Microbes and Infectious Diseases

Overview of Microbes

• Types of Microbes: Viruses, bacteria, protists, fungi.
• Roles:
  • Contribute to diversity and nutrient flow in ecosystems.
  • Help create medicines and foods (e.g., cheese, sourdough).
  • Reside in and on animals, aiding bodily functions (e.g., digestive bacteria).

Infectious Agents

• Definition: Microbes that cause illness in a host.
• Nature of Infectious Agents:
  • Not inherently bad; aim to survive and multiply.
  • Some live harmlessly in hosts; others cause disease.
• Transmission: Movement of agents to new hosts.

Chain of Infection

• Steps in the Chain:
  1. Reservoir: Typical location of the infectious agent (e.g., humans, animals, water).
  2. Portal of Exit: How the agent leaves its reservoir (e.g., mouth, anus, nose).
  3. Mode of Transmission: How the agent spreads between hosts.
  4. Portal of Entry: How the agent enters a new host.
  5. Susceptible Host: A host that can be infected.

Modes of Transmission

• Direct Transmission:
  • Direct Contact: Physical contact with infected source (e.g., kissing, touching).
  • Direct Droplet: Respiratory droplets over short distances.
• Indirect Transmission:
  • Airborne: Small particles stay in the air and can be inhaled later (e.g., measles).
  • Vector-borne: Spread by arthropods like mosquitoes (e.g., malaria).
  • Vehicle-borne: Non-living objects transmit agents (e.g., contaminated surfaces).

Prevention Strategies

• Breaking the Chain:
  • Address reservoirs, portals of exit, modes of transmission, portals of entry, and susceptibility.
  • Examples: hand washing, mask wearing, vaccination, sanitation.
• Contagious Diseases:
  • Spread easily from person to person.
  • Early detection and prevention are crucial.

Specific Example: Salmonella

• Infectious Agent: Salmonella bacteria.
• Reservoir: Digestive/reproductive tracts of chickens.
• Portal of Exit: Cloaca of chickens.
• Transmission: Indirect via contaminated meat or egg products.
• Prevention: Proper cooking, hygiene, and food handling practices.

Summary

• Disease Spread Model: Infectious agent → Reservoir → Portal of Exit → Transmission → Portal of Entry → Susceptible Host.
• Prevention: Layered strategies are more effective; akin to the Swiss cheese model of overlapping protections.