Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 881: Man is the only reservoir for which of the following diseases?

A. Rabies
B. Measles (Correct Answer)
C. Typhoid
D. Japanese B encephalitis

Explanation: **Explanation:** The concept of a **reservoir** refers to the natural habitat of an infectious agent where it lives, grows, and multiplies. For a disease to be eradicated (like Smallpox), it typically must have **no animal reservoir** and no long-term carrier state in humans. **Why Measles is Correct:** Measles is caused by the Rubeola virus (a Paramyxovirus). It is an obligatory human pathogen. **Man is the only known reservoir**, and there is no subclinical or chronic carrier state. Once an individual is infected, they either recover with lifelong immunity or succumb to the disease. This lack of an animal reservoir makes Measles a prime candidate for global eradication. **Analysis of Incorrect Options:** * **Rabies:** This is a classic **zoonosis**. The primary reservoirs are wild and domestic animals (dogs, bats, foxes, raccoons). Humans are "dead-end hosts." * **Typhoid:** While humans are the only reservoir for *Salmonella Typhi*, this question is categorized under **Virology**. Typhoid is a bacterial disease. (Note: If the question were "In which of these is man the only reservoir?" without a subject constraint, Typhoid would also be technically correct, but in a Virology context, Measles is the intended answer). * **Japanese B Encephalitis:** This is an arboviral disease. The **pig** acts as the "amplifier host," and **Ardeid birds** (herons, egrets) act as the natural reservoir. Humans are accidental, dead-end hosts. **NEET-PG High-Yield Pearls:** * **Other Viral diseases with only human reservoirs:** Smallpox, Polio, Mumps, Rubella, and Hepatitis B. * **Measles Infectivity:** Most infectious during the **pre-eruptive (prodromal) stage**. * **Secondary Attack Rate (SAR):** Measles has one of the highest SARs (>90% among susceptible contacts).

Question 882: Hepatitis B is not transmitted by which of the following?

A. Blood transfusion
B. Pasteurised albumin (Correct Answer)
C. Cryoprecipitate
D. Sexual contact

Explanation: **Explanation:** Hepatitis B Virus (HBV) is a blood-borne pathogen primarily transmitted through parenteral routes, sexual contact, and vertical transmission (mother-to-child). **Why Pasteurised Albumin is the Correct Answer:** Human albumin solutions undergo a rigorous stabilization and sterilization process. During manufacturing, albumin is subjected to **pasteurization** (heating at **60°C for 10 hours**). This specific temperature and duration are sufficient to inactivate heat-labile viruses, including HBV, HCV, and HIV. Therefore, pasteurized albumin is considered safe and does not transmit Hepatitis B. **Analysis of Incorrect Options:** * **Blood Transfusion:** Whole blood and its components (RBCs, Platelets) are classic vehicles for HBV transmission if the donor is in the "window period" or has occult HBV infection. * **Cryoprecipitate:** This is a fraction of plasma rich in Factor VIII, von Willebrand factor, and fibrinogen. Since it is prepared by thawing fresh frozen plasma and is **not** subjected to heat inactivation or viral filtration like albumin, it carries a risk of transmitting HBV. * **Sexual Contact:** HBV is found in high concentrations in semen and vaginal secretions. It is significantly more infectious (approx. 50–100 times) than HIV via sexual routes. **High-Yield Clinical Pearls for NEET-PG:** * **HBsAg** is the first serological marker to appear after infection. * **HBV DNA** is the most sensitive indicator of viral replication. * **Heat Stability:** HBV is relatively heat-stable but is inactivated by autoclaving (121°C) and pasteurization (60°C for 10 hours). * **Risk of Transmission:** The risk of HBV transmission after a needle-stick injury from an HBeAg-positive source is approximately **30%** (compared to 3% for HCV and 0.3% for HIV).

Question 883: Which of the following viruses is NOT transmitted through the sexual route?

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

Explanation: **Explanation:** The transmission of Hepatitis viruses is a high-yield topic for NEET-PG. To differentiate them, remember the mnemonic: **"Vowels (A and E) go through the Bowels (Fecal-oral route)."** **1. Why Hepatitis E is the correct answer:** Hepatitis E virus (HEV) is transmitted almost exclusively via the **fecal-oral route**, primarily through contaminated water. Unlike other Hepatitis viruses, there is no documented evidence of HEV transmission through sexual contact or blood transfusions. It is characterized by self-limiting acute infection, except in pregnant women, where it can cause fulminant hepatic failure (high mortality). **2. Analysis of Incorrect Options:** * **Hepatitis A:** While primarily fecal-oral, Hepatitis A (HAV) **can be transmitted sexually**, particularly among men who have sex with men (MSM), due to oral-anal contact. This makes it distinct from HEV in terms of transmission potential. * **Hepatitis D:** HDV is a "defective" virus that requires the presence of HBsAg (Hepatitis B) to replicate. Since Hepatitis B is a classic sexually transmitted infection (STI), Hepatitis D is also transmitted via **sexual**, parenteral, and perinatal routes. * **Option C:** This is incorrect because HAV has a documented sexual transmission route, whereas HEV does not. **Clinical Pearls for NEET-PG:** * **HEV & Pregnancy:** Highest mortality (up to 20%) occurs in the 3rd trimester due to fulminant hepatitis. * **HEV Genotypes:** Genotypes 1 and 2 are human-only (waterborne); Genotypes 3 and 4 are zoonotic (undercooked pork/deer). * **Chronic Infection:** HEV can cause chronic hepatitis **only** in immunocompromised individuals (e.g., organ transplant recipients).

Question 884: Which of the following is true regarding influenza?

A. It is caused by an enveloped RNA virus.
B. Laboratory studies may show neutropenia early in the course of disease.
C. Primary infectious pneumonia is less common than secondary bacterial pneumonia. (Correct Answer)
D. Antiviral agents given early prevent complications.

Explanation: **Explanation:** **1. Why Option C is Correct:** In influenza infections, pulmonary complications are significant. **Secondary bacterial pneumonia** (most commonly caused by *S. pneumoniae*, *S. aureus*, or *H. influenzae*) is clinically more frequent than **Primary Viral Pneumonia**. While primary viral pneumonia is more severe and carries a higher mortality rate, it is relatively rare. Secondary bacterial pneumonia typically presents as a "biphasic illness," where the patient improves for a few days before experiencing a recrudescence of fever and cough. **2. Why the other options are incorrect:** * **Option A:** While Influenza is indeed an enveloped RNA virus (Orthomyxoviridae), this is a general characteristic. In NEET-PG, when multiple statements are technically true, you must select the "most clinical" or "most specific" truth defined by standard textbooks (like Harrison’s). However, in many versions of this classic question, Option A is considered a basic fact, but C is the specific clinical hallmark. * **Option B:** Early in the course of influenza, laboratory findings typically show **leukopenia** or a normal WBC count, but **leukocytosis** (not neutropenia) is more common if secondary bacterial infections occur. * **Option D:** While neuraminidase inhibitors (Oseltamivir) reduce the duration of symptoms by 1–1.5 days if given within 48 hours, there is **no definitive evidence** that they prevent serious complications like pneumonia or hospitalization in otherwise healthy individuals. **Clinical Pearls for NEET-PG:** * **Antigenic Drift:** Point mutations (causes epidemics). * **Antigenic Shift:** Genetic reassortment (causes pandemics; seen only in Influenza A). * **Drug of Choice:** Oseltamivir (inhibits Neuraminidase, preventing viral release). * **Most common secondary invader:** *Streptococcus pneumoniae*. * **Most serious secondary invader:** *Staphylococcus aureus* (often necrotizing).

Question 885: What is the primary portal of entry for poliovirus?

A. Gastrointestinal tract (Correct Answer)
B. Nasal mucosa
C. Lung
D. Skin

Explanation: ### Explanation **Correct Option: A. Gastrointestinal tract** Poliovirus is a member of the **Picornaviridae** family (genus *Enterovirus*). The primary mode of transmission is the **fecal-oral route**. Upon ingestion, the virus survives the acidic environment of the stomach and enters the body through the gastrointestinal tract. It initially multiplies in the lymphoid tissues of the pharynx (tonsils) and the **Peyer’s patches** of the ileum. From here, it spreads to the regional lymph nodes and enters the bloodstream (primary viremia). **Analysis of Incorrect Options:** * **B. Nasal mucosa:** While some respiratory transmission can occur via oropharyngeal secretions in the very early stages of infection, it is not the primary portal of entry. * **C. Lung:** Poliovirus does not cause primary respiratory infections or enter via the lower respiratory tract. * **D. Skin:** Poliovirus cannot penetrate intact skin. Unlike viruses like Rabies or Hepatitis B, it is not transmitted through bites or percutaneous injury. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Replication:** The virus primarily replicates in the **motor neurons of the anterior horn cells** of the spinal cord, leading to flaccid paralysis. * **Specimen of Choice:** For diagnosis, **stool samples** are superior to throat swabs because viral shedding in feces persists for several weeks. * **Vaccine Differences:** * **Sabin (OPV):** Live attenuated; induces local **IgA immunity** in the gut (blocks transmission). * **Salk (IPV):** Killed/Inactivated; induces humoral **IgG immunity** (prevents paralysis but not gut infection). * **Most Common Outcome:** In >90% of cases, polio infection is **asymptomatic** or a minor flu-like illness (Abortive Polio).

Question 886: Which of the following statements regarding HIV transmission from mother to fetus is FALSE?

A. The most common mode of transmission is during breastfeeding, accounting for approximately 15-30% of cases. (Correct Answer)
B. Vertical transmission is more common in preterm infants.
C. Cesarean and vaginal deliveries have an equal chance of transmitting the virus.
D. Breastfeeding is not absolutely contraindicated in developing countries.

Explanation: ### Explanation **1. Why Option A is the Correct (False) Statement:** The most common mode of vertical transmission is **intrapartum** (during labor and delivery), accounting for approximately **60–75%** of cases due to exposure to infected maternal blood and vaginal secretions. While breastfeeding does pose a risk (15–30%), it is not the *most* common mode. In the absence of intervention, the overall transmission rate is roughly 25–40%, with the majority occurring during the birth process. **2. Analysis of Other Options:** * **Option B (True):** Preterm infants are at a higher risk because they have thinner skin and a less developed immune system, making them more susceptible to viral entry during delivery. * **Option C (False/Controversial but generally accepted as a distractor):** Elective Cesarean section (before labor/rupture of membranes) significantly **reduces** transmission risk compared to vaginal delivery. However, if the viral load is undetectable (<50 copies/mL), the risks are nearly equal. In the context of standard NEET-PG questions, C-section is considered protective. * **Option D (True):** According to WHO guidelines, in developing countries where safe water and formula are unavailable, the risk of infant mortality from malnutrition and diarrhea outweighs the risk of HIV. Thus, exclusive breastfeeding with maternal ART is recommended. **3. Clinical Pearls for NEET-PG:** * **Timing of Transmission:** In utero (5–10%), Intrapartum (60–75%), Postpartum/Breastfeeding (15–30%). * **Most Important Risk Factor:** Maternal plasma viral load. * **Prophylaxis:** Zidovudine (AZT) was the first drug used to reduce vertical transmission. Current protocols use Highly Active Antiretroviral Therapy (HAART). * **Diagnosis in Infants:** HIV DNA PCR is the gold standard (Antibody tests like ELISA are unreliable until 18 months due to persistent maternal IgG).

Question 887: What is the most common cause of genital herpes?

A. Herpes Simplex Virus type 1 (HSV-1)
B. Herpes Simplex Virus type 2 (HSV-2) (Correct Answer)
C. Varicella-Zoster Virus (VZV)
D. Epstein-Barr Virus (EBV)

Explanation: **Explanation:** **Herpes Simplex Virus type 2 (HSV-2)** is the most common cause of genital herpes worldwide. While both HSV-1 and HSV-2 can cause orogenital lesions, HSV-2 has a specific predilection for the sacral ganglia (S2-S4), where it establishes latency. It is primarily transmitted through sexual contact and is responsible for the majority of recurrent genital ulcerations. **Analysis of Options:** * **HSV-2 (Correct):** Traditionally and statistically the leading cause of genital herpes. It is associated with a higher rate of viral shedding and more frequent recurrences compared to HSV-1 in the genital tract. * **HSV-1 (Incorrect):** While HSV-1 is the leading cause of orolabial herpes (cold sores) and is increasingly causing genital infections in developed countries (due to oral-genital contact), HSV-2 remains the globally dominant cause of genital herpes. * **VZV (Incorrect):** Varicella-Zoster Virus causes Chickenpox (primary infection) and Herpes Zoster/Shingles (reactivation). It does not typically cause genital herpes. * **EBV (Incorrect):** Epstein-Barr Virus is the causative agent of Infectious Mononucleosis, Burkitt lymphoma, and Nasopharyngeal carcinoma; it is not a cause of genital ulcerative disease. **High-Yield NEET-PG Pearls:** * **Diagnosis:** The gold standard is PCR (most sensitive). Tzanck smear showing **multinucleated giant cells** with **Cowdry Type A** intranuclear inclusion bodies is a classic bedside finding. * **Latency:** HSV-1 stays latent in the **Trigeminal ganglion**, while HSV-2 stays latent in the **Sacral ganglion**. * **Neonatal Herpes:** Usually caused by HSV-2 during vaginal delivery; it can lead to severe encephalitis or disseminated disease. * **Treatment:** Acyclovir is the drug of choice (inhibits viral DNA polymerase).

Question 888: Which of the following is a Group B (flaviviruses) Arbovirus?

A. Dengue fever (Correct Answer)
B. Rift Valley fever
C. Chikungunya fever
D. Japanese encephalitis

Explanation: ### Explanation **Correct Answer: A. Dengue fever** **Concept:** Arboviruses (Arthropod-borne viruses) were historically classified into groups based on antigenic relationships before modern molecular taxonomy. * **Group A:** Corresponds to the **Alphavirus** genus (Family: *Togaviridae*). * **Group B:** Corresponds to the **Flavivirus** genus (Family: *Flaviviridae*). **Dengue fever** is a classic member of the **Flavivirus** genus (Group B). It is transmitted by the *Aedes aegypti* mosquito and exists in four serotypes (DEN 1-4). **Analysis of Incorrect Options:** * **B. Rift Valley fever:** This belongs to the **Phlebovirus** genus within the *Phenuiviridae* family (formerly *Bunyaviridae*). It is not classified under Group A or B. * **C. Chikungunya fever:** This is an **Alphavirus** (Family: *Togaviridae*), making it a **Group A** arbovirus. * **D. Japanese encephalitis (JE):** While JE is indeed a **Flavivirus** (Group B), in the context of standard medical examinations, if both Dengue and JE are present, Dengue is often the prototypical answer for Group B. However, technically, JE is also a Group B arbovirus. *Note: In many competitive exams, Dengue is the preferred "textbook" representative for this classification.* **High-Yield Clinical Pearls for NEET-PG:** * **Group A (Alphaviruses):** Chikungunya, Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE). * **Group B (Flaviviruses):** Dengue, Yellow Fever, Japanese Encephalitis, West Nile Virus, Kyasanur Forest Disease (KFD), and Zika Virus. * **Vector Shortcut:** *Aedes* mosquitoes transmit Dengue, Chikungunya, and Yellow Fever. *Culex* mosquitoes transmit Japanese Encephalitis and West Nile Virus. * **Diagnostic Gold Standard:** IgM ELISA (MAC-ELISA) is commonly used for Dengue and JE diagnosis. For Dengue, NS1 antigen is the marker of choice in the early febrile phase (Days 1–5).

Question 889: Which hepatitis virus is known to cause chronic liver disease?

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

Explanation: ### Explanation The correct answer is **Hepatitis C (Option C)**. **Why Hepatitis C is the correct answer:** Hepatitis C virus (HCV) is the most notorious for its high rate of chronicity. Approximately **75%–85%** of individuals infected with HCV fail to clear the virus and progress to chronic hepatitis. This persistence is primarily due to the virus's high genetic variability (quasispecies), which allows it to evade the host's immune response. Over decades, chronic HCV is a leading cause of liver cirrhosis and hepatocellular carcinoma (HCC). **Analysis of Incorrect Options:** * **Hepatitis A (Option A):** This is an enterically transmitted virus (fecal-oral route). It causes acute, self-limiting hepatitis and **never** leads to chronic liver disease or a carrier state. * **Hepatitis B (Option B):** While HBV does cause chronic disease, the rate of chronicity in adults is only about **5%–10%**. Although it is a major cause of chronic liver disease globally, HCV has a significantly higher *likelihood* of becoming chronic once an individual is infected. * **Hepatitis D (Option D):** HDV is a defective virus that requires the HBsAg coat of Hepatitis B to replicate. While it can cause severe chronic disease (especially in superinfections), it cannot exist or cause disease independently of HBV. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** HCV is most commonly transmitted via **parenteral routes** (IV drug use is the #1 risk factor). * **Screening & Diagnosis:** Anti-HCV antibodies are used for screening, but **HCV-RNA (PCR)** is the gold standard for diagnosing active infection. * **Treatment:** Unlike HBV, HCV is now considered **curable** with Direct-Acting Antivirals (DAAs) like Sofosbuvir. * **Vaccine:** There is **no vaccine** available for Hepatitis C due to its high antigenic variation.

Question 890: In a neonate with classic symptoms of congenital cytomegalovirus (CMV) infection, which one of the following tests would be most useful in establishing a diagnosis?

A. Blood culture for Cytomegalovirus
B. Urine culture for Cytomegalovirus
C. Urine PCR for Cytomegalovirus (Correct Answer)
D. Cerebrospinal fluid PCR for Cytomegalovirus

Explanation: **Explanation:** Congenital Cytomegalovirus (CMV) is the most common intrauterine infection. In a neonate presenting with classic symptoms (microcephaly, periventricular calcifications, sensorineural hearing loss, and petechiae), the diagnosis must be confirmed within the first **3 weeks of life** to differentiate congenital from post-natal acquisition. **Why Option C is Correct:** **Urine PCR** is currently the gold standard and the most sensitive method for diagnosing congenital CMV. CMV is shed in very high titers in the urine of infected neonates. PCR is preferred over culture because it is faster, more sensitive, and less affected by transport conditions. Saliva PCR is also a valid screening tool, but positive results must be confirmed with urine PCR due to potential contamination from breast milk. **Why Other Options are Incorrect:** * **A. Blood culture:** CMV is a slow-growing virus (taking up to 2-3 weeks in conventional culture). Blood cultures have low sensitivity and are not the preferred diagnostic medium for congenital cases. * **B. Urine culture:** While historically the "gold standard" (using Shell Vial culture), it has been largely replaced by PCR due to the longer turnaround time and the requirement for viable viral particles. * **C. CSF PCR:** This is used to evaluate central nervous system involvement but is not the primary diagnostic test for confirming the presence of congenital infection, as it may be negative even in symptomatic cases. **High-Yield Clinical Pearls for NEET-PG:** * **Timing:** Diagnosis must be made within **21 days** of birth. * **Classic Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications (Note: CMV calcifications are **periventricular**, whereas Toxoplasmosis calcifications are **diffuse**). * **Most Common Sequela:** Sensorineural hearing loss (SNHL). * **Treatment:** Intravenous Ganciclovir or oral Valganciclovir (started within the first month).

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Virology — MCQs

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