Virology Practice Questions

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.

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: Pharyngeal-conjunctival fever is caused by

Adenovirus 3 and 7. ***Adenovirus 3 and 7*** - **Adenovirus serotypes 3 and 7** are the most common causes of **pharyngoconjunctival fever**, which presents with combination of **pharyngitis**, **conjunctivitis**, and **fever**. - This syndrome often occurs in outbreaks, particularly in children, and can be spread through **respiratory droplets** or contaminated water. *Adenovirus 11, 21* - **Adenovirus 11 and 21** are primarily associated with **hemorrhagic cystitis**, an inflammation of the bladder often presenting with **hematuria**. - They are less commonly implicated in typical pharyngoconjunctival fever, though adenoviruses can cause a spectrum of respiratory symptoms. *Adenovirus 40, 41* - **Adenovirus serotypes 40 and 41** are leading causes of **infantile gastroenteritis**, characterized by **diarrhea** and **vomiting**. - They are not typically associated with respiratory or ocular manifestations like pharyngoconjunctival fever. *Adenovirus 8, 19* - **Adenovirus 8 and 19** are well-known causes of **epidemic keratoconjunctivitis**, a severe form of conjunctivitis often involving the **cornea**. - While they cause a significant eye infection, they are not the primary serotypes linked to the broader syndrome of **pharyngoconjunctival fever** which includes pharyngitis and fever.

Q: What indicates HBV replication?

HBV DNA. ***HBV DNA*** - **HBV DNA** is the **gold standard and most direct marker of active HBV replication** in modern clinical practice - **Quantitative HBV DNA (viral load)** precisely measures the level of viral replication and is essential for: - Diagnosing active infection - Monitoring disease progression - Guiding treatment decisions - Assessing treatment response - Detected by **PCR (Polymerase Chain Reaction)** or other nucleic acid amplification tests - Directly indicates the presence of replicating virus *HBeAg* - **HBeAg (Hepatitis B e-antigen)** is a marker of high viral replication in **HBeAg-positive chronic hepatitis B** - However, it has significant limitations: - **HBeAg-negative variants** can have active replication without HBeAg presence - Not present in all cases of active replication - Less direct than measuring actual viral DNA - Useful as a supplementary marker but not the primary indicator of replication *DNA polymerase* - **HBV DNA polymerase** is an enzyme essential for viral replication - While its activity correlates with replication, it is **not routinely measured** as a primary clinical marker - HBV DNA testing has replaced DNA polymerase assays in modern practice *IgM Anti-HBc* - **IgM Anti-HBc (IgM antibody to hepatitis B core antigen)** indicates **acute or recent HBV infection** - Reflects the **immune response** to infection, not viral replication itself - Can be present during acute phase even as viral replication is being controlled - Not a marker of ongoing chronic replication

Q: Reverse transcriptase is a RNA-dependent DNA polymerase. Which of the following uses it?

Hepatitis B virus. ***Hepatitis B virus*** - Hepatitis B virus (HBV) is a **DNA virus** that replicates via an **RNA intermediate** using **reverse transcriptase**. - Its genome is a partially double-stranded circular DNA, and the enzyme is crucial for synthesizing the DNA genome from a pregenomic RNA template. *Hepatitis A virus* - Hepatitis A virus (HAV) is a **single-stranded RNA virus** (positive-sense) that replicates without a reverse transcriptase step. - Its replication involves direct translation of its RNA genome into viral proteins and replication via an RNA-dependent RNA polymerase. *Hepatitis E virus* - Hepatitis E virus (HEV) is a **single-stranded RNA virus** (positive-sense) that, like HAV, does not utilize reverse transcriptase for its replication. - It replicates in the cytoplasm of host cells using an **RNA-dependent RNA polymerase**. *Hepatitis C virus* - Hepatitis C virus (HCV) is a **single-stranded RNA virus** (positive-sense) belonging to the Flaviviridae family. - It replicates its RNA genome directly using an **RNA-dependent RNA polymerase** and does not involve a DNA intermediate or reverse transcription.

Q: All are true regarding mumps, EXCEPT:

Spreads through Stensen's duct to parotid gland. ***Spreads through Stensen's duct to parotid gland*** - Mumps virus does NOT primarily enter the parotid gland via **Stensen's duct**; rather, it reaches the parotid glands via **hematogenous spread** after initial replication in the upper respiratory tract and regional lymph nodes. - Stensen's duct is the **excretory duct** for saliva drainage from the parotid gland, not a viral entry route. - This is the **false statement** in this EXCEPT question. *Incubation period is 18-21 days* - The typical incubation period for mumps is **16-18 days** (range 12-25 days), so 18-21 days falls within the acceptable range. - This relatively long incubation period allows for potential asymptomatic transmission before symptom onset. *Can cause aseptic meningitis* - Mumps is a well-known cause of **aseptic (viral) meningitis**, occurring in approximately **10-15%** of mumps cases. - CNS involvement can also include encephalitis, though this is less common. - Most cases of mumps meningitis resolve without permanent neurological sequelae. *Multiplies in respiratory epithelium* - Mumps virus is transmitted via **respiratory droplets** and initially replicates in the **nasopharyngeal mucosa and respiratory epithelial cells**. - This initial replication site leads to local viral shedding and subsequent viremia with systemic spread to glandular tissues (parotid, pancreas, testes, ovaries).

Q: Which additional gene is present in the Human T-cell Leukemia Virus (HTLV)?

Tax. ***Tax*** - The **Tax gene** is a unique regulatory gene found in **Human T-cell Leukemia Virus (HTLV)** that is crucial for its oncogenic potential. - It plays a vital role in **viral replication** and **cellular transformation** by modulating host gene expression. *Gag* - The **Gag gene** encodes for **structural proteins** (e.g., matrix, capsid, nucleocapsid) that form the **viral core** and are essential for assembly but are not unique to HTLV. - This gene is present in all retroviruses, including HIV, and is not an "additional" gene specific to HTLV. *Pol* - The **Pol gene** encodes for essential viral enzymes such as **reverse transcriptase**, **protease**, and **integrase**, which are necessary for viral replication and integration. - This gene is also conserved across all retroviruses and does not represent an additional gene specific to HTLV. *Env* - The **Env gene** codes for the **envelope glycoproteins** (e.g., surface and transmembrane proteins) that mediate viral entry into host cells and are involved in receptor binding. - This gene is also a common feature of retroviruses and is therefore not an "additional" gene unique to HTLV.

Q: Which virus is most commonly recognized as a prototypical viral hemorrhagic fever in endemic regions of West Africa?

Lassa fever virus. ***Lassa fever virus*** - Lassa fever is a prototypical **viral hemorrhagic fever (VHF)** endemic to West Africa, caused by an **Arenavirus** transmitted through contact with rodent (Mastomys) excreta. - Characterized by fever, hemorrhagic manifestations in severe cases (15-20%), and multi-organ involvement with high mortality in hospitalized patients. - Represents one of the most important VHFs due to its **endemic nature** affecting millions annually in West Africa. *Yellow fever virus* - Yellow fever causes hemorrhagic fever with prominent **jaundice** and **hepatic necrosis**, transmitted by *Aedes* mosquitoes. - A **Flavivirus** causing "yellow" fever due to liver damage, but vaccine-preventable and less commonly seen in modern practice in endemic regions. *West Nile virus* - A **Flavivirus** primarily causing **neuroinvasive disease** (meningitis, encephalitis) rather than hemorrhagic fever. - Hemorrhagic manifestations are **extremely rare** and not characteristic of West Nile virus infection. *Crimean-Congo hemorrhagic fever virus* - CCHF is a severe **tick-borne VHF** (Nairovirus) with prominent hemorrhagic features and high mortality (10-40%). - Endemic to **Africa, Asia, Eastern Europe, and Middle East** but NOT West Africa, distinguishing its geographic distribution from Lassa fever.

Q: Active replication in hepatitis B infection is indicated by:

HBeAg. ***HBeAg*** - **HBeAg (Hepatitis B e-antigen)** indicates **active viral replication** and **high infectivity** in hepatitis B infection. - Its presence signifies that the virus is actively multiplying, leading to a higher risk of transmission. *HBsAg* - **HBsAg (Hepatitis B surface antigen)** is the **first serological marker** to appear following acute infection and indicates **current infection** (either acute or chronic). - Its presence alone does not differentiate between active replication and a chronic carrier state with low viral activity. *HBcAg* - **HBcAg (Hepatitis B core antigen)** is an **intracellular antigen** found within infected hepatocytes and is typically **not detectable in serum**. - Its primary clinical utility is seen through **anti-HBc antibodies**, which indicate past or current infection. *Anti-HBsAg* - **Anti-HBsAg (Antibody to HBsAg)** indicates **immunity** to hepatitis B, either due to successful **vaccination** or **resolved infection**. - Its presence implies that the individual is no longer infected and has protective antibodies, rather than active replication.

Q: Which of the following viruses specifically targets CD4+ T lymphocytes leading to progressive immunodeficiency?

HIV. ***HIV*** - **HIV** primarily targets **CD4+ T lymphocytes**, which are crucial components of the immune system found in lymphoid tissue. - The virus binds to CD4 receptors (along with co-receptors CCR5 or CXCR4) and progressively destroys these cells. - This progressive destruction leads to **immunodeficiency** and the development of AIDS. - HIV's specific tropism for CD4+ T cells distinguishes it from other viruses. *Adenovirus* - **Adenovirus** can infect various cell types, including respiratory epithelium, conjunctival cells, and gastrointestinal tract cells. - It does not have specific tropism for CD4+ T lymphocytes. - While it can cause opportunistic infections in immunocompromised individuals, it does not target T cells specifically. *Herpes virus* - **Herpes viruses** (e.g., HSV, VZV) primarily establish **latency in sensory neurons**. - EBV (a herpes virus) does target B lymphocytes, but not CD4+ T cells. - They do not cause progressive immunodeficiency through CD4+ T cell destruction. *CMV* - **CMV** (Cytomegalovirus) infects a wide range of cell types including fibroblasts, epithelial cells, endothelial cells, and monocytes. - While it can affect immunocompromised individuals, it does not specifically target CD4+ T lymphocytes. - CMV does not cause progressive immunodeficiency through selective CD4+ T cell destruction.

Question 1

Which of the following viruses is classified as a poxvirus?

Accepted Answer

Variola

Answer

Coxsackie

Answer

ECHO

Answer

HSV

Question 2

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 3

Pharyngeal-conjunctival fever is caused by

Accepted Answer

Adenovirus 3 and 7

Answer

Adenovirus 11, 21

Answer

Adenovirus 40, 41

Answer

Adenovirus 8, 19

Question 4

What indicates HBV replication?

Accepted Answer

HBV DNA

Answer

DNA polymerase

Answer

HBeAg

Answer

IgM Anti-HBc

Question 5

Reverse transcriptase is a RNA-dependent DNA polymerase. Which of the following uses it?

Accepted Answer

Hepatitis B virus

Answer

Hepatitis A virus

Answer

Hepatitis E virus

Answer

Hepatitis C virus

Question 6

All are true regarding mumps, EXCEPT:

Accepted Answer

Spreads through Stensen's duct to parotid gland

Answer

Incubation period is 18-21 days

Answer

Multiplies in respiratory epithelium

Answer

Can cause aseptic meningitis

Question 7

Which additional gene is present in the Human T-cell Leukemia Virus (HTLV)?

Accepted Answer

Tax

Answer

Gag

Answer

Pol

Answer

Env

Question 8

Which virus is most commonly recognized as a prototypical viral hemorrhagic fever in endemic regions of West Africa?

Accepted Answer

Lassa fever virus

Answer

West Nile virus

Answer

Yellow fever virus

Answer

Crimean-Congo hemorrhagic fever virus

Question 9

Active replication in hepatitis B infection is indicated by:

Accepted Answer

HBeAg

Answer

HBsAg

Answer

HBcAg

Answer

Anti-HBsAg

Question 10

Which of the following viruses specifically targets CD4+ T lymphocytes leading to progressive immunodeficiency?

Accepted Answer

HIV

Answer

Adenovirus

Answer

Herpes virus

Answer

CMV

Virology — MCQs

Virology — MCQs

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