Viral Pathogenesis and Immunity Quiz

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Questions and Answers

What is the site of pathology for local viral infections?

At distant sites

Body's lymph nodes

Circulatory system

Portal of entry (correct)

Which of the following is NOT a characteristic of systemic viral infections?

Usually life-long immunity

Relatively long incubation period

Occurs at the portal of entry (correct)

Viraemia is present

Which component plays an essential role in the innate immune response against viruses?

Memory B cells

Helper T cells

NK cells (correct)

Neutralizing antibodies

What type of immunity is primarily involved in the defense against viruses before they enter host cells?

Humoral immune response Signup and view all the answers

What is one of the primary functions of neutralizing antibodies against viruses?

Preventing viral attachment to host cells Signup and view all the answers

Which statement about the duration of immunity in local viral infections is accurate?

Immunity lasts for a relatively short time Signup and view all the answers

Type I interferons are produced by which type of cells in response to viral infections?

Virally-infected cells Signup and view all the answers

Which of the following mechanisms describes how opsonizing antibodies enhance the immune response?

They enhance phagocytosis of viruses. Signup and view all the answers

What role does Secretory IgA play in the immune response?

It neutralizes viruses entering through the mucosa. Signup and view all the answers

What is the primary function of Cytotoxic T cells in specific immunity?

They kill infected cells. Signup and view all the answers

Which cytokine is crucial for activating Natural Killer (NK) cells?

IFN-γ Signup and view all the answers

What characterizes a latent viral infection?

The virus remains dormant and can reactivate. Signup and view all the answers

Which type of viral infection has long incubation periods and can be caused by prions?

Slow virus infections Signup and view all the answers

How are viruses classified based on their nucleic acid?

As DNA or RNA viruses. Signup and view all the answers

What is a common method for the direct diagnosis of viral infections?

Isolation of the virus Signup and view all the answers

Which of the following best describes an apparent viral infection?

An infection causing symptoms and clinical signs. Signup and view all the answers

Study Notes

Viral Pathogenesis

Viruses enter the body by inhalation, ingestion, contact (urogenital system), skin (injections, blood transfusion), insect or animal bites.
Viruses replicate at the primary site of entry; some cause local infections, others spread to distant organs via the blood (viremia) or other means (e.g., nerves), resulting in systemic or deep viral infections.

Differences Between Local and Systemic Viral Infections

Local Infections: Example: common cold (rhinovirus). Pathogenesis is at the portal of entry, incubation period is relatively short, viremia is absent, immunity is usually short, and secretory IgA plays a significant role.
Systemic Infections: Example: Measles. Pathogenesis is at distant sites, incubation period is relatively long, viremia is present, immunity is usually long-lasting, and secretory IgA plays a less significant role.

Immunity to Viruses

Innate Immunity (NK cells): Cytotoxic killing of virally infected cells occurs early in the infection process.
Type I Interferon: Virally infected cells produce IFN-α and IFN-β, inhibiting viral replication, inducing an antiviral state, activating NK cells, and increasing MHC I expression for improved viral peptide presentation.

B-Specific Immunity (Humoral Response)

Antibodies: Crucial for defense before and after viral entry.
Antibody Functions: Neutralizing antibodies prevent viral attachment and entry, opsonizing antibodies enhance phagocytosis, and complement activation enhances phagocytosis.
Secretory IgA: Important for neutralizing viruses entering the mucosa, while circulating IgM and IgG defend against viruses circulating in the bloodstream before reaching their target cells.

B-Specific Immunity (T Cell Response)

Cytotoxic T Cells (Tc Cells): The primary mechanism of specific immunity against established viral infections; they kill infected cells.
Helper T Cells (Th Cells): Support the immune response by releasing cytokines. Th1 cytokines, especially IL-2 and IFN-γ, are crucial for Tc cell proliferation, activation, and NK cell activation.

Fate of Viral Infections

Inapparent/Subclinical: Infection with no noticeable signs or symptoms.
Apparent (Disease): Infection with clinical signs and symptoms (local or systemic).
Persistent/Chronic: Virus continuously present, often with minimal clinical symptoms (e.g., chronic hepatitis B).
Latent: Virus persists in a dormant form, intermittently flaring up to produce disease (e.g., herpes viruses).
Slow Virus Infections: Long incubation periods (months or years) caused by conventional viruses (e.g., variant measles viruses causing subacute sclerosing panencephalitis (SSPE)) or unconventional agents (prions).

Viral Zoonosis

Viral transmission from animals to humans. Examples include rabies, influenza A viruses, and various viral hemorrhagic fevers (yellow fever, dengue fever, Rift Valley fever, Ebola and Marburg viruses).

Classification of Viruses

A (Symptomatology): Old classification based on the diseases produced (tropism - e.g., neurotropic viruses, enteroviruses).
B (Families, Genera, Species): Classification based on nucleic acid type (DNA or RNA), virus size, symmetry, presence/absence of envelope, and replication strategy. This is a more modern and structured approach.
Baltimore Classification Scheme: A system used to organize viruses based on their genome structure and the method they use for mRNA production.

Diagnosis of Viral Infections

Direct Methods: Direct detection of viruses or their components (e.g., using PCR or antigen detection). Isolation of viruses.
Indirect Methods: Using serological tests (measuring antibodies) or skin tests to diagnose viral infection.

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Description

Test your knowledge on the pathogenesis of viral infections and the differences between local and systemic infections. This quiz covers key concepts including routes of entry, the role of immunity, and the dynamics of viral replication. Understand the mechanisms underlying viral infections and the body's immune response.