Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 461: Which one of the following viruses is the leading cause of congenital malformations?

A. Rabies virus
B. Rhinovirus
C. Cytomegalovirus (Correct Answer)
D. Respiratory syncytial virus

Explanation: **Explanation:** **Cytomegalovirus (CMV)** is the correct answer as it is the **most common cause of congenital viral infections** worldwide. It belongs to the *Betaherpesvirinae* subfamily. While most maternal infections are asymptomatic, primary infection during pregnancy poses the highest risk of vertical transmission to the fetus. **Why CMV is the correct answer:** CMV is the leading infectious cause of sensorineural hearing loss and intellectual disability. The classic clinical triad of congenital CMV includes **chorioretinitis, periventricular calcifications, and microcephaly**. Other features include "blueberry muffin" rash (extramedullary hematopoiesis), hepatosplenomegaly, and jaundice. **Why the other options are incorrect:** * **Rabies virus:** This is a neurotropic rhabdovirus transmitted via animal bites. It causes fatal encephalitis but is not associated with congenital malformations. * **Rhinovirus:** The most common cause of the "common cold," it remains localized to the upper respiratory tract and does not cause viremia leading to fetal infection. * **Respiratory Syncytial Virus (RSV):** A major cause of bronchiolitis and pneumonia in infants, but it is acquired postnatally and is not a teratogenic virus. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The gold standard for congenital CMV is detecting the virus in **urine or saliva** via PCR or culture within the first 3 weeks of life. * **Histology:** Look for **"Owl’s eye" intranuclear inclusion bodies** in biopsy specimens. * **TORCH infections:** CMV is a key member of the TORCH group (Toxoplasmosis, Others, Rubella, CMV, Herpes). * **Treatment:** Intravenous **Ganciclovir** or oral Valganciclovir is used to reduce the severity of hearing loss and developmental delays.

Question 462: Enterovirus causes all, except?

A. Hemorrhagic fever (Correct Answer)
B. Pleurodynia
C. Herpangina
D. Aseptic meningitis

Explanation: **Explanation** Enteroviruses (a genus within the *Picornaviridae* family) include Polioviruses, Coxsackieviruses A and B, Echoviruses, and numbered Enteroviruses. They are primarily transmitted via the fecal-oral route and are known for causing a wide spectrum of clinical syndromes, but they **do not cause hemorrhagic fever.** **Why Hemorrhagic Fever is the Correct Answer:** Viral Hemorrhagic Fevers (VHF) are caused by four distinct families of RNA viruses: *Arenaviridae* (Lassa), *Filoviridae* (Ebola, Marburg), *Bunyaviridae* (Crimean-Congo), and *Flaviviridae* (Dengue, Yellow Fever). Enteroviruses typically cause mucosal, muscular, or neurological inflammation rather than systemic vascular leak and coagulopathy. **Analysis of Incorrect Options:** * **Pleurodynia (Bornholm disease):** Characterized by sudden onset of lancinating chest pain and fever, this is classically caused by **Coxsackievirus B**. * **Herpangina:** Characterized by fever, sore throat, and vesiculopapular lesions on the posterior oropharynx (soft palate/tonsils). It is primarily caused by **Coxsackievirus A**. * **Aseptic Meningitis:** Enteroviruses are the **most common cause** of viral (aseptic) meningitis, particularly during summer and autumn months. **High-Yield Clinical Pearls for NEET-PG:** * **Hand-Foot-Mouth Disease (HFMD):** Most commonly caused by Coxsackievirus A16 and Enterovirus 71. * **Myocarditis/Pericarditis:** Coxsackievirus B is the most common viral trigger. * **Acute Hemorrhagic Conjunctivitis:** Specifically linked to **Enterovirus 70** and Coxsackievirus A24. (Note: This is a localized ocular hemorrhage, not a systemic "Hemorrhagic Fever"). * **Paralysis:** While Poliovirus is the prototype, Enterovirus 71 can also cause polio-like flaccid paralysis.

Question 463: A patient presented to the emergency department with sudden onset of fever, headache, retro-orbital pain, and back pain. Dengue was suspected. Which is the most sensitive diagnostic test for dengue?

A. IgM ELISA (Correct Answer)
B. Complement fixation test (CFT)
C. Tissue culture
D. Electron microscopy

Explanation: **Explanation:** The clinical presentation of sudden fever, headache, retro-orbital pain, and severe back pain (break-bone fever) is classic for **Dengue virus infection**. **Why IgM ELISA is the correct answer:** In the clinical diagnosis of Dengue, **IgM ELISA** is considered the most sensitive and widely used serological test for routine diagnosis. IgM antibodies become detectable by day 4–5 of the illness and persist for about 2–3 months. While **NS1 Antigen** is the marker of choice during the first 1–3 days (viremic phase), IgM ELISA has a higher diagnostic yield as the patient progresses into the febrile and critical phases, making it the standard "sensitive" test in clinical practice. **Why the other options are incorrect:** * **Complement Fixation Test (CFT):** This is an older serological method. It is less sensitive and more technically demanding than ELISA, often showing cross-reactivity with other flaviviruses. * **Tissue Culture:** While the "gold standard" for definitive diagnosis, virus isolation in mosquito cell lines (e.g., C6/36) is slow (taking 7–10 days), expensive, and not practical for routine clinical use. * **Electron Microscopy:** This is used primarily in research settings to visualize viral morphology. It has very low sensitivity for routine diagnosis due to the high viral load required for detection. **High-Yield Clinical Pearls for NEET-PG:** * **NS1 Antigen:** Best for early diagnosis (Days 1–5). * **IgM ELISA:** Best for diagnosis after Day 5 (MAC-ELISA). * **Vector:** *Aedes aegypti* (Day biter; breeds in clean stagnant water). * **Tourniquet Test:** A positive test (≥10-20 petechiae/square inch) indicates capillary fragility. * **Secondary Infection:** Characterized by a rapid rise in **IgG** titers (anamnestic response), which increases the risk of Dengue Hemorrhagic Fever (DHF) due to antibody-dependent enhancement.

Question 464: Kyanasur forest disease is transmitted by which vector?

A. Haema physalis spinigera (Correct Answer)
B. Culex vishnui
C. Aedes
D. Anopheles

Explanation: **Explanation:** **Kyasanur Forest Disease (KFD)**, commonly known as "Monkey Fever," is a viral hemorrhagic fever endemic to the South Indian state of Karnataka. It is caused by the KFD virus, a member of the family *Flaviviridae*. 1. **Why Option A is Correct:** The primary vector for KFD is the **hard tick**, specifically ***Haemaphysalis spinigera***. Humans typically contract the infection through the bite of an infected nymphal tick or via contact with an infected animal (most notably monkeys like Langurs and Bonnet macaques, which act as sentinel animals). 2. **Why Other Options are Incorrect:** * **Option B (Culex vishnui):** This is the principal vector for **Japanese Encephalitis (JE)**. While it is a mosquito-borne Flavivirus, it is not involved in KFD transmission. * **Option C (Aedes):** *Aedes aegypti* and *Aedes albopictus* are vectors for **Dengue, Chikungunya, Zika, and Yellow Fever**. * **Option D (Anopheles):** This mosquito genus is the definitive host and vector for **Malaria**. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoirs:** Wild rodents are the natural reservoirs; monkeys are the amplifying hosts (high mortality in monkeys precedes human outbreaks). * **Clinical Presentation:** Characterized by sudden onset high fever, frontal headache, severe myalgia, and hemorrhagic manifestations. A "bimodal" illness pattern is often seen (fever followed by a brief afebrile period, then neurological symptoms). * **Diagnosis:** PCR (early phase) or IgM ELISA. * **Prevention:** A **formalin-inactivated vaccine** is available and used in endemic areas of Karnataka.

Question 465: Which is the most commonly used test for screening of hepatitis-B?

A. Microtitre assay
B. Radioimmunoassay (RIA)
C. Double diffusion
D. Polymerase Chain Reaction (PCR) (Correct Answer)

Explanation: **Explanation:** **Hepatitis B Virus (HBV)** screening and diagnosis rely on detecting specific viral markers. While HBsAg (Hepatitis B surface Antigen) is the standard initial serological marker used in clinical practice, **Polymerase Chain Reaction (PCR)** has emerged as the most sensitive and definitive tool for screening, especially in blood bank settings and for detecting occult infections. * **Why PCR is correct:** PCR detects **HBV-DNA**, the most sensitive marker of viral replication. It is the gold standard for screening because it can detect the virus during the "window period" (before HBsAg appears) and in cases of Occult Hepatitis B (where HBsAg is negative but DNA is present). In the context of modern competitive exams, Nucleic Acid Testing (NAT) via PCR is emphasized for its high sensitivity. **Analysis of Incorrect Options:** * **A. Microtitre assay:** This is a general laboratory technique (often used for ELISA) rather than a specific test. While ELISA is used for HBsAg, "Microtitre assay" is too vague to be the primary answer. * **B. Radioimmunoassay (RIA):** Although highly sensitive, RIA is rarely used today due to the hazards of handling radioactive isotopes and the superiority of Chemiluminescence (CLIA) and PCR. * **C. Double diffusion:** This is an obsolete immunodiffusion technique (e.g., Ouchterlony) with very low sensitivity, unsuitable for modern screening. **Clinical Pearls for NEET-PG:** * **First marker to appear:** HBsAg (appears before symptoms). * **Marker of infectivity:** HBeAg and HBV-DNA. * **Window Period Marker:** Anti-HBc IgM (HBsAg and Anti-HBs are both negative). * **Indicator of recovery/immunity:** Anti-HBs. * **Screening in Blood Banks:** NAT (PCR) is now preferred to reduce the risk of transfusion-transmitted HBV.

Question 466: Kaposi sarcoma is related to which virus?

A. Human Papillomavirus 16
B. Human Herpesvirus 8 (Correct Answer)
C. Epstein-Barr Virus
D. Cytomegalovirus

Explanation: **Explanation:** **Kaposi Sarcoma (KS)** is a multicentric angioproliferative tumor of endothelial origin. The correct answer is **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi Sarcoma-associated Herpesvirus (KSHV). **Why HHV-8 is correct:** HHV-8 belongs to the *Gammaherpesvirinae* subfamily. It encodes viral oncogenes (like viral cyclin and v-FLIP) that dysregulate the cell cycle and inhibit apoptosis. It is the primary etiological agent for all four clinical types of Kaposi Sarcoma: Classic (Mediterranean), Endemic (African), Iatrogenic (transplant-related), and Epidemic (AIDS-associated). **Why other options are incorrect:** * **Human Papillomavirus 16 (HPV-16):** A high-risk DNA virus primarily associated with squamous cell carcinomas, specifically cervical, vulvar, and oropharyngeal cancers. * **Epstein-Barr Virus (EBV/HHV-4):** Associated with Burkitt lymphoma, Nasopharyngeal carcinoma, and Hodgkin lymphoma, but not Kaposi Sarcoma. * **Cytomegalovirus (CMV/HHV-5):** While often found as a co-infection in immunocompromised patients, it is not the causative agent of Kaposi Sarcoma. **High-Yield Clinical Pearls for NEET-PG:** * **Histology:** Look for "spindle-shaped cells" and slit-like vascular spaces containing extravasated RBCs. * **Other HHV-8 Associations:** Primary Effusion Lymphoma (PEL) and Multicentric Castleman Disease. * **Transmission:** Primarily through saliva (most common) and sexual contact. * **AIDS-Defining Illness:** Kaposi Sarcoma is one of the most common malignancies seen in HIV patients with low CD4 counts.

Question 467: What is the most sensitive diagnostic test for dengue?

A. IgM ELISA (Correct Answer)
B. Complement fixation test
C. Neutralization test
D. Electron microscopy

Explanation: **Explanation:** The diagnosis of Dengue virus infection relies on the timing of clinical presentation. **IgM ELISA** is considered the most sensitive and widely used diagnostic test for routine clinical diagnosis, particularly after the first 5 days of fever. * **Why IgM ELISA is correct:** IgM antibodies appear as early as day 3–5 of the illness and persist for about 2–3 months. Due to its high sensitivity, ease of performance, and ability to detect recent infection, it is the gold standard for serological diagnosis in a clinical setting. * **Why other options are incorrect:** * **Complement Fixation Test (CFT):** This is a classical serological method but is less sensitive and more technically demanding than ELISA. It is rarely used in modern diagnostics. * **Neutralization Test (NT):** While this is the most **specific** test and the "gold standard" for differentiating flaviviruses, it is labor-intensive, requires live virus culture, and is primarily used in research rather than routine diagnosis. * **Electron Microscopy:** This is used to visualize viral morphology but has extremely low sensitivity for diagnostic purposes and is not practical for clinical management. **High-Yield Clinical Pearls for NEET-PG:** * **NS1 Antigen:** The best marker for the **early/viremic phase** (Day 1–5). It is highly specific. * **RT-PCR:** The most sensitive method during the first 5 days (viremic phase), but less commonly available than NS1. * **Secondary Dengue:** Characterized by a rapid rise in **IgG** titers with low or absent IgM. * **Vector:** *Aedes aegypti* (Day biter; breeds in clean stagnant water).

Question 468: Which of the following is a non-enveloped ss-RNA virus?

A. Picornavirus (Correct Answer)
B. Poxvirus
C. Retrovirus
D. Bunyavirus

Explanation: **Explanation:** To answer this question, one must classify viruses based on their genome (DNA vs. RNA), strand type (ss vs. ds), and the presence of a lipid envelope. **1. Why Picornavirus is Correct:** Picornaviruses (e.g., Poliovirus, Rhinovirus, Hepatitis A) are the classic example of **non-enveloped (naked), single-stranded, positive-sense RNA viruses**. A helpful mnemonic for non-enveloped RNA viruses is **"PCR"** (**P**icornavirus, **C**alicivirus, **R**eovirus—though Reovirus is dsRNA). Because they lack an envelope, they are resistant to detergents and acidic environments (like the stomach), allowing them to be transmitted via the fecal-oral route. **2. Why the Other Options are Incorrect:** * **Poxvirus:** This is a **DNA virus** (the largest and most complex). It is double-stranded and enveloped. * **Retrovirus:** While it is ssRNA, it is a prominent **enveloped** virus (e.g., HIV). * **Bunyavirus:** These are **enveloped**, single-stranded, negative-sense RNA viruses (e.g., Hantavirus, Crimean-Congo hemorrhagic fever). **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Naked (Non-enveloped) Viruses:** * **DNA:** PAPP (**P**arvovirus, **A**denovirus, **P**apillomavirus, **P**olyomavirus). * **RNA:** CPR (**C**alicivirus, **P**icornavirus, **R**eovirus) + Hepevirus (Hepatitis E). * **Smallest RNA Virus:** Picornavirus (*Pico* = small, *rna* = RNA). * **Smallest DNA Virus:** Parvovirus (also the only medically important ssDNA virus). * **Exception:** Most RNA viruses replicate in the cytoplasm, but **Influenza** and **Retroviruses** replicate in the nucleus.

Question 469: A person tests positive for HBsAg and HBeAg. What does this indicate?

A. Recovery from Hepatitis B infection
B. Active replication of the Hepatitis B virus (Correct Answer)
C. Successful Hepatitis B vaccination
D. Chronic Hepatitis B infection

Explanation: ### Explanation The presence of **HBsAg** (Hepatitis B Surface Antigen) and **HBeAg** (Hepatitis B e-Antigen) is a hallmark of an active Hepatitis B infection with high viral activity. **1. Why the correct answer is right:** * **HBsAg:** This is the first marker to appear in the blood during an infection. Its presence indicates that the person is currently infected (either acute or chronic). * **HBeAg:** This antigen is a byproduct of viral replication. Its presence in the serum serves as a surrogate marker for **active viral replication**, high HBV DNA levels, and high infectivity (the patient is highly contagious). **2. Why the other options are incorrect:** * **Option A (Recovery):** Recovery is characterized by the disappearance of HBsAg and the appearance of **Anti-HBs** antibodies. * **Option C (Vaccination):** A vaccinated individual will test positive **only for Anti-HBs**. They will be negative for HBsAg, HBeAg, and Anti-HBc (core antibody). * **Option D (Chronic Infection):** While HBsAg is present in chronic infection (defined as HBsAg persistence for >6 months), the presence of **HBeAg specifically signifies the replicative phase**. Chronic infection can also exist in a "low-replicative" state where HBeAg is negative and Anti-HBe is positive. **3. High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs. The only marker present here is **Anti-HBc IgM**. * **Best indicator of HBV DNA replication:** HBV DNA levels (by PCR), but **HBeAg** is the classic serological marker. * **Indicator of Infectivity:** HBeAg is the primary marker for vertical transmission risk (mother to child). * **Anti-HBc:** The "footprint" of a natural infection. It is never present after vaccination.

Question 470: Coxsackie A virus causes all except:

A. Aseptic meningitis
B. Herpangina
C. Hand foot and mouth disease
D. Bornholm's disease (Correct Answer)

Explanation: **Explanation:** The question asks for the condition *not* caused by Coxsackie A virus. The correct answer is **Bornholm’s disease**, which is classically associated with **Coxsackie B virus**. **1. Why Bornholm’s disease is the correct answer:** Bornholm’s disease (also known as epidemic pleurodynia or "Devil’s Grip") is characterized by sudden onset of severe, paroxysmal chest and upper abdominal pain due to inflammation of the intercostal muscles. This condition is a hallmark clinical manifestation of **Group B Coxsackieviruses**, not Group A. **2. Analysis of incorrect options (Diseases caused by Coxsackie A):** * **Herpangina:** Characterized by fever, sore throat, and vesiculopapular lesions on the posterior oropharynx (tonsils and soft palate). It is a classic presentation of Coxsackie A. * **Hand, Foot, and Mouth Disease (HFMD):** Presents with vesicular eruptions on the palms, soles, and oral mucosa. While Enterovirus 71 can also cause it, **Coxsackie A16** is the most common etiology. * **Aseptic Meningitis:** Both Coxsackie A and B are leading causes of viral (aseptic) meningitis. **Clinical Pearls for NEET-PG:** * **Mnemonic for Coxsackie A:** "A" for **A**ngina (Herpangina) and **A**ppendages (Hand, Foot, and Mouth). * **Mnemonic for Coxsackie B:** "B" for **B**ody (Bornholm’s), **B**eating (Myocarditis/Pericarditis), and **B**eta cells (linked to Type 1 Diabetes). * **High-Yield Fact:** Coxsackie B is the most common viral cause of **myocarditis** and **pericarditis**. * Both groups belong to the *Picornaviridae* family and are non-enveloped, positive-sense ssRNA viruses.

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Virology — MCQs

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