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.
Chain of Transmission
By Shimels D.