Mechanisms of Viral Infection

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Questions and Answers

During viral infection, if the host immune response exacerbates the disease rather than resolving it, which mechanism is most likely contributing to this outcome?

  • Direct cytopathic effects of the virus overwhelm the host cells before an immune response can mount.
  • Antibody-dependent enhancement leads to increased viral entry into immune cells, amplifying the infection.
  • Systemic inflammation triggered by the immune response causes more damage to tissues than the virus itself. (correct)
  • The virus directly suppresses the host's immune system, preventing it from targeting infected cells effectively.

If a virus primarily targets macrophages for replication, what is the most likely consequence regarding viral dissemination within the host?

  • Reduced viral spread due to the immediate destruction of the virus by macrophages.
  • Localized infection at the primary site, preventing systemic spread via the bloodstream.
  • Direct neutralization of the virus by macrophage-produced antibodies.
  • Enhanced transport of the virus to various tissues, facilitating widespread dissemination. (correct)

Which factor most significantly influences a virus's ability to initiate an infection in a host?

  • The number of circulating antibodies against the virus in the host's bloodstream.
  • The thickness of the host's skin as a barrier against viral entry.
  • The host's age and general physical fitness level.
  • The presence of specific viral receptors on host cells that the virus can bind to. (correct)

A patient undergoing immunosuppressive therapy is at an increased risk of severe viral infections because of which compromised defense mechanism?

<p>Ineffective adaptive immune responses, limiting the control of viral replication. (D)</p> Signup and view all the answers

Which aspect of viral infection is the most relevant for determining the length of the incubation period?

<p>The time required for the virus to reach and replicate in target tissues, causing clinical symptoms. (A)</p> Signup and view all the answers

If a virus establishes a persistent infection, which of these mechanisms is most likely to contribute to this outcome?

<p>Evasion of immune detection through latency or chronic low-level replication. (A)</p> Signup and view all the answers

Which mechanism of viral entry is most effectively circumvented by viruses that target the respiratory tract?

<p>Mucociliary clearance. (D)</p> Signup and view all the answers

What is the primary distinction between viremia and secondary viremia in the context of viral infections?

<p>Viremia is the initial spread of the virus into the bloodstream from the primary infection site, whereas secondary viremia occurs after the virus has replicated in other tissues and re-entered the circulation. (D)</p> Signup and view all the answers

How does the lymphatic system contribute to the dissemination of viral infections within the body?

<p>It transports viruses from the primary infection site to lymph nodes, where they can infect immune cells and spread systemically. (C)</p> Signup and view all the answers

In what scenario would a virus's ability to replicate within endothelial cells lining blood vessels most significantly contribute to disease progression?

<p>When the virus causes systemic inflammation and vascular leakage, leading to conditions like hemorrhagic fever. (C)</p> Signup and view all the answers

Flashcards

Viral Acquisition/Entry

The initial phase when a virus enters the body through routes like skin or mucous membranes.

Incubation Period

The period between viral entry and symptom appearance, during which the virus replicates and spreads.

Replication in Target Tissue

The replication of a virus within specific tissues, leading to the emergence of clinical signs and symptoms.

Disease Resolution/Chronic Infection

The termination of a viral infection via a host's immune response, or its persistence, leading to chronic disease.

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Viremia

The transport of viruses within the bloodstream, either freely or within infected cells.

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Common Viral Entry Points

Infection initiated in the oral mucosa or upper respiratory tract.

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Primary Viral Transfer Systems

The bloodstream and lymphatic system.

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Cells Supporting Viral Replication

Macrophages, endothelial cells, and liver cells.

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Study Notes

  • The purpose of this video is to outline the learning objective to discuss the mechanisms of viral infection

Basic Steps in Viral Disease:

  • The first step of the viral disease process is the acquisition, or entry, of the virus into the body
  • After the virus is in the body, it initiates infection at a primary site
  • Initiation of an infection induces activation of the innate immune response
  • There is an incubation period between the initiation of the infection and the appearance of clinical symptoms
  • During the incubation period, the virus is amplified and spreads to secondary sites
  • The virus replicates in the target tissue, which causes clinical symptoms to appear
  • The host immune response limits the spread of infection, but can contribute to disease via inflammatory response
  • Virus production in the tissue releases the virus and spreads the disease to others
  • Resolution of the disease occurs due to host immunity, persistent infection, or chronic disease

Stages of Viral Infections:

  • The first step in viral infection is when the virus enters the body
  • Entry can occur through various routes, such as the skin, mucous membranes, the eyes, respiratory tract, mouth, genitalia, or gastrointestinal tract
  • The skin is a strong barrier against infection, but viruses can bypass it and enter through mucous membranes like tears, mucus, stomach acid, bile, and immunoglobulins for protection
  • After the virus enters the body, it starts infecting cells at a primary site of infection such as the respiratory tract or oral mucosa
  • The presence of the virus activates the innate immune response, which defends the body against the infection
  • There is a period between the virus entering the body and the appearance of symptoms called the incubation period
  • During the incubation period, the virus replicates and spreads to secondary sites in the body
  • The virus begins replicating in specific target tissues, causing clinical symptoms to appear
  • The body’s immune response is triggered to try to control and limit the virus spread, but sometimes this immune response can contribute to disease which leads to inflammation
  • The virus replicates in tissues and releases more virus particles, spreading the infection to other people
  • The infection can be resolved by the host immune response
  • The infection may become persistent or chronic, leading to ongoing health issues

Entry Routes and Spread:

  • A virus enters through the respiratory tract, oral mucosa, upper respiratory tract, skin, genitalia, and gastrointestinal tract
  • Viruses replicate in cells that showcase viral receptors and the necessary machinery for replication
  • After initial replication, the virus can stay at the primary site or spread via the bloodstream, mononuclear phagocytes, macrophages, and lymphocytes
  • Viruses can also travel through neurons
  • The bloodstream and lymphatic system are the major means of viral transfer, through viremia
  • In the bloodstream, the virus may be free or cell-associated with infected cells like lymphocytes or macrophages
  • Once in the bloodstream, the virus can spread to other tissues such as the liver, brain, or skin, which leads to secondary viremia
  • A virus can replicate in macrophages, endothelial cells, and the liver, amplifying the infection, and leading to secondary viremia, causing it to reach new organs and tissues, contributing to the development of symptoms

Key Takeaways:

  • The viral infection process includes entry, primary infection, immune response, viral replication, spread, and resolution or chronic disease
  • A key component to viral spread is the bloodstream and lymphatic system
  • The immune response can help control the infection, but it can sometimes contribute to symptoms

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