Viral Infections and Immune Response Quiz
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Questions and Answers

What is primarily required for a virus to initiate an infection?

  • Infection by multiple virus strains simultaneously
  • Susceptibility and permissiveness of host cells (correct)
  • High levels of antibodies in the host
  • Presence of virus particles in large quantities

    • Which type of interferon is primarily produced by epithelial cells during a viral infection?

  • IFN-α
  • IFN-β
  • IFN-λ (correct)
  • None of the above

    • Which component of the immune system is primarily responsible for lysis of infected cells?

  • Antibodies
  • Natural killer cells (correct)
  • Macrophages
  • B cells

    • What immune response is primarily affected in AIDS patients?

    <p>Ratio of T-helper to T-suppressor cells</p> Signup and view all the answers

    What is the role of interferon-sensitive genes in viral defense?

    <p>Transcription results in antiviral effects</p> Signup and view all the answers

    Which type of antibody is NOT typically produced in response to viral infections?

    <p>IgE</p> Signup and view all the answers

    How do natural killer cells contribute to the antiviral immune response?

    <p>They are an early source of cytokines and chemokines.</p> Signup and view all the answers

    What mechanism is NOT involved in the adaptive immune response to viral infections?

    <p>Inflammatory response by macrophages</p> Signup and view all the answers

    What is an important factor in determining a successful viral infection?

    <p>Both viral characteristics and host immune response</p> Signup and view all the answers

    What is one method by which viruses can evade host defenses?

    <p>Changing antigenic targets through genome reassortment</p> Signup and view all the answers

    Which of the following best describes a chronic viral infection?

    <p>The virus replicates continuously, causing persistent symptoms</p> Signup and view all the answers

    What role do interferons play in the innate immune response to viral infection?

    <p>They help regulate the immune response and viral replication</p> Signup and view all the answers

    Which virus is primarily associated with a persistent-latent infection?

    <p>Herpes simplex</p> Signup and view all the answers

    How do viruses typically evade the host immune response?

    <p>By altering their surface antigens or using immune subversion tactics</p> Signup and view all the answers

    What role does the innate immune response play in acute viral infections?

    <p>It is crucial for limiting the initial infection</p> Signup and view all the answers

    Which virus is characterized by high mutation rates during genome replication, leading to immune evasion?

    <p>HIV</p> Signup and view all the answers

    In which type of viral infection does the virus remain dormant and can reactivate later?

    <p>Latent infection</p> Signup and view all the answers

    What is a characteristic of slow viral infections?

    <p>They cause a gradual accumulation of viral particles and symptoms over time</p> Signup and view all the answers

    What is the main characteristic of the adaptive immune response during acute viral infections?

    <p>Takes several days to influence viral growth</p> Signup and view all the answers

    What is necessary for initiating a viral infection according to the processes involved?

    <p>Sufficient virus must be present to initiate an infection</p> Signup and view all the answers

    What type of viral infection involves an initiation of a non-cytopathic state to avoid an immune response?

    <p>Latent infection</p> Signup and view all the answers

    What role do dendritic cells play in the adaptive immune response to viral infections?

    <p>They present viral antigens to T-cells to activate them</p> Signup and view all the answers

    Which of the following viruses is known for causing persistent-slow infections?

    <p>Measles SSPE</p> Signup and view all the answers

    What effect does an immunocompromised state have on viral infections?

    <p>May allow spread beyond the primary infection site</p> Signup and view all the answers

    What characterizes chronic infections in persistent viral infections?

    <p>They may eventually be cleared unless fatal.</p> Signup and view all the answers

    Which of the following viruses is associated with persistent-latent infections?

    <p>Varicella zoster</p> Signup and view all the answers

    What is one way viruses evade the host immune response?

    <p>By hiding in immune privileged sites.</p> Signup and view all the answers

    Which of the following best describes slow persistent infections?

    <p>They last the life of the host without being cleared.</p> Signup and view all the answers

    How do high-frequency variations in antigenic epitopes aid viral persistence?

    <p>They help the virus evade recognition by the immune system.</p> Signup and view all the answers

    What principle underlies the establishment of persistent viral infections?

    <p>The virus minimizing damage to the host, avoiding death.</p> Signup and view all the answers

    Which of the following pathogens is an example of a persistent-slow infection?

    <p>Measles SSPE</p> Signup and view all the answers

    What is a common feature shared by chronic, latent, and slow viral infections?

    <p>They can produce virus particles for extended periods.</p> Signup and view all the answers

    Which mechanism is NOT involved in the direct subversion of the immune system by a virus?

    <p>Promotion of apoptosis</p> Signup and view all the answers

    Which virus is associated with persistent chronic infection?

    <p>Hepatitis B</p> Signup and view all the answers

    What characterizes a latent virus infection?

    <p>Immune detection of the infected cell is significantly reduced.</p> Signup and view all the answers

    What occurs during the reactivation of a latent virus like Herpes simplex?

    <p>The virus replicates and travels down sensory nerve fibers.</p> Signup and view all the answers

    Which virus is known to cause acute symptoms in its initial infection phase?

    <p>Influenza virus</p> Signup and view all the answers

    Which of the following is a characteristic of persistent slow viral infections?

    <p>Gradual decline in the immune response over time</p> Signup and view all the answers

    What is the primary consequence of a virus directly infecting immune system cells like lymphocytes?

    <p>Facilitated viral spread and reduced immune competence</p> Signup and view all the answers

    Which of the following statements about herpes simplex virus is true?

    <p>It can remain asymptomatic as viral DNA persists in sensory nerve cells.</p> Signup and view all the answers

    Which virus is associated with a slow infection that can lead to progressive neurologic deterioration?

    <p>Measles virus</p> Signup and view all the answers

    What type of infection is characterized by the detection of defective virus in the brain years after the initial infection?

    <p>Slow infection</p> Signup and view all the answers

    Which of the following viruses is primarily associated with a chronic persistent infection?

    <p>Hepatitis C</p> Signup and view all the answers

    In a persistent infection, what role do antibodies produced during an acute infection play?

    <p>They can drive the virus into a persistent state.</p> Signup and view all the answers

    What is a characteristic feature of transmissible spongiform encephalopathies (TSEs)?

    <p>They can develop years after contact with the infectious agent.</p> Signup and view all the answers

    Which of the following viruses has the potential to cause both acute and persistent outcomes?

    <p>Measles virus</p> Signup and view all the answers

    What factor primarily determines the outcome of a viral infection?

    <p>The host’s immune response and virus properties</p> Signup and view all the answers

    What type of persistent infection involves the virus reactivating after latency?

    <p>Latent infection</p> Signup and view all the answers

    Which of the following is a potential symptom caused by direct cellular damage from a virus?

    <p>Nausea</p> Signup and view all the answers

    What characterizes clinically inapparent acute viral infections?

    <p>They are rapidly controlled by the host immune system.</p> Signup and view all the answers

    What term describes the first phase of an acute viral infection where the virus spreads from the initial site to the bloodstream?

    <p>Primary viraemia</p> Signup and view all the answers

    Which of the following viruses is known for causing multiple acute infections in succession?

    <p>Poliovirus</p> Signup and view all the answers

    Which symptom is NOT typically associated with direct viral action on cells?

    <p>Fatigue</p> Signup and view all the answers

    What is a common characteristic of acute viral infections that contributes to public health challenges?

    <p>They can spread before symptoms appear.</p> Signup and view all the answers

    What role do toxic viral proteins play in the pathogenesis of viral infections?

    <p>They directly damage host cells.</p> Signup and view all the answers

    In the case of an acute infection, what is a possible outcome of the immune response to a virus?

    <p>Complete elimination of the virus.</p> Signup and view all the answers

    What is a primary characteristic of acute viral infections?

    <p>Immediate immune response and symptoms</p> Signup and view all the answers

    Which type of persistent viral infection is characterized by the virus remaining dormant and potentially reactivating later?

    <p>Latent infections</p> Signup and view all the answers

    What is one of the main roles of interferons in the context of viral infections?

    <p>Inhibit viral replication and modulate immune responses</p> Signup and view all the answers

    What mechanism do viruses commonly use to evade the host's immune response?

    <p>Antigenic variation to alter detectable markers</p> Signup and view all the answers

    How do natural barriers such as skin and mucus contribute to the prevention of viral infections?

    <p>By trapping and preventing virus entry into the body</p> Signup and view all the answers

    Which immune cells play a crucial role during the innate response to a viral infection?

    <p>Natural killer cells and macrophages</p> Signup and view all the answers

    What defines a chronic persistent viral infection?

    <p>The virus remains in the host for an extended period, causing ongoing effects</p> Signup and view all the answers

    Which of the following best describes the role of CD8+ T-cells during a viral infection?

    <p>They recognize and eliminate virus-infected cells</p> Signup and view all the answers

    What role does cell-mediated immunity play in viral infections compared to humoral immunity?

    <p>It is more important than humoral immunity for controlling many virus infections.</p> Signup and view all the answers

    Which statement best describes the function of interferons during a viral infection?

    <p>They lead to the transcription of interferon sensitive genes, resulting in antiviral effects.</p> Signup and view all the answers

    What is meant by the term 'tropism' in the context of viral infections?

    <p>The pattern of infection, pathogenesis, and viral survival.</p> Signup and view all the answers

    In the context of innate defenses against viral infections, what role do natural killer cells play?

    <p>They are non-specific cytotoxic effector cells that lyse infected cells.</p> Signup and view all the answers

    What is a potential consequence of congenital defects in cell-mediated immunity?

    <p>Increased susceptibility to viral and parasitic infections.</p> Signup and view all the answers

    What primarily induces the production of Type I interferons?

    <p>Viral infections and double-stranded RNA.</p> Signup and view all the answers

    Which antibodies are typically induced in response to viral infections?

    <p>IgM, IgA, and IgG.</p> Signup and view all the answers

    What is a common characteristic of immune evasion strategies employed by viruses?

    <p>Overwhelming host defenses with massive viral particles.</p> Signup and view all the answers

    Which virus is known for rapidly evolving its antigenic targets to evade the immune system?

    <p>HIV</p> Signup and view all the answers

    How does a virus like herpes simplex manage to avoid robust immune responses?

    <p>By initiating a non-cytopathic infection</p> Signup and view all the answers

    Which of the following describes a persistent-latent viral infection?

    <p>Virus can reactivate after a period of dormancy</p> Signup and view all the answers

    What is a major consequence of an immunocompromised host during a viral infection?

    <p>Infection may spread beyond the initial site</p> Signup and view all the answers

    Which of the following viruses is primarily associated with acute viral infections?

    <p>SARS-CoV-2</p> Signup and view all the answers

    What distinguishes a slow viral infection from other types of viral infections?

    <p>The virus replicates at a slow rate over a long period</p> Signup and view all the answers

    Which mechanism is employed by viruses like influenza to evade immune system defenses?

    <p>Replacing surface proteins through genetic reassortment</p> Signup and view all the answers

    What is a characteristic feature of latent virus infections?

    <p>Viral genes involved in particle production are inefficiently expressed.</p> Signup and view all the answers

    Which of the following best describes the initial infection symptoms of Herpes Simplex virus Type 1?

    <p>Cold sores and sore throat.</p> Signup and view all the answers

    What mechanism is frequently employed by viruses to inhibit the immune response?

    <p>Mimicking normal immune system regulators.</p> Signup and view all the answers

    Which of the following viruses is known for its ability to cause persistent-latent infections?

    <p>Varicella zoster.</p> Signup and view all the answers

    What is NOT a common effect of direct infection of the immune system by viruses?

    <p>Increased cytokine production.</p> Signup and view all the answers

    Which of the following represents a persistent-slow viral infection?

    <p>HIV.</p> Signup and view all the answers

    Which statement about viral infections and immune system interactions is accurate?

    <p>Chronic infections involve continuous presence of the virus with potential disease manifestation.</p> Signup and view all the answers

    What is a typical outcome of a virus that has successfully evaded host immune defenses?

    <p>Sustained replication and potential reactivation.</p> Signup and view all the answers

    What outcomes can arise from viral infections?

    <p>Acute, persistent: chronic, latent, and slow</p> Signup and view all the answers

    Which virus is known to cause a slow infection leading to progressive neurological deterioration?

    <p>Measles virus</p> Signup and view all the answers

    What is a characteristic of transmissible spongiform encephalopathies (TSEs)?

    <p>They are associated with an extreme variation of persistent infection.</p> Signup and view all the answers

    What role do antibodies produced during an acute infection play in persistent infections?

    <p>They may drive the virus into a persistent infection.</p> Signup and view all the answers

    Which of the following symptoms is associated with a slow viral infection like SSPE?

    <p>Gradual neurological decline</p> Signup and view all the answers

    Which of these viruses is classified as having a persistent-chronic infection?

    <p>Hepatitis C</p> Signup and view all the answers

    How long may pass between the initial contact with certain viruses and the development of fatal disease in slow infections?

    <p>Years to decades</p> Signup and view all the answers

    Which of the following statements is true regarding latent viral infections?

    <p>Latent infections can remain dormant and reactivate later.</p> Signup and view all the answers

    Study Notes

    Viral Infection Patterns

    • Viral infections are successful when a balance exists between the host's defenses and the virus' properties.
    • Characteristic outcomes include acute, persistent (chronic, latent, and slow persistent).
    • Some viruses exhibit a combination of these outcomes.
    • The different outcomes have implications for pathogenicity, public health, and treatment.

    Overview of Viral Infection

    • Factors determining successful viral infection: viral and host immune determinants.
    • Acute viral infections detail: definition, host defense and viral pathogenesis, importance.
    • Persistent viral infections detail: definitions (chronic, latent, slow persistent), host defense evasion, latent infections, and slow infections.

    Intended Learning Outcomes

    • Understand the host immune system's role in preventing viral infection.
    • Describe general patterns of viral infection.
    • Describe the typical acute infection pattern and host/viral interactions that lead to disease.
    • Understand the significance of acute infections.
    • Understand persistent infection types (chronic, latent, and slow).
    • Explain how viruses evade the host immune response for persistent infections.
    • Describe latent infection characteristics and provide examples.
    • Define slow infections and provide examples.
    • Identify specific types of infections as well as describe general patterns.

    Viral Life Cycle

    • The viral life cycle involves attachment, penetration, uncoating, replication, assembly, and release.
    • Host functions during this cycle include transcription and translation.

    Infection: A Delicate Balance

    • Human defenses include natural barriers, innate response (interferons, NK cells, macrophages, apoptosis), and adaptive response (dendritic cells, CD4+ T-cells, CD8+ T-cells, antibodies).
    • Viral factors include establishing infection, regulating gene expression, antigenic variation, immune evasion, and immune subversion.

    Initiation of Infection

    • Basic requirements for infection include sufficient virus and environmental stability.
    • Virus particles need susceptible host cells for infection.
    • Tropism influences the infection pattern and viral survival.
    • Host defenses can be overwhelmed, for example by massive viral loads (aerosol droplet), or through injuries and compromised immunity (cuts, abrasions, organ transplantation).
    • Immune evasion helps establish persistent infections.

    Innate Defence Against Viral Infections

    • Type I and III interferons act as antiviral cytokines.
    • IFN-α, IFN-β, and IFN-γ are produced by various cells, targeting viral infections, often in response to dsRNA.
    • Interferon signaling triggers the transcription of interferon-sensitive genes.
    • Natural killer cells are crucial in the lysis of infected cells.

    Adaptive Defence Against Viral Infections

    • Antibody responses target viral infections, including neutralization, complement activation, opsonization (for phagocytosis), and antibody-dependent cell-mediated cytotoxicity (ADCC).
    • Cell-mediated immunity also plays a role in controlling viral infections.
    • Congenital defects in cell-mediated immunity can predispose individuals to viral infections, rather than bacterial infections.
    • AIDS involves a reduction in the ratio of CD4+ to CD8+ T cells, making individuals susceptible to opportunistic viral infections.

    Cell-Mediated Defence Against Viral Infections

    • This defense mechanism involves non-specific (e.g., NK cells) and specific (e.g., CTL) killing of infected cells.
    • Immune cells target virus-infected cells through: non-specific killing (not MHC-restricted, like from NK cells, that release perforin); and specific killing.

    Successful Viral Infections Evasive Strategies

    • Antigenic target evolution (e.g., reassortment and mutation) is common among viruses to avoid the host immune response.
    • Viruses may block specific immune defenses or initiate non-cytopathic infections to delay or avoid a significant immune response (as seen in Herpes viruses, HIV, adenoviruses, and Papillomaviruses).

    General Patterns of Viral Infection – Types and Outcomes

    • Viral infections exhibit varied outcomes:
      • Acute: high viral load, rapid onset (e.g. SARS-CoV-2, influenza virus, poliovirus).
      • Persistent (Chronic): ongoing infection (e.g., hepatitis B and C).
      • Persistent (Latent): virus remains dormant (e.g., herpes simplex, varicella zoster).
      • Persistent (Slow): gradually progressive (deterioration) and often fatal (e.g., HIV's progression, measles SSPE).

    Types of Persistent Viral Infections of Humans

    • Information provided in a tabular format depicting persistent viral infections, their related viral agents, and the sites of persistence.

    Evasion of the Host Immune Response

    • Strategies for immune evasion include infecting immune privileged sites (e.g., eye, brain, and central nervous system).
    • Viruses control antigen production.
    • Antigenic variation can occur in high frequency.
    • Viruses may hide from the host's immune system.
    • Direct subversion of the immune system, production of compounds mimicking normal immune system functions, and directly infecting immune cells are some mechanisms of evasion.
    • Direct subversion includes inhibiting MHC class I and class II restricted antigen presentation, natural killer cell lysis, interference with apoptosis, and the inhibition of cytokine action (e.g., interferon).

    Clinically Inapparent Acute Viral Infections

    • Some acute viral infections produce no disease symptoms despite sufficient virus production.
    • Host immune systems promptly control these infections.
    • This response may be detected through antiviral antibodies.

    Multiple Acute Viral Infections

    • A single infection can be followed by secondary viral infections, potentially leading to a second acute infection or a different disease pattern (e.g., poliovirus).

    An Acute Infection: Human Poliomyelitis

    • Includes the stages of invasion, multiplication, and the path of this viral infection in the host.

    Acute Infections and Public Health

    • Acute viral infections often have a significant impact on public health and safety, manifested by outbreaks.
    • Difficulty arises from diagnosing the virus before it spreads to other hosts.

    Latent Viral Infections

    • Characteristics of latent viral infections are: non-replicating cells, reduced or eliminated immune detection of infected cells, absent or inefficient expression of viral genes for virus particle production, and persistence of the viral genome.

    Disease Herpes Simplex—Type 1

    • Includes primary infection, latent, and reactivation phases, describing the symptoms and the viral presence.

    Slow Infections

    • Some fatal brain diseases result from extreme persistent viral variations.
    • Many years may pass between initial infection and disease onset.
    • Well-known viruses associated with other diseases can result in slow diseases.
    • Unconventional agents such as transmissible spongiform encephalopathies (TSEs) cause slow diseases (examples: Kuru, Creutzfeldt-Jakob, Scrapie, and bovine spongiform encephalopathy).
    • Measles virus may result in subacute sclerosing panencephalitis (SSPE).
      • This involves a chronic form of the measles virus disease and neurological deterioration and death.

    Summary

    • Summarizing the key aspects of viral infections and the components required for their pathogenesis.
    • Host defenses and viral properties determine the outcome of viral infections.

    Further Reading

    • Provides relevant books for in-depth study of the subject.

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    Related Documents

    Patterns of Viral Infection Lecture 18 PDF

    Description

    Test your knowledge on the immune mechanisms involved in combating viral infections. This quiz covers topics such as interferons, natural killer cells, and the impacts of AIDS on immune responses. Answer questions related to viral evasion strategies and chronic infections.

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