VMED280: Introduction to Virology

Introduction to Virology

• Viruses differ from bacteria in structure, classification, and properties.
• Viral diseases have been recognized for centuries, with evidence of smallpox around 1500 BC and poliomyelitis-related leg deformities.

Virus Structure and Classification

• Viruses can be categorized based on their genetic material: DNA or RNA.
• DNA viruses:
  • Examples include Papillomavirus (naked), Herpes viruses (enveloped), and Pox viruses (complex).
• RNA viruses:
  • Examples include Picornaviruses (naked), Influenza (enveloped), and Retroviruses (enveloped).

Modes of Virus Entry

• Common routes of viral entry include:
  • Inhaled droplets (e.g., rhinovirus).
  • Ingestion through contaminated food or water (e.g., hepatitis A).
  • Direct transfer from infected hosts (e.g., HIV).
  • Arthropod bites (e.g., yellow fever).

Infection Acquisition

• Transmission methods:
  • Direct contact (e.g., herpes viruses, HIV).
  • Airborne spread (e.g., chickenpox).
  • Parenteral exposure (e.g., HIV, hepatitis B and C).
  • Contact with fomites (e.g., enteroviruses).
  • Vectors (e.g., West Nile virus).
  • Vertical transmission (e.g., HIV, rubella).
  • Foodborne routes (e.g., hepatitis A).

Viral Replication Process

• A single host cell can produce thousands of viral particles.
• Enveloped RNA viruses (e.g., Influenza A) replicate by budding through the host cell membrane.

Consequences of Virus-Cell Interaction

• Viral infections can lead to various outcomes:
  • Lysis of host cells, as seen in cold sores and chickenpox.
  • Latent infections with non-replicating viruses (e.g., herpes viruses).
  • Persistent infections with ongoing viral replication, resulting in tissue injury (e.g., hepatitis B and C, HIV).
  • Induction of oncogenesis, linking certain viruses to cancer (e.g., human papillomavirus, EBV).
  • Asymptomatic infections may occur (e.g., hepatitis G).

Diagnosis of Viral Infections

• Diagnosis relies on clinical features and laboratory tests, including:
  • Histology and cytology techniques.
  • Electron microscopy for direct examination.
  • Detection of viral antigens in tissues and serum.
  • Antibody testing (IgG, IgM detection).
  • Virus isolation and amplification of viral DNA or RNA.

Important Virus Characteristics

• Viruses depend on host cells for replication and require cellular machinery to process genetic information.
• Virus envelopes or capsids play critical roles in host cell attachment and entry.
• Transmission typically occurs through respiratory droplets or contaminated food/water.

This quiz covers key aspects of virology, including the classification, structure, and properties of viruses. Learn how viruses differ from bacteria and explore the history of viral diseases. Test your understanding of these critical concepts in Infection and Immunity II.