Virology Practice Questions

Q: Which of the following is a primary cell line?

Chick embryo fibroblasts. ***Chick embryo fibroblasts*** - Primary cell lines are directly derived from **tissues** and have a limited lifespan in culture before undergoing senescence. - **Chick embryo fibroblasts** are isolated directly from chick embryos and propagated for a limited number of passages, making them a true primary cell culture. *Hela cells* - HeLa cells are a well-known example of a **continuous cell line**, meaning they can be cultured indefinitely. - They were originally derived from a cervical cancer patient and are considered **immortalized**. *Vero cells* - Vero cells are an **immortalized cell line** derived from the kidney of an African green monkey. - They are used extensively in virology and vaccine production due to their ability to be propagated for many passages. *WI-38* - WI-38 is a **diploid human cell strain** derived from lung tissue. - While they have a finite lifespan similar to primary cells, they represent a **cell strain** that has been subcultured and characterized, with more homogeneous growth characteristics than fresh primary cultures.

Q: What is the role of p24 in HIV?

Core antigen of HIV. ***Core antigen of HIV*** - **p24** is a **structural protein** that forms the viral capsid, which is the shell enclosing the genetic material of the virus. - Due to its abundance and immunogenicity, **p24** serves as a crucial **biomarker** for initial **HIV infection** and is targeted in diagnostic tests. *Envelop antigen in HIV* - The **envelope antigens** of HIV are typically **glycoproteins** like **gp120** and **gp41**, which are involved in viral attachment and entry into host cells. - These envelope proteins are distinct from **p24**, which is an internal core protein. *Genome of HIV* - The **genome of HIV** consists of **two copies of single-stranded RNA**, not a protein. - This **RNA genome** is contained within the viral capsid, which is primarily composed of **p24 protein**. *Shell antigen* - While **p24** does form a "shell" (the capsid) around the viral genome, the term **shell antigen** is not a standard specific classification in virology for p24. - The more precise term for its location and function is **core antigen**.

Q: Binding of gp120 causes:

Facilitation of co-receptor binding. ***Facilitation of co-receptor*** - **gp120** binding to the **CD4 receptor** on target cells induces a conformational change in gp120, which then exposes or creates a binding site for a **chemokine co-receptor** (CCR5 or CXCR4). - This interaction is crucial for the subsequent steps of viral entry, as it allows the virus to make further contact with the cell surface. *Infection of target cell* - While binding of gp120 is the *first step* in infection, it does not directly cause the infection itself. - Infection occurs after a series of events including co-receptor binding, membrane fusion, and reverse transcription. *Fusing of virus and target cell* - **Fusion** of the viral and cellular membranes is primarily mediated by **gp41**, which is part of the gp160 envelope glycoprotein complex alongside gp120. - This fusion event *follows* the binding of gp120 to CD4 and the co-receptor, as gp120 binding initiates the conformational changes that expose and activate gp41. *None of the options* - One of the provided options accurately describes a direct consequence of gp120 binding, making this option incorrect.

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: Colorado Tick fever is caused by:

Reoviridae. ***Reoviridae*** - Colorado Tick Fever (CTF) is caused by the **Colorado Tick Fever Virus (CTFV)**, which belongs to the genus **Coltivirus** within the family **Reoviridae**. - Reoviridae viruses are **non-enveloped**, double-stranded RNA viruses. *Filoviridae* - This family includes viruses like **Ebola virus** and **Marburg virus**, which cause severe hemorrhagic fevers. - They are **enveloped**, negative-sense single-stranded RNA viruses, distinct from the CTFV. *Coronaviridae* - This family includes viruses like **SARS-CoV-2 (COVID-19)** and SARS-CoV, which cause respiratory illnesses. - They are **enveloped**, positive-sense single-stranded RNA viruses, structurally different from CTFV. *Caliciviridae* - This family includes viruses like **Norovirus**, a common cause of acute gastroenteritis (viral stomach flu). - They are **non-enveloped**, positive-sense single-stranded RNA viruses and do not cause tick-borne illnesses.

Q: Influenza virus culture is done on ?

Allantoic cavity. ***Allantoic cavity*** - The **allantoic cavity** of embryonated chicken eggs is the standard and most effective site for isolating and propagating **influenza viruses** for vaccine production and research. - This cavity provides an optimal environment for viral replication, particularly yielding high titers of **hemagglutinin**, a key influenza antigen. *Chorioallantoic membrane* - While embryonated eggs are used for virus culture, the **chorioallantoic membrane (CAM)** is primarily used for cultivating viruses that produce **pocks** (visible lesions), such as Vaccinia and Herpes Simplex Virus. - Influenza virus growth on the CAM is less efficient and typically doesn't produce distinct pocks, making it unsuitable for high-yield propagation compared to the allantoic cavity. *Yolk sac* - The **yolk sac** of embryonated eggs is ideal for growing viruses or bacteria that require a **lipid-rich environment** and replicate intracellularly, such as Chlamydia or Rickettsia. - It is not the preferred site for influenza virus isolation or proliferation due to suboptimal conditions for viral replication and lower viral yields. *All of the options* - While all these sites are components of an embryonated chicken egg, each serves as a host for different types of microorganisms or for specific purposes in virology. - For **influenza virus culture**, the **allantoic cavity** is the specifically utilized site for optimal growth and high viral yield.

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: 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: 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.

Question 1

Which of the following is a primary cell line?

Accepted Answer

Chick embryo fibroblasts

Answer

Hela cells

Answer

Vero cells

Answer

WI-38

Question 2

What is the role of p24 in HIV?

Accepted Answer

Core antigen of HIV

Answer

Envelope antigen in HIV

Answer

Genome of HIV

Answer

Shell antigen

Question 3

Binding of gp120 causes:

Accepted Answer

Facilitation of co-receptor binding

Answer

Infection of target cell

Answer

Fusing of virus and target cell

Answer

None of the options

Question 4

Smallpox belongs to which genus of poxviruses?

Accepted Answer

Orthopoxvirus

Answer

Leporipoxvirus

Answer

Capripoxvirus

Answer

Parapoxvirus

Question 5

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 6

Colorado Tick fever is caused by:

Accepted Answer

Reoviridae

Answer

Coronaviridae

Answer

Filoviridae

Answer

Caliciviridae

Question 7

Influenza virus culture is done on ?

Accepted Answer

Allantoic cavity

Answer

Chorioallantoic membrane

Answer

Yolk sac

Answer

All of the options

Question 8

Virus quantification is done by-

Accepted Answer

Plaque assay

Answer

Studying virus-cell interactions

Answer

Visualizing virus particles

Answer

Virus isolation using eggs

Question 9

Which poxvirus does not grow in eggs or animal cells?

Accepted Answer

Molluscum contagiosum

Answer

Cow pox

Answer

Vaccinia

Answer

Variola

Question 10

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)

Virology — MCQs

Virology — MCQs

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