The Chain of Transmission of infectious disease is basically described as the Agent / Host / Environment triad . The 6 elements of the chain are:
- Infectious Agent - e.g. virus, bacteria, protozoa, fungi, animals (worms)
- Reservoir - Where the agent normally resides
- Portal of Exit - How the agent leaves the host
- Mode of transmission - Direct or indirect contact
- Portal of Entry - How the agent enters the susceptible host
- Susceptible Host - Impacted by overall health, genetic factors, etc.