma, not localized painful vesicles on the lip. * **C. Cytomegalovirus (CMV):** Also a herpesvirus, but it usually presents as a mononucleosis-like syndrome or opportunistic infections in immunocompromised patients (e.g., retinitis). It does not cause labial blisters. * **D. Poxvirus:** Although Poxviruses (like Molluscum contagiosum or Variola) have DS DNA and an envelope, their DNA is **complex/brick-shaped** rather than simple icosahedral, and they replicate in the **cytoplasm** (unlike other DNA viruses). Clinically, they do not present as typical herpetic vesicles. **NEET-PG High-Yield Pearls:** * **Tzanck Smear:** Look for **Multinucleated Giant Cells** and **Cowdry Type A** intranuclear inclusion bodies in HSV lesions. * **Latency:** HSV-1 remains latent in the **Trigeminal ganglion**, while HSV-2 remains latent in the **Sacral ganglion**. * **Enveloping:** Herpesviruses are unique because they acquire their envelope by budding through the **inner nuclear membrane** of the host cell. * **Drug of Choice:** Acyclovir (inhibits viral DNA polymerase).

Question 1

A 33-year-old nurse suffered a needle stick injury. The patient used illicit intravenous drugs. One month later, the nurse developed jaundice. Which of the following findings would implicate hepatitis B as the etiology?

Accepted Answer

Positive hepatitis B surface antigen

Answer

Positive anti-hepatitis A antibody

Answer

Positive anti-hepatitis B-core antibody

Answer

Positive anti-hepatitis B surface antibody

Question 2

Which of the following is NOT a prion disease?

Accepted Answer

Progressive multifocal leucoencephalopathy

Answer

Bovine spongiform encephalopathy

Answer

Transmissible mink encephalopathy

Answer

Scrapie

Question 3

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

Accepted Answer

Human parvovirus B19

Answer

Scarlet fever

Answer

Arthus phenomenon

Answer

Epstein-barr virus

Question 4

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

Accepted Answer

Antigenic drift

Answer

Antigenic shift

Answer

Both antigenic shift and drift

Answer

Neither antigenic shift nor drift

Question 5

Which of the following is NOT true of Kyasanur Forest Disease?

Accepted Answer

Caused by a retrovirus

Answer

Transmitted by soft ticks

Answer

Incubation period is 3-8 days

Answer

A killed vaccine is available

Question 6

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

Accepted Answer

C

Answer

S

Answer

p

Answer

x

Question 7

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

Accepted Answer

IgM anti-HBc

Answer

Anti HBs

Answer

Anti HBe

Answer

IgG anti HBc

Question 8

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

Accepted Answer

Ingestion

Answer

Bite

Answer

Lick

Answer

Aerosol

Question 9

Which of the following infections has the highest chance of transmission by blood transfusion?

Accepted Answer

HBV

Answer

HIV

Answer

HTLV-1

Answer

HCV

Question 10

A viral organism was isolated from a painful blister on the lip of a girl. The agent was found to have double-stranded, linear DNA and was enveloped. What is the most likely causative organism?

Accepted Answer

Herpes simplex virus (HSV)

Answer

Epstein-Barr virus (EBV)

Answer

Cytomegalovirus (CMV)

Answer

Poxvirus

Virology — MCQs

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