Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1301: A patient presents with fever, sore throat, and splenomegaly. A blood smear shows atypical lymphocytes, and a Monospot test is positive. What is the likely etiological agent?

A. Cytomegalovirus
B. Epstein-Barr virus (Correct Answer)
C. Hepatitis B virus
D. Toxoplasma gondii

Explanation: ***Epstein-Barr virus*** - The combination of **fever**, **sore throat**, **splenomegaly**, **atypical lymphocytes** on a blood smear, and a **positive Monospot test** is classic for **infectious mononucleosis**, which is caused by the Epstein-Barr virus (EBV). - EBV primarily infects **B lymphocytes** and epithelial cells, leading to a robust cytotoxic T-cell response responsible for the atypical lymphocytes. *Cytomegalovirus* - CMV can cause a **mononucleosis-like syndrome** with fever and atypical lymphocytes, but it typically results in a **negative Monospot test**. - While CMV can cause **splenomegaly**, the specific constellation of symptoms with a positive Monospot points away from CMV. *Hepatitis B virus* - **Hepatitis B virus (HBV)** primarily causes **liver inflammation** (hepatitis), which can manifest with jaundice, fatigue, and abdominal pain. - HBV does not typically cause the triad of **splenomegaly, sore throat, and atypical lymphocytes** characteristic of mononucleosis, nor does it result in a positive Monospot test. *Toxoplasma gondii* - *Toxoplasma gondii* can cause **lymphadenopathy** and a **mononucleosis-like illness** in immunocompetent individuals. - However, **splenomegaly** is less common, and it is not associated with a **positive Monospot test**.

Question 1302: A neonate presents with vesicular lesions on the scalp, face, and mouth. A Tzanck smear from the base of a vesicle shows multinucleated giant cells. Which virus is the most likely cause?

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

Explanation: ***Herpes simplex virus*** - The presence of **vesicular lesions** on the scalp, face, and mouth in a neonate, combined with **multinucleated giant cells** on a Tzanck smear, is highly suggestive of **neonatal herpes simplex virus (HSV) infection**. - HSV can be acquired during passage through the birth canal if the mother has active genital lesions, leading to disseminated or localized skin, eye, and mouth (SEM) disease or central nervous system involvement. *Varicella-zoster virus* - While VZV can cause **vesicular lesions** and **multinucleated giant cells** on Tzanck smear, neonatal chickenpox (acquired postnatally) or congenital varicella syndrome (acquired in utero) typically present with more widespread lesions or specific congenital anomalies, respectively, rather than primarily concentrated on the face and mouth. - The description of lesions on the scalp, face, and mouth is more classic for neonatal HSV. *Cytomegalovirus* - CMV infection in neonates can cause a variety of symptoms, including petechiae rash, but it rarely presents with **vesicular lesions** as the primary dermatological manifestation. - Although CMV is a herpesvirus, it does not produce the characteristic **multinucleated giant cells** on Tzanck smear that are seen with HSV and VZV infections. *Epstein-Barr virus* - EBV infection in neonates is rare and typically presents as a mononucleosis-like illness with fever, lymphadenopathy, and hepatosplenomegaly, or occasionally with a non-specific rash. - It does not cause **vesicular lesions** or yield **multinucleated giant cells** on Tzanck smear.

Question 1303: Which viral genome characteristic is typically found in the Hepatitis B virus, distinguishing it from other hepatitis viruses?

A. Partial double-stranded DNA (Correct Answer)
B. Single-stranded RNA
C. Double-stranded RNA
D. Single-stranded DNA

Explanation: ***Partial double-stranded DNA*** - **Hepatitis B virus (HBV)** uniquely possesses a **partially double-stranded, relaxed circular DNA genome** among all hepatitis viruses. - This unique structure requires HBV to replicate through an **RNA intermediate** using **reverse transcriptase** enzyme, making it a **hepadnavirus**. - This is the key distinguishing genomic feature that sets HBV apart from other hepatitis viruses. *Single-stranded RNA* - **Hepatitis A, C, D (delta agent), and E viruses** all have single-stranded RNA genomes. - HBV is the only DNA-based hepatitis virus, while all others are RNA viruses. *Double-stranded RNA* - **Double-stranded RNA (dsRNA) genomes** are rare in human pathogens (example: **rotaviruses**). - No hepatitis virus possesses a dsRNA genome. *Single-stranded DNA* - Some viruses like **parvoviruses** have single-stranded DNA genomes. - HBV's genome is **partially double-stranded**, not single-stranded, which classifies it as a hepadnavirus.

Question 1304: How does the influenza virus achieve genetic variation that leads to antigenic shift?

A. Reassortment of segmented genome (Correct Answer)
B. Through use of reverse transcriptase
C. Incorporation of host genetic material
D. Mutations in viral genes

Explanation: ***Reassortment of segmented genome*** - **Antigenic shift** in influenza viruses occurs when two different influenza viruses co-infect the same host cell, leading to the exchange of **entire gene segments** between them. - This process, called **reassortment**, is possible because influenza has a **segmented RNA genome** (8 separate segments). - It results in the emergence of a new influenza virus subtype with drastically altered **surface antigens (hemagglutinin and neuraminidase)**, to which the population has little or no pre-existing immunity, potentially causing **pandemics**. *Incorporation of host genetic material* - While some viruses can incorporate host genetic material, this is not the primary mechanism by which influenza viruses achieve **antigenic shift**. - **Genetic recombination** between viral and host DNA is rare in RNA viruses like influenza. *Through use of reverse transcriptase* - **Reverse transcriptase** is characteristic of **retroviruses (e.g., HIV)**, which use it to transcribe their RNA genome into DNA. - Influenza viruses are **RNA viruses** that replicate directly from their RNA genome using **RNA-dependent RNA polymerase** and do not use reverse transcriptase in their life cycle. *Mutations in viral genes* - **Mutations** refer to small, gradual changes in the viral genes that code for surface proteins (hemagglutinin and neuraminidase) over time. - This process is called **antigenic drift** (not shift) and produces less dramatic changes that typically lead to **seasonal epidemics** rather than pandemics.

Question 1305: What is the significance of detecting 'owl's eye' inclusion bodies in cells from an immunocompromised patient?

A. A viral infection causing vesicular lesions and multinucleated giant cells.
B. A viral infection characterized by a vesicular rash.
C. A viral infection associated with atypical lymphocytes.
D. A viral infection associated with intranuclear inclusions in immunocompromised patients. (Correct Answer)

Explanation: ***A viral infection associated with intranuclear inclusions in immunocompromised patients.*** - The presence of **'owl's eye' inclusion bodies** is a hallmark cytopathic effect of **cytomegalovirus (CMV) infection**, particularly significant in **immunocompromised patients** due to higher risk of severe disease. - These characteristic **intranuclear inclusions** are seen in infected cells, representing viral replication within the nucleus. *A viral infection causing vesicular lesions and multinucleated giant cells.* - This description is more indicative of **herpes simplex virus (HSV)** or **varicella-zoster virus (VZV)** infections, which typically cause **vesicular lesions** and often show **Tzanck smear** with multinucleated giant cells. - **'Owl's eye' inclusions** are not characteristic of HSV or VZV. *A viral infection characterized by a vesicular rash.* - A **vesicular rash** is characteristic of several viral infections, including those caused by **herpesviruses** (e.g., VZV causing chickenpox/shingles) and **coxsackieviruses**, but does not specifically point to **'owl's eye' inclusions**. - **CMV infection** in immunocompromised patients typically manifests with systemic symptoms or organ-specific disease without a classic vesicular rash. *A viral infection associated with atypical lymphocytes.* - The presence of **atypical lymphocytes** (Downey cells) is characteristic of **Epstein-Barr virus (EBV) infection** causing infectious mononucleosis. - While CMV can also cause a mononucleosis-like syndrome with atypical lymphocytes, the **'owl's eye' inclusions** are more specific to CMV's cytopathic effect in tissue samples.

Question 1306: Which of the following mechanisms allows HIV to evade the immune system despite the presence of specific antibodies?

A. It mutates rapidly, altering its surface proteins. (Correct Answer)
B. It remains dormant within host cells.
C. It suppresses antibody production.
D. It destroys immune cells directly.

Explanation: ***It mutates rapidly, altering its surface proteins.*** - HIV's **high mutation rate**, particularly in its envelope glycoproteins (e.g., gp120), leads to continuous changes in its **surface antigens**. - This antigenic variation allows new viral strains to emerge that are no longer recognized by pre-existing antibodies, enabling immune evasion. *It remains dormant within host cells.* - While HIV can establish **latency** by integrating its DNA into the host genome, this primarily helps it evade cell-mediated immunity and antiviral drugs, rather than specific circulating antibodies recognizing surface proteins. - Latency prevents active viral replication and presentation of viral antigens on the cell surface, but doesn't directly explain evasion of antibodies that have already formed against prior viral strains. *It suppresses antibody production.* - HIV primarily targets and destroys **CD4+ T cells**, which are crucial for the activation of B cells and subsequent antibody production. - While this ultimately compromises the immune system's ability to produce new antibodies effectively, the direct suppression of *existing* antibody production by HIV itself is not its primary mechanism of evading *already formed* specific antibodies. *It destroys immune cells directly.* - HIV infection leads to the progressive destruction of **CD4+ T cells**, which are central to both humoral and cell-mediated immunity. - This broad immune suppression contributes to vulnerability to opportunistic infections but doesn't specifically explain how the virus evades antibodies that *recognize* its circulating forms.

Question 1307: Which disease is primarily associated with the herpes simplex virus?

A. Chickenpox
B. Cold sores (Correct Answer)
C. Smallpox
D. Measles

Explanation: ***Cold sores*** - **Cold sores**, also known as **fever blisters**, are caused by the **herpes simplex virus (HSV-1)**, which primarily affects the mouth and lips. - The virus remains **latent** in sensory ganglia and can reactivate, leading to recurrent outbreaks. *Chickenpox* - **Chickenpox** is caused by the **varicella-zoster virus (VZV)**, not herpes simplex virus. - It presents as an **itchy rash** with fluid-filled blisters all over the body. *Smallpox* - **Smallpox** is caused by the **variola virus**, a highly contagious and eradicated disease. - It is characterized by a distinctive, **deep-seated pustular rash**. *Measles* - **Measles** is caused by the **measles virus**, a paramyxovirus. - It is known for its characteristic **maculopapular rash**, fever, cough, coryza, and conjunctivitis.

Question 1308: Which test is considered the gold standard for diagnosing genital herpes?

A. Tzanck smear
B. PCR for HSV (Correct Answer)
C. Viral culture
D. Serology for HSV antibodies

Explanation: ***PCR for HSV*** - **Polymerase Chain Reaction (PCR)** is the gold standard due to its high **sensitivity** and **specificity** in detecting HSV DNA directly from lesion fluid or tissue samples. - It can differentiate between **HSV-1** and **HSV-2**, which is crucial for prognosis and counseling. *Tzanck smear* - This test identifies **multinucleated giant cells** and **intranuclear inclusions**, suggesting herpes but lacks specificity to differentiate HSV from other herpesviruses. - Its **sensitivity is low**, especially in healed or atypical lesions, making it unreliable for definitive diagnosis. *Viral culture* - While it can detect viable virus, **viral culture** has a lower sensitivity than PCR, especially in later stages of lesions or recurrent outbreaks. - It is **time-consuming**, with results often taking several days, which can delay diagnosis and treatment. *Serology for HSV antibodies* - **Serology** detects antibodies to HSV-1 or HSV-2, indicating past exposure but not necessarily active infection. - It is useful for **epidemiological studies** and for diagnosing asymptomatic individuals or those with atypical symptoms to determine prior exposure.

Question 1309: What is the primary mechanism by which the influenza virus changes antigenically over time?

A. Antigenic drift (Correct Answer)
B. Recombination
C. Reassortment
D. Antigenic shift

Explanation: ***Antigenic drift*** - This involves **gradual accumulation of point mutations** in the genes encoding for **hemagglutinin (HA)** and **neuraminidase (NA)** glycoproteins - These **minor changes** allow the virus to **evade immune recognition** partially, necessitating **frequent updates to influenza vaccines** - Occurs **continuously** in both influenza A and B viruses - Responsible for **seasonal epidemics** of influenza *Antigenic shift* - This involves **major changes** due to **reassortment of gene segments** between different influenza virus strains - Results in a **novel subtype** with different HA and/or NA proteins - Can lead to **pandemics** when human population has no immunity - This is a **sudden, major change** rather than the gradual change described in the question *Reassortment* - This is the **mechanism underlying antigenic shift**, where gene segments from different strains exchange during co-infection - While related to influenza variation, the question asks for the **primary ongoing mechanism**, which is antigenic drift - Reassortment is less frequent but creates more dramatic changes *Recombination* - This involves **exchange of genetic material** between viral genomes - **Uncommon in influenza viruses** due to their segmented genome structure - Reassortment, not recombination, is the dominant mechanism for genetic exchange in influenza

Question 1310: Which disease is caused by Coxsackievirus A16?

A. Yellow fever
B. Hand-foot-mouth disease (Correct Answer)
C. Rocky Mountain spotted fever
D. Encephalomyocarditis

Explanation: ***Hand-foot-mouth disease*** - **Coxsackievirus A16** is one of the most common causes of **hand-foot-mouth disease (HFMD)**, along with Enterovirus 71. - HFMD typically presents with **fever**, **painful vesicles and ulcers in the mouth** (on the tongue, gums, and inside of cheeks), and a **vesicular rash on the palms, soles, and sometimes buttocks**. - It primarily affects young children and is highly contagious. *Yellow fever* - Yellow fever is caused by the **yellow fever virus**, a **flavivirus**, which is transmitted by mosquitoes. - It leads to symptoms like fever, jaundice, and hemorrhage, distinctly different from Coxsackievirus A16 infections. *Rocky Mountain spotted fever* - This disease is caused by the bacterium **Rickettsia rickettsii** and is transmitted by ticks. - It presents with fever, headache, and a characteristic rash that often starts on the ankles and wrists. *Encephalomyocarditis* - While Coxsackieviruses (particularly Coxsackievirus B serotypes) can cause myocarditis and encephalitis, **encephalomyocarditis virus (EMCV)** is a distinct cardiovirus within the Picornaviridae family. - Coxsackievirus A16 is not typically associated with encephalomyocarditis as its primary manifestation.

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Virology — MCQs

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