Virology Practice Questions

Q: Which test is primarily used for the quantification of viral infectivity?

Plaque assay. ***Plaque assay*** - The **plaque assay** directly measures the number of **infectious viral particles** in a sample, expressed as plaque-forming units (PFU) per milliliter. - It involves inoculating host cells with serially diluted virus, leading to localized areas of cell lysis or destruction called **plaques**, which are then counted. *Cytopathic effect* - **Cytopathic effect (CPE)** refers to the visual changes induced in host cells by viral infection, such as cell rounding, lysis, or syncytia formation. - While it indicates an infection is occurring, it does not reliably **quantify** the number of infectious viral particles. *Haemagglutination* - **Hemagglutination assay** measures the ability of certain viruses to agglutinate red blood cells due to binding of viral proteins to receptors on the cell surface. - This method quantifies the **total number of viral particles** (infectious or non-infectious) that possess hemagglutinating activity, not specifically their infectivity. *Electron microscopy* - **Electron microscopy** allows for direct visualization of virus particles and their morphological characteristics. - It can determine the **total number of physical viral particles** in a sample but cannot distinguish between infectious and non-infectious particles.

Q: Fifth disease is caused by which virus?

Parvovirus B19. ***Parvovirus B19*** - **Parvovirus B19** is the sole member of the *Erythrovirus* genus known to cause disease in humans, primarily responsible for **Fifth disease**, also known as **erythema infectiosum**. - This virus targets and replicates in **erythroid progenitor cells**, leading to a characteristic rash and, in some cases, transient aplastic crisis. *Human Papillomavirus (HPV)* - HPV is known to cause **warts** and is a major risk factor for various cancers, including **cervical cancer**, not Fifth disease. - It infects epithelial cells and leads to proliferative lesions, with over 100 different types identified. *Hepatitis Virus* - Hepatitis viruses (e.g., A, B, C, D, E) primarily cause **inflammation of the liver** and are associated with acute or chronic liver disease. - They are not associated with the characteristic rash or symptoms of Fifth disease. *Cytomegalovirus (CMV)* - CMV is a common virus that usually causes **asymptomatic infection** but can lead to severe disease in immunocompromised individuals or newborns. - It is known for causing **congenital infections** and opportunistic infections in transplant recipients, not Fifth disease.

Q: Which of the following viruses is not spread by the fecal-oral route?

Hepatitis B virus (HBV). ***Hepatitis B virus (HBV)*** - HBV is primarily transmitted through **percutaneous** or **mucosal exposure** to infectious blood or body fluids, such as during sex, sharing needles, or from mother to child. - It is not typically spread via the **fecal-oral route**. *Hepatitis E virus (HEV)* - HEV is a common cause of **acute viral hepatitis** and is predominantly transmitted through the **fecal-oral route**, often via contaminated drinking water. - High viral loads are shed in the feces of infected individuals, leading to environmental contamination. *Rotavirus* - Rotavirus is a major cause of **severe diarrheal disease** in infants and young children, and its transmission occurs almost exclusively through the **fecal-oral route**. - The virus is highly stable in the environment and can spread rapidly in settings with poor hygiene. *Norwalk virus (Norovirus)* - Norovirus is a highly contagious virus that causes **gastroenteritis** and is notorious for outbreaks in crowded settings; its primary mode of transmission is the **fecal-oral route**. - It can also spread through contaminated food and water, or direct contact with infected individuals.

Q: Which of the following statements about Zika virus is false?

Zika virus does not cause microcephaly. ***Zika virus does not cause microcephaly*** - This statement is false because **Zika virus** is well-known for causing **microcephaly** and other severe birth defects in infants whose mothers were infected during pregnancy. - The association between maternal Zika infection and fetal microcephaly has been extensively documented and is one of the most critical public health concerns related to the virus. *Transmitted by Aedes mosquito* - This statement is true; **Aedes aegypti** and **Aedes albopictus** mosquitoes are the primary vectors responsible for transmitting the Zika virus to humans. - These mosquitoes are also known to transmit other arboviruses like **dengue** and **chikungunya**. *Zika is Flavi virus* - This statement is true; Zika virus belongs to the **Flaviridae family** and the *Flavivirus genus*, which also includes dengue, yellow fever, and West Nile viruses. - Members of this family are typically **single-stranded RNA viruses** with an enveloped capsid. *Zika virus cannot be transmitted through breast milk* - This statement is true; while Zika virus RNA has been detected in breast milk, there is currently **no confirmed evidence** of transmission to infants through breastfeeding. - Current guidelines from health organizations generally recommend that mothers in Zika-affected areas continue to breastfeed due to the benefits of breastfeeding outweighing the theoretical risk.

Q: Dengue fever is caused by:

Flavivirus. ***Flavivirus*** - Dengue fever is caused by the **dengue virus**, which belongs to the **Flaviviridae family** (genus Flavivirus). - There are **four serotypes** of dengue virus (DENV-1, DENV-2, DENV-3, DENV-4), all of which can cause dengue fever. - Flaviviruses are **RNA viruses** transmitted by **arthropod vectors** (primarily *Aedes aegypti* and *Aedes albopictus* mosquitoes). - Other important flaviviruses include **Yellow fever virus**, **Zika virus**, **West Nile virus**, and **Japanese encephalitis virus**. *Orthomyxo virus* - This family includes the **influenza viruses** (influenza A, B, C, D) which cause seasonal flu and pandemic influenza. - They are **segmented RNA viruses** transmitted via **respiratory droplets**, not arthropod vectors. - Characterized by surface proteins **hemagglutinin (H)** and **neuraminidase (N)**. *Paramyxo virus* - This family includes viruses causing **measles**, **mumps**, **parainfluenza**, and **respiratory syncytial virus (RSV)**. - These are **non-segmented negative-sense RNA viruses** transmitted through **respiratory secretions** and close contact. - Not transmitted by arthropod vectors. *Bunya virus* - The **Bunyaviridae family** (now reclassified into multiple families) includes various arboviruses like **Crimean-Congo hemorrhagic fever virus** and **Rift Valley fever virus**. - Also includes **hantaviruses** transmitted by rodents (not arthropods). - While some bunyaviruses cause hemorrhagic fevers, dengue virus specifically belongs to the **Flaviviridae family**, not Bunyaviridae.

Q: Which of the following serves as the cellular receptor for Epstein-Barr Virus (EBV)?

CD 21. ***CD 21*** - **CD21**, also known as the **complement receptor 2 (CR2)**, is the primary cellular receptor for Epstein-Barr Virus (EBV). - EBV predominantly infects **B lymphocytes** by binding to CD21, allowing viral entry. *CD 20* - **CD20** is a transmembrane protein found on **B-lymphocytes**, but it is **not** the receptor for EBV. - It is often targeted in cancer therapy for B-cell lymphomas (e.g., with **Rituximab**). *CD 22* - **CD22** is an inhibitory co-receptor on B-lymphocytes that **regulates B-cell activation**. - While present on B-cells, it does **not** serve as the entry receptor for EBV. *CD 23* - **CD23** is the **low-affinity IgE receptor (FcεRII)**, found on activated B cells, macrophages, and other immune cells. - It is **not** the receptor used by EBV for cellular entry; rather, it is involved in **IgE-mediated immune responses**.

Q: Virus lacking hemagglutinin and neuraminidase but having a prominent membrane fusion (F) protein as its major surface glycoprotein is?

Respiratory Syncytial Virus (RSV). ***Respiratory Syncytial Virus (RSV)*** - RSV is characterized by the presence of a **prominent fusion (F) protein** as its major surface glycoprotein, which mediates membrane fusion and viral entry into host cells. - Unlike influenza viruses, RSV **lacks hemagglutinin and neuraminidase proteins**. - The **F protein is the primary virulence factor** and target for antibody-mediated immunity. *Cytomegalovirus (CMV)* - CMV is a **herpesvirus** that does not possess hemagglutinin or neuraminidase. - Its entry mechanism involves **multiple glycoproteins** (gB, gH, gL) that work together for fusion, rather than a single prominent F protein like RSV. *Herpes Simplex Virus (HSV)* - HSV is another **herpesvirus** that utilizes **various glycoproteins** (gB, gD, gH, gL) working in concert for binding and membrane fusion. - It **lacks hemagglutinin and neuraminidase** but does not have a single prominent fusion protein. *Epstein-Barr Virus (EBV)* - EBV, a member of the **herpesvirus family**, also does not have hemagglutinin or neuraminidase. - Its entry involves **specific glycoproteins** (gH, gL, gp42, gB) that are responsible for receptor binding and membrane fusion in a coordinated manner.

Q: Which of the following viruses is considered a defective virus that requires another virus for its replication?

Hepatitis D virus (HDV). ***Hepatitis D virus (HDV)*** - **Hepatitis D virus (HDV)** is a unique RNA virus that is **defective** and requires the presence of **Hepatitis B virus (HBV)** and its surface antigen **(HBsAg)** for replication and assembly. - HDV infection can occur as **co-infection** (simultaneous HBV and HDV) or **superinfection** (HDV infection in an existing HBV carrier), often leading to **more severe liver disease**. - HDV is a **satellite virus** that cannot complete its life cycle independently. *Incorrect: Hepatitis A virus (HAV)* - **Hepatitis A virus (HAV)** is a **picornavirus** that causes acute hepatitis and **replicates independently** without the need for another helper virus. - It is transmitted via the **fecal-oral route** and does **not cause chronic infection**. *Incorrect: Hepatitis B virus (HBV)* - **Hepatitis B virus (HBV)** is a **hepadnavirus** that **replicates independently** and produces its own viral envelopes. - HBV is the **helper virus required for HDV replication**, but HBV itself does not require another virus to complete its life cycle. *Incorrect: Hepatitis C virus (HCV)* - **Hepatitis C virus (HCV)** is a **flavivirus** that can **replicate autonomously** and cause both acute and chronic hepatitis. - It does **not require a helper virus** for its replication, unlike HDV.

Q: Herpes zoster ophthalmicus is caused by:

VZV. ***Correct Answer: VZV*** - **Varicella-zoster virus (VZV)** is the causative agent of **herpes zoster ophthalmicus**, which is a reactivation of the virus in the ophthalmic division of the trigeminal nerve. - The initial infection with VZV causes **chickenpox (varicella)**, and the virus remains dormant in sensory ganglia to reactivate later as shingles. *Incorrect - HPV* - **Human papillomavirus (HPV)** is primarily known for causing **warts** and is a significant risk factor for certain **cancers**, particularly cervical cancer. - HPV does not cause vesicular rashes associated with herpes zoster or ophthalmic involvement. *Incorrect - HSV* - **Herpes simplex virus (HSV)** causes different forms of herpes infections, such as **oral (cold sores)** and **genital herpes**, and can also cause keratitis but is distinct from zoster ophthalmicus. - While HSV can affect the eye, leading to **herpes simplex keratitis**, it produces a different clinical picture and does not involve the dermatomal rash characteristic of zoster. *Incorrect - CMV* - **Cytomegalovirus (CMV)** is a common virus often causing asymptomatic infections in healthy individuals. - In immunocompromised patients, CMV can cause serious diseases, including **retinitis**, but it does not cause herpes zoster ophthalmicus.

Question 1

Which test is primarily used for the quantification of viral infectivity?

Accepted Answer

Plaque assay

Answer

Haemagglutination

Answer

Cytopathic effect

Answer

Electron microscopy

Question 2

Fifth disease is caused by which virus?

Accepted Answer

Parvovirus B19

Answer

Human Papillomavirus (HPV)

Answer

Hepatitis Virus

Answer

Cytomegalovirus (CMV)

Question 3

Which of the following viruses is not spread by the fecal-oral route?

Accepted Answer

Hepatitis B virus (HBV)

Answer

Rotavirus

Answer

Hepatitis E virus (HEV)

Answer

Norwalk virus (Norovirus)

Question 4

Which of the following statements about Zika virus is false?

Accepted Answer

Zika virus does not cause microcephaly

Answer

Transmitted by Aedes mosquito

Answer

Zika is Flavi virus

Answer

Zika virus cannot be transmitted through breast milk

Question 5

Dengue fever is caused by:

Accepted Answer

Flavivirus

Answer

Orthomyxo virus

Answer

Paramyxo virus

Answer

Bunya virus

Question 6

Which of the following serves as the cellular receptor for Epstein-Barr Virus (EBV)?

Accepted Answer

CD 21

Answer

CD 22

Answer

CD 20

Answer

CD 23

Question 7

Virus lacking hemagglutinin and neuraminidase but having a prominent membrane fusion (F) protein as its major surface glycoprotein is?

Accepted Answer

Respiratory Syncytial Virus (RSV)

Answer

Herpes Simplex Virus (HSV)

Answer

Cytomegalovirus (CMV)

Answer

Epstein-Barr Virus (EBV)

Question 8

Which of the following viruses is considered a defective virus that requires another virus for its replication?

Accepted Answer

Hepatitis D virus (HDV)

Answer

Hepatitis A virus (HAV)

Answer

Hepatitis B virus (HBV)

Answer

Hepatitis C virus (HCV)

Question 9

Dengue hemorrhagic fever is primarily associated with which type of infection?

Accepted Answer

Secondary infection with a different serotype of the dengue virus

Answer

Infection with the same dengue virus repeatedly

Answer

Infection with dengue virus in an immunocompromised host

Answer

Infection with multiple serotypes of the dengue virus

Question 10

Herpes zoster ophthalmicus is caused by:

Accepted Answer

VZV

Answer

HPV

Answer

HSV

Answer

CMV

Virology — MCQs

Virology — MCQs

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