Virology Practice Questions

Q: Which of the following pathogens is most commonly associated with acute infectious diarrhea?

Rotavirus. ***Rotavirus*** - **Rotavirus** is the leading cause of **severe, acute diarrheal disease** in **infants and young children worldwide**, especially in unvaccinated populations. - It causes significant **morbidity and mortality** globally, primarily through dehydration. *Salmonella* - While *Salmonella* can cause acute infectious diarrhea, particularly **foodborne outbreaks**, it is **less common overall** than rotavirus, especially in children. - It often presents with **fever, abdominal cramps**, and **bloody or non-bloody diarrhea**, and can lead to systemic infections. *Escherichia coli* - Various strains of *E. coli* can cause diarrhea (e.g., **ETEC, EPEC, EHEC**), but collectively they do not surpass rotavirus as the single most common cause of acute infectious diarrhea globally. - **Enterohemorrhagic *E. coli* (EHEC)**, particularly O157:H7, is known for causing **hemorrhagic colitis** and **hemolytic uremic syndrome**. *Shigella* - *Shigella* species cause **bacillary dysentery**, characterized by **bloody diarrhea, fever, and severe abdominal cramps**. - While it is a significant cause of diarrheal disease, its prevalence is generally **lower than rotavirus**, especially in developed countries.

Q: 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?

Epstein-Barr virus. ***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**.

Q: A 45-year-old woman presents with jaundice and elevated liver enzymes. A serological test is positive for HBsAg and anti-HBc IgM. What is the stage of her hepatitis B infection?

Acute. ***Acute*** - The presence of **HBsAg** (hepatitis B surface antigen) indicates active infection, while **anti-HBc IgM** (antibody to hepatitis B core antigen, IgM class) specifically points to a recent, **acute infection** [1]. - Elevated liver enzymes and jaundice further support a recent, **active inflammatory process** in the liver. *Chronic* - Chronic hepatitis B is characterized by the presence of **HBsAg for more than 6 months**, often with **anti-HBc IgG** rather than IgM [1]. - The presence of **anti-HBc IgM** rules out a purely chronic infection, as it signifies recent exposure. *Resolved* - A resolved infection typically shows **negative HBsAg** and **positive anti-HBs** (antibody to hepatitis B surface antigen), indicating immunity [1]. - The presence of **HBsAg** means the infection is still active, not resolved. *Carrier* - The term "carrier" refers to a person with chronic hepatitis B infection (HBsAg positive for >6 months), often with relatively stable liver enzymes and minimal liver damage, but can also refer to chronic active hepatitis. - The presence of **anti-HBc IgM** indicates an **acute phase**, not a stable carrier state without acute viral replication.

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.

Question 1

Which of the following pathogens is most commonly associated with acute infectious diarrhea?

Accepted Answer

Rotavirus

Answer

Salmonella

Answer

Escherichia coli

Answer

Shigella

Question 2

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?

Accepted Answer

Epstein-Barr virus

Answer

Cytomegalovirus

Answer

Hepatitis B virus

Answer

Toxoplasma gondii

Question 3

A 45-year-old woman presents with jaundice and elevated liver enzymes. A serological test is positive for HBsAg and anti-HBc IgM. What is the stage of her hepatitis B infection?

Accepted Answer

Acute

Answer

Chronic

Answer

Resolved

Answer

Carrier

Question 4

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 5

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 6

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 7

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 8

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 9

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 10

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.

Virology — MCQs

Virology — MCQs

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