L4.4: Chain of Infection

• CHAIN OF INFECTION

  ● The result of continuous interaction of the elements that could lead to the transmission of agent from one susceptible host to another
• COMPONENTS OF THE CHAIN

  1. Infectious Agent – PATHOGEN
  2. Reservoir – SOURCE
  3. Portal of Exit – PATHOGEN LEAVING HOST
  4. Mode of Transmission – PATTERN
  5. Portal of Entry – PATHOGEN TO HOST
  6. Susceptible Host – HOST DEVELOPS DISEASE
• Infectious Agent – PATHOGEN

  ● Involves microorganism that brings forth disease towards the host
• Reservoir – SOURCE

  ● Starting point for the occurrence of communicable disease

  ● “Habitat” in which the agent normally lives, grows, and multiplies
• Reservoir – SOURCE

  • Human Reservoir
  • Animal Reservoir
  • Environmental Reservoir
• Human Reservoir

  • Most common type for infectious diseases transmitted from person to person
  • Case (SYMPTOMATIC) : Person identified as having the particular disease and is under investigation
  • Carrier (ASYMPTOMATIC) : Person with inapparent infection that is capable of transmitting pathogen to others
• Human Reservoir

  To be a carrier:

  1. The presence of disease agent in the body

  2. The absence of recognizable signs and symptoms of disease s

  3. The shedding of disease agent in the discharge or excretions
• Animal Reservoir

  • Focuses on humans being incidental hosts in an animal to animal transmission
  • Zoonosis : Infectious disease from vertebrate animals to humans
• Environmental Reservoir

  • Can be in the form of soil and other inanimate matter
• Portal of Exit – PATHOGEN LEAVING HOST

  ● The path by which a pathogen leaves its host

  ● Usually corresponds to the site where the pathogen is localized
• Mode of Transmission – PATTERN

  ● Involves the pattern as to how the infectious agent is spread from reservoir to susceptible host
• Direct Transmission

  • Infectious agent transferred from a reservoir to susceptible host
• Direct Transmission

  Direct Contact

  - Skin-to-skin contact

  - Kissing

  - Sexual intercourse

  Droplet Spread

  - Sneezing

  - Coughing

  - Talking
• Indirect Transmission

  • Infectious agent from reservoir to susceptible host by suspended air particles, inanimate objects, animate intermediaries
• Indirect Transmission

  • Airborne - carried by dust or droplet nuclei suspended in air
  • Vehicles - transmit include food, water, biologic products, and fomites
  • Vectors - carry an infectious agent through purely mechanical means
• Portal of Entry – PATHOGEN TO HOST

  ● Refers to the manner in which a pathogen enters a susceptible host
• Susceptible Host – HOST DEVELOPS DISEASE

  ● The final link in the chain of infection where an individual potentiates the development of disease