Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 471: Herpangina is caused by which virus?

A. Adenovirus
B. Enterovirus-72
C. Coxsackie virus A (Correct Answer)
D. Coxsackie virus B

Explanation: **Explanation:** **Herpangina** is a common febrile illness characterized by sudden onset of fever, sore throat, and distinctive **vesicular-ulcerative lesions** on the posterior oropharynx (soft palate, tonsils, and uvula). 1. **Why Coxsackie virus A is correct:** The primary causative agents of Herpangina are **Coxsackie A viruses** (specifically types 1–10, 16, and 22). These are members of the *Picornaviridae* family. The virus is transmitted via the fecal-oral or respiratory route, leading to the characteristic enanthem. 2. **Why other options are incorrect:** * **Adenovirus:** Typically causes Pharyngoconjunctival fever (fever, pharyngitis, and conjunctivitis) or epidemic keratoconjunctivitis, rather than vesicular palatal ulcers. * **Enterovirus-72:** This is the former name for **Hepatitis A virus**, which causes acute viral hepatitis, not oral vesicular lesions. * **Coxsackie virus B:** While closely related, Coxsackie B is more classically associated with **Pleurodynia** (Bornholm disease), **Myocarditis**, and **Pericarditis**. **High-Yield Clinical Pearls for NEET-PG:** * **Hand-Foot-Mouth Disease (HFMD):** Also caused by **Coxsackie A16** and **Enterovirus 71**. Unlike Herpangina, HFMD involves the anterior oral cavity and includes a rash on the palms and soles. * **Seasonality:** These infections peak during summer and autumn months. * **Management:** Treatment is purely supportive (hydration and analgesics) as the condition is self-limiting. * **Differential Diagnosis:** Differentiate from **Herpetic Gingivostomatitis** (HSV-1), which typically involves the anterior mouth and gingiva (gums), unlike the posterior involvement in Herpangina.

Question 472: Which marker indicates the level of liver injury in cases of hepatitis B?

A. HBsAg
B. HBV DNA (Correct Answer)
C. Anti HBeAg
D. Anti HBc

Explanation: **Explanation:** The level of liver injury in Hepatitis B is primarily determined by the intensity of the host's immune response against the virus. **HBV DNA** is the most accurate marker for this because it represents the **viral load** (the actual quantity of virus in the blood). High levels of HBV DNA correlate with active viral replication, which triggers a more robust T-cell mediated immune attack on hepatocytes, leading to inflammation, necrosis, and subsequent elevation of liver enzymes (ALT/AST). In clinical practice, HBV DNA levels are the gold standard for deciding when to initiate antiviral therapy and for monitoring treatment response. **Analysis of Incorrect Options:** * **HBsAg (Hepatitis B Surface Antigen):** This is the first marker to appear and indicates **infection** (acute or chronic), but it does not quantify the severity of liver damage or the rate of viral replication. * **Anti-HBeAg:** The presence of antibodies to the 'e' antigen usually signifies **seroconversion**, indicating a transition from high to low infectivity. It does not directly measure the degree of liver injury. * **Anti-HBc (Antibody to Core Antigen):** This is a marker of **exposure**. IgM anti-HBc indicates acute infection (and is the only marker positive during the "window period"), while IgG anti-HBc indicates past or chronic infection. Neither reflects the current level of liver damage. **High-Yield Clinical Pearls for NEET-PG:** * **HBV DNA** is the most sensitive marker for monitoring **treatment efficacy**. * **HBeAg** is a qualitative marker of **high infectivity** and active replication. * **ALT (Alanine Aminotransferase)** is the biochemical marker used alongside HBV DNA to assess liver injury (necroinflammation). * The **"Window Period"** is defined by the disappearance of HBsAg and the appearance of Anti-HBs; during this time, **IgM Anti-HBc** is the diagnostic marker of choice.

Question 473: Interferon interferes with virus replication at which stage?

A. Protein synthesis (Correct Answer)
B. DNA/RNA replication
C. When the virus enters the cell
D. Uncoating of the virus protein capsule

Explanation: **Explanation:** Interferons (IFNs) are host-encoded glycoproteins produced in response to viral infections. They do not directly kill viruses but induce an **antiviral state** in neighboring uninfected cells. **Why Protein Synthesis is the Correct Answer:** Once IFN binds to the receptors of a healthy cell, it triggers the production of several antiviral proteins. The two most critical pathways target the translation machinery: 1. **Protein Kinase R (PKR):** This enzyme phosphorylates and inactivates the elongation factor **eIF-2**, effectively halting the initiation of protein synthesis. 2. **2',5'-Oligoadenylate Synthetase:** This activates **RNase L**, which degrades viral (and cellular) mRNA. By destroying mRNA and disabling the translation initiation complex, interferons specifically block the **synthesis of viral proteins**. **Analysis of Incorrect Options:** * **B. DNA/RNA Replication:** While some secondary mechanisms exist, the primary and most characteristic action of IFN is the inhibition of translation, not the direct inhibition of the polymerase enzymes responsible for genome replication. * **C & D. Entry and Uncoating:** These are early stages of the viral life cycle. Interferons do not prevent the virus from attaching to, entering, or uncoating within the host cell; the virus enters the cell normally, but its genetic message cannot be translated into functional proteins. **High-Yield Clinical Pearls for NEET-PG:** * **Type I IFNs (IFN-α, IFN-β):** Produced by most nucleated cells; primarily antiviral. * **Type II IFN (IFN-γ):** Produced by T-cells and NK cells; primarily immunomodulatory (activates macrophages). * **Clinical Use:** IFN-α is used in the treatment of Chronic Hepatitis B, Hepatitis C, and Kaposi Sarcoma. * **Side Effect:** "Flu-like symptoms" (fever, myalgia) are the most common side effects of IFN therapy.

Question 474: Which of the following is spread by Aedes mosquitoes?

A. Loa Loa
B. Malaria
C. Dengue (Correct Answer)
D. Japanese encephalitis

Explanation: **Explanation:** **Correct Option: C (Dengue)** Dengue virus (a Flavivirus) is primarily transmitted by the **Aedes aegypti** mosquito, and secondarily by *Aedes albopictus*. These mosquitoes are "day-biters" and typically breed in clean, stagnant water (e.g., flower pots, coolers). The virus is transmitted to humans through the bite of an infected female mosquito. **Analysis of Incorrect Options:** * **A. Loa Loa:** This filarial parasite (African eye worm) is transmitted by the bite of the **Chrysops** (deer fly or horse fly), not mosquitoes. * **B. Malaria:** This protozoal infection is transmitted by the bite of the infected female **Anopheles** mosquito. * **C. Japanese Encephalitis (JE):** While also a Flavivirus, JE is transmitted by **Culex** mosquitoes (specifically *Culex tritaeniorhynchus*), which typically breed in rice fields. **High-Yield Clinical Pearls for NEET-PG:** * **Aedes-transmitted diseases:** Remember the mnemonic **"Zika, Dengue, Chikungunya, and Yellow Fever"** are all spread by *Aedes aegypti*. * **Aedes Characteristics:** Known as the "Tiger Mosquito" due to white stripes on its body. It has a short flight range (approx. 100 meters). * **Dengue Markers:** **NS1 antigen** is the earliest marker (Day 1-5); **IgM** appears after Day 5. * **Vector Comparison:** * *Anopheles:* Bites at an angle; breeds in clean water. * *Culex:* Bites horizontally; breeds in dirty/polluted water; transmits JE, Filariasis, and West Nile Virus.

Question 475: Which of the following is NOT a cytopathic effect of a virus?

A. Syncytium formation
B. Budding (Correct Answer)
C. Ballooning and floating
D. Focal degeneration

Explanation: **Explanation:** **Cytopathic Effect (CPE)** refers to the structural changes in host cells caused by viral invasion. These changes are typically degenerative and often lead to cell death. **Why "Budding" is the correct answer:** Budding is a method of **viral release** used primarily by enveloped viruses (e.g., HIV, Influenza). During budding, the virus acquires its envelope from the host cell membrane. Unlike lysis, budding does not necessarily cause immediate structural damage or visible morphological changes to the host cell; therefore, it is considered a part of the viral replication cycle rather than a "cytopathic effect." **Analysis of incorrect options:** * **Syncytium formation:** This is a classic CPE where infected cells fuse to form multinucleated giant cells. It is characteristic of viruses like **RSV, Measles, and Herpes simplex.** * **Ballooning and floating:** This occurs when cells lose their attachment to the culture vessel, swell (ballooning), and detach. This is a hallmark CPE of the **Herpesviridae** family. * **Focal degeneration:** This refers to localized areas of cell death and morphological change within a cell monolayer, typical of viruses like **Adenovirus** (which shows "grape-like clusters"). **High-Yield Clinical Pearls for NEET-PG:** * **Inclusion Bodies:** A specific type of CPE. Examples include **Negri bodies** (Rabies - intracytoplasmic), **Owl’s eye appearance** (CMV - intranuclear), and **Guarnieri bodies** (Smallpox). * **Steatocystis:** Seen in Hepatitis B (Ground glass hepatocytes). * **Koilocytes:** Characteristic CPE of HPV (Human Papillomavirus) seen on Pap smears. * **Total destruction:** Poliovirus causes rapid, complete destruction of the cell monolayer.

Question 476: Which of the following statements is true of Rabies?

A. Fluorescent antibody is the test of choice (Correct Answer)
B. HDCV is a live attenuated vaccine
C. Vaccine is given deep IM in the buttock
D. Local wound care is of no use

Explanation: **Explanation:** **1. Why Option A is Correct:** The **Direct Fluorescent Antibody (DFA)** test is considered the "gold standard" and the test of choice for diagnosing rabies in both animals and humans. It detects rabies virus antigens in brain tissue (post-mortem) or skin biopsies from the nape of the neck (ante-mortem). It is highly sensitive, specific, and provides rapid results, which is critical for clinical decision-making. **2. Why Other Options are Incorrect:** * **Option B:** Human Diploid Cell Vaccine (HDCV) is an **inactivated (killed)** vaccine, not live attenuated. All modern rabies vaccines used in humans (HDCV, PCECV, PVRV) are inactivated. * **Option C:** Rabies vaccines must be administered **intramuscularly in the deltoid region** (adults) or anterolateral thigh (children). It should **never** be given in the gluteal region (buttock) because the thick overlying fat layer can lead to poor absorption and lower neutralizing antibody titers. * **Option D:** Local wound care is the **most important first step** in post-exposure prophylaxis (PEP). Immediate flushing and washing of the wound with soap and water for at least 15 minutes can reduce the viral load at the site by up to 80%. **Clinical Pearls for NEET-PG:** * **Negri Bodies:** Intracytoplasmic eosinophilic inclusion bodies found most commonly in **Hippocampus (Ammon’s horn)** and Cerebellum (Purkinje cells). * **Street Virus:** Freshly isolated from natural cases; has a long incubation period and produces Negri bodies. * **Fixed Virus:** Adapted by serial passage in brains; has a short, fixed incubation period (4–6 days) and does **not** produce Negri bodies. * **Post-Exposure Prophylaxis (PEP):** Includes wound care, Rabies Immunoglobulin (RIG), and vaccination (Essen or Thai Red Cross regimen).

Question 477: The Monospot test is used to diagnose which condition?

A. Pernicious anemia
B. Sickle cell anemia
C. Infectious mononucleosis (Correct Answer)
D. Leukemia

Explanation: **Explanation:** The **Monospot test** (also known as the heterophile antibody test) is the classic screening tool for **Infectious Mononucleosis (IM)**, primarily caused by the **Epstein-Barr Virus (EBV)**. **Why the correct answer is right:** In response to an EBV infection, the body produces **heterophile antibodies** (IgM). These are unique because they are not specific to EBV antigens but instead have the ability to agglutinate red blood cells (RBCs) from other species, such as sheep, horses, or cows. The Monospot test utilizes horse RBCs; if agglutination occurs when mixed with the patient's serum, the test is positive for IM. **Why the incorrect options are wrong:** * **Pernicious Anemia:** Diagnosed via Vitamin B12 levels, anti-intrinsic factor antibodies, or the (now historical) Schilling test. * **Sickle Cell Anemia:** Diagnosed using peripheral blood smears (sickle cells), the Sickling test (sodium metabisulfite), or the gold standard, **Hb electrophoresis**. * **Leukemia:** While IM can present with "atypical lymphocytes" (Downey cells) resembling leukemic blasts, leukemia is diagnosed via peripheral smear, bone marrow biopsy, and flow cytometry. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of IM:** Fever, pharyngitis, and lymphadenopathy (usually posterior cervical). * **Atypical Lymphocytes:** These are actually **CD8+ T-cells** reacting against infected B-cells. * **False Negatives:** The Monospot test is often negative in the first week of illness and is typically **negative in children under 4 years old**. * **CMV Infection:** Cytomegalovirus can cause a "mononucleosis-like syndrome," but it is characteristically **Monospot negative**. * **Ampicillin Rash:** If a patient with IM is mistakenly treated with Ampicillin or Amoxicillin, they often develop a characteristic maculopapular rash.

Question 478: A 1-month-old baby presents with microcephaly and hepatosplenomegaly. A Giemsa-stained urine sample shows owl's eye inclusion bodies. What is the diagnosis?

A. Cytomegalovirus (CMV) (Correct Answer)
B. Epstein-Barr virus (EBV)
C. Herpes simplex virus
D. Varicella zoster virus

Explanation: ### Explanation **Correct Answer: A. Cytomegalovirus (CMV)** The clinical presentation of **microcephaly** and **hepatosplenomegaly** in a neonate, combined with the pathognomonic finding of **"Owl’s eye" inclusion bodies**, is diagnostic of **Congenital Cytomegalovirus infection**. CMV is the most common intrauterine infection. The "Owl's eye" appearance refers to large, **intranuclear, basophilic inclusion bodies** surrounded by a clear halo, typically found in renal tubular epithelial cells (hence detectable in urine) or vascular endothelial cells. **Why other options are incorrect:** * **Epstein-Barr virus (EBV):** Primarily causes Infectious Mononucleosis. While it can cause hepatosplenomegaly, it is not a classic cause of congenital microcephaly and is characterized by **atypical lymphocytes (Downey cells)** on blood smear, not owl's eye inclusions. * **Herpes simplex virus (HSV):** Congenital HSV typically presents with the triad of skin vesicles, eye involvement (chorioretinitis), and CNS abnormalities. Histology shows **Cowdry Type A** inclusions. * **Varicella zoster virus (VZV):** Congenital Varicella Syndrome is characterized by **cicatricial skin scarring**, limb hypoplasia, and rudimentary digits, rather than the specific inclusion bodies described. --- ### High-Yield Clinical Pearls for NEET-PG: * **Most common** cause of sensorineural hearing loss (SNHL) and mental retardation among congenital infections. * **Classic Triad:** Microcephaly, Periventricular calcifications, and Hepatosplenomegaly/Petechiae ("Blueberry muffin rash"). * **Diagnosis:** Culture or PCR of saliva/urine within the first 3 weeks of life is the gold standard. * **Treatment:** Ganciclovir or Valganciclovir is used to reduce the severity of hearing loss and developmental delay. * **Histology Note:** Do not confuse "Owl's eye" appearance of CMV with the "Owl's eye" nuclei of **Reed-Sternberg cells** in Hodgkin Lymphoma.

Question 479: A student developed fever, nausea, vomiting, and diarrhea after consuming shellfish. What is the most likely causative agent?

A. Adenovirus
B. Norwalk virus (Correct Answer)
C. Enterovirus
D. Rotavirus

Explanation: ### Explanation **Correct Option: B. Norwalk virus (Norovirus)** The clinical presentation of acute gastroenteritis (fever, nausea, vomiting, and diarrhea) following the consumption of **shellfish** (especially raw oysters) is a classic association for **Norovirus**. * **Mechanism:** Noroviruses are highly contagious, low-infectious-dose members of the *Caliciviridae* family. They are the leading cause of epidemic non-bacterial gastroenteritis worldwide. * **Transmission:** While the fecal-oral route is primary, outbreaks are frequently linked to contaminated water and seafood (shellfish concentrate the virus from contaminated water). **Why other options are incorrect:** * **A. Adenovirus:** Serotypes 40 and 41 cause gastroenteritis, primarily in children. It is not typically associated with shellfish outbreaks. * **C. Enterovirus:** While transmitted via the fecal-oral route, these viruses (like Polio, Coxsackie) more commonly cause systemic illnesses, rashes, or meningitis rather than isolated acute diarrheal disease. * **D. Rotavirus:** This is the most common cause of severe dehydrating diarrhea in **infants and young children**. While it causes similar symptoms, it is not the classic agent associated with adult outbreaks linked to shellfish. **High-Yield Clinical Pearls for NEET-PG:** * **Norovirus** is the most common cause of gastroenteritis outbreaks on **cruise ships**, in schools, and in nursing homes. * **Key Buzzword:** "Shellfish/Oysters" + "Vomiting/Diarrhea" = Norovirus (or *Vibrio parahaemolyticus* if bacterial). * **Resistance:** Noroviruses are resistant to many common disinfectants, including alcohol-based hand sanitizers; handwashing with soap and water is preferred. * **Seasonality:** Often referred to as the "Winter Vomiting Bug."

Question 480: Suckling mice are used for the isolation of which of the following viruses?

A. Coxsackie virus (Correct Answer)
B. Pox virus
C. Herpes virus
D. Adenovirus

Explanation: **Explanation:** The use of **suckling mice** (mice less than 48 hours old) is a classic method for isolating specific viruses that do not grow well in standard cell cultures or embryonated eggs. **1. Why Coxsackie virus is correct:** Coxsackie viruses (members of the *Picornaviridae* family) are traditionally classified based on their histopathological effects in suckling mice: * **Group A:** Causes widespread **flaccid paralysis** due to generalized myositis of skeletal muscles. * **Group B:** Causes **spastic paralysis** due to focal myositis and necrotizing steatitis (inflammation of brown fat), as well as encephalitis and pancreatitis. This differential pathology in suckling mice remains a hallmark of Coxsackie virus identification. **2. Why the other options are incorrect:** * **Pox virus:** These are typically isolated using the **Chorioallantoic Membrane (CAM)** of embryonated chicken eggs, where they produce characteristic visible lesions called **pocks**. * **Herpes virus:** While they can grow on CAM (producing small pocks), they are most commonly isolated using **cell cultures** (e.g., human fibroblast lines), where they produce rapid cytopathic effects (CPE) like Cowdry Type A inclusion bodies. * **Adenovirus:** These are best isolated in **continuous epithelial cell lines** (e.g., HeLa, HEp-2), showing characteristic "grape-like clusters" as CPE. **High-Yield Clinical Pearls for NEET-PG:** * **Arboviruses** (like Dengue and Japanese Encephalitis) are also frequently isolated by intracerebral inoculation in suckling mice. * **Rabies virus** diagnosis via the **Mouse Inoculation Test** is considered a gold standard confirmatory test (though largely replaced by FAT). * Remember: **Group A** = **A**ll muscle (Flaccid); **Group B** = **B**ody/Brain/Brown fat (Spastic).

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Virology — MCQs

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