Virology Practice Questions

Q: What is the primary function of the Nef gene in HIV?

Enhancing viral pathogenesis. ***Enhancing viral pathogenesis*** - The **Nef protein** is critical for efficient viral replication and disease progression in HIV-infected individuals, significantly increasing **viral load** and contributing to immune evasion. - It achieves this by downregulating **CD4** and **MHC class I** molecules on the surface of infected cells, thereby preventing immune recognition and increasing viral infectivity. *Enhancing the expression of host genes* - While Nef interacts with various host proteins, its primary function is not to globally enhance the expression of host genes but rather to modulate specific host pathways to favor viral replication. - Instead, Nef often leads to **downregulation** of specific host proteins important for immune response, such as CD4 and MHC class I. *Decreasing viral replication* - Nef's role is to **increase**, not decrease, viral replication and spread within the host. - Viruses lacking a functional Nef gene show **attenuated replication** in vivo and often reduced pathogenicity. *Promoting host cell apoptosis* - While Nef can influence cellular processes, its direct and primary function is not to promote host cell apoptosis. - In fact, Nef can sometimes prevent early apoptosis of infected cells, allowing more time for virus production and release, thereby contributing to viral persistence.

Q: A patient with sore throat has a positive Paul Bunnell test, indicating infectious mononucleosis. The causative organism is?

EBV. ***Correct: EBV*** - The **Paul-Bunnell test** (monospot test) detects **heterophile antibodies**, which are characteristic of acute **Epstein-Barr virus (EBV)** infection. - **EBV** is the primary causative agent of **infectious mononucleosis**, commonly known as "mono." *Incorrect: Adenovirus* - **Adenoviruses** can cause various infections, including **pharyngitis** and **conjunctivitis**, but are not associated with a positive **Paul-Bunnell test** or heterophile antibodies. - While it can cause sore throat, the presence of a **positive Paul-Bunnell test** differentiates it from EBV. *Incorrect: CMV* - **Cytomegalovirus (CMV)** can cause a mononucleosis-like syndrome, but it typically results in a **negative Paul-Bunnell test** (i.e., it is heterophile antibody-negative). - CMV mononucleosis is often seen in individuals who are **immunocompromised** or in infants as a congenital infection. *Incorrect: HSV (Herpes Simplex Virus)* - **Herpes simplex virus (HSV)** causes infections such as **oral herpes (cold sores)** and **genital herpes**, and in some cases, **pharyngitis**. - HSV infection is not associated with a positive **Paul-Bunnell test** or the production of heterophile antibodies.

Q: Which poxvirus does not grow in eggs or animal cells?

Molluscum contagiosum. ***Molluscum contagiosum*** - This poxvirus is unique among human poxviruses as it **cannot be propagated in cell culture** or embryonated eggs. - It specifically replicates in **human epidermal cells**, causing characteristic skin lesions. *Cow pox* - Cowpox virus can be readily grown in **cell cultures** (e.g., Vero cells) and in **embryonated eggs**, where it produces pocks on the chorioallantoic membrane (CAM). - It is known for its ability to **infect a wide range of host cells and animals**. *Vaccinia* - Vaccinia virus is a widely studied poxvirus that grows efficiently in various **mammalian cell lines** (e.g., Hela, Vero cells) and on the **chorioallantoic membrane of embryonated eggs**. - Its broad host range and ease of culture make it a popular **viral vector** for research and vaccine development. *Variola* - Variola virus, the causative agent of smallpox, was successfully propagated in **cell cultures** (e.g., primary human embryonic kidney cells) and in **embryonated chicken eggs**, producing characteristic pock lesions. - Its ability to grow in these systems was crucial for **vaccine production** and research before its eradication.

Q: Which virus is known for its brick-shaped morphology?

Smallpox. ***Smallpox*** - The **variola virus**, responsible for smallpox, is a type of **poxvirus** which characteristically exhibits a **brick-shaped** or ovoid morphology. - This distinctive shape is due to its **large, complex virion structure** containing a dumbbell-shaped core. *Chickenpox* - Chickenpox is caused by the **varicella-zoster virus (VZV)**, which is a member of the **herpesviridae family**. - Herpesviruses are typically **spherical** with an icosahedral capsid. *CMV* - **Cytomegalovirus (CMV)** is another member of the **herpesviridae family**, sharing the characteristic **spherical shape** with an icosahedral capsid. - Its morphology is not brick-shaped. *EBV* - **Epstein-Barr virus (EBV)** is also a **herpesvirus** and thus possesses a **spherical, icosahedral capsid morphology**. - Its structure is distinct from the brick-shaped poxviruses.

Q: Which of the following statements about p24 is false?

Cannot be detected after seroconversion. ***Cannot be detected after seroconversion*** - This statement is **FALSE** and is the correct answer to this question. - **p24 antigen levels do decrease** after seroconversion due to immune complex formation with antibodies, but p24 can still be detected using modern assays. - In **advanced HIV disease** with declining CD4 counts, p24 antigen often becomes detectable again due to high viral loads. - Fourth-generation HIV tests detect both antibodies and p24 antigen throughout the infection course. *Cannot be seen in the first week* - This statement is **TRUE** (not the answer). - p24 antigen typically appears around **10-14 days** (1.5-2 weeks) after infection, which is after the first week (days 1-7). - The eclipse period (first 7-10 days) precedes p24 detection. *Can be detected after 3 weeks of infection* - This statement is **TRUE** (not the answer). - p24 antigen is consistently detectable at 3 weeks post-infection during the acute viremic phase. - Peak p24 levels occur around **2-4 weeks** after infection. *All of the above* - This is a distractor option and is incorrect since only one statement is false.

Q: Virus quantification is done by-

Plaque assay. ***Plaque assay*** - The **plaque assay** is a widely used and quantitative method to determine the number of **infectious viral particles** in a sample. - It involves infecting a monolayer of host cells with serially diluted virus samples, leading to the formation of visible **plaques** (zones of lysed cells), which are then counted. *Studying virus-cell interactions* - Studying **virus-cell interactions** helps understand the mechanisms of viral entry, replication, and egress but does not directly quantify the number of viral particles. - While critical for understanding viral pathogenesis, this approach is qualitative rather than quantitative in nature. *Visualizing virus particles* - **Visualizing virus particles** (e.g., using electron microscopy) allows for counting individual virions, but it quantifies both infectious and non-infectious particles. - This method provides a total particle count rather than a measure of infectivity. *Virus isolation using eggs* - **Virus isolation using eggs** (e.g., embryonated chicken eggs) is a method for propagating and isolating certain viruses, particularly influenza. - While it can be optimized for relative comparisons, it is not primarily a direct quantitative method like the plaque assay for determining infectious viral titers.

Q: Smallpox belongs to which genus of poxviruses?

Orthopoxvirus. ***Orthopoxvirus*** - **Smallpox** (caused by the **variola virus**) is a classic member of the Orthopoxvirus genus. - This genus includes other human pathogens like **monkeypox** and vaccinia virus (used in the smallpox vaccine). *Parapoxvirus* - This genus includes viruses like **Orf virus** (causing contagious pustular dermatitis in sheep and goats) and pseudocowpox virus. - These viruses typically cause milder, localized lesions and are morphologically distinct from orthopoxviruses. *Capripoxvirus* - This genus includes viruses primarily affecting livestock, such as **lumpy skin disease virus**, sheep pox virus, and goat pox virus. - They cause systemic infections and skin lesions in their respective animal hosts and are not associated with human disease like smallpox. *Leporipox virus* - This genus includes viruses that primarily infect rabbits and hares, such as **myxoma virus** and fibroma virus. - These viruses typically cause tumors or severe systemic disease in their rabbit hosts and are not known to infect humans.

Q: Which virus is primarily responsible for causing Ebola virus disease, a type of hemorrhagic fever?

Ebola virus. ***Ebola virus*** - The disease is named after the **Ebola River** in Congo, where it was first identified. - The **Ebola virus** is a member of the **Filoviridae family**, known for causing severe hemorrhagic fevers. *West Nile virus* - This virus is primarily transmitted by **mosquitoes** and causes **West Nile fever**, which can lead to neurological disease. - It does not cause the hemorrhagic fever associated with Ebola virus disease. *Phlebovirus* - **Phlebovirus** is a genus of viruses that includes several species capable of causing **encephalitis** or **febrile illness** with headache and myalgia. - While some can cause hemorrhagic fevers, it is not the primary agent for the disease specifically known as **Ebola virus disease**. *None of the options* - This option is incorrect because the **Ebola virus** is indeed listed as an option and is the correct pathogen responsible for Ebola virus disease.

Q: Bollinger bodies are seen in ?

Fowlpox. **IMPORTANT NOTE:** In **human pathology**, the term "Bollinger bodies" classically refers to **sulfur granules** seen in **actinomycosis** (Actinomyces infection), which appear as basophilic masses with radiating eosinophilic clubs. However, this question uses the **veterinary pathology** definition, where Bollinger bodies refer to viral inclusions in avian diseases. ***Fowlpox*** - In **veterinary pathology**, **Bollinger bodies** are characteristic large, eosinophilic **intracytoplasmic inclusion bodies** found in cells infected with the **fowlpox virus** (avipoxvirus). - These inclusions are visible under light microscopy and are a diagnostic feature of **fowlpox**, a widespread avian disease. - Note: Fowlpox is **not a human disease** but affects birds. *Chickenpox* - Chickenpox, caused by the **varicella-zoster virus (VZV)**, is characterized by **intranuclear inclusion bodies** (Cowdry type A) [1]. - It does not form **Bollinger bodies**. *Cowpox* - Cowpox is caused by the **cowpox virus**, an **orthopoxvirus**, and produces **A-type cytoplasmic inclusion bodies** (A-type inclusions). - While these are cytoplasmic inclusions, they are not referred to as **Bollinger bodies**. *Smallpox* - Smallpox, caused by the **variola virus** (orthopoxvirus), is associated with **Guarnieri bodies**, which are **cytoplasmic inclusion bodies**. - These inclusions are distinct from **Bollinger bodies**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 366-367.

Q: Which of the following viruses is classified as a poxvirus?

Variola. ***Variola virus*** - **Variola virus** is the causative agent of **smallpox**, a historically significant and highly contagious disease. - It belongs to the **Orthopoxvirus** genus within the **Poxviridae family**, characterized by its large, brick-shaped virion and dsDNA genome. *Coxsackie virus* - **Coxsackieviruses** are part of the **Picornaviridae family**, specifically the **Enterovirus** genus. - They are known to cause a range of diseases including **hand-foot-and-mouth disease**, myocarditis, and aseptic meningitis, and are much smaller than poxviruses. *ECHO virus* - **Echoviruses** (Enteric Cytopathic Human Orphan viruses) are also members of the **Picornaviridae family** and the **Enterovirus** genus. - They are associated with diseases such as **aseptic meningitis**, gastroenteritis, and respiratory infections, completely distinct from poxviruses. *HSV (Herpes Simplex Virus)* - **Herpes Simplex Viruses** belong to the **Herpesviridae family**, characterized by a **linear dsDNA genome** and an enveloped icosahedral capsid. - They cause diseases like **oral and genital herpes** and are structurally and genetically distinct from poxviruses.

Question 1

What is the primary function of the Nef gene in HIV?

Accepted Answer

Enhancing viral pathogenesis

Answer

Enhancing the expression of host genes

Answer

Decreasing viral replication

Answer

Promoting host cell apoptosis

Question 2

A patient with sore throat has a positive Paul Bunnell test, indicating infectious mononucleosis. The causative organism is?

Accepted Answer

EBV

Answer

Adenovirus

Answer

CMV

Answer

HSV (Herpes Simplex Virus)

Question 3

Which poxvirus does not grow in eggs or animal cells?

Accepted Answer

Molluscum contagiosum

Answer

Cow pox

Answer

Vaccinia

Answer

Variola

Question 4

Which virus is known for its brick-shaped morphology?

Accepted Answer

Smallpox

Answer

Chickenpox

Answer

CMV

Answer

EBV

Question 5

Which of the following statements about p24 is false?

Accepted Answer

Cannot be detected after seroconversion

Answer

Cannot be seen in the first week

Answer

All of the above

Answer

Can be detected after 3 weeks of infection

Question 6

Virus quantification is done by-

Accepted Answer

Plaque assay

Answer

Studying virus-cell interactions

Answer

Visualizing virus particles

Answer

Virus isolation using eggs

Question 7

Smallpox belongs to which genus of poxviruses?

Accepted Answer

Orthopoxvirus

Answer

Leporipoxvirus

Answer

Capripoxvirus

Answer

Parapoxvirus

Question 8

Which virus is primarily responsible for causing Ebola virus disease, a type of hemorrhagic fever?

Accepted Answer

Ebola virus

Answer

Phlebovirus

Answer

West Nile virus

Answer

None of the options

Question 9

Bollinger bodies are seen in ?

Accepted Answer

Fowlpox

Answer

Chickenpox

Answer

Cowpox

Answer

Smallpox

Question 10

Which of the following viruses is classified as a poxvirus?

Accepted Answer

Variola

Answer

Coxsackie

Answer

ECHO

Answer

HSV

Virology — MCQs

Virology — MCQs

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