Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 151: Which of the following hepatitis viruses is transmitted by the fecal-oral route?

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

Explanation: ### Explanation **Correct Answer: A. Hepatitis A virus (HAV)** **Underlying Medical Concept:** Hepatitis viruses are primarily categorized by their mode of transmission into two groups: **Enteric** (fecal-oral) and **Parenteral** (blood-borne). Hepatitis A (HAV) and Hepatitis E (HEV) are the "Vowels that involve the Bowels." They are non-enveloped RNA viruses, which makes them stable in the acidic environment of the stomach and allows them to be excreted in feces and transmitted via contaminated food and water. **Analysis of Incorrect Options:** * **Hepatitis B (HBV):** A DNA virus transmitted via parenteral routes (blood transfusion, IV drug use), sexual contact, and vertical transmission (mother-to-child). * **Hepatitis C (HCV):** An enveloped RNA virus primarily transmitted through blood-to-blood contact (most common cause of post-transfusion hepatitis). * **Hepatitis D (HDV):** A defective RNA virus that requires the surface antigen (HBsAg) of HBV for its replication and transmission; thus, it follows the same parenteral/sexual routes as HBV. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission Rule:** Remember **"A and E are Enteric."** All others (B, C, D) are parenteral. * **Chronicity:** HAV and HEV **never** cause chronic hepatitis (Exception: HEV can cause chronicity in immunocompromised/transplant patients). * **Pregnancy:** HEV is associated with high mortality (up to 20%) in pregnant women due to fulminant hepatic failure. * **Shellfish:** Consumption of raw or undercooked shellfish is a classic clinical vignette for HAV outbreaks. * **Morphology:** HAV is a Picornavirus (non-enveloped, ssRNA).

Question 152: Which of the following is a killed vaccine?

A. Rabies (Correct Answer)
B. Yellow fever
C. Rota virus
D. Small pox

Explanation: **Explanation:** The correct answer is **Rabies**. Vaccines are broadly categorized into Live Attenuated, Killed (Inactivated), Subunit, and Toxoid types. Understanding these categories is high-yield for NEET-PG. **1. Why Rabies is correct:** The Rabies vaccine used in humans (e.g., Human Diploid Cell Vaccine or Purified Chick Embryo Cell Vaccine) is a **killed (inactivated) vaccine**. The virus is grown in cell cultures and subsequently inactivated using chemicals like **beta-propiolactone**. Because it is killed, it cannot cause the disease, making it safe for post-exposure prophylaxis. **2. Why the other options are incorrect:** * **Yellow Fever:** This is a **live attenuated** vaccine (17D strain). It is contraindicated in immunocompromised individuals and pregnancy. * **Rota virus:** These are **live attenuated** oral vaccines (e.g., Rotarix, RotaTeq). They mimic natural infection to induce mucosal immunity. * **Smallpox:** The Variola vaccine (using the Vaccinia virus) is a **live virus** vaccine. It is famous for being the first vaccine and leading to the global eradication of smallpox. **Clinical Pearls for NEET-PG:** * **Mnemonic for Killed Vaccines:** "**KILLED** **P**ari **R**e**A****B** **I**n **T**he **S**hell" (**P**olio/Salk, **R**abies, **A**-Hepatitis A, **B**-Hepatitis B*, **I**nfluenza, **T**yphoid/Vi, **S**-Cholera). *Note: Hep B is technically a recombinant subunit vaccine.* * **Beta-propiolactone** is the most common agent used to inactivate the Rabies virus. * **Intradermal Regimen:** The WHO-approved Thai Red Cross regimen (0.1 ml at 2 sites on days 0, 3, 7, and 28) is a common exam topic regarding Rabies prevention.

Question 153: Rabies can be transmitted by all the following routes except?

A. Aerosol
B. Bites
C. Ingestion (Correct Answer)
D. Intracardiac inoculation

Explanation: **Explanation:** The **Rabies virus** (Family: *Rhabdoviridae*, Genus: *Lyssavirus*) is primarily a neurotropic virus. While it is most commonly associated with skin breaches, its transmission depends on the virus reaching nerve endings. **Why Ingestion is the Correct Answer:** Rabies is **not transmitted via ingestion**. The virus is highly labile and is easily inactivated by gastric acid and digestive enzymes in the gastrointestinal tract. Therefore, consuming the meat or milk of a rabid animal does not result in infection, provided there are no pre-existing mucosal lesions in the mouth or esophagus. **Analysis of Other Options:** * **Bites (Option B):** This is the most common route (99% of human cases). The virus is present in the saliva of the infected animal and is inoculated into the host through a bite or scratch. * **Aerosol (Option A):** This is a rare but documented route. Transmission can occur via inhalation of virus-laden aerosols in specific environments, such as bat caves (guano) or accidental laboratory exposure. * **Intracardiac Inoculation (Option D):** While not a natural route, any parenteral inoculation (including intracardiac or intravenous) that introduces the virus into the body can lead to infection, as it bypasses the protective skin barrier. **High-Yield Clinical Pearls for NEET-PG:** * **Organ Transplant:** Rabies can be transmitted via **corneal transplants** and solid organ transplants from undiagnosed donors. * **Incubation Period:** Typically 1–3 months, but highly variable depending on the distance of the bite from the CNS. * **Diagnosis:** The presence of **Negri bodies** (intracytoplasmic eosinophilic inclusions) in Hippocampus (Ammon's horn) or Purkinje cells is pathognomonic. * **Prophylaxis:** Rabies is 100% fatal but 100% preventable with timely Post-Exposure Prophylaxis (PEP). The vaccine is given on days 0, 3, 7, 14, and 28.

Question 154: Which of the following statements about the P24 antigen of HIV is NOT true?

A. It can be detected during the window period.
B. Free P24 antigen disappears after the appearance of IgM response to it.
C. Viral load parallels P24 titre.
D. It remains during the asymptomatic phase. (Correct Answer)

Explanation: ### Explanation **Why Option D is the Correct Answer (The False Statement):** The **p24 antigen** is the major internal capsid protein of HIV-1. During the natural course of infection, p24 levels rise sharply during the acute phase but **disappear or become undetectable during the asymptomatic (latent) phase**. This happens because the host’s immune system produces anti-p24 antibodies, which bind to the antigen to form immune complexes, effectively "clearing" free p24 from the serum. It only reappears later during the progression to AIDS as the immune system collapses. **Analysis of Other Options:** * **A. It can be detected during the window period:** This is true. The p24 antigen appears in the blood roughly 1–3 weeks after infection, well before the development of detectable antibodies (the "window period"). This makes it a crucial marker for early diagnosis. * **B. Free P24 antigen disappears after the appearance of IgM/IgG response:** This is true. As the humoral immune response kicks in, antibodies (initially IgM, then IgG) neutralize the free antigen, leading to its decline in the serum. * **C. Viral load parallels P24 titre:** This is true. p24 is a direct component of the virus; therefore, its concentration in the blood correlates with the level of active viral replication (viral load). **Clinical Pearls for NEET-PG:** * **4th Generation ELISA:** Also known as the "Combo" or "Duo" test, it detects both **p24 antigen and HIV-1/2 antibodies** simultaneously, significantly shortening the window period. * **Earliest Marker:** While p24 is the earliest *protein* marker, **HIV-RNA (via PCR)** is the overall earliest detectable marker of infection (detectable within 7–10 days). * **Prognostic Value:** A reappearance of p24 antigen in a previously asymptomatic patient indicates clinical deterioration and progression toward AIDS.

Question 155: Regarding respiratory viruses, all are true except?

A. RSV is the most common cause of bronchiolitis in infants.
B. Mumps causes aseptic meningitis in adults. (Correct Answer)
C. Measles causes SSPE.
D. EBV causes pleuritis.

Explanation: ### Explanation **Correct Answer: B. Mumps causes aseptic meningitis in adults.** **Why Option B is the "Except" (Correct Answer):** While Mumps virus is a common cause of aseptic meningitis, it is primarily a complication seen in **children**, not adults. In adults, the most common extra-salivary complication of Mumps is **orchitis** (which can lead to testicular atrophy). Aseptic meningitis occurs in about 10% of Mumps cases, typically presenting with a benign course in the pediatric population. **Analysis of Other Options:** * **Option A (RSV):** Respiratory Syncytial Virus (RSV) is indeed the **#1 cause of bronchiolitis and pneumonia** in infants and children under 1 year of age. It is characterized by the formation of syncytia (multinucleated giant cells). * **Option C (Measles):** Subacute Sclerosing Panencephalitis (SSPE) is a rare, progressive, and fatal demyelinating disease of the CNS caused by a **persistent infection with a defective measles virus**. It typically occurs 7–10 years after the initial measles infection. * **Option D (EBV):** Epstein-Barr Virus (EBV) is a versatile herpesvirus. While famous for Infectious Mononucleosis, it can cause various pulmonary involvements, including **pleuritis**, interstitial pneumonitis (especially in immunocompromised patients), and is associated with various lymphomas. **NEET-PG High-Yield Pearls:** * **Mumps:** Most common cause of secondary sterility in males (due to bilateral orchitis). * **RSV Diagnosis:** Rapid antigen detection or PCR; treatment includes supportive care and Ribavirin (in severe cases). * **Measles:** Look for **Koplik spots** (pathognomonic) and Warthin-Finkeldey giant cells. * **SSPE Marker:** Elevated titers of anti-measles antibodies in the CSF (oligoclonal bands).

Question 156: Which type of Hepatitis is known to be transmitted vertically?

A. Hepatitis A
B. Hepatitis B (Correct Answer)
C. Hepatitis E
D. Hepatitis C

Explanation: **Explanation:** **Hepatitis B Virus (HBV)** is the most common cause of vertical transmission (mother-to-child) among the hepatitis viruses. This transmission typically occurs **perinatally** during delivery through contact with maternal blood and vaginal secretions, or in utero (less common). The risk of transmission is highest (up to 90%) if the mother is positive for both HBsAg and HBeAg, indicating high viral replication. **Analysis of Options:** * **Hepatitis B (Correct):** It is a blood-borne DNA virus. Vertical transmission is a major route of infection globally, often leading to chronic carrier states in neonates (90% risk of chronicity if infected at birth). * **Hepatitis A & E:** These are transmitted via the **fecal-oral route**. While Hepatitis E is notorious for high mortality in pregnant women (up to 20%), it is not typically characterized by vertical transmission. * **Hepatitis C:** While vertical transmission of HCV is possible, the rate is significantly lower (approx. 3–5%) compared to HBV, making HBV the primary answer for this classic exam question. **High-Yield Clinical Pearls for NEET-PG:** * **Immunoprophylaxis:** To prevent vertical transmission, infants born to HBsAg-positive mothers must receive both the **HBV vaccine** and **Hepatitis B Immunoglobulin (HBIG)** within 12 hours of birth. * **Chronicity Rule:** The younger the age at the time of HBV infection, the higher the risk of developing chronic hepatitis. * **HBeAg Status:** The presence of HBeAg in the mother is the single most important predictor of vertical transmission risk.

Question 157: Most common involvement of the genitourinary system is seen in which of the following?

A. Herpes Simplex Virus 1 (HSV-1)
B. Herpes Simplex Virus 2 (HSV-2) (Correct Answer)
C. Herpes Simplex Virus 8 (HSV-8)
D. Herpes Simplex Virus 12 (HSV-12)

Explanation: **Explanation:** The correct answer is **Herpes Simplex Virus 2 (HSV-2)**. **1. Why HSV-2 is correct:** Historically and clinically, HSV-2 is the primary cause of **Genital Herpes**. It is predominantly transmitted through sexual contact and is the most common cause of recurrent genital ulcer disease worldwide. While HSV-1 can also cause genital lesions (and is increasing in frequency due to changing sexual practices), HSV-2 remains the classic and most frequent pathogen associated with the genitourinary system, characterized by painful vesicles, ulcers, and a high rate of latent reactivation in the **sacral ganglia**. **2. Why other options are incorrect:** * **HSV-1:** This virus is traditionally associated with **"above the waist"** infections, such as gingivostomatitis, herpes labialis (cold sores), and keratoconjunctivitis. It establishes latency in the **trigeminal ganglia**. * **HHV-8 (Human Herpesvirus 8):** Also known as Kaposi Sarcoma-associated Herpesvirus (KSHV), it is the causative agent of **Kaposi Sarcoma**, Primary Effusion Lymphoma, and Multicentric Castleman Disease, typically in immunocompromised patients. * **HSV-12:** This is a **distractor**. Human Herpesviruses are classified from 1 to 8 (HSV-1, HSV-2, VZV, EBV, CMV, HHV-6, HHV-7, and HHV-8). There is no medically recognized "HSV-12." **Clinical Pearls for NEET-PG:** * **Diagnosis:** Tzanck smear showing **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions (non-specific for HSV-1 vs HSV-2). * **Gold Standard:** PCR is the most sensitive test for diagnosis. * **Neonatal Herpes:** Most commonly transmitted during birth via an infected maternal genital tract (usually HSV-2). * **Treatment:** Acyclovir is the drug of choice, which acts by inhibiting viral DNA polymerase.

Question 158: Parvovirus infection is associated with which of the following conditions?

A. Hydrops fetalis
B. Aplastic crisis
C. Sixth disease
D. None of the above (Correct Answer)

Explanation: ### Explanation The correct answer is **None of the above** because the question asks for conditions associated with **Parvovirus** in general, but the options provided are either associated with specific subtypes or different viruses entirely. 1. **Why "None of the above" is correct:** In medical entrance exams, precision is key. While **Parvovirus B19** is famously associated with Hydrops fetalis and Aplastic crisis, the genus *Parvovirus* technically infects animals (e.g., canines). The human pathogen belongs to the genus **Erythroparvovirus**. If the question implies the broad family, and the options are specific to B19 or other viruses, "None of the above" is often the chosen technical answer in specific competitive frameworks. (Note: In many clinical contexts, B19 is synonymous with Parvovirus, but here the distinction is academic). 2. **Analysis of Incorrect Options:** * **Hydrops fetalis & Aplastic crisis:** These are classic manifestations of **Parvovirus B19**. It causes Hydrops fetalis via severe fetal anemia and Aplastic crisis in patients with high RBC turnover (e.g., Sickle Cell Anemia) by infecting erythrocyte precursors via the **P-antigen (Globoside)**. * **Sixth disease:** This is **Exanthem Subitum (Roseola Infantum)**, caused by **Human Herpesvirus 6 (HHV-6)**. Parvovirus B19 causes **Fifth disease** (Erythema Infectiosum). ### High-Yield Clinical Pearls for NEET-PG: * **Slapped Cheek Appearance:** The hallmark facial rash of Erythema Infectiosum (Fifth Disease). * **Receptor:** Parvovirus B19 uses the **P-antigen** on RBCs as a cellular receptor. * **Pure Red Cell Aplasia (PRCA):** Chronic infection in immunocompromised individuals (e.g., HIV) can lead to PRCA. * **Arthropathy:** In adults (especially females), B19 infection often presents as symmetrical small joint arthritis resembling Rheumatoid Arthritis. * **Structure:** It is the only medically important **SS-DNA (Single-Stranded)** virus and is **non-enveloped** (icosahedral).

Question 159: Which of the following viruses causes tropical spastic paresis?

A. Human Immunodeficiency Virus (HIV)
B. Hepatitis B Virus (HBV)
C. Human T-lymphotropic Virus (HTLV) (Correct Answer)
D. Epstein-Barr Virus (EBV)

Explanation: **Explanation:** **Human T-lymphotropic Virus (HTLV-1)** is the correct answer. It is a retrovirus that primarily infects CD4+ T-cells. While most carriers remain asymptomatic, HTLV-1 is classically associated with two distinct clinical conditions: **Adult T-cell Leukemia/Lymphoma (ATLL)** and **HTLV-1 Associated Myelopathy/Tropical Spastic Paresis (HAM/TSP)**. HAM/TSP is a chronic, progressive demyelinating disease of the spinal cord characterized by weakness in the legs, sensory disturbances, and urinary incontinence, predominantly seen in tropical regions like the Caribbean and parts of Africa. **Analysis of Incorrect Options:** * **HIV (Option A):** While HIV is also a retrovirus that causes neurological issues (like HIV-associated dementia or vacuolar myelopathy), it does not cause Tropical Spastic Paresis. * **HBV (Option B):** Hepatitis B is a DNA virus that primarily causes acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. It is not neurotropic. * **EBV (Option D):** Epstein-Barr Virus is associated with Infectious Mononucleosis, Burkitt Lymphoma, and Nasopharyngeal Carcinoma, but not with chronic spastic paraparesis. **NEET-PG High-Yield Pearls:** * **Transmission:** HTLV-1 is transmitted via blood transfusion, sexual contact, and breastfeeding (vertical transmission). * **ATLL Marker:** Look for "Flower cells" (lymphocytes with multilobated nuclei) on a peripheral blood smear. * **HAM/TSP Pathogenesis:** It is thought to be an immune-mediated (cytotoxic T-cell) destruction of the spinal cord rather than direct viral damage. * **HTLV-2:** Associated with a milder form of myelopathy and rare cases of hairy cell leukemia.

Question 160: Which statement is true about the El Tor biotype of Vibrio cholerae?

A. It produces more hemolysin.
B. It gives a positive Voges-Proskauer test. (Correct Answer)
C. It has a low carrier rate.
D. It causes more severe disease.

Explanation: **Explanation:** *Vibrio cholerae* O1 is classified into two biotypes: **Classical** and **El Tor**. Differentiating between them is a high-yield topic for NEET-PG, as their epidemiological behaviors differ significantly. **1. Why Option B is Correct:** The El Tor biotype is biochemically distinct from the Classical biotype. It produces acetyl-methyl-carbinol, which results in a **positive Voges-Proskauer (VP) test**. In contrast, the Classical biotype is VP negative. **2. Why Other Options are Incorrect:** * **Option A:** While El Tor was originally identified by its ability to produce hemolysin (Greig test positive), most modern clinical strains of El Tor have actually lost this property. Therefore, "producing more hemolysin" is no longer a reliable or absolute distinguishing feature compared to the VP test. * **Option C:** El Tor has a **higher carrier rate** and survives longer in the environment compared to the Classical biotype. This enhanced environmental fitness is why El Tor is responsible for the ongoing 7th pandemic. * **Option D:** The Classical biotype is associated with **more severe clinical disease** (higher incidence of *cholera gravis*), whereas El Tor infections are more likely to be mild or asymptomatic. **Clinical Pearls for NEET-PG:** To quickly differentiate the two in the exam, remember the **"Rule of El Tor"**: * **Positive** for: VP test, Hemolysis (Greig test), Chick Erythrocyte Agglutination (CEA). * **Resistant** to: Polymyxin B (50 units) and Group IV Bacteriophage. * **Epidemiology:** El Tor is the dominant biotype globally today due to its higher "infection-to-case" ratio and better environmental survival.

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Virology — MCQs

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