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viruses .

Overview of Viruses

  • Definition: Viruses are acellular pathogens that cannot reproduce independently and require a host.

Virus Classification

  • Types of Viruses: Influenza A (many forms, a common flu)

  • Characteristics: Size smaller than bacteria, requires a host to replicate.

Discovery of Viruses

  • Tobacco Mosaic Virus: Used a filter that allowed viruses to pass but blocked bacteria indicating smaller sizes of pathogens.

  • Host Exploitation: Viruses use the host's machinery and components to reproduce and spread.

Structure of Viruses

  • Components:

    • Nucleic Acids: Can be DNA or RNA.

    • Capsid: Protein coat surrounding the viral genome.

    • Envelopes: Some viruses acquire lipid membranes from the host.

  • Types of Viral Genomes:

    • Single-stranded, Double-stranded (DNA/RNA)

    • Linear, Circular, Segmented Structures

    • Positive-sense, Negative-sense, Ambisense

Modes of Transmission

  • Direct Contact: Physical interaction between hosts.

  • Fomites: Inanimate objects carrying virus.

  • Vectors: Animals transmitting the virus between hosts.

Virus Life Cycle

  • Steps:

    1. Attachment: Virus binds to specific receptors on the host cell.

    2. Entry: Penetration or fusion into the host membrane.

    3. Uncoating: Capsid opens, releasing viral nucleic acids.

    4. Replication: Host cell machinery synthesizes viral components.

    5. Assembly: Newly formed virus particles are packaged.

    6. Release: Viruses can either lyse (burst) the host cell or extrude gently.

Viral Immunology

  • Cytopathogenicity: Ability of a virus to cause cell damage or death.

  • Evasion of Immune Response: Envelopes help viruses evade detection by the immune system.

  • Tropism: Specificity of a virus for particular host cells based on receptor compatibility.

Treatment Strategies

  • Acyclovir: A nucleoside analog that inhibits viral enzymes necessary for replication. Primarily used for treating:

    • Herpes simplex virus

    • Epstein-Barr virus

  • Viral Enzyme Targeting: Focuses on enzymes that are specific to viruses, minimizing harm to the host cells.

Conclusion

  • Viruses display significant diversity in structure and life cycles. Understanding their mechanisms provides avenues for effective treatments and aids in vaccine development.