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.