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.