Influenza Virus Structure and Function
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Questions and Answers

What is the typical duration of a fever associated with influenza, assuming no complications arise?

  • 1 to 3 days
  • 3 to 8 days (correct)
  • 8 to 12 days
  • 12 to 15 days

Which of the following processes contributes most significantly to local symptoms of influenza?

  • Compromised junctional proteins (correct)
  • Elevated cytokine activity
  • Gastrointestinal distress
  • Interferon response to the virus

What is the primary mechanism by which the influenza virus causes damage to the respiratory tract?

  • Triggering of the immune system as a target
  • Infecting epithelial cells expressing sialic acid receptors (correct)
  • Weakening the epithelial cells in the respiratory tract
  • Directly targeting the brain cells

Which of the following is LEAST likely to be directly a part of influenza infections in adults?

<p>Gastrointestinal illness (A)</p> Signup and view all the answers

How long can the regeneration of the respiratory epithelium take after an influenza infection subsides?

<p>Up to a month (C)</p> Signup and view all the answers

Which of the following is a characteristic of the Orthomyxoviridae family?

<p>Segmented, single-stranded negative-sense RNA genome (D)</p> Signup and view all the answers

What is the function of the hemagglutinin (HA) protein in Orthomyxoviridae viruses?

<p>Binds to sialic acid on epithelial cells and promotes membrane fusion. (C)</p> Signup and view all the answers

How many RNA segments are found in the genome of influenza A and B viruses?

<p>8 (B)</p> Signup and view all the answers

What is the role of the neuraminidase (NA) protein in the lifecycle of Orthomyxoviridae viruses?

<p>Cleaves sialic acid to prevent viral aggregation and promotes virion release. (C)</p> Signup and view all the answers

Which of the following describes how the Orthomyxoviridae RNA genome is replicated?

<p>The negative-sense RNA genome is replicated in the nucleus using viral polymerase. (C)</p> Signup and view all the answers

What is the nucleoprotein (NP) associated with in Orthomyxoviridae viruses?

<p>Each RNA segment. (D)</p> Signup and view all the answers

Which viral proteins are responsible for the transcription of the Orthomyxoviridae genome?

<p>PA, PB1, and PB2 (A)</p> Signup and view all the answers

From which surface of the infected cell does the Orthomyxoviridae virus preferentially bud?

<p>The apical surface. (C)</p> Signup and view all the answers

Which of the following is a complication directly caused by influenza viral replication in alveolar epithelial cells?

<p>Primary viral pneumonia (C)</p> Signup and view all the answers

What mechanism of action do zanamivir and oseltamivir share in combating influenza?

<p>Blocking of the release of new viral particles (B)</p> Signup and view all the answers

Which diagnostic method is MOST likely to be used for influenza virus detection in severe cases or hospitalized patients?

<p>RT-PCR amplification of the viral genome (B)</p> Signup and view all the answers

What is a primary reason annual influenza vaccines are updated each year?

<p>Due to the influenza virus's rapid mutation rate and the emergence of new strains. (A)</p> Signup and view all the answers

Secondary bacterial pneumonia that occurs after influenza infection is usually due to which of the following factors?

<p>The loss of natural barriers and exposure of binding sites on epithelial cells (B)</p> Signup and view all the answers

What is the primary cause of antigenic shift in influenza A viruses?

<p>Reassortment of genes between different influenza strains from different species. (A)</p> Signup and view all the answers

Which type of influenza virus is MOST likely to undergo antigenic shift?

<p>Influenza A virus. (A)</p> Signup and view all the answers

What is a key consequence of antigenic shift in influenza A viruses?

<p>Potential emergence of pandemic strains due to lack of pre-existing immunity. (A)</p> Signup and view all the answers

What is characteristic of antigenic drift in influenza viruses?

<p>It involves minor changes in the viral genes over time. (B)</p> Signup and view all the answers

How are influenza A subtypes classified?

<p>Based on their Hemagglutinin (H) and Neuraminidase (N) protein subtypes. (D)</p> Signup and view all the answers

Which of the following is a common characteristic of strains of influenza B?

<p>Classified by type, geography, and date of isolation. (B)</p> Signup and view all the answers

What are the two primary surface proteins used to classify influenza A virus subtypes?

<p>Hemagglutinin (H) and Neuraminidase (N). (B)</p> Signup and view all the answers

What is the significance of the pig as a host in the context of influenza virus evolution?

<p>Pigs may be intermediate hosts for interspecies viral spread due to the presence of both avian and mammalian receptor types. (D)</p> Signup and view all the answers

Where does the influenza virus typically replicate within the human body?

<p>Upper and lower respiratory tract epithelial cells. (C)</p> Signup and view all the answers

Which of the following is true regarding influenza B virus infection in humans?

<p>It only infects humans. (A)</p> Signup and view all the answers

Flashcards

Orthomyxoviridae

A family of viruses with a segmented, single-stranded RNA genome. They are enveloped (surrounded by a membrane) and have a pleomorphic (variable in shape) capsid.

Hemagglutinin (HA)

A protein on the surface of influenza viruses that binds to sialic acid on host cells. It facilitates attachment and entry of the virus.

Neuraminidase (NA)

An enzyme on the surface of influenza viruses that breaks down sialic acid. This is crucial for the release of new virus particles from infected cells.

Nucleoprotein (NP)

An internal protein of influenza viruses that helps assemble the viral particles and interacts with the RNA segments.

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Transcriptase (PA, PB1, PB2)

A complex of proteins important for the transcription and replication of viral RNA. It helps the virus copy its genetic material.

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Influenza Life Cycle

The process by which a virus attaches to a host cell, enters, and then replicates its genetic material.

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Antigenic Drift

Small changes in the HA and NA proteins of influenza viruses. These changes can make it harder for the immune system to recognize the virus.

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Antigenic Shift

Major changes in the HA and NA proteins of influenza viruses. These changes can cause large outbreaks because the immune system is less prepared.

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Primary viral pneumonia

A type of pneumonia caused by viral replication directly within the alveoli of the lungs.

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Secondary bacterial pneumonia

A type of pneumonia caused by bacteria taking advantage of weakened lung defenses following a viral infection.

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Neuraminidase inhibitors (Zanamivir and Oseltamivir)

Antiviral medications that block the release of new influenza virus particles, preventing further infection.

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M2 inhibitors (Amantadine and Rimantadine)

Antiviral medications that target the M2 protein, inhibiting its function in influenza A viruses.

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Moving vaccine target

The continual evolution of influenza viruses, making it challenging to develop effective long-term vaccines.

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Respiratory Tract Damage

Viral replication and the immune response can lead to destruction of cells in the respiratory tract, particularly the epithelial lining.

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Epithelial Regeneration

The process of regeneration of damaged epithelial cells in the respiratory tract after a viral infection can take up to a month.

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Lingering Symptoms

Symptoms like cough and weakness can persist for up to two weeks after an influenza infection.

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Systemic Symptoms

Symptoms like fever, chills, muscle aches, and sore throat are caused by the body's inflammatory response to the virus.

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Compromised Barrier

Damage to epithelial cells, which line the respiratory tract, disrupts the physical barrier and can weaken the body's defense against other pathogens.

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What causes Antigenic Shift?

Gene swapping between animal and human influenza viruses.

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Pandemic Strain

A pandemic strain emerges when a new influenza A virus, created by an antigenic shift, spreads widely and most people lack immunity.

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Pigs as Intermediate Hosts

Pigs can host both avian and mammalian influenza viruses, facilitating the spread of the virus between species.

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Antigenic Drift Effect on Viruses

Antigenic Drift results in viruses that are closely related to their predecessors and share similar antigenic properties.

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Antigenic Drift and Re-Infection

Antigenic Drift can lead to a virus becoming unrecognizable to antibodies, allowing it to re-infect individuals.

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Influenza A Subtype Classification

Influenza A viruses are categorized based on their hemagglutinin (H) and neuraminidase (N) subtypes.

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Number of Influenza A Subtypes

There are 16 hemagglutinin (H1-H16) subtypes and 9 neuraminidase (N1-N9) subtypes.

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Influenza B Strain Designation

Influenza B strains are classified by type, geography, and date of isolation.

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Study Notes

Orthomyxoviridae Family

  • The family of viruses that includes influenza viruses
  • Genome is segmented, single-stranded (ss) negative-sense RNA
  • Pleomorphic capsid
  • Enveloped viruses (80-120 nm diameter)

Influenza Virus Structure

  • Contains proteins crucial to the virus's function
    • Hemagglutinin (HA): spike-shaped trimer, binds to sialic acid receptor, promotes fusion with endosome, elicits neutralizing antibodies
    • Neuraminidase (NA): tetramer, cleaves sialic acid residues on host cells, which helps release new virions from infected cells
    • M2: membrane protein
    • M1: matrix protein
    • NP: nucleoprotein, associated with RNA segments
    • NS: nuclear export protein
  • The genome segments are associated with NP (RNP) and the transcribed RNA polymerase (components PB1, PB2, PA)
  • Influenza A and B viruses possess 8 different segments, while Influenza C contains 7
  • The images in the document show the structural components of the influenza A and B viruses.
  • Different types have different proteins (A, B, C)

Types of influenza Viruses

  • Influenza A: causes most human illness and flu season
    • Subtypes (H1N1), (H3N2) and others based on HA and NA protein subtypes. -Lineages: (Victoria), (Yamagata) and others -Multiple Clades and sub-clades in the tree
  • Influenza B: infects only humans -Lineages: (Victoria), (Yamagata) and and others
  • Influenza C: infects humans more rarely

Influenza Virus Replication Cycle

  • Viral attachment, internalization into vesicles
  • Acidification of endosome; Membrane fusion and nucleocapsid release
  • Viral mRNA transcription occurs
  • Viral mRNA translation
  • Genome replication in the nucleus; assembly process
  • Budding of new virions

Antigenic Shift and Drift

  • Shift: Major change in HA and/or NA proteins, caused by reassortment between animal and human viruses, leading to pandemic strains
  • Drift: Smaller changes in HA and NA proteins continually occurring as the virus replicates over time. Accumulated mutations lead to antigenically different viruses the antibodies cannot recognize.

Influenza Virus Pathogenesis

  • Infection of epithelial cells (upper and lower respiratory tract)
  • Viral replication causes damage to these cells
  • Loss of cells lining respiratory tract; secondary infections
  • Symptoms such as cough, fever, body aches - Local symptoms (from damaged epithelial cells) - Systemic symptoms (from interferon and cytokine response to the virus)

Diagnosis of Influenza

  • Molecular methods (RT-PCR): amplifying viral genome in respiratory samples.

Antiviral Therapy

  • Inhibitors of viral neuraminidase activity(Zanamivir, Oseltamivir)
  • Inhibitors of the viral M2 protein ion channels (Amantadine, Rimantadine)

Influenza Vaccine

  • Vaccines should contain antigens of prevalent A and B strains.
  • Egg and Recombinant-based vaccines are highlighted.
  • Different specific influenza strains are listed, with examples of vaccines used.

Severe Complications

  • Primary and secondary viral pneumonia
  • Myocarditis and pericarditis
  • Myositis
  • Encephalopathy

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Description

Explore the intricate structure and function of the influenza virus, focusing on its proteins and segmented RNA genome. This quiz delves into the Orthomyxoviridae family and details the key components essential for the virus's lifecycle. Test your understanding of hemagglutinin, neuraminidase, and more.

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