Virology Practice Questions

Q: 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?

Herpes simplex virus. ***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.

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

Partial double-stranded DNA. ***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.

Q: Which of the following is the most common cause of viral meningitis in children?

Enterovirus. ***Enterovirus*** - **Enteroviruses** (e.g., Coxsackievirus, Echovirus) are the most frequent cause of **aseptic meningitis** in children, particularly during summer and fall. - They are typically transmitted via the **fecal-oral route** and cause a relatively mild, self-limiting illness. *Herpes simplex virus* - While **Herpes simplex virus (HSV)** can cause meningitis, it is a less common cause than enteroviruses, especially in children, and is more often associated with **encephalitis**. - HSV meningitis can be recurrent (Mollaret's meningitis) but is not the most common overall cause of viral meningitis in children. *Adenovirus* - **Adenovirus** can cause a range of infections, including respiratory, gastrointestinal, and conjunctivitis, but it is a relatively uncommon cause of **viral meningitis** compared to enteroviruses. - When it does cause meningitis, it is often in immunocompromised individuals. *Cytomegalovirus* - **Cytomegalovirus (CMV)** is a significant cause of viral infections, particularly in immunocompromised individuals and congenitally infected infants, where it can cause neurological complications. - However, it is not the most common cause of **viral meningitis** in the general pediatric population.

Q: A 7-year-old boy presents with a barking cough and stridor. What is the most likely causative agent?

Parainfluenza virus. ***Parainfluenza virus*** - **Parainfluenza virus** is the most common cause of **croup** (laryngotracheobronchitis), characterized by a **barking cough**, **stridor**, and hoarseness. - The patient's age and clinical presentation are highly consistent with parainfluenza infection. *Respiratory syncytial virus* - **RSV** is a primary cause of **bronchiolitis** and **pneumonia** in infants and young children, often leading to wheezing and respiratory distress. - While it can cause upper respiratory symptoms, it typically does not present with the classic **barking cough** and **stridor** of croup. *Adenovirus* - **Adenovirus** can cause a variety of infections, including **pharyngoconjunctival fever**, acute respiratory disease, and gastroenteritis. - Although it can cause respiratory symptoms, it is not the most common etiology for croup. *Influenza virus* - **Influenza virus** typically causes abrupt onset of fever, myalgia, headache, and a **non-barking cough**. - While it can cause severe respiratory illness, it is less commonly associated with the distinct **barking cough** and **stridor** seen in croup.

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

Reassortment of segmented genome. ***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.

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

It mutates rapidly, altering its surface proteins.. ***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.

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

Antigenic drift. ***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

Q: A patient presents with painful blisters around the angle of the mouth. What is the most likely pathogen responsible for this condition?

Herpes Simplex Virus. ***Herpes Simplex Virus*** - The image shows a cluster of **small, painful vesicles** on an erythematous base around the mouth, characteristic of **herpes labialis** or cold sores. - HSV-1 is the primary cause of oral herpes, which typically presents with these recurrent painful blister outbreaks. *Coxsackievirus* - Coxsackievirus typically causes **Hand, Foot, and Mouth Disease**, characterized by oral lesions (herpangina) and a rash on the hands and feet. - The painful blisters are usually in the **posterior oral cavity** (soft palate, tonsillar pillars) and are not typically perioral in the depicted clustered vesicular pattern. *Varicella-Zoster Virus* - VZV causes **chickenpox** (widespread vesicular rash) and **shingles** (painful, dermatomal vesicular rash). - While it causes vesicles, they would present as either widespread and generalized or in a unilateral, **dermatomal distribution**, which is not consistent with the perioral presentation shown. *Epstein-Barr Virus* - EBV is primarily known for causing **infectious mononucleosis**, which can lead to fatigue, fever, and lymphadenopathy, and sometimes oral manifestations like palatal petechiae or oral hairy leukoplakia. - It does not typically cause the **painful vesicular lesions** around the mouth as depicted.

Q: Which disease is caused by Coxsackievirus A16?

Hand-foot-mouth disease. ***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.

Question 1

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?

Accepted Answer

Herpes simplex virus

Answer

Varicella-zoster virus

Answer

Cytomegalovirus

Answer

Epstein-Barr virus

Question 2

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

Accepted Answer

Partial double-stranded DNA

Answer

Single-stranded RNA

Answer

Double-stranded RNA

Answer

Single-stranded DNA

Question 3

Which of the following is the most common cause of viral meningitis in children?

Accepted Answer

Enterovirus

Answer

Herpes simplex virus

Answer

Adenovirus

Answer

Cytomegalovirus

Question 4

A 7-year-old boy presents with a barking cough and stridor. What is the most likely causative agent?

Accepted Answer

Parainfluenza virus

Answer

Respiratory syncytial virus

Answer

Adenovirus

Answer

Influenza virus

Question 5

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

Accepted Answer

Reassortment of segmented genome

Answer

Through use of reverse transcriptase

Answer

Incorporation of host genetic material

Answer

Mutations in viral genes

Question 6

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

Accepted Answer

A viral infection associated with intranuclear inclusions in immunocompromised patients.

Answer

A viral infection causing vesicular lesions and multinucleated giant cells.

Answer

A viral infection characterized by a vesicular rash.

Answer

A viral infection associated with atypical lymphocytes.

Question 7

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

Accepted Answer

It mutates rapidly, altering its surface proteins.

Answer

It remains dormant within host cells.

Answer

It suppresses antibody production.

Answer

It destroys immune cells directly.

Question 8

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

Accepted Answer

Antigenic drift

Answer

Recombination

Answer

Reassortment

Answer

Antigenic shift

Question 9

A patient presents with painful blisters around the angle of the mouth. What is the most likely pathogen responsible for this condition?

Accepted Answer

Herpes Simplex Virus

Answer

Coxsackievirus

Answer

Varicella-Zoster Virus

Answer

Epstein-Barr Virus

Question 10

Which disease is caused by Coxsackievirus A16?

Accepted Answer

Hand-foot-mouth disease

Answer

Yellow fever

Answer

Rocky Mountain spotted fever

Answer

Encephalomyocarditis

Virology — MCQs

Virology — MCQs

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