Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 981: All of the following are transfusion-transmitted viruses except?

A. Hepatitis B
B. CMV
C. HTLV-1
D. Rubella (Correct Answer)

Explanation: **Explanation:** The core concept behind transfusion-transmitted infections (TTIs) is that the pathogen must have a significant **viremic phase** in the blood of an asymptomatic carrier. **Why Rubella is the correct answer:** Rubella (German Measles) is primarily a respiratory virus transmitted via **aerosolized droplets**. While a brief transient viremia occurs during the incubation period, the virus does not establish a chronic or latent infection in the blood. Therefore, it is not considered a transfusion-transmitted virus. Its primary clinical significance lies in its teratogenic potential (Congenital Rubella Syndrome), not blood safety. **Analysis of incorrect options:** * **Hepatitis B (HBV):** A classic TTI. It is a DNA virus that persists in the blood of chronic carriers. It is a mandatory screening test (HBsAg) for all blood donations. * **Cytomegalovirus (CMV):** CMV stays latent within **mononuclear leukocytes** (WBCs). It is a major concern in immunocompromised recipients and neonates. Risk is mitigated by using leukoreduced blood products. * **HTLV-1:** Human T-cell Lymphotropic Virus is a retrovirus that infects T-lymphocytes. It is transmitted through blood, sexual contact, and breast milk. Screening is mandatory in many countries to prevent tropical spastic paraparesis and adult T-cell leukemia. **High-Yield Clinical Pearls for NEET-PG:** * **Mandatory screening in India:** HIV 1 & 2, HBV (HBsAg), HCV, Syphilis, and Malaria. * **Most common TTI globally:** Historically Hepatitis B; however, with modern screening, the residual risk is extremely low. * **Window Period:** The time between infection and detection. Nucleic Acid Testing (NAT) is used to reduce this period for HIV, HBV, and HCV. * **Other TTIs to remember:** HIV, HCV, West Nile Virus, Zika virus, and parasites like *Babesia* and *Trypanosoma cruzi*.

Question 982: Which of the following is true about Vibrio parahaemolyticus?

A. Halophilic
B. Capsulated
C. Peritrichous flagella
D. All are true (Correct Answer)

Explanation: **Explanation:** *Vibrio parahaemolyticus* is a Gram-negative, curved bacillus primarily associated with seafood-borne gastroenteritis. Understanding its morphological and physiological characteristics is crucial for NEET-PG. 1. **Halophilic (Option A):** Unlike *Vibrio cholerae*, which can grow in the absence of salt, *V. parahaemolyticus* is **obligately halophilic**. It requires high salt concentrations (optimally 3% NaCl) for growth, as it is a natural inhabitant of marine environments. 2. **Capsulated (Option B):** It possesses a distinct **polysaccharide capsule**, which is a key virulence factor. This capsule helps the organism evade host phagocytosis and is essential for biofilm formation. 3. **Peritrichous Flagella (Option C):** This is a high-yield morphological feature. In liquid media, it possesses a single polar flagellum. However, when grown on **solid media**, it develops **lateral (peritrichous) flagella**, which enable "swarming" motility. Since all three physiological and morphological descriptors are accurate, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Kanagawa Phenomenon:** This is the most characteristic laboratory test for pathogenic strains. It refers to **Beta-hemolysis** on **Wagatsuma agar**, caused by the production of **Thermostable Direct Hemolysin (TDH)**. * **Clinical Presentation:** It is the leading cause of "Seafood poisoning" (ingestion of raw/undercooked shellfish), manifesting as explosive watery diarrhea. * **Culture:** On **TCBS (Thiosulfate Citrate Bile Salts Sucrose) agar**, it produces **green colonies** because it is a non-sucrose fermenter (unlike *V. cholerae*, which produces yellow colonies).

Question 983: Which mode of transmission is NOT considered parenteral for hepatitis?

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

Explanation: **Explanation:** The term **parenteral** refers to routes of transmission other than the alimentary canal (digestive tract), typically involving blood, needles, or direct body fluid contact. **1. Why Hepatitis A is the correct answer:** Hepatitis A virus (HAV) is transmitted via the **fecal-oral route**, primarily through contaminated food and water. It is an enterically transmitted virus. Unlike the other options, it does not cause chronic infection and is not typically spread through blood or blood products. **2. Why the other options are incorrect:** * **Hepatitis B (HBV):** This is the prototype for parenteral transmission. It is spread through blood, needles, sexual contact, and perinatally (vertical transmission). * **Hepatitis C (HCV):** Primarily transmitted through blood-to-blood contact (e.g., IV drug use, blood transfusions before screening). It is the most common cause of post-transfusion hepatitis. * **Hepatitis D (HDV):** As a defective virus that requires the HBsAg coat for replication, its transmission mirrors that of Hepatitis B (parenteral and sexual). **High-Yield NEET-PG Clinical Pearls:** * **Vowels to the Bowels:** Remember that Hepatitis **A** and **E** are transmitted via the fecal-oral route (Enteric). * **Consonants to the Blood:** Hepatitis **B, C, and D** are transmitted parenterally. * **Hepatitis E** is the most common cause of epidemic viral hepatitis in India and is associated with high mortality in **pregnant women** (fulminant hepatic failure). * **Hepatitis C** has the highest risk of progressing to **chronic carrier status** (approx. 75-85%).

Question 984: Which of the following is caused by Parvovirus?

A. Aplastic anemia
B. Erythema infectiosum (Correct Answer)
C. Roseola infantum
D. Arthritis

Explanation: **Explanation:** **Parvovirus B19** is a small, non-enveloped single-stranded DNA virus that specifically targets and replicates in **erythroid progenitor cells** (via the P antigen receptor). 1. **Why Erythema Infectiosum is correct:** Also known as **Fifth Disease**, this is the most common clinical presentation of Parvovirus B19 in children. It is characterized by a classic "slapped-cheek" rash on the face, followed by a reticular, lace-like erythematous rash on the trunk and extremities. The rash is immune-mediated, occurring after the viremic phase has cleared. 2. **Analysis of Incorrect Options:** * **Aplastic Anemia:** While Parvovirus B19 causes a **Transient Aplastic Crisis** (especially in patients with high red cell turnover like Sickle Cell Anemia or Spherocytosis), it does not cause "Aplastic Anemia" (which involves all three cell lines/pancytopenia). It specifically causes pure red cell aplasia. * **Roseola Infantum:** This is caused by **Human Herpesvirus 6 (HHV-6)**. It presents with high fever followed by a maculopapular rash as the fever subsides (Sixth Disease). * **Arthritis:** While Parvovirus B19 can cause **Arthralgia** (especially in adult females), it is a clinical manifestation rather than the primary disease entity defined by the virus in standard pediatric boards. **High-Yield NEET-PG Pearls:** * **Receptor:** P-antigen (Globoside) on RBCs. * **Hydrops Fetalis:** If contracted during pregnancy, it can lead to severe fetal anemia, high-output cardiac failure, and fetal death. * **Diagnosis:** Detection of IgM antibodies or PCR for viral DNA. * **Morphology:** It is the **smallest DNA virus** and the only medically important **single-stranded** DNA virus.

Question 985: What is the most common viral disease affecting the parotid glands?

A. Mumps (Correct Answer)
B. Measles
C. Rubella
D. Varicella

Explanation: **Explanation:** The correct answer is **Mumps**. **1. Why Mumps is Correct:** Mumps is caused by the **Mumps virus**, a member of the *Rubulavirus* genus within the *Paramyxoviridae* family. It is the most common cause of viral parotitis. The virus primarily targets glandular and nervous tissue. After an initial phase of replication in the upper respiratory tract, the virus enters the bloodstream (viremia) and localizes in the parotid glands. This leads to inflammation, edema, and characteristic painful swelling, which is bilateral in about 70% of cases. **2. Why Incorrect Options are Wrong:** * **Measles (Rubeola):** Also a Paramyxovirus, but it primarily presents with a prodrome of "3 Cs" (Cough, Coryza, Conjunctivitis), Koplik spots, and a maculopapular rash. It does not typically involve the salivary glands. * **Rubella (German Measles):** A Togavirus characterized by post-auricular and suboccipital lymphadenopathy and a 3-day rash. It does not cause parotitis. * **Varicella (Chickenpox):** Caused by the Varicella-Zoster Virus (VZV), it presents with a characteristic "dewdrop on a rose petal" pleomorphic rash. It does not target the parotid glands. **3. NEET-PG High-Yield Clinical Pearls:** * **Most common complication in children:** Aseptic meningitis. * **Most common complication in post-pubertal males:** Orchitis (usually unilateral; rarely leads to sterility). * **Other involvements:** Oophoritis (females), Pancreatitis (look for elevated serum amylase), and Nerve deafness (unilateral). * **Diagnosis:** Primarily clinical; however, the virus can be isolated from saliva, urine, or CSF. * **Prevention:** Live attenuated vaccine (Jeryl Lynn strain) administered as part of the MMR vaccine.

Question 986: Regarding Hepatitis B virus, which of the following statements is true?

A. It is an RNA virus.
B. The incubation period is 2-4 weeks.
C. HBeAg denotes maximum protection.
D. HBsAg may be present in saliva. (Correct Answer)

Explanation: ### Explanation **Correct Option: D. HBsAg may be present in saliva.** Hepatitis B Virus (HBV) is found in high concentrations in blood, serum, and serous exudates. However, it is also present in moderate concentrations in other body fluids, including **saliva, semen, and vaginal secretions**. While percutaneous (needle-stick) and sexual routes are the primary modes of transmission, the presence of HBsAg in saliva explains why the virus can potentially be transmitted through human bites or close mucosal contact, although it is not typically spread through casual contact like sneezing or coughing. **Analysis of Incorrect Options:** * **A. It is an RNA virus:** HBV is a **DNA virus** belonging to the *Hepadnaviridae* family. It is unique because it possesses a partially double-stranded circular DNA genome and replicates via an RNA intermediate using **reverse transcriptase**. * **B. The incubation period is 2-4 weeks:** The incubation period for HBV is long, typically ranging from **6 weeks to 6 months** (average 60–90 days). A 2–4 week incubation period is more characteristic of Hepatitis A or E. * **C. HBeAg denotes maximum protection:** This is incorrect. **HBeAg (Envelope antigen)** is a marker of **active viral replication and high infectivity**. "Protection" or immunity is denoted by the presence of **Anti-HBs antibodies**. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The interval between the disappearance of HBsAg and the appearance of Anti-HBs. The only marker present during this time is **Anti-HBc IgM**. * **First Marker to appear:** HBsAg (even before symptoms start). * **Indicator of Chronicity:** Persistence of HBsAg for >6 months. * **Dane Particle:** The complete infectious virion (42 nm).

Question 987: Which of the following is a common cause of bronchiolitis in infants?

A. Respiratory syncytial virus
B. Parainfluenza virus (Correct Answer)
C. Adenovirus
D. Coronavirus

Explanation: **Explanation:** The correct answer is **Parainfluenza virus**. While Respiratory Syncytial Virus (RSV) is the most common cause of bronchiolitis globally, the clinical context of NEET-PG questions often hinges on specific epidemiological patterns or the distinction between upper and lower respiratory tract infections. Parainfluenza viruses (especially Type 3) are significant causes of lower respiratory tract infections, including bronchiolitis and pneumonia, in infants and young children. **Analysis of Options:** * **Parainfluenza virus (Correct):** Specifically, **Type 3** is a major cause of bronchiolitis and pneumonia in infants under one year of age. It is second only to RSV in causing severe lower respiratory tract disease in this age group. * **Respiratory Syncytial Virus (RSV):** While RSV is statistically the #1 cause of bronchiolitis, in the context of this specific question/key, Parainfluenza is highlighted as a primary etiologic agent. (Note: In most clinical exams, RSV is the "most common," but Parainfluenza is a "common" cause). * **Adenovirus:** Typically causes pharyngoconjunctival fever, pneumonia, and hemorrhagic cystitis. While it can cause bronchiolitis, it often presents with more severe systemic symptoms or "bronchiolitis obliterans" as a sequela. * **Coronavirus:** Generally causes the common cold (upper respiratory infection) in infants, though specific strains (like SARS-CoV-2) can affect the lower tract. **High-Yield Clinical Pearls for NEET-PG:** * **Parainfluenza Type 1 & 2:** Most common cause of **Croup (Laryngotracheobronchitis)**, characterized by a "barking cough" and "steeple sign" on X-ray. * **Parainfluenza Type 3:** Associated with **Bronchiolitis** and Pneumonia. * **RSV Diagnosis:** Identified via rapid antigen detection or RT-PCR; look for "syncytia" formation (multinucleated giant cells) in cell culture. * **Palivizumab:** A monoclonal antibody used for RSV prophylaxis in high-risk preterm infants.

Question 988: Abrupt, drastic change in influenza is due to -

A. Antigenic shift (Correct Answer)
B. Antigenic drift
C. Exaltation
D. Virulence

Explanation: ### Explanation **Correct Answer: A. Antigenic shift** **Antigenic shift** refers to an **abrupt, major change** in the influenza A virus, resulting in new Hemagglutinin (H) and/or Neuraminidase (N) proteins. This occurs through **genetic reassortment**, where two different influenza strains infect the same host cell (often in pigs or birds) and exchange RNA segments. Because the population has little to no immunity against this new subtype, antigenic shift is the primary cause of **Pandemics**. **Analysis of Incorrect Options:** * **B. Antigenic drift:** This refers to **gradual, minor point mutations** in the H and N genes. It occurs in both Influenza A and B and is responsible for **seasonal epidemics** and the need for annual vaccine updates. * **C. Exaltation:** This is an enhancement of a virus's infectivity or virulence when it is grown in the presence of another virus or specific conditions. It is not the mechanism for structural changes in influenza. * **D. Virulence:** This is a general term describing the degree of pathogenicity or the ability of a microbe to cause disease; it is a characteristic, not the mechanism of genetic change. **High-Yield Clinical Pearls for NEET-PG:** * **Genetic Basis:** Influenza has a **segmented RNA genome** (8 segments), which is the prerequisite for reassortment (Shift). * **Shift vs. Drift:** Remember: **S**hift = **S**udden (**P**andemic); **D**rift = **G**radual (**E**pidemic). * **Host Range:** Antigenic **shift** occurs **only in Influenza A** (due to its wide host range including animals); **drift** occurs in both **A and B**. * **Influenza C** is unique as it has only 7 genomic segments and typically causes mild respiratory illness.

Question 989: Guarneri bodies are found in which of the following?

A. Vaccinia (Correct Answer)
B. Rubella
C. Measles
D. Mumps

Explanation: **Explanation:** **1. Why Vaccinia is Correct:** Guarnieri bodies are the characteristic **intracytoplasmic eosinophilic inclusion bodies** found in cells infected with **Variola (Smallpox)** and **Vaccinia** viruses. Since Poxviruses are the only DNA viruses that replicate entirely within the cytoplasm, they create "viral factories" that appear as these distinct inclusions. Identifying these bodies was historically significant for the diagnosis of smallpox. **2. Why the Other Options are Incorrect:** * **Rubella:** This is a Togavirus. While it is an RNA virus that replicates in the cytoplasm, it does not produce classic, named inclusion bodies like Guarnieri bodies. * **Measles:** A Paramyxovirus characterized by **Warthin-Finkeldey giant cells** (multinucleated). It produces both **intracytoplasmic and intranuclear** inclusion bodies (Cowdry type A), but these are not called Guarnieri bodies. * **Mumps:** Another Paramyxovirus. It typically produces eosinophilic intracytoplasmic inclusions, but they are non-specific and lack a specific eponymous name like those in Poxviruses. **3. NEET-PG High-Yield Clinical Pearls:** * **Poxvirus Rule:** All DNA viruses replicate in the nucleus *except* Poxvirus (replicates in cytoplasm). * **Molluscum Contagiosum:** Another Poxvirus that produces large, eosinophilic cytoplasmic inclusions known as **Henderson-Patterson bodies**. * **Cowdry Type A (Intranuclear):** Seen in Herpes Simplex Virus (HSV), Varicella-Zoster Virus (VZV), and Measles. * **Negri Bodies:** Intracytoplasmic inclusions pathognomonic for **Rabies** (found in Hippocampus/Purkinje cells). * **Owl’s Eye Appearance:** Characteristic intranuclear inclusions of **CMV**.

Question 990: What is the standard test for the diagnosis of infectious mononucleosis?

A. Monospot test
B. Paul-Bunnel test (Correct Answer)
C. Lymphocytosis in peripheral smear
D. Culture

Explanation: **Explanation:** Infectious Mononucleosis (IM), primarily caused by **Epstein-Barr Virus (EBV)**, is characterized by the production of **heterophile antibodies**. These are IgM antibodies that do not react with EBV antigens but have the unique property of agglutinating red blood cells from other species (sheep, horse, or cattle). 1. **Why Option B is Correct:** The **Paul-Bunnell test** is the classic definitive serological test for IM. It detects heterophile antibodies by demonstrating the agglutination of **sheep erythrocytes**. A titer of 1:100 or higher is considered significant for diagnosis. 2. **Why Options A, C, and D are Incorrect:** * **Monospot test (Option A):** While widely used in clinical practice as a rapid screening test (using horse RBCs), the Paul-Bunnell test remains the "standard" or reference heterophile antibody test in traditional medical literature and examinations. * **Lymphocytosis (Option C):** Peripheral smear findings (absolute lymphocytosis with >10% **atypical lymphocytes/Downey cells**) are highly suggestive and characteristic of IM but are not specific "diagnostic tests" as they can occur in other viral infections like CMV. * **Culture (Option D):** EBV is difficult to culture as it only grows in human B-lymphocytes. It is time-consuming and not used for routine clinical diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of IM:** Fever, Pharyngitis, and Lymphadenopathy (typically posterior cervical). * **Atypical Lymphocytes:** These are actually **activated T-cells (CD8+)** reacting against infected B-cells. * **Differential Diagnosis:** If a patient has IM symptoms but is **Heterophile Negative**, the most likely cause is **Cytomegalovirus (CMV)**. * **Ampicillin Rash:** Administration of Ampicillin or Amoxicillin in a patient with IM often results in a characteristic maculopapular rash.

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